Logo Search packages:      
Sourcecode: cvsnt version File versions  Download package

ssh.c

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <assert.h>

#include "putty.h"
#include "tree234.h"
#include "ssh.h"

#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

#define SSH1_MSG_DISCONNECT                       1   /* 0x1 */
#define SSH1_SMSG_PUBLIC_KEY                      2   /* 0x2 */
#define SSH1_CMSG_SESSION_KEY                     3   /* 0x3 */
#define SSH1_CMSG_USER                            4   /* 0x4 */
#define SSH1_CMSG_AUTH_RSA                        6   /* 0x6 */
#define SSH1_SMSG_AUTH_RSA_CHALLENGE              7   /* 0x7 */
#define SSH1_CMSG_AUTH_RSA_RESPONSE               8   /* 0x8 */
#define SSH1_CMSG_AUTH_PASSWORD                   9   /* 0x9 */
#define SSH1_CMSG_REQUEST_PTY                     10  /* 0xa */
#define SSH1_CMSG_WINDOW_SIZE                     11  /* 0xb */
#define SSH1_CMSG_EXEC_SHELL                      12  /* 0xc */
#define SSH1_CMSG_EXEC_CMD                        13  /* 0xd */
#define SSH1_SMSG_SUCCESS                         14  /* 0xe */
#define SSH1_SMSG_FAILURE                         15  /* 0xf */
#define SSH1_CMSG_STDIN_DATA                      16  /* 0x10 */
#define SSH1_SMSG_STDOUT_DATA                     17  /* 0x11 */
#define SSH1_SMSG_STDERR_DATA                     18  /* 0x12 */
#define SSH1_CMSG_EOF                             19  /* 0x13 */
#define SSH1_SMSG_EXIT_STATUS                     20  /* 0x14 */
#define SSH1_MSG_CHANNEL_OPEN_CONFIRMATION        21  /* 0x15 */
#define SSH1_MSG_CHANNEL_OPEN_FAILURE             22  /* 0x16 */
#define SSH1_MSG_CHANNEL_DATA                     23  /* 0x17 */
#define SSH1_MSG_CHANNEL_CLOSE                    24  /* 0x18 */
#define SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION       25  /* 0x19 */
#define SSH1_SMSG_X11_OPEN                        27  /* 0x1b */
#define SSH1_CMSG_PORT_FORWARD_REQUEST            28  /* 0x1c */
#define SSH1_MSG_PORT_OPEN                        29  /* 0x1d */
#define SSH1_CMSG_AGENT_REQUEST_FORWARDING        30  /* 0x1e */
#define SSH1_SMSG_AGENT_OPEN                      31  /* 0x1f */
#define SSH1_MSG_IGNORE                           32  /* 0x20 */
#define SSH1_CMSG_EXIT_CONFIRMATION               33  /* 0x21 */
#define SSH1_CMSG_X11_REQUEST_FORWARDING          34  /* 0x22 */
#define SSH1_CMSG_AUTH_RHOSTS_RSA                 35  /* 0x23 */
#define SSH1_MSG_DEBUG                            36  /* 0x24 */
#define SSH1_CMSG_REQUEST_COMPRESSION             37  /* 0x25 */
#define SSH1_CMSG_AUTH_TIS                        39  /* 0x27 */
#define SSH1_SMSG_AUTH_TIS_CHALLENGE              40  /* 0x28 */
#define SSH1_CMSG_AUTH_TIS_RESPONSE               41  /* 0x29 */
#define SSH1_CMSG_AUTH_CCARD                      70  /* 0x46 */
#define SSH1_SMSG_AUTH_CCARD_CHALLENGE            71  /* 0x47 */
#define SSH1_CMSG_AUTH_CCARD_RESPONSE             72  /* 0x48 */

#define SSH1_AUTH_TIS                             5   /* 0x5 */
#define SSH1_AUTH_CCARD                           16  /* 0x10 */

#define SSH1_PROTOFLAG_SCREEN_NUMBER              1   /* 0x1 */
/* Mask for protoflags we will echo back to server if seen */
#define SSH1_PROTOFLAGS_SUPPORTED                 0   /* 0x1 */

#define SSH2_MSG_DISCONNECT                       1   /* 0x1 */
#define SSH2_MSG_IGNORE                           2   /* 0x2 */
#define SSH2_MSG_UNIMPLEMENTED                    3   /* 0x3 */
#define SSH2_MSG_DEBUG                            4   /* 0x4 */
#define SSH2_MSG_SERVICE_REQUEST                  5   /* 0x5 */
#define SSH2_MSG_SERVICE_ACCEPT                   6   /* 0x6 */
#define SSH2_MSG_KEXINIT                          20  /* 0x14 */
#define SSH2_MSG_NEWKEYS                          21  /* 0x15 */
#define SSH2_MSG_KEXDH_INIT                       30  /* 0x1e */
#define SSH2_MSG_KEXDH_REPLY                      31  /* 0x1f */
#define SSH2_MSG_KEX_DH_GEX_REQUEST               30  /* 0x1e */
#define SSH2_MSG_KEX_DH_GEX_GROUP                 31  /* 0x1f */
#define SSH2_MSG_KEX_DH_GEX_INIT                  32  /* 0x20 */
#define SSH2_MSG_KEX_DH_GEX_REPLY                 33  /* 0x21 */
#define SSH2_MSG_USERAUTH_REQUEST                 50  /* 0x32 */
#define SSH2_MSG_USERAUTH_FAILURE                 51  /* 0x33 */
#define SSH2_MSG_USERAUTH_SUCCESS                 52  /* 0x34 */
#define SSH2_MSG_USERAUTH_BANNER                  53  /* 0x35 */
#define SSH2_MSG_USERAUTH_PK_OK                   60  /* 0x3c */
#define SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ        60  /* 0x3c */
#define SSH2_MSG_USERAUTH_INFO_REQUEST            60  /* 0x3c */
#define SSH2_MSG_USERAUTH_INFO_RESPONSE           61  /* 0x3d */
#define SSH2_MSG_GLOBAL_REQUEST                   80  /* 0x50 */
#define SSH2_MSG_REQUEST_SUCCESS                  81  /* 0x51 */
#define SSH2_MSG_REQUEST_FAILURE                  82  /* 0x52 */
#define SSH2_MSG_CHANNEL_OPEN                     90  /* 0x5a */
#define SSH2_MSG_CHANNEL_OPEN_CONFIRMATION        91  /* 0x5b */
#define SSH2_MSG_CHANNEL_OPEN_FAILURE             92  /* 0x5c */
#define SSH2_MSG_CHANNEL_WINDOW_ADJUST            93  /* 0x5d */
#define SSH2_MSG_CHANNEL_DATA                     94  /* 0x5e */
#define SSH2_MSG_CHANNEL_EXTENDED_DATA            95  /* 0x5f */
#define SSH2_MSG_CHANNEL_EOF                      96  /* 0x60 */
#define SSH2_MSG_CHANNEL_CLOSE                    97  /* 0x61 */
#define SSH2_MSG_CHANNEL_REQUEST                  98  /* 0x62 */
#define SSH2_MSG_CHANNEL_SUCCESS                  99  /* 0x63 */
#define SSH2_MSG_CHANNEL_FAILURE                  100 /* 0x64 */

/*
 * Packet type contexts, so that ssh2_pkt_type can correctly decode
 * the ambiguous type numbers back into the correct type strings.
 */
#define SSH2_PKTCTX_DHGROUP1         0x0001
#define SSH2_PKTCTX_DHGEX            0x0002
#define SSH2_PKTCTX_PUBLICKEY        0x0010
#define SSH2_PKTCTX_PASSWORD         0x0020
#define SSH2_PKTCTX_KBDINTER         0x0040
#define SSH2_PKTCTX_AUTH_MASK        0x00F0

#define SSH2_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT 1 /* 0x1 */
#define SSH2_DISCONNECT_PROTOCOL_ERROR            2   /* 0x2 */
#define SSH2_DISCONNECT_KEY_EXCHANGE_FAILED       3   /* 0x3 */
#define SSH2_DISCONNECT_HOST_AUTHENTICATION_FAILED 4  /* 0x4 */
#define SSH2_DISCONNECT_MAC_ERROR                 5   /* 0x5 */
#define SSH2_DISCONNECT_COMPRESSION_ERROR         6   /* 0x6 */
#define SSH2_DISCONNECT_SERVICE_NOT_AVAILABLE     7   /* 0x7 */
#define SSH2_DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED 8    /* 0x8 */
#define SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE   9   /* 0x9 */
#define SSH2_DISCONNECT_CONNECTION_LOST           10  /* 0xa */
#define SSH2_DISCONNECT_BY_APPLICATION            11  /* 0xb */
#define SSH2_DISCONNECT_TOO_MANY_CONNECTIONS      12  /* 0xc */
#define SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER    13  /* 0xd */
#define SSH2_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE 14   /* 0xe */
#define SSH2_DISCONNECT_ILLEGAL_USER_NAME         15  /* 0xf */

static const char *const ssh2_disconnect_reasons[] = {
    NULL,
    "SSH_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT",
    "SSH_DISCONNECT_PROTOCOL_ERROR",
    "SSH_DISCONNECT_KEY_EXCHANGE_FAILED",
    "SSH_DISCONNECT_HOST_AUTHENTICATION_FAILED",
    "SSH_DISCONNECT_MAC_ERROR",
    "SSH_DISCONNECT_COMPRESSION_ERROR",
    "SSH_DISCONNECT_SERVICE_NOT_AVAILABLE",
    "SSH_DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED",
    "SSH_DISCONNECT_HOST_KEY_NOT_VERIFIABLE",
    "SSH_DISCONNECT_CONNECTION_LOST",
    "SSH_DISCONNECT_BY_APPLICATION",
    "SSH_DISCONNECT_TOO_MANY_CONNECTIONS",
    "SSH_DISCONNECT_AUTH_CANCELLED_BY_USER",
    "SSH_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE",
    "SSH_DISCONNECT_ILLEGAL_USER_NAME",
};

#define SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED     1   /* 0x1 */
#define SSH2_OPEN_CONNECT_FAILED                  2   /* 0x2 */
#define SSH2_OPEN_UNKNOWN_CHANNEL_TYPE            3   /* 0x3 */
#define SSH2_OPEN_RESOURCE_SHORTAGE               4   /* 0x4 */

#define SSH2_EXTENDED_DATA_STDERR                 1   /* 0x1 */

/*
 * Various remote-bug flags.
 */
#define BUG_CHOKES_ON_SSH1_IGNORE                 1
#define BUG_SSH2_HMAC                             2
#define BUG_NEEDS_SSH1_PLAIN_PASSWORD             4
#define BUG_CHOKES_ON_RSA                   8
#define BUG_SSH2_RSA_PADDING               16
#define BUG_SSH2_DERIVEKEY                       32
#define BUG_SSH2_DH_GEX                          64
#define BUG_SSH2_PK_SESSIONID                   128

#define translate(x) if (type == x) return #x
#define translatec(x,ctx) if (type == x && (pkt_ctx & ctx)) return #x
static char *ssh1_pkt_type(int type)
{
    translate(SSH1_MSG_DISCONNECT);
    translate(SSH1_SMSG_PUBLIC_KEY);
    translate(SSH1_CMSG_SESSION_KEY);
    translate(SSH1_CMSG_USER);
    translate(SSH1_CMSG_AUTH_RSA);
    translate(SSH1_SMSG_AUTH_RSA_CHALLENGE);
    translate(SSH1_CMSG_AUTH_RSA_RESPONSE);
    translate(SSH1_CMSG_AUTH_PASSWORD);
    translate(SSH1_CMSG_REQUEST_PTY);
    translate(SSH1_CMSG_WINDOW_SIZE);
    translate(SSH1_CMSG_EXEC_SHELL);
    translate(SSH1_CMSG_EXEC_CMD);
    translate(SSH1_SMSG_SUCCESS);
    translate(SSH1_SMSG_FAILURE);
    translate(SSH1_CMSG_STDIN_DATA);
    translate(SSH1_SMSG_STDOUT_DATA);
    translate(SSH1_SMSG_STDERR_DATA);
    translate(SSH1_CMSG_EOF);
    translate(SSH1_SMSG_EXIT_STATUS);
    translate(SSH1_MSG_CHANNEL_OPEN_CONFIRMATION);
    translate(SSH1_MSG_CHANNEL_OPEN_FAILURE);
    translate(SSH1_MSG_CHANNEL_DATA);
    translate(SSH1_MSG_CHANNEL_CLOSE);
    translate(SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION);
    translate(SSH1_SMSG_X11_OPEN);
    translate(SSH1_CMSG_PORT_FORWARD_REQUEST);
    translate(SSH1_MSG_PORT_OPEN);
    translate(SSH1_CMSG_AGENT_REQUEST_FORWARDING);
    translate(SSH1_SMSG_AGENT_OPEN);
    translate(SSH1_MSG_IGNORE);
    translate(SSH1_CMSG_EXIT_CONFIRMATION);
    translate(SSH1_CMSG_X11_REQUEST_FORWARDING);
    translate(SSH1_CMSG_AUTH_RHOSTS_RSA);
    translate(SSH1_MSG_DEBUG);
    translate(SSH1_CMSG_REQUEST_COMPRESSION);
    translate(SSH1_CMSG_AUTH_TIS);
    translate(SSH1_SMSG_AUTH_TIS_CHALLENGE);
    translate(SSH1_CMSG_AUTH_TIS_RESPONSE);
    translate(SSH1_CMSG_AUTH_CCARD);
    translate(SSH1_SMSG_AUTH_CCARD_CHALLENGE);
    translate(SSH1_CMSG_AUTH_CCARD_RESPONSE);
    return "unknown";
}
static char *ssh2_pkt_type(int pkt_ctx, int type)
{
    translate(SSH2_MSG_DISCONNECT);
    translate(SSH2_MSG_IGNORE);
    translate(SSH2_MSG_UNIMPLEMENTED);
    translate(SSH2_MSG_DEBUG);
    translate(SSH2_MSG_SERVICE_REQUEST);
    translate(SSH2_MSG_SERVICE_ACCEPT);
    translate(SSH2_MSG_KEXINIT);
    translate(SSH2_MSG_NEWKEYS);
    translatec(SSH2_MSG_KEXDH_INIT, SSH2_PKTCTX_DHGROUP1);
    translatec(SSH2_MSG_KEXDH_REPLY, SSH2_PKTCTX_DHGROUP1);
    translatec(SSH2_MSG_KEX_DH_GEX_REQUEST, SSH2_PKTCTX_DHGEX);
    translatec(SSH2_MSG_KEX_DH_GEX_GROUP, SSH2_PKTCTX_DHGEX);
    translatec(SSH2_MSG_KEX_DH_GEX_INIT, SSH2_PKTCTX_DHGEX);
    translatec(SSH2_MSG_KEX_DH_GEX_REPLY, SSH2_PKTCTX_DHGEX);
    translate(SSH2_MSG_USERAUTH_REQUEST);
    translate(SSH2_MSG_USERAUTH_FAILURE);
    translate(SSH2_MSG_USERAUTH_SUCCESS);
    translate(SSH2_MSG_USERAUTH_BANNER);
    translatec(SSH2_MSG_USERAUTH_PK_OK, SSH2_PKTCTX_PUBLICKEY);
    translatec(SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ, SSH2_PKTCTX_PASSWORD);
    translatec(SSH2_MSG_USERAUTH_INFO_REQUEST, SSH2_PKTCTX_KBDINTER);
    translatec(SSH2_MSG_USERAUTH_INFO_RESPONSE, SSH2_PKTCTX_KBDINTER);
    translate(SSH2_MSG_GLOBAL_REQUEST);
    translate(SSH2_MSG_REQUEST_SUCCESS);
    translate(SSH2_MSG_REQUEST_FAILURE);
    translate(SSH2_MSG_CHANNEL_OPEN);
    translate(SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
    translate(SSH2_MSG_CHANNEL_OPEN_FAILURE);
    translate(SSH2_MSG_CHANNEL_WINDOW_ADJUST);
    translate(SSH2_MSG_CHANNEL_DATA);
    translate(SSH2_MSG_CHANNEL_EXTENDED_DATA);
    translate(SSH2_MSG_CHANNEL_EOF);
    translate(SSH2_MSG_CHANNEL_CLOSE);
    translate(SSH2_MSG_CHANNEL_REQUEST);
    translate(SSH2_MSG_CHANNEL_SUCCESS);
    translate(SSH2_MSG_CHANNEL_FAILURE);
    return "unknown";
}
#undef translate
#undef translatec

#define GET_32BIT(cp) \
    (((unsigned long)(unsigned char)(cp)[0] << 24) | \
    ((unsigned long)(unsigned char)(cp)[1] << 16) | \
    ((unsigned long)(unsigned char)(cp)[2] << 8) | \
    ((unsigned long)(unsigned char)(cp)[3]))

#define PUT_32BIT(cp, value) { \
    (cp)[0] = (unsigned char)((value) >> 24); \
    (cp)[1] = (unsigned char)((value) >> 16); \
    (cp)[2] = (unsigned char)((value) >> 8); \
    (cp)[3] = (unsigned char)(value); }

enum { PKT_END, PKT_INT, PKT_CHAR, PKT_DATA, PKT_STR, PKT_BIGNUM };

/*
 * Coroutine mechanics for the sillier bits of the code. If these
 * macros look impenetrable to you, you might find it helpful to
 * read
 * 
 *   http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html
 * 
 * which explains the theory behind these macros.
 * 
 * In particular, if you are getting `case expression not constant'
 * errors when building with MS Visual Studio, this is because MS's
 * Edit and Continue debugging feature causes their compiler to
 * violate ANSI C. To disable Edit and Continue debugging:
 * 
 *  - right-click ssh.c in the FileView
 *  - click Settings
 *  - select the C/C++ tab and the General category
 *  - under `Debug info:', select anything _other_ than `Program
 *    Database for Edit and Continue'.
 */
#define crBegin(v)      { int *crLine = &v; switch(v) { case 0:;
#define crState(t) \
    struct t *s; \
    if (!ssh->t) ssh->t = snew(struct t); \
    s = ssh->t;
#define crFinish(z)     } *crLine = 0; return (z); }
#define crFinishV } *crLine = 0; return; }
#define crReturn(z)     \
      do {\
          *crLine =__LINE__; return (z); case __LINE__:;\
      } while (0)
#define crReturnV \
      do {\
          *crLine=__LINE__; return; case __LINE__:;\
      } while (0)
#define crStop(z) do{ *crLine = 0; return (z); }while(0)
#define crStopV         do{ *crLine = 0; return; }while(0)
#define crWaitUntil(c)  do { crReturn(0); } while (!(c))
#define crWaitUntilV(c) do { crReturnV; } while (!(c))

typedef struct ssh_tag *Ssh;

static void ssh2_pkt_init(Ssh, int pkt_type);
static void ssh2_pkt_addbool(Ssh, unsigned char value);
static void ssh2_pkt_adduint32(Ssh, unsigned long value);
static void ssh2_pkt_addstring_start(Ssh);
static void ssh2_pkt_addstring_str(Ssh, char *data);
static void ssh2_pkt_addstring_data(Ssh, char *data, int len);
static void ssh2_pkt_addstring(Ssh, char *data);
static unsigned char *ssh2_mpint_fmt(Bignum b, int *len);
static void ssh2_pkt_addmp(Ssh, Bignum b);
static int ssh2_pkt_construct(Ssh);
static void ssh2_pkt_send(Ssh);
static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen, int ispkt);
static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt);

/*
 * Buffer management constants. There are several of these for
 * various different purposes:
 * 
 *  - SSH1_BUFFER_LIMIT is the amount of backlog that must build up
 *    on a local data stream before we throttle the whole SSH
 *    connection (in SSH1 only). Throttling the whole connection is
 *    pretty drastic so we set this high in the hope it won't
 *    happen very often.
 * 
 *  - SSH_MAX_BACKLOG is the amount of backlog that must build up
 *    on the SSH connection itself before we defensively throttle
 *    _all_ local data streams. This is pretty drastic too (though
 *    thankfully unlikely in SSH2 since the window mechanism should
 *    ensure that the server never has any need to throttle its end
 *    of the connection), so we set this high as well.
 * 
 *  - OUR_V2_WINSIZE is the maximum window size we present on SSH2
 *    channels.
 */

#define SSH1_BUFFER_LIMIT 32768
#define SSH_MAX_BACKLOG 32768
#define OUR_V2_WINSIZE 16384

const static struct ssh_kex *kex_algs[] = {
    &ssh_diffiehellman_gex,
    &ssh_diffiehellman
};

const static struct ssh_signkey *hostkey_algs[] = { &ssh_rsa, &ssh_dss };

static void *nullmac_make_context(void)
{
    return NULL;
}
static void nullmac_free_context(void *handle)
{
}
static void nullmac_key(void *handle, unsigned char *key)
{
}
static void nullmac_generate(void *handle, unsigned char *blk, int len,
                       unsigned long seq)
{
}
static int nullmac_verify(void *handle, unsigned char *blk, int len,
                    unsigned long seq)
{
    return 1;
}
const static struct ssh_mac ssh_mac_none = {
    nullmac_make_context, nullmac_free_context, nullmac_key,
    nullmac_generate, nullmac_verify, "none", 0
};
const static struct ssh_mac *macs[] = {
    &ssh_sha1, &ssh_md5, &ssh_mac_none
};
const static struct ssh_mac *buggymacs[] = {
    &ssh_sha1_buggy, &ssh_md5, &ssh_mac_none
};

static void *ssh_comp_none_init(void)
{
    return NULL;
}
static void ssh_comp_none_cleanup(void *handle)
{
}
static int ssh_comp_none_block(void *handle, unsigned char *block, int len,
                         unsigned char **outblock, int *outlen)
{
    return 0;
}
static int ssh_comp_none_disable(void *handle)
{
    return 0;
}
const static struct ssh_compress ssh_comp_none = {
    "none",
    ssh_comp_none_init, ssh_comp_none_cleanup, ssh_comp_none_block,
    ssh_comp_none_init, ssh_comp_none_cleanup, ssh_comp_none_block,
    ssh_comp_none_disable, NULL
};
extern const struct ssh_compress ssh_zlib;
const static struct ssh_compress *compressions[] = {
    &ssh_zlib, &ssh_comp_none
};

enum {                               /* channel types */
    CHAN_MAINSESSION,
    CHAN_X11,
    CHAN_AGENT,
    CHAN_SOCKDATA,
    CHAN_SOCKDATA_DORMANT            /* one the remote hasn't confirmed */
};

/*
 * 2-3-4 tree storing channels.
 */
struct ssh_channel {
    Ssh ssh;                         /* pointer back to main context */
    unsigned remoteid, localid;
    int type;
    /*
     * In SSH1, this value contains four bits:
     * 
     *   1   We have sent SSH1_MSG_CHANNEL_CLOSE.
     *   2   We have sent SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION.
     *   4   We have received SSH1_MSG_CHANNEL_CLOSE.
     *   8   We have received SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION.
     * 
     * A channel is completely finished with when all four bits are set.
     */
    int closes;
    union {
      struct ssh1_data_channel {
          int throttling;
      } v1;
      struct ssh2_data_channel {
          bufchain outbuffer;
          unsigned remwindow, remmaxpkt;
          unsigned locwindow;
      } v2;
    } v;
    union {
      struct ssh_agent_channel {
          unsigned char *message;
          unsigned char msglen[4];
          int lensofar, totallen;
      } a;
      struct ssh_x11_channel {
          Socket s;
      } x11;
      struct ssh_pfd_channel {
          Socket s;
      } pfd;
    } u;
};

/*
 * 2-3-4 tree storing remote->local port forwardings. SSH 1 and SSH
 * 2 use this structure in different ways, reflecting SSH 2's
 * altogether saner approach to port forwarding.
 * 
 * In SSH 1, you arrange a remote forwarding by sending the server
 * the remote port number, and the local destination host:port.
 * When a connection comes in, the server sends you back that
 * host:port pair, and you connect to it. This is a ready-made
 * security hole if you're not on the ball: a malicious server
 * could send you back _any_ host:port pair, so if you trustingly
 * connect to the address it gives you then you've just opened the
 * entire inside of your corporate network just by connecting
 * through it to a dodgy SSH server. Hence, we must store a list of
 * host:port pairs we _are_ trying to forward to, and reject a
 * connection request from the server if it's not in the list.
 * 
 * In SSH 2, each side of the connection minds its own business and
 * doesn't send unnecessary information to the other. You arrange a
 * remote forwarding by sending the server just the remote port
 * number. When a connection comes in, the server tells you which
 * of its ports was connected to; and _you_ have to remember what
 * local host:port pair went with that port number.
 * 
 * Hence: in SSH 1 this structure stores host:port pairs we intend
 * to allow connections to, and is indexed by those host:port
 * pairs. In SSH 2 it stores a mapping from source port to
 * destination host:port pair, and is indexed by source port.
 */
struct ssh_rportfwd {
    unsigned sport, dport;
    char dhost[256];
};

struct Packet {
    long length;
    int type;
    unsigned char *data;
    unsigned char *body;
    long savedpos;
    long maxlen;
};

static void ssh1_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt);
static void ssh2_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt);
static void ssh_size(void *handle, int width, int height);
static void ssh_special(void *handle, Telnet_Special);
static int ssh2_try_send(struct ssh_channel *c);
static void ssh2_add_channel_data(struct ssh_channel *c, char *buf, int len);
static void ssh_throttle_all(Ssh ssh, int enable, int bufsize);
static void ssh2_set_window(struct ssh_channel *c, unsigned newwin);
static int ssh_sendbuffer(void *handle);
static void ssh_do_close(Ssh ssh);

struct rdpkt1_state_tag {
    long len, pad, biglen, to_read;
    unsigned long realcrc, gotcrc;
    unsigned char *p;
    int i;
    int chunk;
};

struct rdpkt2_state_tag {
    long len, pad, payload, packetlen, maclen;
    int i;
    int cipherblk;
    unsigned long incoming_sequence;
};

struct ssh_tag {
    const struct plug_function_table *fn;
    /* the above field _must_ be first in the structure */

    SHA_State exhash, exhashbase;

    Socket s;

    void *ldisc;
    void *logctx;

    unsigned char session_key[32];
    int v1_compressing;
    int v1_remote_protoflags;
    int v1_local_protoflags;
    int agentfwd_enabled;
    int X11_fwd_enabled;
    int remote_bugs;
    const struct ssh_cipher *cipher;
    void *v1_cipher_ctx;
    void *crcda_ctx;
    const struct ssh2_cipher *cscipher, *sccipher;
    void *cs_cipher_ctx, *sc_cipher_ctx;
    const struct ssh_mac *csmac, *scmac;
    void *cs_mac_ctx, *sc_mac_ctx;
    const struct ssh_compress *cscomp, *sccomp;
    void *cs_comp_ctx, *sc_comp_ctx;
    const struct ssh_kex *kex;
    const struct ssh_signkey *hostkey;
    unsigned char v2_session_id[20];
    void *kex_ctx;

    char *savedhost;
    int savedport;
    int send_ok;
    int echoing, editing;

    void *frontend;

    int ospeed, ispeed;              /* temporaries */
    int term_width, term_height;

    tree234 *channels;               /* indexed by local id */
    struct ssh_channel *mainchan;      /* primary session channel */
    int exitcode;

    tree234 *rportfwds;

    enum {
      SSH_STATE_PREPACKET,
      SSH_STATE_BEFORE_SIZE,
      SSH_STATE_INTERMED,
      SSH_STATE_SESSION,
      SSH_STATE_CLOSED
    } state;

    int size_needed, eof_needed;

    struct Packet pktin;
    struct Packet pktout;
    unsigned char *deferred_send_data;
    int deferred_len, deferred_size;

    /*
     * Gross hack: pscp will try to start SFTP but fall back to
     * scp1 if that fails. This variable is the means by which
     * scp.c can reach into the SSH code and find out which one it
     * got.
     */
    int fallback_cmd;

    /*
     * Used for username and password input.
     */
    char *userpass_input_buffer;
    int userpass_input_buflen;
    int userpass_input_bufpos;
    int userpass_input_echo;

    char *portfwd_strptr;
    int pkt_ctx;

    void *x11auth;

    int version;
    int v1_throttle_count;
    int overall_bufsize;
    int throttled_all;
    int v1_stdout_throttling;
    int v2_outgoing_sequence;

    int ssh1_rdpkt_crstate;
    int ssh2_rdpkt_crstate;
    int do_ssh_init_crstate;
    int ssh_gotdata_crstate;
    int ssh1_protocol_crstate;
    int do_ssh1_login_crstate;
    int do_ssh2_transport_crstate;
    int do_ssh2_authconn_crstate;

    void *do_ssh_init_state;
    void *do_ssh1_login_state;
    void *do_ssh2_transport_state;
    void *do_ssh2_authconn_state;

    struct rdpkt1_state_tag rdpkt1_state;
    struct rdpkt2_state_tag rdpkt2_state;

    void (*protocol) (Ssh ssh, unsigned char *in, int inlen, int ispkt);
    int (*s_rdpkt) (Ssh ssh, unsigned char **data, int *datalen);

    /*
     * We maintain a full _copy_ of a Config structure here, not
     * merely a pointer to it. That way, when we're passed a new
     * one for reconfiguration, we can check the differences and
     * potentially reconfigure port forwardings etc in mid-session.
     */
    Config cfg;

    /*
     * Used to transfer data back from async agent callbacks.
     */
    void *agent_response;
    int agent_response_len;
};

#define logevent(s) logevent(ssh->frontend, s)

/* logevent, only printf-formatted. */
static void logeventf(Ssh ssh, const char *fmt, ...)
{
    va_list ap;
    char *buf;

    va_start(ap, fmt);
    buf = dupvprintf(fmt, ap);
    va_end(ap);
    logevent(buf);
    sfree(buf);
}

#define bombout(msg) \
    do { \
        char *text = dupprintf msg; \
      ssh_do_close(ssh); \
        logevent(text); \
        connection_fatal(ssh->frontend, "%s", text); \
        sfree(text); \
    } while (0)

static int ssh_channelcmp(void *av, void *bv)
{
    struct ssh_channel *a = (struct ssh_channel *) av;
    struct ssh_channel *b = (struct ssh_channel *) bv;
    if (a->localid < b->localid)
      return -1;
    if (a->localid > b->localid)
      return +1;
    return 0;
}
static int ssh_channelfind(void *av, void *bv)
{
    unsigned *a = (unsigned *) av;
    struct ssh_channel *b = (struct ssh_channel *) bv;
    if (*a < b->localid)
      return -1;
    if (*a > b->localid)
      return +1;
    return 0;
}

static int ssh_rportcmp_ssh1(void *av, void *bv)
{
    struct ssh_rportfwd *a = (struct ssh_rportfwd *) av;
    struct ssh_rportfwd *b = (struct ssh_rportfwd *) bv;
    int i;
    if ( (i = strcmp(a->dhost, b->dhost)) != 0)
      return i < 0 ? -1 : +1;
    if (a->dport > b->dport)
      return +1;
    if (a->dport < b->dport)
      return -1;
    return 0;
}

static int ssh_rportcmp_ssh2(void *av, void *bv)
{
    struct ssh_rportfwd *a = (struct ssh_rportfwd *) av;
    struct ssh_rportfwd *b = (struct ssh_rportfwd *) bv;

    if (a->sport > b->sport)
      return +1;
    if (a->sport < b->sport)
      return -1;
    return 0;
}

static int alloc_channel_id(Ssh ssh)
{
    const unsigned CHANNEL_NUMBER_OFFSET = 256;
    unsigned low, high, mid;
    int tsize;
    struct ssh_channel *c;

    /*
     * First-fit allocation of channel numbers: always pick the
     * lowest unused one. To do this, binary-search using the
     * counted B-tree to find the largest channel ID which is in a
     * contiguous sequence from the beginning. (Precisely
     * everything in that sequence must have ID equal to its tree
     * index plus CHANNEL_NUMBER_OFFSET.)
     */
    tsize = count234(ssh->channels);

    low = -1;
    high = tsize;
    while (high - low > 1) {
      mid = (high + low) / 2;
      c = index234(ssh->channels, mid);
      if (c->localid == mid + CHANNEL_NUMBER_OFFSET)
          low = mid;                 /* this one is fine */
      else
          high = mid;                /* this one is past it */
    }
    /*
     * Now low points to either -1, or the tree index of the
     * largest ID in the initial sequence.
     */
    {
      unsigned i = low + 1 + CHANNEL_NUMBER_OFFSET;
      assert(NULL == find234(ssh->channels, &i, ssh_channelfind));
    }
    return low + 1 + CHANNEL_NUMBER_OFFSET;
}

static void c_write(Ssh ssh, const char *buf, int len)
{
    if ((flags & FLAG_STDERR)) {
      int i;
      for (i = 0; i < len; i++)
          if (buf[i] != '\r')
            fputc(buf[i], stderr);
      return;
    }
    from_backend(ssh->frontend, 1, buf, len);
}

static void c_write_untrusted(Ssh ssh, const char *buf, int len)
{
    int i;
    for (i = 0; i < len; i++) {
      if (buf[i] == '\n')
          c_write(ssh, "\r\n", 2);
      else if ((buf[i] & 0x60) || (buf[i] == '\r'))
          c_write(ssh, buf + i, 1);
    }
}

static void c_write_str(Ssh ssh, const char *buf)
{
    c_write(ssh, buf, strlen(buf));
}

/*
 * Collect incoming data in the incoming packet buffer.
 * Decipher and verify the packet when it is completely read.
 * Drop SSH1_MSG_DEBUG and SSH1_MSG_IGNORE packets.
 * Update the *data and *datalen variables.
 * Return the additional nr of bytes needed, or 0 when
 * a complete packet is available.
 */
static int ssh1_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
{
    struct rdpkt1_state_tag *st = &ssh->rdpkt1_state;

    crBegin(ssh->ssh1_rdpkt_crstate);

  next_packet:

    ssh->pktin.type = 0;
    ssh->pktin.length = 0;

    for (st->i = st->len = 0; st->i < 4; st->i++) {
      while ((*datalen) == 0)
          crReturn(4 - st->i);
      st->len = (st->len << 8) + **data;
      (*data)++, (*datalen)--;
    }

    st->pad = 8 - (st->len % 8);
    st->biglen = st->len + st->pad;
    ssh->pktin.length = st->len - 5;

    if (ssh->pktin.maxlen < st->biglen) {
      ssh->pktin.maxlen = st->biglen;
      ssh->pktin.data = sresize(ssh->pktin.data, st->biglen + APIEXTRA,
                          unsigned char);
    }

    st->to_read = st->biglen;
    st->p = ssh->pktin.data;
    while (st->to_read > 0) {
      st->chunk = st->to_read;
      while ((*datalen) == 0)
          crReturn(st->to_read);
      if (st->chunk > (*datalen))
          st->chunk = (*datalen);
      memcpy(st->p, *data, st->chunk);
      *data += st->chunk;
      *datalen -= st->chunk;
      st->p += st->chunk;
      st->to_read -= st->chunk;
    }

    if (ssh->cipher && detect_attack(ssh->crcda_ctx, ssh->pktin.data,
                             st->biglen, NULL)) {
        bombout(("Network attack (CRC compensation) detected!"));
        crStop(0);
    }

    if (ssh->cipher)
      ssh->cipher->decrypt(ssh->v1_cipher_ctx, ssh->pktin.data, st->biglen);

    st->realcrc = crc32_compute(ssh->pktin.data, st->biglen - 4);
    st->gotcrc = GET_32BIT(ssh->pktin.data + st->biglen - 4);
    if (st->gotcrc != st->realcrc) {
      bombout(("Incorrect CRC received on packet"));
      crStop(0);
    }

    ssh->pktin.body = ssh->pktin.data + st->pad + 1;
    ssh->pktin.savedpos = 0;

    if (ssh->v1_compressing) {
      unsigned char *decompblk;
      int decomplen;
      if (!zlib_decompress_block(ssh->sc_comp_ctx,
                           ssh->pktin.body - 1, ssh->pktin.length + 1,
                           &decompblk, &decomplen)) {
          bombout(("Zlib decompression encountered invalid data"));
          crStop(0);
      }

      if (ssh->pktin.maxlen < st->pad + decomplen) {
          ssh->pktin.maxlen = st->pad + decomplen;
          ssh->pktin.data = sresize(ssh->pktin.data,
                              ssh->pktin.maxlen + APIEXTRA,
                              unsigned char);
          ssh->pktin.body = ssh->pktin.data + st->pad + 1;
      }

      memcpy(ssh->pktin.body - 1, decompblk, decomplen);
      sfree(decompblk);
      ssh->pktin.length = decomplen - 1;
    }

    ssh->pktin.type = ssh->pktin.body[-1];

    if (ssh->logctx)
      log_packet(ssh->logctx,
               PKT_INCOMING, ssh->pktin.type,
               ssh1_pkt_type(ssh->pktin.type),
               ssh->pktin.body, ssh->pktin.length);

    if (ssh->pktin.type == SSH1_SMSG_STDOUT_DATA ||
      ssh->pktin.type == SSH1_SMSG_STDERR_DATA ||
      ssh->pktin.type == SSH1_MSG_DEBUG ||
      ssh->pktin.type == SSH1_SMSG_AUTH_TIS_CHALLENGE ||
      ssh->pktin.type == SSH1_SMSG_AUTH_CCARD_CHALLENGE) {
      long stringlen = GET_32BIT(ssh->pktin.body);
      if (stringlen + 4 != ssh->pktin.length) {
          bombout(("Received data packet with bogus string length"));
          crStop(0);
      }
    }

    if (ssh->pktin.type == SSH1_MSG_DEBUG) {
      /* log debug message */
      char buf[512];
      int stringlen = GET_32BIT(ssh->pktin.body);
      strcpy(buf, "Remote debug message: ");
      if (stringlen > 480)
          stringlen = 480;
      memcpy(buf + 8, ssh->pktin.body + 4, stringlen);
      buf[8 + stringlen] = '\0';
      logevent(buf);
      goto next_packet;
    } else if (ssh->pktin.type == SSH1_MSG_IGNORE) {
      /* do nothing */
      goto next_packet;
    }

    if (ssh->pktin.type == SSH1_MSG_DISCONNECT) {
      /* log reason code in disconnect message */
      char buf[256];
      unsigned msglen = GET_32BIT(ssh->pktin.body);
      unsigned nowlen;
      strcpy(buf, "Remote sent disconnect: ");
      nowlen = strlen(buf);
      if (msglen > sizeof(buf) - nowlen - 1)
          msglen = sizeof(buf) - nowlen - 1;
      memcpy(buf + nowlen, ssh->pktin.body + 4, msglen);
      buf[nowlen + msglen] = '\0';
      /* logevent(buf); (this is now done within the bombout macro) */
      bombout(("Server sent disconnect message:\n\"%s\"", buf+nowlen));
      crStop(0);
    }

    crFinish(0);
}

static int ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
{
    struct rdpkt2_state_tag *st = &ssh->rdpkt2_state;

    crBegin(ssh->ssh2_rdpkt_crstate);

  next_packet:
    ssh->pktin.type = 0;
    ssh->pktin.length = 0;
    if (ssh->sccipher)
      st->cipherblk = ssh->sccipher->blksize;
    else
      st->cipherblk = 8;
    if (st->cipherblk < 8)
      st->cipherblk = 8;

    if (ssh->pktin.maxlen < st->cipherblk) {
      ssh->pktin.maxlen = st->cipherblk;
      ssh->pktin.data = sresize(ssh->pktin.data, st->cipherblk + APIEXTRA,
                          unsigned char);
    }

    /*
     * Acquire and decrypt the first block of the packet. This will
     * contain the length and padding details.
     */
    for (st->i = st->len = 0; st->i < st->cipherblk; st->i++) {
      while ((*datalen) == 0)
          crReturn(st->cipherblk - st->i);
      ssh->pktin.data[st->i] = *(*data)++;
      (*datalen)--;
    }

    if (ssh->sccipher)
      ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                         ssh->pktin.data, st->cipherblk);

    /*
     * Now get the length and padding figures.
     */
    st->len = GET_32BIT(ssh->pktin.data);
    st->pad = ssh->pktin.data[4];

    /*
     * _Completely_ silly lengths should be stomped on before they
     * do us any more damage.
     */
    if (st->len < 0 || st->pad < 0 || st->len + st->pad < 0) {
      bombout(("Incoming packet was garbled on decryption"));
      crStop(0);
    }

    /*
     * This enables us to deduce the payload length.
     */
    st->payload = st->len - st->pad - 1;

    ssh->pktin.length = st->payload + 5;

    /*
     * So now we can work out the total packet length.
     */
    st->packetlen = st->len + 4;
    st->maclen = ssh->scmac ? ssh->scmac->len : 0;

    /*
     * Adjust memory allocation if packet is too big.
     */
    if (ssh->pktin.maxlen < st->packetlen + st->maclen) {
      ssh->pktin.maxlen = st->packetlen + st->maclen;
      ssh->pktin.data = sresize(ssh->pktin.data,
                          ssh->pktin.maxlen + APIEXTRA,
                          unsigned char);
    }

    /*
     * Read and decrypt the remainder of the packet.
     */
    for (st->i = st->cipherblk; st->i < st->packetlen + st->maclen;
       st->i++) {
      while ((*datalen) == 0)
          crReturn(st->packetlen + st->maclen - st->i);
      ssh->pktin.data[st->i] = *(*data)++;
      (*datalen)--;
    }
    /* Decrypt everything _except_ the MAC. */
    if (ssh->sccipher)
      ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                         ssh->pktin.data + st->cipherblk,
                         st->packetlen - st->cipherblk);

    /*
     * Check the MAC.
     */
    if (ssh->scmac
      && !ssh->scmac->verify(ssh->sc_mac_ctx, ssh->pktin.data, st->len + 4,
                         st->incoming_sequence)) {
      bombout(("Incorrect MAC received on packet"));
      crStop(0);
    }
    st->incoming_sequence++;         /* whether or not we MACed */

    /*
     * Decompress packet payload.
     */
    {
      unsigned char *newpayload;
      int newlen;
      if (ssh->sccomp &&
          ssh->sccomp->decompress(ssh->sc_comp_ctx,
                            ssh->pktin.data + 5, ssh->pktin.length - 5,
                            &newpayload, &newlen)) {
          if (ssh->pktin.maxlen < newlen + 5) {
            ssh->pktin.maxlen = newlen + 5;
            ssh->pktin.data = sresize(ssh->pktin.data,
                                ssh->pktin.maxlen + APIEXTRA,
                                unsigned char);
          }
          ssh->pktin.length = 5 + newlen;
          memcpy(ssh->pktin.data + 5, newpayload, newlen);
          sfree(newpayload);
      }
    }

    ssh->pktin.savedpos = 6;
    ssh->pktin.body = ssh->pktin.data;
    ssh->pktin.type = ssh->pktin.data[5];

    if (ssh->logctx)
      log_packet(ssh->logctx, PKT_INCOMING, ssh->pktin.type,
               ssh2_pkt_type(ssh->pkt_ctx, ssh->pktin.type),
               ssh->pktin.data+6, ssh->pktin.length-6);

    switch (ssh->pktin.type) {
        /*
         * These packets we must handle instantly.
         */
      case SSH2_MSG_DISCONNECT:
        {
            /* log reason code in disconnect message */
            char *buf;
          int nowlen;
            int reason = GET_32BIT(ssh->pktin.data + 6);
            unsigned msglen = GET_32BIT(ssh->pktin.data + 10);

            if (reason > 0 && reason < lenof(ssh2_disconnect_reasons)) {
                buf = dupprintf("Received disconnect message (%s)",
                        ssh2_disconnect_reasons[reason]);
            } else {
                buf = dupprintf("Received disconnect message (unknown"
                        " type %d)", reason);
            }
            logevent(buf);
          sfree(buf);
            buf = dupprintf("Disconnection message text: %n%.*s",
                      &nowlen, msglen, ssh->pktin.data + 14);
            logevent(buf);
            bombout(("Server sent disconnect message\ntype %d (%s):\n\"%s\"",
                     reason,
                     (reason > 0 && reason < lenof(ssh2_disconnect_reasons)) ?
                     ssh2_disconnect_reasons[reason] : "unknown",
                     buf+nowlen));
          sfree(buf);
            crStop(0);
        }
        break;
      case SSH2_MSG_IGNORE:
      goto next_packet;
      case SSH2_MSG_DEBUG:
      {
          /* log the debug message */
          char buf[512];
          /* int display = ssh->pktin.body[6]; */
          int stringlen = GET_32BIT(ssh->pktin.data+7);
          int prefix;
          strcpy(buf, "Remote debug message: ");
          prefix = strlen(buf);
          if (stringlen > (int)(sizeof(buf)-prefix-1))
            stringlen = sizeof(buf)-prefix-1;
          memcpy(buf + prefix, ssh->pktin.data + 11, stringlen);
          buf[prefix + stringlen] = '\0';
          logevent(buf);
      }
        goto next_packet;              /* FIXME: print the debug message */

        /*
         * These packets we need do nothing about here.
         */
      case SSH2_MSG_UNIMPLEMENTED:
      case SSH2_MSG_SERVICE_REQUEST:
      case SSH2_MSG_SERVICE_ACCEPT:
      case SSH2_MSG_KEXINIT:
      case SSH2_MSG_NEWKEYS:
      case SSH2_MSG_KEXDH_INIT:
      case SSH2_MSG_KEXDH_REPLY:
      /* case SSH2_MSG_KEX_DH_GEX_REQUEST: duplicate case value */
      /* case SSH2_MSG_KEX_DH_GEX_GROUP: duplicate case value */
      case SSH2_MSG_KEX_DH_GEX_INIT:
      case SSH2_MSG_KEX_DH_GEX_REPLY:
      case SSH2_MSG_USERAUTH_REQUEST:
      case SSH2_MSG_USERAUTH_FAILURE:
      case SSH2_MSG_USERAUTH_SUCCESS:
      case SSH2_MSG_USERAUTH_BANNER:
      case SSH2_MSG_USERAUTH_PK_OK:
      /* case SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ: duplicate case value */
      /* case SSH2_MSG_USERAUTH_INFO_REQUEST: duplicate case value */
      case SSH2_MSG_USERAUTH_INFO_RESPONSE:
      case SSH2_MSG_GLOBAL_REQUEST:
      case SSH2_MSG_REQUEST_SUCCESS:
      case SSH2_MSG_REQUEST_FAILURE:
      case SSH2_MSG_CHANNEL_OPEN:
      case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
      case SSH2_MSG_CHANNEL_OPEN_FAILURE:
      case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
      case SSH2_MSG_CHANNEL_DATA:
      case SSH2_MSG_CHANNEL_EXTENDED_DATA:
      case SSH2_MSG_CHANNEL_EOF:
      case SSH2_MSG_CHANNEL_CLOSE:
      case SSH2_MSG_CHANNEL_REQUEST:
      case SSH2_MSG_CHANNEL_SUCCESS:
      case SSH2_MSG_CHANNEL_FAILURE:
        break;

        /*
         * For anything else we send SSH2_MSG_UNIMPLEMENTED.
         */
      default:
      ssh2_pkt_init(ssh, SSH2_MSG_UNIMPLEMENTED);
      ssh2_pkt_adduint32(ssh, st->incoming_sequence - 1);
      ssh2_pkt_send(ssh);
        break;
    }

    crFinish(0);
}

static void ssh1_pktout_size(Ssh ssh, int len)
{
    int pad, biglen;

    len += 5;                        /* type and CRC */
    pad = 8 - (len % 8);
    biglen = len + pad;

    ssh->pktout.length = len - 5;
    if (ssh->pktout.maxlen < biglen) {
      ssh->pktout.maxlen = biglen;
#ifdef MSCRYPTOAPI
      /* Allocate enough buffer space for extra block
       * for MS CryptEncrypt() */
      ssh->pktout.data = sresize(ssh->pktout.data, biglen + 12,
                           unsigned char);
#else
      ssh->pktout.data = sresize(ssh->pktout.data, biglen + 4,
                           unsigned char);
#endif
    }
    ssh->pktout.body = ssh->pktout.data + 4 + pad + 1;
}

static void s_wrpkt_start(Ssh ssh, int type, int len)
{
    ssh1_pktout_size(ssh, len);
    ssh->pktout.type = type;
}

static int s_wrpkt_prepare(Ssh ssh)
{
    int pad, biglen, i;
    unsigned long crc;
#ifdef __SC__
    /*
     * XXX various versions of SC (including 8.8.4) screw up the
     * register allocation in this function and use the same register
     * (D6) for len and as a temporary, with predictable results.  The
     * following sledgehammer prevents this.
     */
    volatile
#endif
    int len;

    ssh->pktout.body[-1] = ssh->pktout.type;

    if (ssh->logctx)
      log_packet(ssh->logctx, PKT_OUTGOING, ssh->pktout.type,
               ssh1_pkt_type(ssh->pktout.type),
               ssh->pktout.body, ssh->pktout.length);

    if (ssh->v1_compressing) {
      unsigned char *compblk;
      int complen;
      zlib_compress_block(ssh->cs_comp_ctx,
                      ssh->pktout.body - 1, ssh->pktout.length + 1,
                      &compblk, &complen);
      ssh1_pktout_size(ssh, complen - 1);
      memcpy(ssh->pktout.body - 1, compblk, complen);
      sfree(compblk);
    }

    len = ssh->pktout.length + 5;          /* type and CRC */
    pad = 8 - (len % 8);
    biglen = len + pad;

    for (i = 0; i < pad; i++)
      ssh->pktout.data[i + 4] = random_byte();
    crc = crc32_compute(ssh->pktout.data + 4, biglen - 4);
    PUT_32BIT(ssh->pktout.data + biglen, crc);
    PUT_32BIT(ssh->pktout.data, len);

    if (ssh->cipher)
      ssh->cipher->encrypt(ssh->v1_cipher_ctx, ssh->pktout.data + 4, biglen);

    return biglen + 4;
}

static void s_wrpkt(Ssh ssh)
{
    int len, backlog;
    len = s_wrpkt_prepare(ssh);
    backlog = sk_write(ssh->s, (char *)ssh->pktout.data, len);
    if (backlog > SSH_MAX_BACKLOG)
      ssh_throttle_all(ssh, 1, backlog);
}

static void s_wrpkt_defer(Ssh ssh)
{
    int len;
    len = s_wrpkt_prepare(ssh);
    if (ssh->deferred_len + len > ssh->deferred_size) {
      ssh->deferred_size = ssh->deferred_len + len + 128;
      ssh->deferred_send_data = sresize(ssh->deferred_send_data,
                                ssh->deferred_size,
                                unsigned char);
    }
    memcpy(ssh->deferred_send_data + ssh->deferred_len, ssh->pktout.data, len);
    ssh->deferred_len += len;
}

/*
 * Construct a packet with the specified contents.
 */
static void construct_packet(Ssh ssh, int pkttype, va_list ap1, va_list ap2)
{
    unsigned char *p, *argp, argchar;
    unsigned long argint;
    int pktlen, argtype, arglen;
    Bignum bn;

    pktlen = 0;
    while ((argtype = va_arg(ap1, int)) != PKT_END) {
      switch (argtype) {
        case PKT_INT:
          (void) va_arg(ap1, int);
          pktlen += 4;
          break;
        case PKT_CHAR:
          (void) va_arg(ap1, int);
          pktlen++;
          break;
        case PKT_DATA:
          (void) va_arg(ap1, unsigned char *);
          arglen = va_arg(ap1, int);
          pktlen += arglen;
          break;
        case PKT_STR:
          argp = va_arg(ap1, unsigned char *);
          arglen = strlen((char *)argp);
          pktlen += 4 + arglen;
          break;
        case PKT_BIGNUM:
          bn = va_arg(ap1, Bignum);
          pktlen += ssh1_bignum_length(bn);
          break;
        default:
          assert(0);
      }
    }

    s_wrpkt_start(ssh, pkttype, pktlen);
    p = ssh->pktout.body;

    while ((argtype = va_arg(ap2, int)) != PKT_END) {
      switch (argtype) {
        case PKT_INT:
          argint = va_arg(ap2, int);
          PUT_32BIT(p, argint);
          p += 4;
          break;
        case PKT_CHAR:
          argchar = (unsigned char) va_arg(ap2, int);
          *p = argchar;
          p++;
          break;
        case PKT_DATA:
          argp = va_arg(ap2, unsigned char *);
          arglen = va_arg(ap2, int);
          memcpy(p, argp, arglen);
          p += arglen;
          break;
        case PKT_STR:
          argp = va_arg(ap2, unsigned char *);
          arglen = strlen((char *)argp);
          PUT_32BIT(p, arglen);
          memcpy(p + 4, argp, arglen);
          p += 4 + arglen;
          break;
        case PKT_BIGNUM:
          bn = va_arg(ap2, Bignum);
          p += ssh1_write_bignum(p, bn);
          break;
      }
    }
}

static void send_packet(Ssh ssh, int pkttype, ...)
{
    va_list ap1, ap2;
    va_start(ap1, pkttype);
    va_start(ap2, pkttype);
    construct_packet(ssh, pkttype, ap1, ap2);
    s_wrpkt(ssh);
}

static void defer_packet(Ssh ssh, int pkttype, ...)
{
    va_list ap1, ap2;
    va_start(ap1, pkttype);
    va_start(ap2, pkttype);
    construct_packet(ssh, pkttype, ap1, ap2);
    s_wrpkt_defer(ssh);
}

static int ssh_versioncmp(char *a, char *b)
{
    char *ae, *be;
    unsigned long av, bv;

    av = strtoul(a, &ae, 10);
    bv = strtoul(b, &be, 10);
    if (av != bv)
      return (av < bv ? -1 : +1);
    if (*ae == '.')
      ae++;
    if (*be == '.')
      be++;
    av = strtoul(ae, &ae, 10);
    bv = strtoul(be, &be, 10);
    if (av != bv)
      return (av < bv ? -1 : +1);
    return 0;
}

/*
 * Utility routines for putting an SSH-protocol `string' and
 * `uint32' into a SHA state.
 */
#include <stdio.h>
static void sha_string(SHA_State * s, void *str, int len)
{
    unsigned char lenblk[4];
    PUT_32BIT(lenblk, len);
    SHA_Bytes(s, lenblk, 4);
    SHA_Bytes(s, str, len);
}

static void sha_uint32(SHA_State * s, unsigned i)
{
    unsigned char intblk[4];
    PUT_32BIT(intblk, i);
    SHA_Bytes(s, intblk, 4);
}

/*
 * SSH2 packet construction functions.
 */
static void ssh2_pkt_ensure(Ssh ssh, int length)
{
    if (ssh->pktout.maxlen < length) {
      ssh->pktout.maxlen = length + 256;
      ssh->pktout.data = sresize(ssh->pktout.data,
                           ssh->pktout.maxlen + APIEXTRA,
                           unsigned char);
      if (!ssh->pktout.data)
          fatalbox("Out of memory");
    }
}
static void ssh2_pkt_adddata(Ssh ssh, void *data, int len)
{
    ssh->pktout.length += len;
    ssh2_pkt_ensure(ssh, ssh->pktout.length);
    memcpy(ssh->pktout.data + ssh->pktout.length - len, data, len);
}
static void ssh2_pkt_addbyte(Ssh ssh, unsigned char byte)
{
    ssh2_pkt_adddata(ssh, &byte, 1);
}
static void ssh2_pkt_init(Ssh ssh, int pkt_type)
{
    ssh->pktout.length = 5;
    ssh2_pkt_addbyte(ssh, (unsigned char) pkt_type);
}
static void ssh2_pkt_addbool(Ssh ssh, unsigned char value)
{
    ssh2_pkt_adddata(ssh, &value, 1);
}
static void ssh2_pkt_adduint32(Ssh ssh, unsigned long value)
{
    unsigned char x[4];
    PUT_32BIT(x, value);
    ssh2_pkt_adddata(ssh, x, 4);
}
static void ssh2_pkt_addstring_start(Ssh ssh)
{
    ssh2_pkt_adduint32(ssh, 0);
    ssh->pktout.savedpos = ssh->pktout.length;
}
static void ssh2_pkt_addstring_str(Ssh ssh, char *data)
{
    ssh2_pkt_adddata(ssh, data, strlen(data));
    PUT_32BIT(ssh->pktout.data + ssh->pktout.savedpos - 4,
            ssh->pktout.length - ssh->pktout.savedpos);
}
static void ssh2_pkt_addstring_data(Ssh ssh, char *data, int len)
{
    ssh2_pkt_adddata(ssh, data, len);
    PUT_32BIT(ssh->pktout.data + ssh->pktout.savedpos - 4,
            ssh->pktout.length - ssh->pktout.savedpos);
}
static void ssh2_pkt_addstring(Ssh ssh, char *data)
{
    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_str(ssh, data);
}
static unsigned char *ssh2_mpint_fmt(Bignum b, int *len)
{
    unsigned char *p;
    int i, n = (bignum_bitcount(b) + 7) / 8;
    p = snewn(n + 1, unsigned char);
    if (!p)
      fatalbox("out of memory");
    p[0] = 0;
    for (i = 1; i <= n; i++)
      p[i] = bignum_byte(b, n - i);
    i = 0;
    while (i <= n && p[i] == 0 && (p[i + 1] & 0x80) == 0)
      i++;
    memmove(p, p + i, n + 1 - i);
    *len = n + 1 - i;
    return p;
}
static void ssh2_pkt_addmp(Ssh ssh, Bignum b)
{
    unsigned char *p;
    int len;
    p = ssh2_mpint_fmt(b, &len);
    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_data(ssh, (char *)p, len);
    sfree(p);
}

/*
 * Construct an SSH2 final-form packet: compress it, encrypt it,
 * put the MAC on it. Final packet, ready to be sent, is stored in
 * ssh->pktout.data. Total length is returned.
 */
static int ssh2_pkt_construct(Ssh ssh)
{
    int cipherblk, maclen, padding, i;

    if (ssh->logctx)
      log_packet(ssh->logctx, PKT_OUTGOING, ssh->pktout.data[5],
               ssh2_pkt_type(ssh->pkt_ctx, ssh->pktout.data[5]),
               ssh->pktout.data + 6, ssh->pktout.length - 6);

    /*
     * Compress packet payload.
     */
    {
      unsigned char *newpayload;
      int newlen;
      if (ssh->cscomp &&
          ssh->cscomp->compress(ssh->cs_comp_ctx, ssh->pktout.data + 5,
                          ssh->pktout.length - 5,
                          &newpayload, &newlen)) {
          ssh->pktout.length = 5;
          ssh2_pkt_adddata(ssh, newpayload, newlen);
          sfree(newpayload);
      }
    }

    /*
     * Add padding. At least four bytes, and must also bring total
     * length (minus MAC) up to a multiple of the block size.
     */
    cipherblk = ssh->cscipher ? ssh->cscipher->blksize : 8;  /* block size */
    cipherblk = cipherblk < 8 ? 8 : cipherblk;  /* or 8 if blksize < 8 */
    padding = 4;
    padding +=
      (cipherblk - (ssh->pktout.length + padding) % cipherblk) % cipherblk;
    maclen = ssh->csmac ? ssh->csmac->len : 0;
    ssh2_pkt_ensure(ssh, ssh->pktout.length + padding + maclen);
    ssh->pktout.data[4] = padding;
    for (i = 0; i < padding; i++)
      ssh->pktout.data[ssh->pktout.length + i] = random_byte();
    PUT_32BIT(ssh->pktout.data, ssh->pktout.length + padding - 4);
    if (ssh->csmac)
      ssh->csmac->generate(ssh->cs_mac_ctx, ssh->pktout.data,
                       ssh->pktout.length + padding,
                       ssh->v2_outgoing_sequence);
    ssh->v2_outgoing_sequence++;       /* whether or not we MACed */

    if (ssh->cscipher)
      ssh->cscipher->encrypt(ssh->cs_cipher_ctx,
                         ssh->pktout.data, ssh->pktout.length + padding);

    /* Ready-to-send packet starts at ssh->pktout.data. We return length. */
    return ssh->pktout.length + padding + maclen;
}

/*
 * Construct and send an SSH2 packet immediately.
 */
static void ssh2_pkt_send(Ssh ssh)
{
    int len;
    int backlog;
    len = ssh2_pkt_construct(ssh);
    backlog = sk_write(ssh->s, (char *)ssh->pktout.data, len);
    if (backlog > SSH_MAX_BACKLOG)
      ssh_throttle_all(ssh, 1, backlog);
}

/*
 * Construct an SSH2 packet and add it to a deferred data block.
 * Useful for sending multiple packets in a single sk_write() call,
 * to prevent a traffic-analysing listener from being able to work
 * out the length of any particular packet (such as the password
 * packet).
 * 
 * Note that because SSH2 sequence-numbers its packets, this can
 * NOT be used as an m4-style `defer' allowing packets to be
 * constructed in one order and sent in another.
 */
static void ssh2_pkt_defer(Ssh ssh)
{
    int len = ssh2_pkt_construct(ssh);
    if (ssh->deferred_len + len > ssh->deferred_size) {
      ssh->deferred_size = ssh->deferred_len + len + 128;
      ssh->deferred_send_data = sresize(ssh->deferred_send_data,
                                ssh->deferred_size,
                                unsigned char);
    }
    memcpy(ssh->deferred_send_data + ssh->deferred_len, ssh->pktout.data, len);
    ssh->deferred_len += len;
}

/*
 * Send the whole deferred data block constructed by
 * ssh2_pkt_defer() or SSH1's defer_packet().
 */
static void ssh_pkt_defersend(Ssh ssh)
{
    int backlog;
    backlog = sk_write(ssh->s, (char *)ssh->deferred_send_data,
                   ssh->deferred_len);
    ssh->deferred_len = ssh->deferred_size = 0;
    sfree(ssh->deferred_send_data);
    ssh->deferred_send_data = NULL;
    if (backlog > SSH_MAX_BACKLOG)
      ssh_throttle_all(ssh, 1, backlog);
}

#if 0
void bndebug(char *string, Bignum b)
{
    unsigned char *p;
    int i, len;
    p = ssh2_mpint_fmt(b, &len);
    debug(("%s", string));
    for (i = 0; i < len; i++)
      debug((" %02x", p[i]));
    debug(("\n"));
    sfree(p);
}
#endif

static void sha_mpint(SHA_State * s, Bignum b)
{
    unsigned char *p;
    int len;
    p = ssh2_mpint_fmt(b, &len);
    sha_string(s, p, len);
    sfree(p);
}

/*
 * Packet decode functions for both SSH1 and SSH2.
 */
static unsigned long ssh_pkt_getuint32(Ssh ssh)
{
    unsigned long value;
    if (ssh->pktin.length - ssh->pktin.savedpos < 4)
      return 0;                /* arrgh, no way to decline (FIXME?) */
    value = GET_32BIT(ssh->pktin.body + ssh->pktin.savedpos);
    ssh->pktin.savedpos += 4;
    return value;
}
static int ssh2_pkt_getbool(Ssh ssh)
{
    unsigned long value;
    if (ssh->pktin.length - ssh->pktin.savedpos < 1)
      return 0;                /* arrgh, no way to decline (FIXME?) */
    value = ssh->pktin.body[ssh->pktin.savedpos] != 0;
    ssh->pktin.savedpos++;
    return value;
}
static void ssh_pkt_getstring(Ssh ssh, char **p, int *length)
{
    int len;
    *p = NULL;
    *length = 0;
    if (ssh->pktin.length - ssh->pktin.savedpos < 4)
      return;
    len = GET_32BIT(ssh->pktin.body + ssh->pktin.savedpos);
    if (len < 0)
      return;
    *length = len;
    ssh->pktin.savedpos += 4;
    if (ssh->pktin.length - ssh->pktin.savedpos < *length)
      return;
    *p = (char *)(ssh->pktin.body + ssh->pktin.savedpos);
    ssh->pktin.savedpos += *length;
}
static void *ssh_pkt_getdata(Ssh ssh, int length)
{
    if (ssh->pktin.length - ssh->pktin.savedpos < length)
      return NULL;
    ssh->pktin.savedpos += length;
    return ssh->pktin.body + (ssh->pktin.savedpos - length);
}
static int ssh1_pkt_getrsakey(Ssh ssh, struct RSAKey *key,
                        unsigned char **keystr)
{
    int j;

    j = makekey(ssh->pktin.body + ssh->pktin.savedpos,
            ssh->pktin.length - ssh->pktin.savedpos,
            key, keystr, 0);

    if (j < 0)
      return FALSE;
    
    ssh->pktin.savedpos += j;
    assert(ssh->pktin.savedpos < ssh->pktin.length);

    return TRUE;
}
static Bignum ssh1_pkt_getmp(Ssh ssh)
{
    int j;
    Bignum b;

    j = ssh1_read_bignum(ssh->pktin.body + ssh->pktin.savedpos,
                   ssh->pktin.length - ssh->pktin.savedpos, &b);

    if (j < 0)
      return NULL;

    ssh->pktin.savedpos += j;
    return b;
}
static Bignum ssh2_pkt_getmp(Ssh ssh)
{
    char *p;
    int length;
    Bignum b;

    ssh_pkt_getstring(ssh, &p, &length);
    if (!p)
      return NULL;
    if (p[0] & 0x80) {
      bombout(("internal error: Can't handle negative mpints"));
      return NULL;
    }
    b = bignum_from_bytes((unsigned char *)p, length);
    return b;
}

/*
 * Helper function to add an SSH2 signature blob to a packet.
 * Expects to be shown the public key blob as well as the signature
 * blob. Normally works just like ssh2_pkt_addstring, but will
 * fiddle with the signature packet if necessary for
 * BUG_SSH2_RSA_PADDING.
 */
static void ssh2_add_sigblob(Ssh ssh, void *pkblob_v, int pkblob_len,
                       void *sigblob_v, int sigblob_len)
{
    unsigned char *pkblob = (unsigned char *)pkblob_v;
    unsigned char *sigblob = (unsigned char *)sigblob_v;

    /* dmemdump(pkblob, pkblob_len); */
    /* dmemdump(sigblob, sigblob_len); */

    /*
     * See if this is in fact an ssh-rsa signature and a buggy
     * server; otherwise we can just do this the easy way.
     */
    if ((ssh->remote_bugs & BUG_SSH2_RSA_PADDING) &&
      (GET_32BIT(pkblob) == 7 && !memcmp(pkblob+4, "ssh-rsa", 7))) {
      int pos, len, siglen;

      /*
       * Find the byte length of the modulus.
       */

      pos = 4+7;               /* skip over "ssh-rsa" */
      pos += 4 + GET_32BIT(pkblob+pos);   /* skip over exponent */
      len = GET_32BIT(pkblob+pos);   /* find length of modulus */
      pos += 4;                /* find modulus itself */
      while (len > 0 && pkblob[pos] == 0)
          len--, pos++;
      /* debug(("modulus length is %d\n", len)); */

      /*
       * Now find the signature integer.
       */
      pos = 4+7;               /* skip over "ssh-rsa" */
      siglen = GET_32BIT(sigblob+pos);
      /* debug(("signature length is %d\n", siglen)); */

      if (len != siglen) {
          unsigned char newlen[4];
          ssh2_pkt_addstring_start(ssh);
          ssh2_pkt_addstring_data(ssh, (char *)sigblob, pos);
          /* dmemdump(sigblob, pos); */
          pos += 4;                  /* point to start of actual sig */
          PUT_32BIT(newlen, len);
          ssh2_pkt_addstring_data(ssh, (char *)newlen, 4);
          /* dmemdump(newlen, 4); */
          newlen[0] = 0;
          while (len-- > siglen) {
            ssh2_pkt_addstring_data(ssh, (char *)newlen, 1);
            /* dmemdump(newlen, 1); */
          }
          ssh2_pkt_addstring_data(ssh, (char *)(sigblob+pos), siglen);
          /* dmemdump(sigblob+pos, siglen); */
          return;
      }

      /* Otherwise fall through and do it the easy way. */
    }

    ssh2_pkt_addstring_start(ssh);
    ssh2_pkt_addstring_data(ssh, (char *)sigblob, sigblob_len);
}

/*
 * Examine the remote side's version string and compare it against
 * a list of known buggy implementations.
 */
static void ssh_detect_bugs(Ssh ssh, char *vstring)
{
    char *imp;                       /* pointer to implementation part */
    imp = vstring;
    imp += strcspn(imp, "-");
    if (*imp) imp++;
    imp += strcspn(imp, "-");
    if (*imp) imp++;

    ssh->remote_bugs = 0;

    if (ssh->cfg.sshbug_ignore1 == FORCE_ON ||
      (ssh->cfg.sshbug_ignore1 == AUTO &&
       (!strcmp(imp, "1.2.18") || !strcmp(imp, "1.2.19") ||
        !strcmp(imp, "1.2.20") || !strcmp(imp, "1.2.21") ||
        !strcmp(imp, "1.2.22") || !strcmp(imp, "Cisco-1.25") ||
        !strcmp(imp, "OSU_1.4alpha3")))) {
      /*
       * These versions don't support SSH1_MSG_IGNORE, so we have
       * to use a different defence against password length
       * sniffing.
       */
      ssh->remote_bugs |= BUG_CHOKES_ON_SSH1_IGNORE;
      logevent("We believe remote version has SSH1 ignore bug");
    }

    if (ssh->cfg.sshbug_plainpw1 == FORCE_ON ||
      (ssh->cfg.sshbug_plainpw1 == AUTO &&
       (!strcmp(imp, "Cisco-1.25") || !strcmp(imp, "OSU_1.4alpha3")))) {
      /*
       * These versions need a plain password sent; they can't
       * handle having a null and a random length of data after
       * the password.
       */
      ssh->remote_bugs |= BUG_NEEDS_SSH1_PLAIN_PASSWORD;
      logevent("We believe remote version needs a plain SSH1 password");
    }

    if (ssh->cfg.sshbug_rsa1 == FORCE_ON ||
      (ssh->cfg.sshbug_rsa1 == AUTO &&
       (!strcmp(imp, "Cisco-1.25")))) {
      /*
       * These versions apparently have no clue whatever about
       * RSA authentication and will panic and die if they see
       * an AUTH_RSA message.
       */
      ssh->remote_bugs |= BUG_CHOKES_ON_RSA;
      logevent("We believe remote version can't handle RSA authentication");
    }

    if (ssh->cfg.sshbug_hmac2 == FORCE_ON ||
      (ssh->cfg.sshbug_hmac2 == AUTO &&
       !wc_match("* VShell", imp) &&
       (wc_match("2.1.0*", imp) || wc_match("2.0.*", imp) ||
        wc_match("2.2.0*", imp) || wc_match("2.3.0*", imp) ||
        wc_match("2.1 *", imp)))) {
      /*
       * These versions have the HMAC bug.
       */
      ssh->remote_bugs |= BUG_SSH2_HMAC;
      logevent("We believe remote version has SSH2 HMAC bug");
    }

    if (ssh->cfg.sshbug_derivekey2 == FORCE_ON ||
      (ssh->cfg.sshbug_derivekey2 == AUTO &&
       !wc_match("* VShell", imp) &&
       (wc_match("2.0.0*", imp) || wc_match("2.0.10*", imp) ))) {
      /*
       * These versions have the key-derivation bug (failing to
       * include the literal shared secret in the hashes that
       * generate the keys).
       */
      ssh->remote_bugs |= BUG_SSH2_DERIVEKEY;
      logevent("We believe remote version has SSH2 key-derivation bug");
    }

    if (ssh->cfg.sshbug_rsapad2 == FORCE_ON ||
      (ssh->cfg.sshbug_rsapad2 == AUTO &&
       (wc_match("OpenSSH_2.[5-9]*", imp) ||
        wc_match("OpenSSH_3.[0-2]*", imp)))) {
      /*
       * These versions have the SSH2 RSA padding bug.
       */
      ssh->remote_bugs |= BUG_SSH2_RSA_PADDING;
      logevent("We believe remote version has SSH2 RSA padding bug");
    }

    if (ssh->cfg.sshbug_pksessid2 == FORCE_ON ||
      (ssh->cfg.sshbug_pksessid2 == AUTO &&
       wc_match("OpenSSH_2.[0-2]*", imp))) {
      /*
       * These versions have the SSH2 session-ID bug in
       * public-key authentication.
       */
      ssh->remote_bugs |= BUG_SSH2_PK_SESSIONID;
      logevent("We believe remote version has SSH2 public-key-session-ID bug");
    }

    if (ssh->cfg.sshbug_dhgex2 == FORCE_ON) {
      /*
       * User specified the SSH2 DH GEX bug.
       */
      ssh->remote_bugs |= BUG_SSH2_DH_GEX;
      logevent("We believe remote version has SSH2 DH group exchange bug");
    }
}

static int do_ssh_init(Ssh ssh, unsigned char c)
{
    struct do_ssh_init_state {
      int vslen;
      char version[10];
      char *vstring;
      int vstrsize;
      int i;
      int proto1, proto2;
    };
    crState(do_ssh_init_state);

    crBegin(ssh->do_ssh_init_crstate);

    /* Search for the string "SSH-" in the input. */
    s->i = 0;
    while (1) {
      static const int transS[] = { 1, 2, 2, 1 };
      static const int transH[] = { 0, 0, 3, 0 };
      static const int transminus[] = { 0, 0, 0, -1 };
      if (c == 'S')
          s->i = transS[s->i];
      else if (c == 'H')
          s->i = transH[s->i];
      else if (c == '-')
          s->i = transminus[s->i];
      else
          s->i = 0;
      if (s->i < 0)
          break;
      crReturn(1);                   /* get another character */
    }

    s->vstrsize = 16;
    s->vstring = snewn(s->vstrsize, char);
    strcpy(s->vstring, "SSH-");
    s->vslen = 4;
    s->i = 0;
    while (1) {
      crReturn(1);                   /* get another char */
      if (s->vslen >= s->vstrsize - 1) {
          s->vstrsize += 16;
          s->vstring = sresize(s->vstring, s->vstrsize, char);
      }
      s->vstring[s->vslen++] = c;
      if (s->i >= 0) {
          if (c == '-') {
            s->version[s->i] = '\0';
            s->i = -1;
          } else if (s->i < sizeof(s->version) - 1)
            s->version[s->i++] = c;
      } else if (c == '\n')
          break;
    }

    ssh->agentfwd_enabled = FALSE;
    ssh->rdpkt2_state.incoming_sequence = 0;

    s->vstring[s->vslen] = 0;
    s->vstring[strcspn(s->vstring, "\r\n")] = '\0';/* remove EOL chars */
    {
      char *vlog;
      vlog = snewn(20 + s->vslen, char);
      sprintf(vlog, "Server version: %s", s->vstring);
      logevent(vlog);
      sfree(vlog);
    }
    ssh_detect_bugs(ssh, s->vstring);

    /*
     * Decide which SSH protocol version to support.
     */

    /* Anything strictly below "2.0" means protocol 1 is supported. */
    s->proto1 = ssh_versioncmp(s->version, "2.0") < 0;
    /* Anything greater or equal to "1.99" means protocol 2 is supported. */
    s->proto2 = ssh_versioncmp(s->version, "1.99") >= 0;

    if (ssh->cfg.sshprot == 0 && !s->proto1) {
      bombout(("SSH protocol version 1 required by user but not provided by server"));
      crStop(0);
    }
    if (ssh->cfg.sshprot == 3 && !s->proto2) {
      bombout(("SSH protocol version 2 required by user but not provided by server"));
      crStop(0);
    }

    if (s->proto2 && (ssh->cfg.sshprot >= 2 || !s->proto1)) {
      /*
       * Use v2 protocol.
       */
      char verstring[80], vlog[100];
      sprintf(verstring, "SSH-2.0-%s", sshver);
      SHA_Init(&ssh->exhashbase);
      /*
       * Hash our version string and their version string.
       */
      sha_string(&ssh->exhashbase, verstring, strlen(verstring));
      sha_string(&ssh->exhashbase, s->vstring, strcspn(s->vstring, "\r\n"));
      sprintf(vlog, "We claim version: %s", verstring);
      logevent(vlog);
      strcat(verstring, "\n");
      logevent("Using SSH protocol version 2");
      sk_write(ssh->s, verstring, strlen(verstring));
      ssh->protocol = ssh2_protocol;
      ssh->version = 2;
      ssh->s_rdpkt = ssh2_rdpkt;
    } else {
      /*
       * Use v1 protocol.
       */
      char verstring[80], vlog[100];
      sprintf(verstring, "SSH-%s-%s",
            (ssh_versioncmp(s->version, "1.5") <= 0 ? s->version : "1.5"),
            sshver);
      sprintf(vlog, "We claim version: %s", verstring);
      logevent(vlog);
      strcat(verstring, "\n");

      logevent("Using SSH protocol version 1");
      sk_write(ssh->s, verstring, strlen(verstring));
      ssh->protocol = ssh1_protocol;
      ssh->version = 1;
      ssh->s_rdpkt = ssh1_rdpkt;
    }
    update_specials_menu(ssh->frontend);
    ssh->state = SSH_STATE_BEFORE_SIZE;

    sfree(s->vstring);

    crFinish(0);
}

static void ssh_gotdata(Ssh ssh, unsigned char *data, int datalen)
{
    crBegin(ssh->ssh_gotdata_crstate);

    /*
     * To begin with, feed the characters one by one to the
     * protocol initialisation / selection function do_ssh_init().
     * When that returns 0, we're done with the initial greeting
     * exchange and can move on to packet discipline.
     */
    while (1) {
      int ret;                 /* need not be kept across crReturn */
      if (datalen == 0)
          crReturnV;                 /* more data please */
      ret = do_ssh_init(ssh, *data);
      data++;
      datalen--;
      if (ret == 0)
          break;
    }

    /*
     * We emerge from that loop when the initial negotiation is
     * over and we have selected an s_rdpkt function. Now pass
     * everything to s_rdpkt, and then pass the resulting packets
     * to the proper protocol handler.
     */
    if (datalen == 0)
      crReturnV;
    while (1) {
      while (datalen > 0) {
          if (ssh->s_rdpkt(ssh, &data, &datalen) == 0) {
            if (ssh->state == SSH_STATE_CLOSED) {
                return;
            }
            ssh->protocol(ssh, NULL, 0, 1);
            if (ssh->state == SSH_STATE_CLOSED) {
                return;
            }
          }
      }
      crReturnV;
    }
    crFinishV;
}

static void ssh_do_close(Ssh ssh)
{
    int i;
    struct ssh_channel *c;

    ssh->state = SSH_STATE_CLOSED;
    if (ssh->s) {
        sk_close(ssh->s);
        ssh->s = NULL;
    }
    /*
     * Now we must shut down any port and X forwardings going
     * through this connection.
     */
    if (ssh->channels) {
      for (i = 0; NULL != (c = index234(ssh->channels, i)); i++) {
          switch (c->type) {
            case CHAN_X11:
            x11_close(c->u.x11.s);
            break;
            case CHAN_SOCKDATA:
            pfd_close(c->u.pfd.s);
            break;
          }
          del234(ssh->channels, c);
          if (ssh->version == 2)
            bufchain_clear(&c->v.v2.outbuffer);
          sfree(c);
      }
    }
}

static int ssh_closing(Plug plug, const char *error_msg, int error_code,
                   int calling_back)
{
    Ssh ssh = (Ssh) plug;
    ssh_do_close(ssh);
    if (error_msg) {
      /* A socket error has occurred. */
      logevent(error_msg);
      connection_fatal(ssh->frontend, "%s", error_msg);
    } else {
      /* Otherwise, the remote side closed the connection normally. */
    }
    return 0;
}

static int ssh_receive(Plug plug, int urgent, char *data, int len)
{
    Ssh ssh = (Ssh) plug;
    ssh_gotdata(ssh, (unsigned char *)data, len);
    if (ssh->state == SSH_STATE_CLOSED) {
      ssh_do_close(ssh);
      return 0;
    }
    return 1;
}

static void ssh_sent(Plug plug, int bufsize)
{
    Ssh ssh = (Ssh) plug;
    /*
     * If the send backlog on the SSH socket itself clears, we
     * should unthrottle the whole world if it was throttled.
     */
    if (bufsize < SSH_MAX_BACKLOG)
      ssh_throttle_all(ssh, 0, bufsize);
}

/*
 * Connect to specified host and port.
 * Returns an error message, or NULL on success.
 * Also places the canonical host name into `realhost'. It must be
 * freed by the caller.
 */
static const char *connect_to_host(Ssh ssh, char *host, int port,
                           char **realhost, int nodelay, int keepalive)
{
    static const struct plug_function_table fn_table = {
      ssh_closing,
      ssh_receive,
      ssh_sent,
      NULL
    };

    SockAddr addr;
    const char *err;

    ssh->savedhost = snewn(1 + strlen(host), char);
    if (!ssh->savedhost)
      fatalbox("Out of memory");
    strcpy(ssh->savedhost, host);

    if (port < 0)
      port = 22;               /* default ssh port */
    ssh->savedport = port;

    /*
     * Try to find host.
     */
    logeventf(ssh, "Looking up host \"%s\"", host);
    addr = name_lookup(host, port, realhost, &ssh->cfg);
    if ((err = sk_addr_error(addr)) != NULL) {
      sk_addr_free(addr);
      return err;
    }

    /*
     * Open socket.
     */
    {
      char addrbuf[100];
      sk_getaddr(addr, addrbuf, 100);
      logeventf(ssh, "Connecting to %s port %d", addrbuf, port);
    }
    ssh->fn = &fn_table;
    ssh->s = new_connection(addr, *realhost, port,
                      0, 1, nodelay, keepalive, (Plug) ssh, &ssh->cfg);
    if ((err = sk_socket_error(ssh->s)) != NULL) {
      ssh->s = NULL;
      return err;
    }

    return NULL;
}

/*
 * Throttle or unthrottle the SSH connection.
 */
static void ssh1_throttle(Ssh ssh, int adjust)
{
    int old_count = ssh->v1_throttle_count;
    ssh->v1_throttle_count += adjust;
    assert(ssh->v1_throttle_count >= 0);
    if (ssh->v1_throttle_count && !old_count) {
      sk_set_frozen(ssh->s, 1);
    } else if (!ssh->v1_throttle_count && old_count) {
      sk_set_frozen(ssh->s, 0);
    }
}

/*
 * Throttle or unthrottle _all_ local data streams (for when sends
 * on the SSH connection itself back up).
 */
static void ssh_throttle_all(Ssh ssh, int enable, int bufsize)
{
    int i;
    struct ssh_channel *c;

    if (enable == ssh->throttled_all)
      return;
    ssh->throttled_all = enable;
    ssh->overall_bufsize = bufsize;
    if (!ssh->channels)
      return;
    for (i = 0; NULL != (c = index234(ssh->channels, i)); i++) {
      switch (c->type) {
        case CHAN_MAINSESSION:
          /*
           * This is treated separately, outside the switch.
           */
          break;
        case CHAN_X11:
          x11_override_throttle(c->u.x11.s, enable);
          break;
        case CHAN_AGENT:
          /* Agent channels require no buffer management. */
          break;
        case CHAN_SOCKDATA:
          pfd_override_throttle(c->u.pfd.s, enable);
          break;
      }
    }
}

/*
 * Username and password input, abstracted off into routines
 * reusable in several places - even between SSH1 and SSH2.
 */

/* Set up a username or password input loop on a given buffer. */
static void setup_userpass_input(Ssh ssh, char *buffer, int buflen, int echo)
{
    ssh->userpass_input_buffer = buffer;
    ssh->userpass_input_buflen = buflen;
    ssh->userpass_input_bufpos = 0;
    ssh->userpass_input_echo = echo;
}

/*
 * Process some terminal data in the course of username/password
 * input. Returns >0 for success (line of input returned in
 * buffer), <0 for failure (user hit ^C/^D, bomb out and exit), 0
 * for inconclusive (keep waiting for more input please).
 */
static int process_userpass_input(Ssh ssh, unsigned char *in, int inlen)
{
    char c;

    while (inlen--) {
      switch (c = *in++) {
        case 10:
        case 13:
          ssh->userpass_input_buffer[ssh->userpass_input_bufpos] = 0;
          ssh->userpass_input_buffer[ssh->userpass_input_buflen-1] = 0;
          return +1;
          break;
        case 8:
        case 127:
          if (ssh->userpass_input_bufpos > 0) {
            if (ssh->userpass_input_echo)
                c_write_str(ssh, "\b \b");
            ssh->userpass_input_bufpos--;
          }
          break;
        case 21:
        case 27:
          while (ssh->userpass_input_bufpos > 0) {
            if (ssh->userpass_input_echo)
                c_write_str(ssh, "\b \b");
            ssh->userpass_input_bufpos--;
          }
          break;
        case 3:
        case 4:
          return -1;
          break;
        default:
          /*
           * This simplistic check for printability is disabled
           * when we're doing password input, because some people
           * have control characters in their passwords.o
           */
          if ((!ssh->userpass_input_echo ||
             (c >= ' ' && c <= '~') ||
             ((unsigned char) c >= 160))
            && ssh->userpass_input_bufpos < ssh->userpass_input_buflen-1) {
            ssh->userpass_input_buffer[ssh->userpass_input_bufpos++] = c;
            if (ssh->userpass_input_echo)
                c_write(ssh, &c, 1);
          }
          break;
      }
    }
    return 0;
}

static void ssh_agent_callback(void *sshv, void *reply, int replylen)
{
    Ssh ssh = (Ssh) sshv;

    ssh->agent_response = reply;
    ssh->agent_response_len = replylen;

    if (ssh->version == 1)
      do_ssh1_login(ssh, NULL, -1, 0);
    else
      do_ssh2_authconn(ssh, NULL, -1, 0);
}

static void ssh_agentf_callback(void *cv, void *reply, int replylen)
{
    struct ssh_channel *c = (struct ssh_channel *)cv;
    Ssh ssh = c->ssh;
    void *sentreply = reply;

    if (!sentreply) {
      /* Fake SSH_AGENT_FAILURE. */
      sentreply = "\0\0\0\1\5";
      replylen = 5;
    }
    if (ssh->version == 2) {
      ssh2_add_channel_data(c, sentreply, replylen);
      ssh2_try_send(c);
    } else {
      send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                PKT_INT, c->remoteid,
                PKT_INT, replylen,
                PKT_DATA, sentreply, replylen,
                PKT_END);
    }
    if (reply)
      sfree(reply);
}

/*
 * Handle the key exchange and user authentication phases.
 */
static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    int i, j, ret;
    unsigned char cookie[8], *ptr;
    struct RSAKey servkey, hostkey;
    struct MD5Context md5c;
    struct do_ssh1_login_state {
      int len;
      unsigned char *rsabuf, *keystr1, *keystr2;
      unsigned long supported_ciphers_mask, supported_auths_mask;
      int tried_publickey, tried_agent;
      int tis_auth_refused, ccard_auth_refused;
      unsigned char session_id[16];
      int cipher_type;
      char username[100];
      void *publickey_blob;
      int publickey_bloblen;
      char password[100];
      char prompt[200];
      int pos;
      char c;
      int pwpkt_type;
      unsigned char request[5], *response, *p;
      int responselen;
      int keyi, nkeys;
      int authed;
      struct RSAKey key;
      Bignum challenge;
      char *commentp;
      int commentlen;
    };
    crState(do_ssh1_login_state);

    crBegin(ssh->do_ssh1_login_crstate);

    if (!ispkt)
      crWaitUntil(ispkt);

    if (ssh->pktin.type != SSH1_SMSG_PUBLIC_KEY) {
      bombout(("Public key packet not received"));
      crStop(0);
    }

    logevent("Received public keys");

    ptr = ssh_pkt_getdata(ssh, 8);
    if (!ptr) {
      bombout(("SSH1 public key packet stopped before random cookie"));
      crStop(0);
    }
    memcpy(cookie, ptr, 8);

    if (!ssh1_pkt_getrsakey(ssh, &servkey, &s->keystr1) ||
      !ssh1_pkt_getrsakey(ssh, &hostkey, &s->keystr2)) {    
      bombout(("SSH1 public key packet stopped before public keys"));
      crStop(0);
    }

    /*
     * Log the host key fingerprint.
     */
    {
      char logmsg[80];
      logevent("Host key fingerprint is:");
      strcpy(logmsg, "      ");
      hostkey.comment = NULL;
      rsa_fingerprint(logmsg + strlen(logmsg),
                  sizeof(logmsg) - strlen(logmsg), &hostkey);
      logevent(logmsg);
    }

    ssh->v1_remote_protoflags = ssh_pkt_getuint32(ssh);
    s->supported_ciphers_mask = ssh_pkt_getuint32(ssh);
    s->supported_auths_mask = ssh_pkt_getuint32(ssh);

    ssh->v1_local_protoflags =
      ssh->v1_remote_protoflags & SSH1_PROTOFLAGS_SUPPORTED;
    ssh->v1_local_protoflags |= SSH1_PROTOFLAG_SCREEN_NUMBER;

    MD5Init(&md5c);
    MD5Update(&md5c, s->keystr2, hostkey.bytes);
    MD5Update(&md5c, s->keystr1, servkey.bytes);
    MD5Update(&md5c, cookie, 8);
    MD5Final(s->session_id, &md5c);

    for (i = 0; i < 32; i++)
      ssh->session_key[i] = random_byte();

    /*
     * Verify that the `bits' and `bytes' parameters match.
     */
    if (hostkey.bits > hostkey.bytes * 8 ||
      servkey.bits > servkey.bytes * 8) {
      bombout(("SSH1 public keys were badly formatted"));
      crStop(0);
    }

    s->len = (hostkey.bytes > servkey.bytes ? hostkey.bytes : servkey.bytes);

    s->rsabuf = snewn(s->len, unsigned char);
    if (!s->rsabuf)
      fatalbox("Out of memory");

    /*
     * Verify the host key.
     */
    {
      /*
       * First format the key into a string.
       */
      int len = rsastr_len(&hostkey);
      char fingerprint[100];
      char *keystr = snewn(len, char);
      if (!keystr)
          fatalbox("Out of memory");
      rsastr_fmt(keystr, &hostkey);
      rsa_fingerprint(fingerprint, sizeof(fingerprint), &hostkey);
      verify_ssh_host_key(ssh->frontend,
                      ssh->savedhost, ssh->savedport, "rsa", keystr,
                      fingerprint);
      sfree(keystr);
    }

    for (i = 0; i < 32; i++) {
      s->rsabuf[i] = ssh->session_key[i];
      if (i < 16)
          s->rsabuf[i] ^= s->session_id[i];
    }

    if (hostkey.bytes > servkey.bytes) {
      ret = rsaencrypt(s->rsabuf, 32, &servkey);
      if (ret)
          ret = rsaencrypt(s->rsabuf, servkey.bytes, &hostkey);
    } else {
      ret = rsaencrypt(s->rsabuf, 32, &hostkey);
      if (ret)
          ret = rsaencrypt(s->rsabuf, hostkey.bytes, &servkey);
    }
    if (!ret) {
      bombout(("SSH1 public key encryptions failed due to bad formatting"));
      crStop(0);  
    }

    logevent("Encrypted session key");

    {
      int cipher_chosen = 0, warn = 0;
      char *cipher_string = NULL;
      int i;
      for (i = 0; !cipher_chosen && i < CIPHER_MAX; i++) {
          int next_cipher = ssh->cfg.ssh_cipherlist[i];
          if (next_cipher == CIPHER_WARN) {
            /* If/when we choose a cipher, warn about it */
            warn = 1;
          } else if (next_cipher == CIPHER_AES) {
            /* XXX Probably don't need to mention this. */
            logevent("AES not supported in SSH1, skipping");
          } else {
            switch (next_cipher) {
              case CIPHER_3DES:     s->cipher_type = SSH_CIPHER_3DES;
                              cipher_string = "3DES"; break;
              case CIPHER_BLOWFISH: s->cipher_type = SSH_CIPHER_BLOWFISH;
                              cipher_string = "Blowfish"; break;
              case CIPHER_DES:      s->cipher_type = SSH_CIPHER_DES;
                              cipher_string = "single-DES"; break;
            }
            if (s->supported_ciphers_mask & (1 << s->cipher_type))
                cipher_chosen = 1;
          }
      }
      if (!cipher_chosen) {
          if ((s->supported_ciphers_mask & (1 << SSH_CIPHER_3DES)) == 0)
            bombout(("Server violates SSH 1 protocol by not "
                   "supporting 3DES encryption"));
          else
            /* shouldn't happen */
            bombout(("No supported ciphers found"));
          crStop(0);
      }

      /* Warn about chosen cipher if necessary. */
      if (warn)
          askcipher(ssh->frontend, cipher_string, 0);
    }

    switch (s->cipher_type) {
      case SSH_CIPHER_3DES:
      logevent("Using 3DES encryption");
      break;
      case SSH_CIPHER_DES:
      logevent("Using single-DES encryption");
      break;
      case SSH_CIPHER_BLOWFISH:
      logevent("Using Blowfish encryption");
      break;
    }

    send_packet(ssh, SSH1_CMSG_SESSION_KEY,
            PKT_CHAR, s->cipher_type,
            PKT_DATA, cookie, 8,
            PKT_CHAR, (s->len * 8) >> 8, PKT_CHAR, (s->len * 8) & 0xFF,
            PKT_DATA, s->rsabuf, s->len,
            PKT_INT, ssh->v1_local_protoflags, PKT_END);

    logevent("Trying to enable encryption...");

    sfree(s->rsabuf);

    ssh->cipher = (s->cipher_type == SSH_CIPHER_BLOWFISH ? &ssh_blowfish_ssh1 :
               s->cipher_type == SSH_CIPHER_DES ? &ssh_des :
               &ssh_3des);
    ssh->v1_cipher_ctx = ssh->cipher->make_context();
    ssh->cipher->sesskey(ssh->v1_cipher_ctx, ssh->session_key);
    logeventf(ssh, "Initialised %s encryption", ssh->cipher->text_name);

    ssh->crcda_ctx = crcda_make_context();
    logevent("Installing CRC compensation attack detector");

    if (servkey.modulus) {
      sfree(servkey.modulus);
      servkey.modulus = NULL;
    }
    if (servkey.exponent) {
      sfree(servkey.exponent);
      servkey.exponent = NULL;
    }
    if (hostkey.modulus) {
      sfree(hostkey.modulus);
      hostkey.modulus = NULL;
    }
    if (hostkey.exponent) {
      sfree(hostkey.exponent);
      hostkey.exponent = NULL;
    }
    crWaitUntil(ispkt);

    if (ssh->pktin.type != SSH1_SMSG_SUCCESS) {
      bombout(("Encryption not successfully enabled"));
      crStop(0);
    }

    logevent("Successfully started encryption");

    fflush(stdout);
    {
      if ((flags & FLAG_INTERACTIVE) && !*ssh->cfg.username) {
          if (ssh_get_line && !ssh_getline_pw_only) {
            if (!ssh_get_line("login as: ",
                          s->username, sizeof(s->username), FALSE)) {
                /*
                 * get_line failed to get a username.
                 * Terminate.
                 */
                logevent("No username provided. Abandoning session.");
                    ssh_closing((Plug)ssh, NULL, 0, 0);
                crStop(1);
            }
          } else {
            int ret;           /* need not be kept over crReturn */
            c_write_str(ssh, "login as: ");
            ssh->send_ok = 1;

            setup_userpass_input(ssh, s->username, sizeof(s->username), 1);
            do {
                crWaitUntil(!ispkt);
                ret = process_userpass_input(ssh, in, inlen);
            } while (ret == 0);
            if (ret < 0)
                cleanup_exit(0);
            c_write_str(ssh, "\r\n");
          }
      } else {
          strncpy(s->username, ssh->cfg.username, sizeof(s->username));
          s->username[sizeof(s->username)-1] = '\0';
      }

      send_packet(ssh, SSH1_CMSG_USER, PKT_STR, s->username, PKT_END);
      {
          char userlog[22 + sizeof(s->username)];
          sprintf(userlog, "Sent username \"%s\"", s->username);
          logevent(userlog);
          if (flags & FLAG_INTERACTIVE &&
            (!((flags & FLAG_STDERR) && (flags & FLAG_VERBOSE)))) {
            strcat(userlog, "\r\n");
            c_write_str(ssh, userlog);
          }
      }
    }

    crWaitUntil(ispkt);

    if ((ssh->remote_bugs & BUG_CHOKES_ON_RSA)) {
      /* We must not attempt PK auth. Pretend we've already tried it. */
      s->tried_publickey = s->tried_agent = 1;
    } else {
      s->tried_publickey = s->tried_agent = 0;
    }
    s->tis_auth_refused = s->ccard_auth_refused = 0;
    /* Load the public half of ssh->cfg.keyfile so we notice if it's in Pageant */
    if (!filename_is_null(ssh->cfg.keyfile)) {
      if (!rsakey_pubblob(&ssh->cfg.keyfile,
                      &s->publickey_blob, &s->publickey_bloblen, NULL))
          s->publickey_blob = NULL;
    } else
      s->publickey_blob = NULL;

    while (ssh->pktin.type == SSH1_SMSG_FAILURE) {
      s->pwpkt_type = SSH1_CMSG_AUTH_PASSWORD;

      if (agent_exists() && !s->tried_agent) {
          /*
           * Attempt RSA authentication using Pageant.
           */
          void *r;

          s->authed = FALSE;
          s->tried_agent = 1;
          logevent("Pageant is running. Requesting keys.");

          /* Request the keys held by the agent. */
          PUT_32BIT(s->request, 1);
          s->request[4] = SSH1_AGENTC_REQUEST_RSA_IDENTITIES;
          if (!agent_query(s->request, 5, &r, &s->responselen,
                       ssh_agent_callback, ssh)) {
            do {
                crReturn(0);
                if (ispkt) {
                  bombout(("Unexpected data from server while waiting"
                         " for agent response"));
                  crStop(0);
                }
            } while (ispkt || inlen > 0);
            r = ssh->agent_response;
            s->responselen = ssh->agent_response_len;
          }
          s->response = (unsigned char *) r;
          if (s->response && s->responselen >= 5 &&
            s->response[4] == SSH1_AGENT_RSA_IDENTITIES_ANSWER) {
            s->p = s->response + 5;
            s->nkeys = GET_32BIT(s->p);
            s->p += 4;
            {
                char buf[64];
                sprintf(buf, "Pageant has %d SSH1 keys", s->nkeys);
                logevent(buf);
            }
            for (s->keyi = 0; s->keyi < s->nkeys; s->keyi++) {
                {
                  char buf[64];
                  sprintf(buf, "Trying Pageant key #%d", s->keyi);
                  logevent(buf);
                }
                if (s->publickey_blob &&
                  !memcmp(s->p, s->publickey_blob,
                        s->publickey_bloblen)) {
                  logevent("This key matches configured key file");
                  s->tried_publickey = 1;
                }
                s->p += 4;
                {
                  int n, ok = FALSE;
                  do {         /* do while (0) to make breaking easy */
                      n = ssh1_read_bignum
                        (s->p, s->responselen-(s->p-s->response),
                         &s->key.exponent);
                      if (n < 0)
                        break;
                      s->p += n;
                      n = ssh1_read_bignum
                        (s->p, s->responselen-(s->p-s->response),
                         &s->key.modulus);
                      if (n < 0)
                      break;
                      s->p += n;
                      if (s->responselen - (s->p-s->response) < 4)
                        break;
                      s->commentlen = GET_32BIT(s->p);
                      s->p += 4;
                      if (s->responselen - (s->p-s->response) <
                        s->commentlen)
                        break;
                      s->commentp = (char *)s->p;
                      s->p += s->commentlen;
                      ok = TRUE;
                  } while (0);
                  if (!ok) {
                      logevent("Pageant key list packet was truncated");
                      break;
                  }
                }
                send_packet(ssh, SSH1_CMSG_AUTH_RSA,
                        PKT_BIGNUM, s->key.modulus, PKT_END);
                crWaitUntil(ispkt);
                if (ssh->pktin.type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
                  logevent("Key refused");
                  continue;
                }
                logevent("Received RSA challenge");
                if ((s->challenge = ssh1_pkt_getmp(ssh)) == NULL) {
                  bombout(("Server's RSA challenge was badly formatted"));
                  crStop(0);
                }

                {
                  char *agentreq, *q, *ret;
                  void *vret;
                  int len, retlen;
                  len = 1 + 4;   /* message type, bit count */
                  len += ssh1_bignum_length(s->key.exponent);
                  len += ssh1_bignum_length(s->key.modulus);
                  len += ssh1_bignum_length(s->challenge);
                  len += 16;     /* session id */
                  len += 4;      /* response format */
                  agentreq = snewn(4 + len, char);
                  PUT_32BIT(agentreq, len);
                  q = agentreq + 4;
                  *q++ = SSH1_AGENTC_RSA_CHALLENGE;
                  PUT_32BIT(q, bignum_bitcount(s->key.modulus));
                  q += 4;
                  q += ssh1_write_bignum(q, s->key.exponent);
                  q += ssh1_write_bignum(q, s->key.modulus);
                  q += ssh1_write_bignum(q, s->challenge);
                  memcpy(q, s->session_id, 16);
                  q += 16;
                  PUT_32BIT(q, 1);  /* response format */
                  if (!agent_query(agentreq, len + 4, &vret, &retlen,
                               ssh_agent_callback, ssh)) {
                      sfree(agentreq);
                      do {
                        crReturn(0);
                        if (ispkt) {
                            bombout(("Unexpected data from server"
                                   " while waiting for agent"
                                   " response"));
                            crStop(0);
                        }
                      } while (ispkt || inlen > 0);
                      vret = ssh->agent_response;
                      retlen = ssh->agent_response_len;
                  } else
                      sfree(agentreq);
                  ret = vret;
                  if (ret) {
                      if (ret[4] == SSH1_AGENT_RSA_RESPONSE) {
                        logevent("Sending Pageant's response");
                        send_packet(ssh, SSH1_CMSG_AUTH_RSA_RESPONSE,
                                  PKT_DATA, ret + 5, 16,
                                  PKT_END);
                        sfree(ret);
                        crWaitUntil(ispkt);
                        if (ssh->pktin.type == SSH1_SMSG_SUCCESS) {
                            logevent
                              ("Pageant's response accepted");
                            if (flags & FLAG_VERBOSE) {
                              c_write_str(ssh, "Authenticated using"
                                        " RSA key \"");
                              c_write(ssh, s->commentp,
                                    s->commentlen);
                              c_write_str(ssh, "\" from agent\r\n");
                            }
                            s->authed = TRUE;
                        } else
                            logevent
                              ("Pageant's response not accepted");
                      } else {
                        logevent
                            ("Pageant failed to answer challenge");
                        sfree(ret);
                      }
                  } else {
                      logevent("No reply received from Pageant");
                  }
                }
                freebn(s->key.exponent);
                freebn(s->key.modulus);
                freebn(s->challenge);
                if (s->authed)
                  break;
            }
            sfree(s->response);
          }
          if (s->authed)
            break;
      }
      if (!filename_is_null(ssh->cfg.keyfile) && !s->tried_publickey)
          s->pwpkt_type = SSH1_CMSG_AUTH_RSA;

      if (ssh->cfg.try_tis_auth &&
          (s->supported_auths_mask & (1 << SSH1_AUTH_TIS)) &&
          !s->tis_auth_refused) {
          s->pwpkt_type = SSH1_CMSG_AUTH_TIS_RESPONSE;
          logevent("Requested TIS authentication");
          send_packet(ssh, SSH1_CMSG_AUTH_TIS, PKT_END);
          crWaitUntil(ispkt);
          if (ssh->pktin.type != SSH1_SMSG_AUTH_TIS_CHALLENGE) {
            logevent("TIS authentication declined");
            if (flags & FLAG_INTERACTIVE)
                c_write_str(ssh, "TIS authentication refused.\r\n");
            s->tis_auth_refused = 1;
            continue;
          } else {
            char *challenge;
            int challengelen;

            ssh_pkt_getstring(ssh, &challenge, &challengelen);
            if (!challenge) {
                bombout(("TIS challenge packet was badly formed"));
                crStop(0);
            }
            logevent("Received TIS challenge");
            if (challengelen > sizeof(s->prompt) - 1)
                challengelen = sizeof(s->prompt) - 1;/* prevent overrun */
            memcpy(s->prompt, challenge, challengelen);
            /* Prompt heuristic comes from OpenSSH */
            strncpy(s->prompt + challengelen,
                    memchr(s->prompt, '\n', challengelen) ?
                  "": "\r\nResponse: ",
                  (sizeof s->prompt) - challengelen);
            s->prompt[(sizeof s->prompt) - 1] = '\0';
          }
      }
      if (ssh->cfg.try_tis_auth &&
          (s->supported_auths_mask & (1 << SSH1_AUTH_CCARD)) &&
          !s->ccard_auth_refused) {
          s->pwpkt_type = SSH1_CMSG_AUTH_CCARD_RESPONSE;
          logevent("Requested CryptoCard authentication");
          send_packet(ssh, SSH1_CMSG_AUTH_CCARD, PKT_END);
          crWaitUntil(ispkt);
          if (ssh->pktin.type != SSH1_SMSG_AUTH_CCARD_CHALLENGE) {
            logevent("CryptoCard authentication declined");
            c_write_str(ssh, "CryptoCard authentication refused.\r\n");
            s->ccard_auth_refused = 1;
            continue;
          } else {
            char *challenge;
            int challengelen;

            ssh_pkt_getstring(ssh, &challenge, &challengelen);
            if (!challenge) {
                bombout(("CryptoCard challenge packet was badly formed"));
                crStop(0);
            }
            logevent("Received CryptoCard challenge");
            if (challengelen > sizeof(s->prompt) - 1)
                challengelen = sizeof(s->prompt) - 1;/* prevent overrun */
            memcpy(s->prompt, challenge, challengelen);
            strncpy(s->prompt + challengelen,
                    memchr(s->prompt, '\n', challengelen) ?
                  "" : "\r\nResponse: ",
                  sizeof(s->prompt) - challengelen);
            s->prompt[sizeof(s->prompt) - 1] = '\0';
          }
      }
      if (s->pwpkt_type == SSH1_CMSG_AUTH_PASSWORD) {
          sprintf(s->prompt, "%.90s@%.90s's password: ",
                s->username, ssh->savedhost);
      }
      if (s->pwpkt_type == SSH1_CMSG_AUTH_RSA) {
          char *comment = NULL;
          int type;
          char msgbuf[256];
          if (flags & FLAG_VERBOSE)
            c_write_str(ssh, "Trying public key authentication.\r\n");
          logeventf(ssh, "Trying public key \"%s\"",
                  filename_to_str(&ssh->cfg.keyfile));
          type = key_type(&ssh->cfg.keyfile);
          if (type != SSH_KEYTYPE_SSH1) {
            sprintf(msgbuf, "Key is of wrong type (%s)",
                  key_type_to_str(type));
            logevent(msgbuf);
            c_write_str(ssh, msgbuf);
            c_write_str(ssh, "\r\n");
            s->tried_publickey = 1;
            continue;
          }
          if (!rsakey_encrypted(&ssh->cfg.keyfile, &comment)) {
            if (flags & FLAG_VERBOSE)
                c_write_str(ssh, "No passphrase required.\r\n");
            goto tryauth;
          }
          sprintf(s->prompt, "Passphrase for key \"%.100s\": ", comment);
          sfree(comment);
      }

      /*
       * Show password prompt, having first obtained it via a TIS
       * or CryptoCard exchange if we're doing TIS or CryptoCard
       * authentication.
       */
      if (ssh_get_line) {
          if (!ssh_get_line(s->prompt, s->password,
                        sizeof(s->password), TRUE)) {
            /*
             * get_line failed to get a password (for example
             * because one was supplied on the command line
             * which has already failed to work). Terminate.
             */
            send_packet(ssh, SSH1_MSG_DISCONNECT,
                      PKT_STR, "No more passwords available to try",
                      PKT_END);
            logevent("Unable to authenticate");
            connection_fatal(ssh->frontend, "Unable to authenticate");
                ssh_closing((Plug)ssh, NULL, 0, 0);
            crStop(1);
          }
      } else {
          /* Prompt may have come from server. We've munged it a bit, so
           * we know it to be zero-terminated at least once. */
          int ret;                   /* need not be saved over crReturn */
          c_write_untrusted(ssh, s->prompt, strlen(s->prompt));
          s->pos = 0;

          setup_userpass_input(ssh, s->password, sizeof(s->password), 0);
          do {
            crWaitUntil(!ispkt);
            ret = process_userpass_input(ssh, in, inlen);
          } while (ret == 0);
          if (ret < 0)
            cleanup_exit(0);
          c_write_str(ssh, "\r\n");
      }

      tryauth:
      if (s->pwpkt_type == SSH1_CMSG_AUTH_RSA) {
          /*
           * Try public key authentication with the specified
           * key file.
           */
          s->tried_publickey = 1;
          
          {
            const char *error = NULL;
            int ret = loadrsakey(&ssh->cfg.keyfile, &s->key, s->password,
                             &error);
            if (ret == 0) {
                c_write_str(ssh, "Couldn't load private key from ");
                c_write_str(ssh, filename_to_str(&ssh->cfg.keyfile));
                c_write_str(ssh, " (");
                c_write_str(ssh, error);
                c_write_str(ssh, ").\r\n");
                continue;            /* go and try password */
            }
            if (ret == -1) {
                c_write_str(ssh, "Wrong passphrase.\r\n");
                s->tried_publickey = 0;
                continue;            /* try again */
            }
          }

          /*
           * Send a public key attempt.
           */
          send_packet(ssh, SSH1_CMSG_AUTH_RSA,
                  PKT_BIGNUM, s->key.modulus, PKT_END);

          crWaitUntil(ispkt);
          if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            c_write_str(ssh, "Server refused our public key.\r\n");
            continue;          /* go and try password */
          }
          if (ssh->pktin.type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
            bombout(("Bizarre response to offer of public key"));
            crStop(0);
          }

          {
            int i;
            unsigned char buffer[32];
            Bignum challenge, response;

            if ((challenge = ssh1_pkt_getmp(ssh)) == NULL) {
                bombout(("Server's RSA challenge was badly formatted"));
                crStop(0);
            }
            response = rsadecrypt(challenge, &s->key);
            freebn(s->key.private_exponent);/* burn the evidence */

            for (i = 0; i < 32; i++) {
                buffer[i] = bignum_byte(response, 31 - i);
            }

            MD5Init(&md5c);
            MD5Update(&md5c, buffer, 32);
            MD5Update(&md5c, s->session_id, 16);
            MD5Final(buffer, &md5c);

            send_packet(ssh, SSH1_CMSG_AUTH_RSA_RESPONSE,
                      PKT_DATA, buffer, 16, PKT_END);

            freebn(challenge);
            freebn(response);
          }

          crWaitUntil(ispkt);
          if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            if (flags & FLAG_VERBOSE)
                c_write_str(ssh, "Failed to authenticate with"
                        " our public key.\r\n");
            continue;          /* go and try password */
          } else if (ssh->pktin.type != SSH1_SMSG_SUCCESS) {
            bombout(("Bizarre response to RSA authentication response"));
            crStop(0);
          }

          break;               /* we're through! */
      } else {
          if (s->pwpkt_type == SSH1_CMSG_AUTH_PASSWORD) {
            /*
             * Defence against traffic analysis: we send a
             * whole bunch of packets containing strings of
             * different lengths. One of these strings is the
             * password, in a SSH1_CMSG_AUTH_PASSWORD packet.
             * The others are all random data in
             * SSH1_MSG_IGNORE packets. This way a passive
             * listener can't tell which is the password, and
             * hence can't deduce the password length.
             * 
             * Anybody with a password length greater than 16
             * bytes is going to have enough entropy in their
             * password that a listener won't find it _that_
             * much help to know how long it is. So what we'll
             * do is:
             * 
             *  - if password length < 16, we send 15 packets
             *    containing string lengths 1 through 15
             * 
             *  - otherwise, we let N be the nearest multiple
             *    of 8 below the password length, and send 8
             *    packets containing string lengths N through
             *    N+7. This won't obscure the order of
             *    magnitude of the password length, but it will
             *    introduce a bit of extra uncertainty.
             * 
             * A few servers (the old 1.2.18 through 1.2.22)
             * can't deal with SSH1_MSG_IGNORE. For these
             * servers, we need an alternative defence. We make
             * use of the fact that the password is interpreted
             * as a C string: so we can append a NUL, then some
             * random data.
             * 
             * One server (a Cisco one) can deal with neither
             * SSH1_MSG_IGNORE _nor_ a padded password string.
             * For this server we are left with no defences
             * against password length sniffing.
             */
            if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE)) {
                /*
                 * The server can deal with SSH1_MSG_IGNORE, so
                 * we can use the primary defence.
                 */
                int bottom, top, pwlen, i;
                char *randomstr;

                pwlen = strlen(s->password);
                if (pwlen < 16) {
                  bottom = 0;    /* zero length passwords are OK! :-) */
                  top = 15;
                } else {
                  bottom = pwlen & ~7;
                  top = bottom + 7;
                }

                assert(pwlen >= bottom && pwlen <= top);

                randomstr = snewn(top + 1, char);

                for (i = bottom; i <= top; i++) {
                  if (i == pwlen)
                      defer_packet(ssh, s->pwpkt_type,
                               PKT_STR, s->password, PKT_END);
                  else {
                      for (j = 0; j < i; j++) {
                        do {
                            randomstr[j] = random_byte();
                        } while (randomstr[j] == '\0');
                      }
                      randomstr[i] = '\0';
                      defer_packet(ssh, SSH1_MSG_IGNORE,
                               PKT_STR, randomstr, PKT_END);
                  }
                }
                logevent("Sending password with camouflage packets");
                ssh_pkt_defersend(ssh);
                sfree(randomstr);
            } 
            else if (!(ssh->remote_bugs & BUG_NEEDS_SSH1_PLAIN_PASSWORD)) {
                /*
                 * The server can't deal with SSH1_MSG_IGNORE
                 * but can deal with padded passwords, so we
                 * can use the secondary defence.
                 */
                char string[64];
                char *ss;
                int len;

                len = strlen(s->password);
                if (len < sizeof(string)) {
                  ss = string;
                  strcpy(string, s->password);
                  len++;             /* cover the zero byte */
                  while (len < sizeof(string)) {
                      string[len++] = (char) random_byte();
                  }
                } else {
                  ss = s->password;
                }
                logevent("Sending length-padded password");
                send_packet(ssh, s->pwpkt_type, PKT_INT, len,
                        PKT_DATA, ss, len, PKT_END);
            } else {
                /*
                 * The server has _both_
                 * BUG_CHOKES_ON_SSH1_IGNORE and
                 * BUG_NEEDS_SSH1_PLAIN_PASSWORD. There is
                 * therefore nothing we can do.
                 */
                int len;
                len = strlen(s->password);
                logevent("Sending unpadded password");
                send_packet(ssh, s->pwpkt_type, PKT_INT, len,
                        PKT_DATA, s->password, len, PKT_END);
            }
          } else {
            send_packet(ssh, s->pwpkt_type, PKT_STR, s->password, PKT_END);
          }
      }
      logevent("Sent password");
      memset(s->password, 0, strlen(s->password));
      crWaitUntil(ispkt);
      if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
          if (flags & FLAG_VERBOSE)
            c_write_str(ssh, "Access denied\r\n");
          logevent("Authentication refused");
      } else if (ssh->pktin.type != SSH1_SMSG_SUCCESS) {
          bombout(("Strange packet received, type %d", ssh->pktin.type));
          crStop(0);
      }
    }

    logevent("Authentication successful");

    crFinish(1);
}

void sshfwd_close(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;

    if (ssh->state != SSH_STATE_SESSION) {
      assert(ssh->state == SSH_STATE_CLOSED);
      return;
    }

    if (c && !c->closes) {
      /*
       * If the channel's remoteid is -1, we have sent
       * CHANNEL_OPEN for this channel, but it hasn't even been
       * acknowledged by the server. So we must set a close flag
       * on it now, and then when the server acks the channel
       * open, we can close it then.
       */
      if (((int)c->remoteid) != -1) {
          if (ssh->version == 1) {
            send_packet(ssh, SSH1_MSG_CHANNEL_CLOSE, PKT_INT, c->remoteid,
                      PKT_END);
          } else {
            ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_CLOSE);
            ssh2_pkt_adduint32(ssh, c->remoteid);
            ssh2_pkt_send(ssh);
          }
      }
      c->closes = 1;                 /* sent MSG_CLOSE */
      if (c->type == CHAN_X11) {
          c->u.x11.s = NULL;
          logevent("Forwarded X11 connection terminated");
      } else if (c->type == CHAN_SOCKDATA ||
               c->type == CHAN_SOCKDATA_DORMANT) {
          c->u.pfd.s = NULL;
          logevent("Forwarded port closed");
      }
    }
}

int sshfwd_write(struct ssh_channel *c, char *buf, int len)
{
    Ssh ssh = c->ssh;

    if (ssh->state != SSH_STATE_SESSION) {
      assert(ssh->state == SSH_STATE_CLOSED);
      return 0;
    }

    if (ssh->version == 1) {
      send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                PKT_INT, c->remoteid,
                PKT_INT, len, PKT_DATA, buf, len, PKT_END);
      /*
       * In SSH1 we can return 0 here - implying that forwarded
       * connections are never individually throttled - because
       * the only circumstance that can cause throttling will be
       * the whole SSH connection backing up, in which case
       * _everything_ will be throttled as a whole.
       */
      return 0;
    } else {
      ssh2_add_channel_data(c, buf, len);
      return ssh2_try_send(c);
    }
}

void sshfwd_unthrottle(struct ssh_channel *c, int bufsize)
{
    Ssh ssh = c->ssh;

    if (ssh->state != SSH_STATE_SESSION) {
      assert(ssh->state == SSH_STATE_CLOSED);
      return;
    }

    if (ssh->version == 1) {
      if (c->v.v1.throttling && bufsize < SSH1_BUFFER_LIMIT) {
          c->v.v1.throttling = 0;
          ssh1_throttle(ssh, -1);
      }
    } else {
      ssh2_set_window(c, OUR_V2_WINSIZE - bufsize);
    }
}

static void ssh1_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    crBegin(ssh->ssh1_protocol_crstate);

    random_init();

    while (!do_ssh1_login(ssh, in, inlen, ispkt)) {
      crReturnV;
    }
    if (ssh->state == SSH_STATE_CLOSED)
      crReturnV;

    if (ssh->cfg.agentfwd && agent_exists()) {
      logevent("Requesting agent forwarding");
      send_packet(ssh, SSH1_CMSG_AGENT_REQUEST_FORWARDING, PKT_END);
      do {
          crReturnV;
      } while (!ispkt);
      if (ssh->pktin.type != SSH1_SMSG_SUCCESS
          && ssh->pktin.type != SSH1_SMSG_FAILURE) {
          bombout(("Protocol confusion"));
          crStopV;
      } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
          logevent("Agent forwarding refused");
      } else {
          logevent("Agent forwarding enabled");
          ssh->agentfwd_enabled = TRUE;
      }
    }

    if (ssh->cfg.x11_forward) {
      char proto[20], data[64];
      logevent("Requesting X11 forwarding");
      ssh->x11auth = x11_invent_auth(proto, sizeof(proto),
                               data, sizeof(data), ssh->cfg.x11_auth);
        x11_get_real_auth(ssh->x11auth, ssh->cfg.x11_display);
      if (ssh->v1_local_protoflags & SSH1_PROTOFLAG_SCREEN_NUMBER) {
          send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
                  PKT_STR, proto, PKT_STR, data,
                  PKT_INT, x11_get_screen_number(ssh->cfg.x11_display),
                  PKT_END);
      } else {
          send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
                  PKT_STR, proto, PKT_STR, data, PKT_END);
      }
      do {
          crReturnV;
      } while (!ispkt);
      if (ssh->pktin.type != SSH1_SMSG_SUCCESS
          && ssh->pktin.type != SSH1_SMSG_FAILURE) {
          bombout(("Protocol confusion"));
          crStopV;
      } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
          logevent("X11 forwarding refused");
      } else {
          logevent("X11 forwarding enabled");
          ssh->X11_fwd_enabled = TRUE;
      }
    }

    {
      char type;
      int n;
      int sport,dport,sserv,dserv;
      char sports[256], dports[256], saddr[256], host[256];

      ssh->rportfwds = newtree234(ssh_rportcmp_ssh1);
        /* Add port forwardings. */
      ssh->portfwd_strptr = ssh->cfg.portfwd;
      while (*ssh->portfwd_strptr) {
          type = *ssh->portfwd_strptr++;
          saddr[0] = '\0';
          n = 0;
          while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != '\t') {
            if (*ssh->portfwd_strptr == ':') {
                /*
                 * We've seen a colon in the middle of the
                 * source port number. This means that
                 * everything we've seen until now is the
                 * source _address_, so we'll move it into
                 * saddr and start sports from the beginning
                 * again.
                 */
                ssh->portfwd_strptr++;
                sports[n] = '\0';
                strcpy(saddr, sports);
                n = 0;
            }
            if (n < 255) sports[n++] = *ssh->portfwd_strptr++;
          }
          sports[n] = 0;
          if (type != 'D') {
            if (*ssh->portfwd_strptr == '\t')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != ':') {
                if (n < 255) host[n++] = *ssh->portfwd_strptr++;
            }
            host[n] = 0;
            if (*ssh->portfwd_strptr == ':')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr) {
                if (n < 255) dports[n++] = *ssh->portfwd_strptr++;
            }
            dports[n] = 0;
            ssh->portfwd_strptr++;
            dport = atoi(dports);
            dserv = 0;
            if (dport == 0) {
                dserv = 1;
                dport = net_service_lookup(dports);
                if (!dport) {
                  logeventf(ssh, "Service lookup failed for"
                          " destination port \"%s\"", dports);
                }
            }
          } else {
            while (*ssh->portfwd_strptr) ssh->portfwd_strptr++;
            dport = dserv = -1;
            ssh->portfwd_strptr++; /* eat the NUL and move to next one */
          }
          sport = atoi(sports);
          sserv = 0;
          if (sport == 0) {
            sserv = 1;
            sport = net_service_lookup(sports);
            if (!sport) {
                logeventf(ssh, "Service lookup failed for source"
                        " port \"%s\"", sports);
            }
          }
          if (sport && dport) {
            if (type == 'L') {
                pfd_addforward(host, dport, *saddr ? saddr : NULL,
                           sport, ssh, &ssh->cfg);
                logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
                        " forwarding to %s:%.*s%.*s%d%.*s",
                        (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
                        (int)(*saddr?1:0), ":",
                        (int)(sserv ? strlen(sports) : 0), sports,
                        sserv, "(", sport, sserv, ")",
                        host,
                        (int)(dserv ? strlen(dports) : 0), dports,
                        dserv, "(", dport, dserv, ")");
            } else if (type == 'D') {
                pfd_addforward(NULL, -1, *saddr ? saddr : NULL,
                           sport, ssh, &ssh->cfg);
                logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
                        " doing SOCKS dynamic forwarding",
                        (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
                        (int)(*saddr?1:0), ":",
                        (int)(sserv ? strlen(sports) : 0), sports,
                        sserv, "(", sport, sserv, ")");
            } else {
                struct ssh_rportfwd *pf;
                pf = snew(struct ssh_rportfwd);
                strcpy(pf->dhost, host);
                pf->dport = dport;
                if (saddr) {
                  logeventf(ssh,
                          "SSH1 cannot handle source address spec \"%s:%d\"; ignoring",
                          saddr, sport);
                }
                if (add234(ssh->rportfwds, pf) != pf) {
                  logeventf(ssh, 
                          "Duplicate remote port forwarding to %s:%d",
                          host, dport);
                  sfree(pf);
                } else {
                  logeventf(ssh, "Requesting remote port %.*s%.*s%d%.*s"
                          " forward to %s:%.*s%.*s%d%.*s",
                          (int)(sserv ? strlen(sports) : 0), sports,
                          sserv, "(", sport, sserv, ")",
                          host,
                          (int)(dserv ? strlen(dports) : 0), dports,
                          dserv, "(", dport, dserv, ")");
                  send_packet(ssh, SSH1_CMSG_PORT_FORWARD_REQUEST,
                            PKT_INT, sport,
                            PKT_STR, host,
                            PKT_INT, dport,
                            PKT_END);
                  do {
                      crReturnV;
                  } while (!ispkt);
                  if (ssh->pktin.type != SSH1_SMSG_SUCCESS
                      && ssh->pktin.type != SSH1_SMSG_FAILURE) {
                      bombout(("Protocol confusion"));
                      crStopV;
                  } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
                      c_write_str(ssh, "Server refused port"
                              " forwarding\r\n");
                  }
                  logevent("Remote port forwarding enabled");
                }
            }
          }
      }
    }

    if (!ssh->cfg.nopty) {
      /* Unpick the terminal-speed string. */
      /* XXX perhaps we should allow no speeds to be sent. */
      ssh->ospeed = 38400; ssh->ispeed = 38400; /* last-resort defaults */
      sscanf(ssh->cfg.termspeed, "%d,%d", &ssh->ospeed, &ssh->ispeed);
      /* Send the pty request. */
      send_packet(ssh, SSH1_CMSG_REQUEST_PTY,
                PKT_STR, ssh->cfg.termtype,
                PKT_INT, ssh->term_height,
                PKT_INT, ssh->term_width,
                PKT_INT, 0, PKT_INT, 0, /* width,height in pixels */
                PKT_CHAR, 192, PKT_INT, ssh->ispeed, /* TTY_OP_ISPEED */
                PKT_CHAR, 193, PKT_INT, ssh->ospeed, /* TTY_OP_OSPEED */
                PKT_CHAR, 0, PKT_END);
      ssh->state = SSH_STATE_INTERMED;
      do {
          crReturnV;
      } while (!ispkt);
      if (ssh->pktin.type != SSH1_SMSG_SUCCESS
          && ssh->pktin.type != SSH1_SMSG_FAILURE) {
          bombout(("Protocol confusion"));
          crStopV;
      } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
          c_write_str(ssh, "Server refused to allocate pty\r\n");
          ssh->editing = ssh->echoing = 1;
      }
      logeventf(ssh, "Allocated pty (ospeed %dbps, ispeed %dbps)",
              ssh->ospeed, ssh->ispeed);
    } else {
      ssh->editing = ssh->echoing = 1;
    }

    if (ssh->cfg.compression) {
      send_packet(ssh, SSH1_CMSG_REQUEST_COMPRESSION, PKT_INT, 6, PKT_END);
      do {
          crReturnV;
      } while (!ispkt);
      if (ssh->pktin.type != SSH1_SMSG_SUCCESS
          && ssh->pktin.type != SSH1_SMSG_FAILURE) {
          bombout(("Protocol confusion"));
          crStopV;
      } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
          c_write_str(ssh, "Server refused to compress\r\n");
      }
      logevent("Started compression");
      ssh->v1_compressing = TRUE;
      ssh->cs_comp_ctx = zlib_compress_init();
      logevent("Initialised zlib (RFC1950) compression");
      ssh->sc_comp_ctx = zlib_decompress_init();
      logevent("Initialised zlib (RFC1950) decompression");
    }

    /*
     * Start the shell or command.
     * 
     * Special case: if the first-choice command is an SSH2
     * subsystem (hence not usable here) and the second choice
     * exists, we fall straight back to that.
     */
    {
      char *cmd = ssh->cfg.remote_cmd_ptr;
      
      if (ssh->cfg.ssh_subsys && ssh->cfg.remote_cmd_ptr2) {
          cmd = ssh->cfg.remote_cmd_ptr2;
          ssh->fallback_cmd = TRUE;
      }
      if (*cmd)
          send_packet(ssh, SSH1_CMSG_EXEC_CMD, PKT_STR, cmd, PKT_END);
      else
          send_packet(ssh, SSH1_CMSG_EXEC_SHELL, PKT_END);
      logevent("Started session");
    }

    ssh->state = SSH_STATE_SESSION;
    if (ssh->size_needed)
      ssh_size(ssh, ssh->term_width, ssh->term_height);
    if (ssh->eof_needed)
      ssh_special(ssh, TS_EOF);

    if (ssh->ldisc)
      ldisc_send(ssh->ldisc, NULL, 0, 0);/* cause ldisc to notice changes */
    ssh->send_ok = 1;
    ssh->channels = newtree234(ssh_channelcmp);
    while (1) {
      crReturnV;
      if (ispkt) {
          if (ssh->pktin.type == SSH1_SMSG_STDOUT_DATA ||
            ssh->pktin.type == SSH1_SMSG_STDERR_DATA) {
            char *string;
            int stringlen, bufsize;

            ssh_pkt_getstring(ssh, &string, &stringlen);
            if (string == NULL) {
                bombout(("Incoming terminal data packet was badly formed"));
                crStopV;
            }

            bufsize =
                from_backend(ssh->frontend,
                         ssh->pktin.type == SSH1_SMSG_STDERR_DATA,
                         string, stringlen);
            if (!ssh->v1_stdout_throttling && bufsize > SSH1_BUFFER_LIMIT) {
                ssh->v1_stdout_throttling = 1;
                ssh1_throttle(ssh, +1);
            }
          } else if (ssh->pktin.type == SSH1_MSG_DISCONNECT) {
                ssh_closing((Plug)ssh, NULL, 0, 0);
            logevent("Received disconnect request");
            crStopV;
          } else if (ssh->pktin.type == SSH1_SMSG_X11_OPEN) {
            /* Remote side is trying to open a channel to talk to our
             * X-Server. Give them back a local channel number. */
            struct ssh_channel *c;
            int remoteid = ssh_pkt_getuint32(ssh);

            logevent("Received X11 connect request");
            /* Refuse if X11 forwarding is disabled. */
            if (!ssh->X11_fwd_enabled) {
                send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                        PKT_INT, remoteid, PKT_END);
                logevent("Rejected X11 connect request");
            } else {
                c = snew(struct ssh_channel);
                c->ssh = ssh;

                if (x11_init(&c->u.x11.s, ssh->cfg.x11_display, c,
                         ssh->x11auth, NULL, -1, &ssh->cfg) != NULL) {
                  logevent("Opening X11 forward connection failed");
                  sfree(c);
                  send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                            PKT_INT, remoteid, PKT_END);
                } else {
                  logevent
                      ("Opening X11 forward connection succeeded");
                  c->remoteid = remoteid;
                  c->localid = alloc_channel_id(ssh);
                  c->closes = 0;
                  c->v.v1.throttling = 0;
                  c->type = CHAN_X11;     /* identify channel type */
                  add234(ssh->channels, c);
                  send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                            PKT_INT, c->remoteid, PKT_INT,
                            c->localid, PKT_END);
                  logevent("Opened X11 forward channel");
                }
            }
          } else if (ssh->pktin.type == SSH1_SMSG_AGENT_OPEN) {
            /* Remote side is trying to open a channel to talk to our
             * agent. Give them back a local channel number. */
            struct ssh_channel *c;
            int remoteid = ssh_pkt_getuint32(ssh);

            /* Refuse if agent forwarding is disabled. */
            if (!ssh->agentfwd_enabled) {
                send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                        PKT_INT, remoteid, PKT_END);
            } else {
                c = snew(struct ssh_channel);
                c->ssh = ssh;
                c->remoteid = remoteid;
                c->localid = alloc_channel_id(ssh);
                c->closes = 0;
                c->v.v1.throttling = 0;
                c->type = CHAN_AGENT;     /* identify channel type */
                c->u.a.lensofar = 0;
                add234(ssh->channels, c);
                send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                        PKT_INT, c->remoteid, PKT_INT, c->localid,
                        PKT_END);
            }
          } else if (ssh->pktin.type == SSH1_MSG_PORT_OPEN) {
            /* Remote side is trying to open a channel to talk to a
             * forwarded port. Give them back a local channel number. */
            struct ssh_channel *c;
            struct ssh_rportfwd pf;
            int remoteid;
            int hostsize, port;
            char *host, buf[1024];
            const char *e;
            c = snew(struct ssh_channel);
            c->ssh = ssh;

            remoteid = ssh_pkt_getuint32(ssh);
            ssh_pkt_getstring(ssh, &host, &hostsize);
            port = ssh_pkt_getuint32(ssh);

            if (hostsize >= lenof(pf.dhost))
                hostsize = lenof(pf.dhost)-1;
            memcpy(pf.dhost, host, hostsize);
            pf.dhost[hostsize] = '\0';
            pf.dport = port;

            if (find234(ssh->rportfwds, &pf, NULL) == NULL) {
                sprintf(buf, "Rejected remote port open request for %s:%d",
                      pf.dhost, port);
                logevent(buf);
                    send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                                PKT_INT, remoteid, PKT_END);
            } else {
                sprintf(buf, "Received remote port open request for %s:%d",
                      pf.dhost, port);
                logevent(buf);
                e = pfd_newconnect(&c->u.pfd.s, pf.dhost, port,
                               c, &ssh->cfg);
                if (e != NULL) {
                  char buf[256];
                  sprintf(buf, "Port open failed: %s", e);
                  logevent(buf);
                  sfree(c);
                  send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                            PKT_INT, remoteid, PKT_END);
                } else {
                  c->remoteid = remoteid;
                  c->localid = alloc_channel_id(ssh);
                  c->closes = 0;
                  c->v.v1.throttling = 0;
                  c->type = CHAN_SOCKDATA;      /* identify channel type */
                  add234(ssh->channels, c);
                  send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                            PKT_INT, c->remoteid, PKT_INT,
                            c->localid, PKT_END);
                  logevent("Forwarded port opened successfully");
                }
            }

          } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_OPEN_CONFIRMATION) {
            unsigned int remoteid = ssh_pkt_getuint32(ssh);
            unsigned int localid = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;

            c = find234(ssh->channels, &remoteid, ssh_channelfind);
            if (c && c->type == CHAN_SOCKDATA_DORMANT) {
                c->remoteid = localid;
                c->type = CHAN_SOCKDATA;
                c->v.v1.throttling = 0;
                pfd_confirm(c->u.pfd.s);
            }

            if (c && c->closes) {
                /*
                 * We have a pending close on this channel,
                 * which we decided on before the server acked
                 * the channel open. So now we know the
                 * remoteid, we can close it again.
                 */
                send_packet(ssh, SSH1_MSG_CHANNEL_CLOSE,
                        PKT_INT, c->remoteid, PKT_END);
            }

          } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_OPEN_FAILURE) {
            unsigned int remoteid = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;

            c = find234(ssh->channels, &remoteid, ssh_channelfind);
            if (c && c->type == CHAN_SOCKDATA_DORMANT) {
                logevent("Forwarded connection refused by server");
                pfd_close(c->u.pfd.s);
                del234(ssh->channels, c);
                sfree(c);
            }

          } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE ||
                   ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION) {
            /* Remote side closes a channel. */
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (c && ((int)c->remoteid) != -1) {
                int closetype;
                closetype =
                  (ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE ? 1 : 2);

                if ((c->closes == 0) && (c->type == CHAN_X11)) {
                  logevent("Forwarded X11 connection terminated");
                  assert(c->u.x11.s != NULL);
                  x11_close(c->u.x11.s);
                  c->u.x11.s = NULL;
                }
                if ((c->closes == 0) && (c->type == CHAN_SOCKDATA)) {
                  logevent("Forwarded port closed");
                  assert(c->u.pfd.s != NULL);
                  pfd_close(c->u.pfd.s);
                  c->u.pfd.s = NULL;
                }

                c->closes |= (closetype << 2);   /* seen this message */
                if (!(c->closes & closetype)) {
                  send_packet(ssh, ssh->pktin.type, PKT_INT, c->remoteid,
                            PKT_END);
                  c->closes |= closetype;      /* sent it too */
                }

                if (c->closes == 15) {
                  del234(ssh->channels, c);
                  sfree(c);
                }
            } else {
                bombout(("Received CHANNEL_CLOSE%s for %s channel %d\n",
                       ssh->pktin.type == SSH1_MSG_CHANNEL_CLOSE ? "" :
                       "_CONFIRMATION", c ? "half-open" : "nonexistent",
                       i));
                crStopV;
            }
          } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_DATA) {
            /* Data sent down one of our channels. */
            int i = ssh_pkt_getuint32(ssh);
            char *p;
            int len;
            struct ssh_channel *c;

            ssh_pkt_getstring(ssh, &p, &len);

            c = find234(ssh->channels, &i, ssh_channelfind);
            if (c) {
                int bufsize = 0;
                switch (c->type) {
                  case CHAN_X11:
                  bufsize = x11_send(c->u.x11.s, p, len);
                  break;
                  case CHAN_SOCKDATA:
                  bufsize = pfd_send(c->u.pfd.s, p, len);
                  break;
                  case CHAN_AGENT:
                  /* Data for an agent message. Buffer it. */
                  while (len > 0) {
                      if (c->u.a.lensofar < 4) {
                        int l = min(4 - c->u.a.lensofar, len);
                        memcpy(c->u.a.msglen + c->u.a.lensofar, p,
                               l);
                        p += l;
                        len -= l;
                        c->u.a.lensofar += l;
                      }
                      if (c->u.a.lensofar == 4) {
                        c->u.a.totallen =
                            4 + GET_32BIT(c->u.a.msglen);
                        c->u.a.message = snewn(c->u.a.totallen,
                                           unsigned char);
                        memcpy(c->u.a.message, c->u.a.msglen, 4);
                      }
                      if (c->u.a.lensofar >= 4 && len > 0) {
                        int l =
                            min(c->u.a.totallen - c->u.a.lensofar,
                              len);
                        memcpy(c->u.a.message + c->u.a.lensofar, p,
                               l);
                        p += l;
                        len -= l;
                        c->u.a.lensofar += l;
                      }
                      if (c->u.a.lensofar == c->u.a.totallen) {
                        void *reply;
                        int replylen;
                        if (agent_query(c->u.a.message,
                                    c->u.a.totallen,
                                    &reply, &replylen,
                                    ssh_agentf_callback, c))
                            ssh_agentf_callback(c, reply, replylen);
                        sfree(c->u.a.message);
                        c->u.a.lensofar = 0;
                      }
                  }
                  bufsize = 0;   /* agent channels never back up */
                  break;
                }
                if (!c->v.v1.throttling && bufsize > SSH1_BUFFER_LIMIT) {
                  c->v.v1.throttling = 1;
                  ssh1_throttle(ssh, +1);
                }
            }
          } else if (ssh->pktin.type == SSH1_SMSG_SUCCESS) {
            /* may be from EXEC_SHELL on some servers */
          } else if (ssh->pktin.type == SSH1_SMSG_FAILURE) {
            /* may be from EXEC_SHELL on some servers
             * if no pty is available or in other odd cases. Ignore */
          } else if (ssh->pktin.type == SSH1_SMSG_EXIT_STATUS) {
            char buf[100];
            ssh->exitcode = ssh_pkt_getuint32(ssh);
            sprintf(buf, "Server sent command exit status %d",
                  ssh->exitcode);
            logevent(buf);
            send_packet(ssh, SSH1_CMSG_EXIT_CONFIRMATION, PKT_END);
                /*
                 * In case `helpful' firewalls or proxies tack
                 * extra human-readable text on the end of the
                 * session which we might mistake for another
                 * encrypted packet, we close the session once
                 * we've sent EXIT_CONFIRMATION.
                 */
                ssh_closing((Plug)ssh, NULL, 0, 0);
                crStopV;
          } else {
            bombout(("Strange packet received: type %d", ssh->pktin.type));
            crStopV;
          }
      } else {
          while (inlen > 0) {
            int len = min(inlen, 512);
            send_packet(ssh, SSH1_CMSG_STDIN_DATA,
                      PKT_INT, len, PKT_DATA, in, len, PKT_END);
            in += len;
            inlen -= len;
          }
      }
    }

    crFinishV;
}

/*
 * Utility routine for decoding comma-separated strings in KEXINIT.
 */
static int in_commasep_string(char *needle, char *haystack, int haylen)
{
    int needlen;
    if (!needle || !haystack)        /* protect against null pointers */
      return 0;
    needlen = strlen(needle);
    while (1) {
      /*
       * Is it at the start of the string?
       */
      if (haylen >= needlen &&       /* haystack is long enough */
          !memcmp(needle, haystack, needlen) && /* initial match */
          (haylen == needlen || haystack[needlen] == ',')
          /* either , or EOS follows */
          )
          return 1;
      /*
       * If not, search for the next comma and resume after that.
       * If no comma found, terminate.
       */
      while (haylen > 0 && *haystack != ',')
          haylen--, haystack++;
      if (haylen == 0)
          return 0;
      haylen--, haystack++;          /* skip over comma itself */
    }
}

/*
 * SSH2 key creation method.
 */
static void ssh2_mkkey(Ssh ssh, Bignum K, unsigned char *H,
                   unsigned char *sessid, char chr,
                   unsigned char *keyspace)
{
    SHA_State s;
    /* First 20 bytes. */
    SHA_Init(&s);
    if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
      sha_mpint(&s, K);
    SHA_Bytes(&s, H, 20);
    SHA_Bytes(&s, &chr, 1);
    SHA_Bytes(&s, sessid, 20);
    SHA_Final(&s, keyspace);
    /* Next 20 bytes. */
    SHA_Init(&s);
    if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
      sha_mpint(&s, K);
    SHA_Bytes(&s, H, 20);
    SHA_Bytes(&s, keyspace, 20);
    SHA_Final(&s, keyspace + 20);
}

/*
 * Handle the SSH2 transport layer.
 */
static int do_ssh2_transport(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    struct do_ssh2_transport_state {
      int nbits, pbits, warn;
      Bignum p, g, e, f, K;
      int kex_init_value, kex_reply_value;
      const struct ssh_mac **maclist;
      int nmacs;
      const struct ssh2_cipher *cscipher_tobe;
      const struct ssh2_cipher *sccipher_tobe;
      const struct ssh_mac *csmac_tobe;
      const struct ssh_mac *scmac_tobe;
      const struct ssh_compress *cscomp_tobe;
      const struct ssh_compress *sccomp_tobe;
      char *hostkeydata, *sigdata, *keystr, *fingerprint;
      int hostkeylen, siglen;
      void *hkey;              /* actual host key */
      unsigned char exchange_hash[20];
      int n_preferred_ciphers;
      const struct ssh2_ciphers *preferred_ciphers[CIPHER_MAX];
      const struct ssh_compress *preferred_comp;
      int first_kex;
    };
    crState(do_ssh2_transport_state);

    crBegin(ssh->do_ssh2_transport_crstate);

    s->cscipher_tobe = s->sccipher_tobe = NULL;
    s->csmac_tobe = s->scmac_tobe = NULL;
    s->cscomp_tobe = s->sccomp_tobe = NULL;

    random_init();
    s->first_kex = 1;

    {
      int i;
      /*
       * Set up the preferred ciphers. (NULL => warn below here)
       */
      s->n_preferred_ciphers = 0;
      for (i = 0; i < CIPHER_MAX; i++) {
          switch (ssh->cfg.ssh_cipherlist[i]) {
            case CIPHER_BLOWFISH:
            s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_blowfish;
            break;
            case CIPHER_DES:
            if (ssh->cfg.ssh2_des_cbc) {
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_des;
            }
            break;
            case CIPHER_3DES:
            s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_3des;
            break;
            case CIPHER_AES:
            s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_aes;
            break;
            case CIPHER_WARN:
            /* Flag for later. Don't bother if it's the last in
             * the list. */
            if (i < CIPHER_MAX - 1) {
                s->preferred_ciphers[s->n_preferred_ciphers++] = NULL;
            }
            break;
          }
      }
    }

    /*
     * Set up preferred compression.
     */
    if (ssh->cfg.compression)
      s->preferred_comp = &ssh_zlib;
    else
      s->preferred_comp = &ssh_comp_none;

    /*
     * Be prepared to work around the buggy MAC problem.
     */
    if (ssh->remote_bugs & BUG_SSH2_HMAC)
      s->maclist = buggymacs, s->nmacs = lenof(buggymacs);
    else
      s->maclist = macs, s->nmacs = lenof(macs);

  begin_key_exchange:
    {
      int i, j, cipherstr_started;

      /*
       * Construct and send our key exchange packet.
       */
      ssh2_pkt_init(ssh, SSH2_MSG_KEXINIT);
      for (i = 0; i < 16; i++)
          ssh2_pkt_addbyte(ssh, (unsigned char) random_byte());
      /* List key exchange algorithms. */
      ssh2_pkt_addstring_start(ssh);
      for (i = 0; i < lenof(kex_algs); i++) {
          if (kex_algs[i] == &ssh_diffiehellman_gex &&
            (ssh->remote_bugs & BUG_SSH2_DH_GEX))
            continue;
          ssh2_pkt_addstring_str(ssh, kex_algs[i]->name);
          if (i < lenof(kex_algs) - 1)
            ssh2_pkt_addstring_str(ssh, ",");
      }
      /* List server host key algorithms. */
      ssh2_pkt_addstring_start(ssh);
      for (i = 0; i < lenof(hostkey_algs); i++) {
          ssh2_pkt_addstring_str(ssh, hostkey_algs[i]->name);
          if (i < lenof(hostkey_algs) - 1)
            ssh2_pkt_addstring_str(ssh, ",");
      }
      /* List client->server encryption algorithms. */
      ssh2_pkt_addstring_start(ssh);
      cipherstr_started = 0;
      for (i = 0; i < s->n_preferred_ciphers; i++) {
          const struct ssh2_ciphers *c = s->preferred_ciphers[i];
          if (!c) continue;          /* warning flag */
          for (j = 0; j < c->nciphers; j++) {
            if (cipherstr_started)
                ssh2_pkt_addstring_str(ssh, ",");
            ssh2_pkt_addstring_str(ssh, c->list[j]->name);
            cipherstr_started = 1;
          }
      }
      /* List server->client encryption algorithms. */
      ssh2_pkt_addstring_start(ssh);
      cipherstr_started = 0;
      for (i = 0; i < s->n_preferred_ciphers; i++) {
          const struct ssh2_ciphers *c = s->preferred_ciphers[i];
          if (!c) continue; /* warning flag */
          for (j = 0; j < c->nciphers; j++) {
            if (cipherstr_started)
                ssh2_pkt_addstring_str(ssh, ",");
            ssh2_pkt_addstring_str(ssh, c->list[j]->name);
            cipherstr_started = 1;
          }
      }
      /* List client->server MAC algorithms. */
      ssh2_pkt_addstring_start(ssh);
      for (i = 0; i < s->nmacs; i++) {
          ssh2_pkt_addstring_str(ssh, s->maclist[i]->name);
          if (i < s->nmacs - 1)
            ssh2_pkt_addstring_str(ssh, ",");
      }
      /* List server->client MAC algorithms. */
      ssh2_pkt_addstring_start(ssh);
      for (i = 0; i < s->nmacs; i++) {
          ssh2_pkt_addstring_str(ssh, s->maclist[i]->name);
          if (i < s->nmacs - 1)
            ssh2_pkt_addstring_str(ssh, ",");
      }
      /* List client->server compression algorithms. */
      ssh2_pkt_addstring_start(ssh);
      for (i = 0; i < lenof(compressions) + 1; i++) {
          const struct ssh_compress *c =
            i == 0 ? s->preferred_comp : compressions[i - 1];
          ssh2_pkt_addstring_str(ssh, c->name);
          if (i < lenof(compressions))
            ssh2_pkt_addstring_str(ssh, ",");
      }
      /* List server->client compression algorithms. */
      ssh2_pkt_addstring_start(ssh);
      for (i = 0; i < lenof(compressions) + 1; i++) {
          const struct ssh_compress *c =
            i == 0 ? s->preferred_comp : compressions[i - 1];
          ssh2_pkt_addstring_str(ssh, c->name);
          if (i < lenof(compressions))
            ssh2_pkt_addstring_str(ssh, ",");
      }
      /* List client->server languages. Empty list. */
      ssh2_pkt_addstring_start(ssh);
      /* List server->client languages. Empty list. */
      ssh2_pkt_addstring_start(ssh);
      /* First KEX packet does _not_ follow, because we're not that brave. */
      ssh2_pkt_addbool(ssh, FALSE);
      /* Reserved. */
      ssh2_pkt_adduint32(ssh, 0);
    }

    ssh->exhash = ssh->exhashbase;
    sha_string(&ssh->exhash, ssh->pktout.data + 5, ssh->pktout.length - 5);

    ssh2_pkt_send(ssh);

    if (!ispkt)
      crWaitUntil(ispkt);
    if (ssh->pktin.length > 5)
      sha_string(&ssh->exhash, ssh->pktin.data + 5, ssh->pktin.length - 5);

    /*
     * Now examine the other side's KEXINIT to see what we're up
     * to.
     */
    {
      char *str;
      int i, j, len;

      if (ssh->pktin.type != SSH2_MSG_KEXINIT) {
          bombout(("expected key exchange packet from server"));
          crStop(0);
      }
      ssh->kex = NULL;
      ssh->hostkey = NULL;
      s->cscipher_tobe = NULL;
      s->sccipher_tobe = NULL;
      s->csmac_tobe = NULL;
      s->scmac_tobe = NULL;
      s->cscomp_tobe = NULL;
      s->sccomp_tobe = NULL;
      ssh->pktin.savedpos += 16;            /* skip garbage cookie */
      ssh_pkt_getstring(ssh, &str, &len);    /* key exchange algorithms */
      for (i = 0; i < lenof(kex_algs); i++) {
          if (kex_algs[i] == &ssh_diffiehellman_gex &&
            (ssh->remote_bugs & BUG_SSH2_DH_GEX))
            continue;
          if (in_commasep_string(kex_algs[i]->name, str, len)) {
            ssh->kex = kex_algs[i];
            break;
          }
      }
      ssh_pkt_getstring(ssh, &str, &len);    /* host key algorithms */
      for (i = 0; i < lenof(hostkey_algs); i++) {
          if (in_commasep_string(hostkey_algs[i]->name, str, len)) {
            ssh->hostkey = hostkey_algs[i];
            break;
          }
      }
      ssh_pkt_getstring(ssh, &str, &len);    /* client->server cipher */
      s->warn = 0;
      for (i = 0; i < s->n_preferred_ciphers; i++) {
          const struct ssh2_ciphers *c = s->preferred_ciphers[i];
          if (!c) {
            s->warn = 1;
          } else {
            for (j = 0; j < c->nciphers; j++) {
                if (in_commasep_string(c->list[j]->name, str, len)) {
                  s->cscipher_tobe = c->list[j];
                  break;
                }
            }
          }
          if (s->cscipher_tobe) {
            if (s->warn)
                askcipher(ssh->frontend, s->cscipher_tobe->name, 1);
            break;
          }
      }
      if (!s->cscipher_tobe) {
          bombout(("Couldn't agree a client-to-server cipher (available: %s)",
                 str ? str : "(null)"));
          crStop(0);
      }

      ssh_pkt_getstring(ssh, &str, &len);    /* server->client cipher */
      s->warn = 0;
      for (i = 0; i < s->n_preferred_ciphers; i++) {
          const struct ssh2_ciphers *c = s->preferred_ciphers[i];
          if (!c) {
            s->warn = 1;
          } else {
            for (j = 0; j < c->nciphers; j++) {
                if (in_commasep_string(c->list[j]->name, str, len)) {
                  s->sccipher_tobe = c->list[j];
                  break;
                }
            }
          }
          if (s->sccipher_tobe) {
            if (s->warn)
                askcipher(ssh->frontend, s->sccipher_tobe->name, 2);
            break;
          }
      }
      if (!s->sccipher_tobe) {
          bombout(("Couldn't agree a server-to-client cipher (available: %s)",
                 str ? str : "(null)"));
          crStop(0);
      }

      ssh_pkt_getstring(ssh, &str, &len);    /* client->server mac */
      for (i = 0; i < s->nmacs; i++) {
          if (in_commasep_string(s->maclist[i]->name, str, len)) {
            s->csmac_tobe = s->maclist[i];
            break;
          }
      }
      ssh_pkt_getstring(ssh, &str, &len);    /* server->client mac */
      for (i = 0; i < s->nmacs; i++) {
          if (in_commasep_string(s->maclist[i]->name, str, len)) {
            s->scmac_tobe = s->maclist[i];
            break;
          }
      }
      ssh_pkt_getstring(ssh, &str, &len);  /* client->server compression */
      for (i = 0; i < lenof(compressions) + 1; i++) {
          const struct ssh_compress *c =
            i == 0 ? s->preferred_comp : compressions[i - 1];
          if (in_commasep_string(c->name, str, len)) {
            s->cscomp_tobe = c;
            break;
          }
      }
      ssh_pkt_getstring(ssh, &str, &len);  /* server->client compression */
      for (i = 0; i < lenof(compressions) + 1; i++) {
          const struct ssh_compress *c =
            i == 0 ? s->preferred_comp : compressions[i - 1];
          if (in_commasep_string(c->name, str, len)) {
            s->sccomp_tobe = c;
            break;
          }
      }
    }

    /*
     * Work out the number of bits of key we will need from the key
     * exchange. We start with the maximum key length of either
     * cipher...
     */
    {
      int csbits, scbits;

      csbits = s->cscipher_tobe->keylen;
      scbits = s->sccipher_tobe->keylen;
      s->nbits = (csbits > scbits ? csbits : scbits);
    }
    /* The keys only have 160-bit entropy, since they're based on
     * a SHA-1 hash. So cap the key size at 160 bits. */
    if (s->nbits > 160)
      s->nbits = 160;

    /*
     * If we're doing Diffie-Hellman group exchange, start by
     * requesting a group.
     */
    if (ssh->kex == &ssh_diffiehellman_gex) {
      logevent("Doing Diffie-Hellman group exchange");
      ssh->pkt_ctx |= SSH2_PKTCTX_DHGEX;
      /*
       * Work out how big a DH group we will need to allow that
       * much data.
       */
      s->pbits = 512 << ((s->nbits - 1) / 64);
      ssh2_pkt_init(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST);
      ssh2_pkt_adduint32(ssh, s->pbits);
      ssh2_pkt_send(ssh);

      crWaitUntil(ispkt);
      if (ssh->pktin.type != SSH2_MSG_KEX_DH_GEX_GROUP) {
          bombout(("expected key exchange group packet from server"));
          crStop(0);
      }
      s->p = ssh2_pkt_getmp(ssh);
      s->g = ssh2_pkt_getmp(ssh);
      ssh->kex_ctx = dh_setup_group(s->p, s->g);
      s->kex_init_value = SSH2_MSG_KEX_DH_GEX_INIT;
      s->kex_reply_value = SSH2_MSG_KEX_DH_GEX_REPLY;
    } else {
      ssh->pkt_ctx |= SSH2_PKTCTX_DHGROUP1;
      ssh->kex_ctx = dh_setup_group1();
      s->kex_init_value = SSH2_MSG_KEXDH_INIT;
      s->kex_reply_value = SSH2_MSG_KEXDH_REPLY;
    }

    logevent("Doing Diffie-Hellman key exchange");
    /*
     * Now generate and send e for Diffie-Hellman.
     */
    s->e = dh_create_e(ssh->kex_ctx, s->nbits * 2);
    ssh2_pkt_init(ssh, s->kex_init_value);
    ssh2_pkt_addmp(ssh, s->e);
    ssh2_pkt_send(ssh);

    crWaitUntil(ispkt);
    if (ssh->pktin.type != s->kex_reply_value) {
      bombout(("expected key exchange reply packet from server"));
      crStop(0);
    }
    ssh_pkt_getstring(ssh, &s->hostkeydata, &s->hostkeylen);
    s->f = ssh2_pkt_getmp(ssh);
    ssh_pkt_getstring(ssh, &s->sigdata, &s->siglen);

    s->K = dh_find_K(ssh->kex_ctx, s->f);

    sha_string(&ssh->exhash, s->hostkeydata, s->hostkeylen);
    if (ssh->kex == &ssh_diffiehellman_gex) {
      sha_uint32(&ssh->exhash, s->pbits);
      sha_mpint(&ssh->exhash, s->p);
      sha_mpint(&ssh->exhash, s->g);
    }
    sha_mpint(&ssh->exhash, s->e);
    sha_mpint(&ssh->exhash, s->f);
    sha_mpint(&ssh->exhash, s->K);
    SHA_Final(&ssh->exhash, s->exchange_hash);

    dh_cleanup(ssh->kex_ctx);
    ssh->kex_ctx = NULL;

#if 0
    debug(("Exchange hash is:\n"));
    dmemdump(s->exchange_hash, 20);
#endif

    s->hkey = ssh->hostkey->newkey(s->hostkeydata, s->hostkeylen);
    if (!s->hkey ||
      !ssh->hostkey->verifysig(s->hkey, s->sigdata, s->siglen,
                         (char *)s->exchange_hash, 20)) {
      bombout(("Server's host key did not match the signature supplied"));
      crStop(0);
    }

    /*
     * Authenticate remote host: verify host key. (We've already
     * checked the signature of the exchange hash.)
     */
    s->keystr = ssh->hostkey->fmtkey(s->hkey);
    s->fingerprint = ssh->hostkey->fingerprint(s->hkey);
    verify_ssh_host_key(ssh->frontend,
                  ssh->savedhost, ssh->savedport, ssh->hostkey->keytype,
                  s->keystr, s->fingerprint);
    if (s->first_kex) {              /* don't bother logging this in rekeys */
      logevent("Host key fingerprint is:");
      logevent(s->fingerprint);
    }
    sfree(s->fingerprint);
    sfree(s->keystr);
    ssh->hostkey->freekey(s->hkey);

    /*
     * Send SSH2_MSG_NEWKEYS.
     */
    ssh2_pkt_init(ssh, SSH2_MSG_NEWKEYS);
    ssh2_pkt_send(ssh);

    /*
     * Expect SSH2_MSG_NEWKEYS from server.
     */
    crWaitUntil(ispkt);
    if (ssh->pktin.type != SSH2_MSG_NEWKEYS) {
      bombout(("expected new-keys packet from server"));
      crStop(0);
    }

    /*
     * Create and initialise session keys.
     */
    if (ssh->cs_cipher_ctx)
      ssh->cscipher->free_context(ssh->cs_cipher_ctx);
    ssh->cscipher = s->cscipher_tobe;
    ssh->cs_cipher_ctx = ssh->cscipher->make_context();

    if (ssh->sc_cipher_ctx)
      ssh->sccipher->free_context(ssh->sc_cipher_ctx);
    ssh->sccipher = s->sccipher_tobe;
    ssh->sc_cipher_ctx = ssh->sccipher->make_context();

    if (ssh->cs_mac_ctx)
      ssh->csmac->free_context(ssh->cs_mac_ctx);
    ssh->csmac = s->csmac_tobe;
    ssh->cs_mac_ctx = ssh->csmac->make_context();

    if (ssh->sc_mac_ctx)
      ssh->scmac->free_context(ssh->sc_mac_ctx);
    ssh->scmac = s->scmac_tobe;
    ssh->sc_mac_ctx = ssh->scmac->make_context();

    if (ssh->cs_comp_ctx)
      ssh->cscomp->compress_cleanup(ssh->cs_comp_ctx);
    ssh->cscomp = s->cscomp_tobe;
    ssh->cs_comp_ctx = ssh->cscomp->compress_init();

    if (ssh->sc_comp_ctx)
      ssh->sccomp->decompress_cleanup(ssh->sc_comp_ctx);
    ssh->sccomp = s->sccomp_tobe;
    ssh->sc_comp_ctx = ssh->sccomp->decompress_init();

    /*
     * Set IVs after keys. Here we use the exchange hash from the
     * _first_ key exchange.
     */
    {
      unsigned char keyspace[40];
      if (s->first_kex)
          memcpy(ssh->v2_session_id, s->exchange_hash,
               sizeof(s->exchange_hash));
      ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'C',keyspace);
      ssh->cscipher->setkey(ssh->cs_cipher_ctx, keyspace);
      ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'D',keyspace);
      ssh->sccipher->setkey(ssh->sc_cipher_ctx, keyspace);
      ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'A',keyspace);
      ssh->cscipher->setiv(ssh->cs_cipher_ctx, keyspace);
      ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'B',keyspace);
      ssh->sccipher->setiv(ssh->sc_cipher_ctx, keyspace);
      ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'E',keyspace);
      ssh->csmac->setkey(ssh->cs_mac_ctx, keyspace);
      ssh2_mkkey(ssh,s->K,s->exchange_hash,ssh->v2_session_id,'F',keyspace);
      ssh->scmac->setkey(ssh->sc_mac_ctx, keyspace);
    }
    logeventf(ssh, "Initialised %.200s client->server encryption",
            ssh->cscipher->text_name);
    logeventf(ssh, "Initialised %.200s server->client encryption",
            ssh->sccipher->text_name);
    if (ssh->cscomp->text_name)
      logeventf(ssh, "Initialised %s compression",
              ssh->cscomp->text_name);
    if (ssh->sccomp->text_name)
      logeventf(ssh, "Initialised %s decompression",
              ssh->sccomp->text_name);
    freebn(s->f);
    freebn(s->K);
    if (ssh->kex == &ssh_diffiehellman_gex) {
      freebn(s->g);
      freebn(s->p);
    }

    /*
     * If this is the first key exchange phase, we must pass the
     * SSH2_MSG_NEWKEYS packet to the next layer, not because it
     * wants to see it but because it will need time to initialise
     * itself before it sees an actual packet. In subsequent key
     * exchange phases, we don't pass SSH2_MSG_NEWKEYS on, because
     * it would only confuse the layer above.
     */
    if (!s->first_kex) {
      crReturn(0);
    }
    s->first_kex = 0;

    /*
     * Now we're encrypting. Begin returning 1 to the protocol main
     * function so that other things can run on top of the
     * transport. If we ever see a KEXINIT, we must go back to the
     * start.
     */
    while (!(ispkt && ssh->pktin.type == SSH2_MSG_KEXINIT)) {
      crReturn(1);
    }
    logevent("Server initiated key re-exchange");
    goto begin_key_exchange;

    crFinish(1);
}

/*
 * Add data to an SSH2 channel output buffer.
 */
static void ssh2_add_channel_data(struct ssh_channel *c, char *buf,
                          int len)
{
    bufchain_add(&c->v.v2.outbuffer, buf, len);
}

/*
 * Attempt to send data on an SSH2 channel.
 */
static int ssh2_try_send(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;

    while (c->v.v2.remwindow > 0 && bufchain_size(&c->v.v2.outbuffer) > 0) {
      int len;
      void *data;
      bufchain_prefix(&c->v.v2.outbuffer, &data, &len);
      if ((unsigned)len > c->v.v2.remwindow)
          len = c->v.v2.remwindow;
      if ((unsigned)len > c->v.v2.remmaxpkt)
          len = c->v.v2.remmaxpkt;
      ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_DATA);
      ssh2_pkt_adduint32(ssh, c->remoteid);
      ssh2_pkt_addstring_start(ssh);
      ssh2_pkt_addstring_data(ssh, data, len);
      ssh2_pkt_send(ssh);
      bufchain_consume(&c->v.v2.outbuffer, len);
      c->v.v2.remwindow -= len;
    }

    /*
     * After having sent as much data as we can, return the amount
     * still buffered.
     */
    return bufchain_size(&c->v.v2.outbuffer);
}

/*
 * Potentially enlarge the window on an SSH2 channel.
 */
static void ssh2_set_window(struct ssh_channel *c, unsigned newwin)
{
    Ssh ssh = c->ssh;

    /*
     * Never send WINDOW_ADJUST for a channel that the remote side
     * already thinks it's closed; there's no point, since it won't
     * be sending any more data anyway.
     */
    if (c->closes != 0)
      return;

    if (newwin > c->v.v2.locwindow) {
      ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_WINDOW_ADJUST);
      ssh2_pkt_adduint32(ssh, c->remoteid);
      ssh2_pkt_adduint32(ssh, newwin - c->v.v2.locwindow);
      ssh2_pkt_send(ssh);
      c->v.v2.locwindow = newwin;
    }
}

/*
 * Handle the SSH2 userauth and connection layers.
 */
static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    struct do_ssh2_authconn_state {
      enum {
          AUTH_INVALID, AUTH_PUBLICKEY_AGENT, AUTH_PUBLICKEY_FILE,
            AUTH_PASSWORD,
            AUTH_KEYBOARD_INTERACTIVE
      } method;
      enum {
          AUTH_TYPE_NONE,
            AUTH_TYPE_PUBLICKEY,
            AUTH_TYPE_PUBLICKEY_OFFER_LOUD,
            AUTH_TYPE_PUBLICKEY_OFFER_QUIET,
            AUTH_TYPE_PASSWORD,
            AUTH_TYPE_KEYBOARD_INTERACTIVE,
            AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET
      } type;
      int gotit, need_pw, can_pubkey, can_passwd, can_keyb_inter;
      int tried_pubkey_config, tried_agent, tried_keyb_inter;
      int kbd_inter_running;
      int we_are_in;
      int num_prompts, curr_prompt, echo;
      char username[100];
      int got_username;
      char pwprompt[200];
      char password[100];
      void *publickey_blob;
      int publickey_bloblen;
      unsigned char request[5], *response, *p;
      int responselen;
      int keyi, nkeys;
      int authed;
      char *pkblob, *alg, *commentp;
      int pklen, alglen, commentlen;
      int siglen, retlen, len;
      char *q, *agentreq, *ret;
      int try_send;
    };
    crState(do_ssh2_authconn_state);

    crBegin(ssh->do_ssh2_authconn_crstate);

    /*
     * Request userauth protocol, and await a response to it.
     */
    ssh2_pkt_init(ssh, SSH2_MSG_SERVICE_REQUEST);
    ssh2_pkt_addstring(ssh, "ssh-userauth");
    ssh2_pkt_send(ssh);
    crWaitUntilV(ispkt);
    if (ssh->pktin.type != SSH2_MSG_SERVICE_ACCEPT) {
      bombout(("Server refused user authentication protocol"));
      crStopV;
    }

    /*
     * We repeat this whole loop, including the username prompt,
     * until we manage a successful authentication. If the user
     * types the wrong _password_, they can be sent back to the
     * beginning to try another username, if this is configured on.
     * (If they specify a username in the config, they are never
     * asked, even if they do give a wrong password.)
     * 
     * I think this best serves the needs of
     * 
     *  - the people who have no configuration, no keys, and just
     *    want to try repeated (username,password) pairs until they
     *    type both correctly
     * 
     *  - people who have keys and configuration but occasionally
     *    need to fall back to passwords
     * 
     *  - people with a key held in Pageant, who might not have
     *    logged in to a particular machine before; so they want to
     *    type a username, and then _either_ their key will be
     *    accepted, _or_ they will type a password. If they mistype
     *    the username they will want to be able to get back and
     *    retype it!
     */
    s->username[0] = '\0';
    s->got_username = FALSE;
    do {
      /*
       * Get a username.
       */
      if (s->got_username && !ssh->cfg.change_username) {
          /*
           * We got a username last time round this loop, and
           * with change_username turned off we don't try to get
           * it again.
           */
      } else if ((flags & FLAG_INTERACTIVE) && !*ssh->cfg.username) {
          if (ssh_get_line && !ssh_getline_pw_only) {
            if (!ssh_get_line("login as: ",
                          s->username, sizeof(s->username), FALSE)) {
                /*
                 * get_line failed to get a username.
                 * Terminate.
                 */
                logevent("No username provided. Abandoning session.");
                    ssh_closing((Plug)ssh, NULL, 0, 0);
                crStopV;
            }
          } else {
            int ret;           /* need not be saved across crReturn */
            c_write_str(ssh, "login as: ");
            ssh->send_ok = 1;
            setup_userpass_input(ssh, s->username, sizeof(s->username), 1);
            do {
                crWaitUntilV(!ispkt);
                ret = process_userpass_input(ssh, in, inlen);
            } while (ret == 0);
            if (ret < 0)
                cleanup_exit(0);
            c_write_str(ssh, "\r\n");
          }
          s->username[strcspn(s->username, "\n\r")] = '\0';
      } else {
          char *stuff;
          strncpy(s->username, ssh->cfg.username, sizeof(s->username));
          s->username[sizeof(s->username)-1] = '\0';
          if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE)) {
            stuff = dupprintf("Using username \"%s\".\r\n", s->username);
            c_write_str(ssh, stuff);
            sfree(stuff);
          }
      }
      s->got_username = TRUE;

      /*
       * Send an authentication request using method "none": (a)
       * just in case it succeeds, and (b) so that we know what
       * authentication methods we can usefully try next.
       */
      ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;

      ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
      ssh2_pkt_addstring(ssh, s->username);
      ssh2_pkt_addstring(ssh, "ssh-connection");/* service requested */
      ssh2_pkt_addstring(ssh, "none");    /* method */
      ssh2_pkt_send(ssh);
      s->type = AUTH_TYPE_NONE;
      s->gotit = FALSE;
      s->we_are_in = FALSE;

      s->tried_pubkey_config = FALSE;
      s->tried_agent = FALSE;
      s->tried_keyb_inter = FALSE;
      s->kbd_inter_running = FALSE;
      /* Load the pub half of ssh->cfg.keyfile so we notice if it's in Pageant */
      if (!filename_is_null(ssh->cfg.keyfile)) {
          int keytype;
          logeventf(ssh, "Reading private key file \"%.150s\"",
                  filename_to_str(&ssh->cfg.keyfile));
          keytype = key_type(&ssh->cfg.keyfile);
          if (keytype == SSH_KEYTYPE_SSH2) {
            s->publickey_blob =
                ssh2_userkey_loadpub(&ssh->cfg.keyfile, NULL,
                               &s->publickey_bloblen, NULL);
          } else {
            char *msgbuf;
            logeventf(ssh, "Unable to use this key file (%s)",
                    key_type_to_str(keytype));
            msgbuf = dupprintf("Unable to use key file \"%.150s\""
                           " (%s)\r\n",
                           filename_to_str(&ssh->cfg.keyfile),
                           key_type_to_str(keytype));
            c_write_str(ssh, msgbuf);
            sfree(msgbuf);
            s->publickey_blob = NULL;
          }
      } else
          s->publickey_blob = NULL;

      while (1) {
          /*
           * Wait for the result of the last authentication request.
           */
          if (!s->gotit)
            crWaitUntilV(ispkt);
          while (ssh->pktin.type == SSH2_MSG_USERAUTH_BANNER) {
            char *banner;
            int size;
            /*
             * Don't show the banner if we're operating in
             * non-verbose non-interactive mode. (It's probably
             * a script, which means nobody will read the
             * banner _anyway_, and moreover the printing of
             * the banner will screw up processing on the
             * output of (say) plink.)
             */
            if (flags & (FLAG_VERBOSE | FLAG_INTERACTIVE)) {
                ssh_pkt_getstring(ssh, &banner, &size);
                if (banner)
                  c_write_untrusted(ssh, banner, size);
            }
            crWaitUntilV(ispkt);
          }
          if (ssh->pktin.type == SSH2_MSG_USERAUTH_SUCCESS) {
            logevent("Access granted");
            s->we_are_in = TRUE;
            break;
          }

          if (s->kbd_inter_running &&
            ssh->pktin.type == SSH2_MSG_USERAUTH_INFO_REQUEST) {
            /*
             * This is either a further set-of-prompts packet
             * in keyboard-interactive authentication, or it's
             * the same one and we came back here with `gotit'
             * set. In the former case, we must reset the
             * curr_prompt variable.
             */
            if (!s->gotit)
                s->curr_prompt = 0;
          } else if (ssh->pktin.type != SSH2_MSG_USERAUTH_FAILURE) {
            bombout(("Strange packet received during authentication: type %d",
                   ssh->pktin.type));
            crStopV;
          }

          s->gotit = FALSE;

          /*
           * OK, we're now sitting on a USERAUTH_FAILURE message, so
           * we can look at the string in it and know what we can
           * helpfully try next.
           */
          if (ssh->pktin.type == SSH2_MSG_USERAUTH_FAILURE) {
            char *methods;
            int methlen;
            ssh_pkt_getstring(ssh, &methods, &methlen);
            s->kbd_inter_running = FALSE;
            if (!ssh2_pkt_getbool(ssh)) {
                /*
                 * We have received an unequivocal Access
                 * Denied. This can translate to a variety of
                 * messages:
                 * 
                 *  - if we'd just tried "none" authentication,
                 *    it's not worth printing anything at all
                 * 
                 *  - if we'd just tried a public key _offer_,
                 *    the message should be "Server refused our
                 *    key" (or no message at all if the key
                 *    came from Pageant)
                 * 
                 *  - if we'd just tried anything else, the
                 *    message really should be "Access denied".
                 * 
                 * Additionally, if we'd just tried password
                 * authentication, we should break out of this
                 * whole loop so as to go back to the username
                 * prompt.
                 */
                if (s->type == AUTH_TYPE_NONE) {
                  /* do nothing */
                } else if (s->type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD ||
                         s->type == AUTH_TYPE_PUBLICKEY_OFFER_QUIET) {
                  if (s->type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD)
                      c_write_str(ssh, "Server refused our key\r\n");
                  logevent("Server refused public key");
                } else if (s->type==AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET) {
                  /* server declined keyboard-interactive; ignore */
                } else {
                  c_write_str(ssh, "Access denied\r\n");
                  logevent("Access denied");
                  if (s->type == AUTH_TYPE_PASSWORD) {
                      s->we_are_in = FALSE;
                      break;
                  }
                }
            } else {
                c_write_str(ssh, "Further authentication required\r\n");
                logevent("Further authentication required");
            }

            s->can_pubkey =
                in_commasep_string("publickey", methods, methlen);
            s->can_passwd =
                in_commasep_string("password", methods, methlen);
            s->can_keyb_inter = ssh->cfg.try_ki_auth &&
                in_commasep_string("keyboard-interactive", methods, methlen);
          }

          s->method = 0;
          ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
          s->need_pw = FALSE;

          /*
           * Most password/passphrase prompts will be
           * non-echoing, so we set this to 0 by default.
           * Exception is that some keyboard-interactive prompts
           * can be echoing, in which case we'll set this to 1.
           */
          s->echo = 0;

          if (!s->method && s->can_pubkey &&
            agent_exists() && !s->tried_agent) {
            /*
             * Attempt public-key authentication using Pageant.
             */
            void *r;
            s->authed = FALSE;

            ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
            ssh->pkt_ctx |= SSH2_PKTCTX_PUBLICKEY;

            s->tried_agent = TRUE;

            logevent("Pageant is running. Requesting keys.");

            /* Request the keys held by the agent. */
            PUT_32BIT(s->request, 1);
            s->request[4] = SSH2_AGENTC_REQUEST_IDENTITIES;
            if (!agent_query(s->request, 5, &r, &s->responselen,
                         ssh_agent_callback, ssh)) {
                do {
                  crReturnV;
                  if (ispkt) {
                      bombout(("Unexpected data from server while"
                             " waiting for agent response"));
                      crStopV;
                  }
                } while (ispkt || inlen > 0);
                r = ssh->agent_response;
                s->responselen = ssh->agent_response_len;
            }
            s->response = (unsigned char *) r;
            if (s->response && s->responselen >= 5 &&
                s->response[4] == SSH2_AGENT_IDENTITIES_ANSWER) {
                s->p = s->response + 5;
                s->nkeys = GET_32BIT(s->p);
                s->p += 4;
                {
                  char buf[64];
                  sprintf(buf, "Pageant has %d SSH2 keys", s->nkeys);
                  logevent(buf);
                }
                for (s->keyi = 0; s->keyi < s->nkeys; s->keyi++) {
                  void *vret;

                  {
                      char buf[64];
                      sprintf(buf, "Trying Pageant key #%d", s->keyi);
                      logevent(buf);
                  }
                  s->pklen = GET_32BIT(s->p);
                  s->p += 4;
                  if (s->publickey_blob &&
                      s->pklen == s->publickey_bloblen &&
                      !memcmp(s->p, s->publickey_blob,
                            s->publickey_bloblen)) {
                      logevent("This key matches configured key file");
                      s->tried_pubkey_config = 1;
                  }
                  s->pkblob = (char *)s->p;
                  s->p += s->pklen;
                  s->alglen = GET_32BIT(s->pkblob);
                  s->alg = s->pkblob + 4;
                  s->commentlen = GET_32BIT(s->p);
                  s->p += 4;
                  s->commentp = (char *)s->p;
                  s->p += s->commentlen;
                  ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                  ssh2_pkt_addstring(ssh, s->username);
                  ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
                  ssh2_pkt_addstring(ssh, "publickey");     /* method */
                  ssh2_pkt_addbool(ssh, FALSE); /* no signature included */
                  ssh2_pkt_addstring_start(ssh);
                  ssh2_pkt_addstring_data(ssh, s->alg, s->alglen);
                  ssh2_pkt_addstring_start(ssh);
                  ssh2_pkt_addstring_data(ssh, s->pkblob, s->pklen);
                  ssh2_pkt_send(ssh);

                  crWaitUntilV(ispkt);
                  if (ssh->pktin.type != SSH2_MSG_USERAUTH_PK_OK) {
                      logevent("Key refused");
                      continue;
                  }

                  if (flags & FLAG_VERBOSE) {
                      c_write_str(ssh, "Authenticating with "
                              "public key \"");
                      c_write(ssh, s->commentp, s->commentlen);
                      c_write_str(ssh, "\" from agent\r\n");
                  }

                  /*
                   * Server is willing to accept the key.
                   * Construct a SIGN_REQUEST.
                   */
                  ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                  ssh2_pkt_addstring(ssh, s->username);
                  ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
                  ssh2_pkt_addstring(ssh, "publickey");     /* method */
                  ssh2_pkt_addbool(ssh, TRUE);
                  ssh2_pkt_addstring_start(ssh);
                  ssh2_pkt_addstring_data(ssh, s->alg, s->alglen);
                  ssh2_pkt_addstring_start(ssh);
                  ssh2_pkt_addstring_data(ssh, s->pkblob, s->pklen);

                  s->siglen = ssh->pktout.length - 5 + 4 + 20;
                        if (ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)
                            s->siglen -= 4;
                  s->len = 1;       /* message type */
                  s->len += 4 + s->pklen; /* key blob */
                  s->len += 4 + s->siglen;      /* data to sign */
                  s->len += 4;      /* flags */
                  s->agentreq = snewn(4 + s->len, char);
                  PUT_32BIT(s->agentreq, s->len);
                  s->q = s->agentreq + 4;
                  *s->q++ = SSH2_AGENTC_SIGN_REQUEST;
                  PUT_32BIT(s->q, s->pklen);
                  s->q += 4;
                  memcpy(s->q, s->pkblob, s->pklen);
                  s->q += s->pklen;
                  PUT_32BIT(s->q, s->siglen);
                  s->q += 4;
                  /* Now the data to be signed... */
                        if (!(ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)) {
                            PUT_32BIT(s->q, 20);
                            s->q += 4;
                        }
                  memcpy(s->q, ssh->v2_session_id, 20);
                  s->q += 20;
                  memcpy(s->q, ssh->pktout.data + 5,
                         ssh->pktout.length - 5);
                  s->q += ssh->pktout.length - 5;
                  /* And finally the (zero) flags word. */
                  PUT_32BIT(s->q, 0);
                  if (!agent_query(s->agentreq, s->len + 4,
                               &vret, &s->retlen,
                               ssh_agent_callback, ssh)) {
                      do {
                        crReturnV;
                        if (ispkt) {
                            bombout(("Unexpected data from server"
                                   " while waiting for agent"
                                   " response"));
                            crStopV;
                        }
                      } while (ispkt || inlen > 0);
                      vret = ssh->agent_response;
                      s->retlen = ssh->agent_response_len;
                  }
                  s->ret = vret;
                  sfree(s->agentreq);
                  if (s->ret) {
                      if (s->ret[4] == SSH2_AGENT_SIGN_RESPONSE) {
                        logevent("Sending Pageant's response");
                        ssh2_add_sigblob(ssh, s->pkblob, s->pklen,
                                     s->ret + 9,
                                     GET_32BIT(s->ret + 5));
                        ssh2_pkt_send(ssh);
                        s->authed = TRUE;
                        break;
                      } else {
                        logevent
                            ("Pageant failed to answer challenge");
                        sfree(s->ret);
                      }
                  }
                }
                if (s->authed)
                  continue;
            }
            sfree(s->response);
          }

          if (!s->method && s->can_pubkey && s->publickey_blob
            && !s->tried_pubkey_config) {
            unsigned char *pub_blob;
            char *algorithm, *comment;
            int pub_blob_len;

            s->tried_pubkey_config = TRUE;

            ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
            ssh->pkt_ctx |= SSH2_PKTCTX_PUBLICKEY;

            /*
             * Try the public key supplied in the configuration.
             *
             * First, offer the public blob to see if the server is
             * willing to accept it.
             */
            pub_blob =
                (unsigned char *)ssh2_userkey_loadpub(&ssh->cfg.keyfile,
                                            &algorithm,
                                            &pub_blob_len,
                                            NULL);
            if (pub_blob) {
                ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(ssh, s->username);
                ssh2_pkt_addstring(ssh, "ssh-connection");  /* service requested */
                ssh2_pkt_addstring(ssh, "publickey"); /* method */
                ssh2_pkt_addbool(ssh, FALSE);   /* no signature included */
                ssh2_pkt_addstring(ssh, algorithm);
                ssh2_pkt_addstring_start(ssh);
                ssh2_pkt_addstring_data(ssh, (char *)pub_blob,
                                  pub_blob_len);
                ssh2_pkt_send(ssh);
                logevent("Offered public key"); /* FIXME */

                crWaitUntilV(ispkt);
                if (ssh->pktin.type != SSH2_MSG_USERAUTH_PK_OK) {
                  s->gotit = TRUE;
                  s->type = AUTH_TYPE_PUBLICKEY_OFFER_LOUD;
                  continue;      /* key refused; give up on it */
                }

                logevent("Offer of public key accepted");
                /*
                 * Actually attempt a serious authentication using
                 * the key.
                 */
                if (ssh2_userkey_encrypted(&ssh->cfg.keyfile, &comment)) {
                  sprintf(s->pwprompt,
                        "Passphrase for key \"%.100s\": ",
                        comment);
                  s->need_pw = TRUE;
                } else {
                  s->need_pw = FALSE;
                }
                if (flags & FLAG_VERBOSE) {
                  c_write_str(ssh, "Authenticating with public key \"");
                  c_write_str(ssh, comment);
                  c_write_str(ssh, "\"\r\n");
                }
                s->method = AUTH_PUBLICKEY_FILE;
            }
          }

          if (!s->method && s->can_keyb_inter && !s->tried_keyb_inter) {
            s->method = AUTH_KEYBOARD_INTERACTIVE;
            s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE;
            s->tried_keyb_inter = TRUE;

            ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
            ssh->pkt_ctx |= SSH2_PKTCTX_KBDINTER;

            ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
            ssh2_pkt_addstring(ssh, s->username);
            ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
            ssh2_pkt_addstring(ssh, "keyboard-interactive");      /* method */
            ssh2_pkt_addstring(ssh, ""); /* lang */
            ssh2_pkt_addstring(ssh, "");
            ssh2_pkt_send(ssh);

            crWaitUntilV(ispkt);
            if (ssh->pktin.type != SSH2_MSG_USERAUTH_INFO_REQUEST) {
                if (ssh->pktin.type == SSH2_MSG_USERAUTH_FAILURE)
                  s->gotit = TRUE;
                logevent("Keyboard-interactive authentication refused");
                s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET;
                continue;
            }

            s->kbd_inter_running = TRUE;
            s->curr_prompt = 0;
          }

          if (s->kbd_inter_running) {
            s->method = AUTH_KEYBOARD_INTERACTIVE;
            s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE;
            s->tried_keyb_inter = TRUE;

            ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
            ssh->pkt_ctx |= SSH2_PKTCTX_KBDINTER;

            if (s->curr_prompt == 0) {
                /*
                 * We've got a fresh USERAUTH_INFO_REQUEST.
                 * Display header data, and start going through
                 * the prompts.
                 */
                char *name, *inst, *lang;
                int name_len, inst_len, lang_len;

                ssh_pkt_getstring(ssh, &name, &name_len);
                ssh_pkt_getstring(ssh, &inst, &inst_len);
                ssh_pkt_getstring(ssh, &lang, &lang_len);
                if (name_len > 0) {
                  c_write_untrusted(ssh, name, name_len);
                  c_write_str(ssh, "\r\n");
                }
                if (inst_len > 0) {
                  c_write_untrusted(ssh, inst, inst_len);
                  c_write_str(ssh, "\r\n");
                }
                s->num_prompts = ssh_pkt_getuint32(ssh);
            }

            /*
             * If there are prompts remaining in the packet,
             * display one and get a response.
             */
            if (s->curr_prompt < s->num_prompts) {
                char *prompt;
                int prompt_len;

                ssh_pkt_getstring(ssh, &prompt, &prompt_len);
                if (prompt_len > 0) {
                  strncpy(s->pwprompt, prompt, sizeof(s->pwprompt));
                  s->pwprompt[prompt_len < sizeof(s->pwprompt) ?
                            prompt_len : sizeof(s->pwprompt)-1] = '\0';
                } else {
                  strcpy(s->pwprompt,
                         "<server failed to send prompt>: ");
                }
                s->echo = ssh2_pkt_getbool(ssh);
                s->need_pw = TRUE;
            } else
                s->need_pw = FALSE;
          }

          if (!s->method && s->can_passwd) {
            s->method = AUTH_PASSWORD;
            ssh->pkt_ctx &= ~SSH2_PKTCTX_AUTH_MASK;
            ssh->pkt_ctx |= SSH2_PKTCTX_PASSWORD;
            sprintf(s->pwprompt, "%.90s@%.90s's password: ", s->username,
                  ssh->savedhost);
            s->need_pw = TRUE;
          }

          if (s->need_pw) {
            if (ssh_get_line) {
                if (!ssh_get_line(s->pwprompt, s->password,
                              sizeof(s->password), TRUE)) {
                  /*
                   * get_line failed to get a password (for
                   * example because one was supplied on the
                   * command line which has already failed to
                   * work). Terminate.
                   */
                  ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
                  ssh2_pkt_adduint32(ssh,SSH2_DISCONNECT_BY_APPLICATION);
                  ssh2_pkt_addstring(ssh, "No more passwords available"
                                 " to try");
                  ssh2_pkt_addstring(ssh, "en");      /* language tag */
                  ssh2_pkt_send(ssh);
                  logevent("Unable to authenticate");
                  connection_fatal(ssh->frontend,
                               "Unable to authenticate");
                        ssh_closing((Plug)ssh, NULL, 0, 0);
                  crStopV;
                }
            } else {
                int ret;             /* need not be saved across crReturn */
                c_write_untrusted(ssh, s->pwprompt, strlen(s->pwprompt));
                ssh->send_ok = 1;

                setup_userpass_input(ssh, s->password,
                               sizeof(s->password), s->echo);
                do {
                  crWaitUntilV(!ispkt);
                  ret = process_userpass_input(ssh, in, inlen);
                } while (ret == 0);
                if (ret < 0)
                  cleanup_exit(0);
                c_write_str(ssh, "\r\n");
            }
          }

          if (s->method == AUTH_PUBLICKEY_FILE) {
            /*
             * We have our passphrase. Now try the actual authentication.
             */
            struct ssh2_userkey *key;
            const char *error = NULL;

            key = ssh2_load_userkey(&ssh->cfg.keyfile, s->password,
                              &error);
            if (key == SSH2_WRONG_PASSPHRASE || key == NULL) {
                if (key == SSH2_WRONG_PASSPHRASE) {
                  c_write_str(ssh, "Wrong passphrase\r\n");
                  s->tried_pubkey_config = FALSE;
                } else {
                  c_write_str(ssh, "Unable to load private key (");
                  c_write_str(ssh, error);
                  c_write_str(ssh, ")\r\n");
                  s->tried_pubkey_config = TRUE;
                }
                /* Send a spurious AUTH_NONE to return to the top. */
                ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(ssh, s->username);
                ssh2_pkt_addstring(ssh, "ssh-connection");  /* service requested */
                ssh2_pkt_addstring(ssh, "none");      /* method */
                ssh2_pkt_send(ssh);
                s->type = AUTH_TYPE_NONE;
            } else {
                unsigned char *pkblob, *sigblob, *sigdata;
                int pkblob_len, sigblob_len, sigdata_len;
                    int p;

                /*
                 * We have loaded the private key and the server
                 * has announced that it's willing to accept it.
                 * Hallelujah. Generate a signature and send it.
                 */
                ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(ssh, s->username);
                ssh2_pkt_addstring(ssh, "ssh-connection");  /* service requested */
                ssh2_pkt_addstring(ssh, "publickey"); /* method */
                ssh2_pkt_addbool(ssh, TRUE);
                ssh2_pkt_addstring(ssh, key->alg->name);
                pkblob = key->alg->public_blob(key->data, &pkblob_len);
                ssh2_pkt_addstring_start(ssh);
                ssh2_pkt_addstring_data(ssh, (char *)pkblob, pkblob_len);

                /*
                 * The data to be signed is:
                 *
                 *   string  session-id
                 *
                 * followed by everything so far placed in the
                 * outgoing packet.
                 */
                sigdata_len = ssh->pktout.length - 5 + 4 + 20;
                    if (ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)
                        sigdata_len -= 4;
                sigdata = snewn(sigdata_len, unsigned char);
                    p = 0;
                    if (!(ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)) {
                        PUT_32BIT(sigdata+p, 20);
                        p += 4;
                    }
                memcpy(sigdata+p, ssh->v2_session_id, 20); p += 20;
                memcpy(sigdata+p, ssh->pktout.data + 5,
                     ssh->pktout.length - 5);
                    p += ssh->pktout.length - 5;
                    assert(p == sigdata_len);
                sigblob = key->alg->sign(key->data, (char *)sigdata,
                                   sigdata_len, &sigblob_len);
                ssh2_add_sigblob(ssh, pkblob, pkblob_len,
                             sigblob, sigblob_len);
                sfree(pkblob);
                sfree(sigblob);
                sfree(sigdata);

                ssh2_pkt_send(ssh);
                s->type = AUTH_TYPE_PUBLICKEY;
                key->alg->freekey(key->data);
            }
          } else if (s->method == AUTH_PASSWORD) {
            /*
             * We send the password packet lumped tightly together with
             * an SSH_MSG_IGNORE packet. The IGNORE packet contains a
             * string long enough to make the total length of the two
             * packets constant. This should ensure that a passive
             * listener doing traffic analyis can't work out the length
             * of the password.
             *
             * For this to work, we need an assumption about the
             * maximum length of the password packet. I think 256 is
             * pretty conservative. Anyone using a password longer than
             * that probably doesn't have much to worry about from
             * people who find out how long their password is!
             */
            ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_REQUEST);
            ssh2_pkt_addstring(ssh, s->username);
            ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
            ssh2_pkt_addstring(ssh, "password");
            ssh2_pkt_addbool(ssh, FALSE);
            ssh2_pkt_addstring(ssh, s->password);
            memset(s->password, 0, sizeof(s->password));
            ssh2_pkt_defer(ssh);
            /*
             * We'll include a string that's an exact multiple of the
             * cipher block size. If the cipher is NULL for some
             * reason, we don't do this trick at all because we gain
             * nothing by it.
             */
            if (ssh->cscipher) {
                int stringlen, i;

                stringlen = (256 - ssh->deferred_len);
                stringlen += ssh->cscipher->blksize - 1;
                stringlen -= (stringlen % ssh->cscipher->blksize);
                if (ssh->cscomp) {
                  /*
                   * Temporarily disable actual compression,
                   * so we can guarantee to get this string
                   * exactly the length we want it. The
                   * compression-disabling routine should
                   * return an integer indicating how many
                   * bytes we should adjust our string length
                   * by.
                   */
                  stringlen -= 
                      ssh->cscomp->disable_compression(ssh->cs_comp_ctx);
                }
                ssh2_pkt_init(ssh, SSH2_MSG_IGNORE);
                ssh2_pkt_addstring_start(ssh);
                for (i = 0; i < stringlen; i++) {
                  char c = (char) random_byte();
                  ssh2_pkt_addstring_data(ssh, &c, 1);
                }
                ssh2_pkt_defer(ssh);
            }
            ssh_pkt_defersend(ssh);
            logevent("Sent password");
            s->type = AUTH_TYPE_PASSWORD;
          } else if (s->method == AUTH_KEYBOARD_INTERACTIVE) {
            if (s->curr_prompt == 0) {
                ssh2_pkt_init(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE);
                ssh2_pkt_adduint32(ssh, s->num_prompts);
            }
            if (s->need_pw) {      /* only add pw if we just got one! */
                ssh2_pkt_addstring(ssh, s->password);
                memset(s->password, 0, sizeof(s->password));
                s->curr_prompt++;
            }
            if (s->curr_prompt >= s->num_prompts) {
                ssh2_pkt_send(ssh);
            } else {
                /*
                 * If there are prompts remaining, we set
                 * `gotit' so that we won't attempt to get
                 * another packet. Then we go back round the
                 * loop and will end up retrieving another
                 * prompt out of the existing packet. Funky or
                 * what?
                 */
                s->gotit = TRUE;
            }
            s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE;
          } else {
            c_write_str(ssh, "No supported authentication methods"
                      " left to try!\r\n");
            logevent("No supported authentications offered."
                   " Disconnecting");
            ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
            ssh2_pkt_adduint32(ssh, SSH2_DISCONNECT_BY_APPLICATION);
            ssh2_pkt_addstring(ssh, "No supported authentication"
                           " methods available");
            ssh2_pkt_addstring(ssh, "en");      /* language tag */
            ssh2_pkt_send(ssh);
                ssh_closing((Plug)ssh, NULL, 0, 0);
            crStopV;
          }
      }
    } while (!s->we_are_in);

    /*
     * Now we're authenticated for the connection protocol. The
     * connection protocol will automatically have started at this
     * point; there's no need to send SERVICE_REQUEST.
     */

    /*
     * So now create a channel with a session in it.
     */
    ssh->channels = newtree234(ssh_channelcmp);
    ssh->mainchan = snew(struct ssh_channel);
    ssh->mainchan->ssh = ssh;
    ssh->mainchan->localid = alloc_channel_id(ssh);
    ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN);
    ssh2_pkt_addstring(ssh, "session");
    ssh2_pkt_adduint32(ssh, ssh->mainchan->localid);
    ssh->mainchan->v.v2.locwindow = OUR_V2_WINSIZE;
    ssh2_pkt_adduint32(ssh, ssh->mainchan->v.v2.locwindow);/* our window size */
    ssh2_pkt_adduint32(ssh, 0x4000UL);      /* our max pkt size */
    ssh2_pkt_send(ssh);
    crWaitUntilV(ispkt);
    if (ssh->pktin.type != SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
      bombout(("Server refused to open a session"));
      crStopV;
      /* FIXME: error data comes back in FAILURE packet */
    }
    if (ssh_pkt_getuint32(ssh) != ssh->mainchan->localid) {
      bombout(("Server's channel confirmation cited wrong channel"));
      crStopV;
    }
    ssh->mainchan->remoteid = ssh_pkt_getuint32(ssh);
    ssh->mainchan->type = CHAN_MAINSESSION;
    ssh->mainchan->closes = 0;
    ssh->mainchan->v.v2.remwindow = ssh_pkt_getuint32(ssh);
    ssh->mainchan->v.v2.remmaxpkt = ssh_pkt_getuint32(ssh);
    bufchain_init(&ssh->mainchan->v.v2.outbuffer);
    add234(ssh->channels, ssh->mainchan);
    logevent("Opened channel for session");

    /*
     * Potentially enable X11 forwarding.
     */
    if (ssh->cfg.x11_forward) {
      char proto[20], data[64];
      logevent("Requesting X11 forwarding");
      ssh->x11auth = x11_invent_auth(proto, sizeof(proto),
                               data, sizeof(data), ssh->cfg.x11_auth);
        x11_get_real_auth(ssh->x11auth, ssh->cfg.x11_display);
      ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
      ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
      ssh2_pkt_addstring(ssh, "x11-req");
      ssh2_pkt_addbool(ssh, 1);            /* want reply */
      ssh2_pkt_addbool(ssh, 0);            /* many connections */
      ssh2_pkt_addstring(ssh, proto);
      ssh2_pkt_addstring(ssh, data);
      ssh2_pkt_adduint32(ssh, x11_get_screen_number(ssh->cfg.x11_display));
      ssh2_pkt_send(ssh);

      do {
          crWaitUntilV(ispkt);
          if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */
            c->v.v2.remwindow += ssh_pkt_getuint32(ssh);
          }
      } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

      if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
          if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
            bombout(("Unexpected response to X11 forwarding request:"
                   " packet type %d", ssh->pktin.type));
            crStopV;
          }
          logevent("X11 forwarding refused");
      } else {
          logevent("X11 forwarding enabled");
          ssh->X11_fwd_enabled = TRUE;
      }
    }

    /*
     * Enable port forwardings.
     */
    {
      char type;
      int n;
      int sport,dport,sserv,dserv;
      char sports[256], dports[256], saddr[256], host[256];

      ssh->rportfwds = newtree234(ssh_rportcmp_ssh2);
        /* Add port forwardings. */
      ssh->portfwd_strptr = ssh->cfg.portfwd;
      while (*ssh->portfwd_strptr) {
          type = *ssh->portfwd_strptr++;
          saddr[0] = '\0';
          n = 0;
          while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != '\t') {
            if (*ssh->portfwd_strptr == ':') {
                /*
                 * We've seen a colon in the middle of the
                 * source port number. This means that
                 * everything we've seen until now is the
                 * source _address_, so we'll move it into
                 * saddr and start sports from the beginning
                 * again.
                 */
                ssh->portfwd_strptr++;
                sports[n] = '\0';
                strcpy(saddr, sports);
                n = 0;
            }
            if (n < 255) sports[n++] = *ssh->portfwd_strptr++;
          }
          sports[n] = 0;
          if (type != 'D') {
            if (*ssh->portfwd_strptr == '\t')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr && *ssh->portfwd_strptr != ':') {
                if (n < 255) host[n++] = *ssh->portfwd_strptr++;
            }
            host[n] = 0;
            if (*ssh->portfwd_strptr == ':')
                ssh->portfwd_strptr++;
            n = 0;
            while (*ssh->portfwd_strptr) {
                if (n < 255) dports[n++] = *ssh->portfwd_strptr++;
            }
            dports[n] = 0;
            ssh->portfwd_strptr++;
            dport = atoi(dports);
            dserv = 0;
            if (dport == 0) {
                dserv = 1;
                dport = net_service_lookup(dports);
                if (!dport) {
                  logeventf(ssh, "Service lookup failed for destination"
                          " port \"%s\"", dports);
                }
            }
          } else {
            while (*ssh->portfwd_strptr) ssh->portfwd_strptr++;
            dport = dserv = -1;
            ssh->portfwd_strptr++; /* eat the NUL and move to next one */
          }
          sport = atoi(sports);
          sserv = 0;
          if (sport == 0) {
            sserv = 1;
            sport = net_service_lookup(sports);
            if (!sport) {
                logeventf(ssh, "Service lookup failed for source"
                        " port \"%s\"", sports);
            }
          }
          if (sport && dport) {
            if (type == 'L') {
                pfd_addforward(host, dport, *saddr ? saddr : NULL,
                           sport, ssh, &ssh->cfg);
                logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
                        " forwarding to %s:%.*s%.*s%d%.*s",
                        (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
                        (int)(*saddr?1:0), ":",
                        (int)(sserv ? strlen(sports) : 0), sports,
                        sserv, "(", sport, sserv, ")",
                        host,
                        (int)(dserv ? strlen(dports) : 0), dports,
                        dserv, "(", dport, dserv, ")");
            } else if (type == 'D') {
                pfd_addforward(NULL, -1, *saddr ? saddr : NULL,
                           sport, ssh, &ssh->cfg);
                logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
                        " doing SOCKS dynamic forwarding",
                        (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
                        (int)(*saddr?1:0), ":",
                        (int)(sserv ? strlen(sports) : 0), sports,
                        sserv, "(", sport, sserv, ")");
            } else {
                struct ssh_rportfwd *pf;
                pf = snew(struct ssh_rportfwd);
                strcpy(pf->dhost, host);
                pf->dport = dport;
                pf->sport = sport;
                if (add234(ssh->rportfwds, pf) != pf) {
                  logeventf(ssh, "Duplicate remote port forwarding"
                          " to %s:%d", host, dport);
                  sfree(pf);
                } else {
                  logeventf(ssh, "Requesting remote port "
                          "%.*s%.*s%.*s%.*s%d%.*s"
                          " forward to %s:%.*s%.*s%d%.*s",
                          (int)(*saddr?strlen(saddr):0),
                          *saddr?saddr:NULL,
                          (int)(*saddr?1:0), ":",
                          (int)(sserv ? strlen(sports) : 0), sports,
                          sserv, "(", sport, sserv, ")",
                          host,
                          (int)(dserv ? strlen(dports) : 0), dports,
                          dserv, "(", dport, dserv, ")");
                  ssh2_pkt_init(ssh, SSH2_MSG_GLOBAL_REQUEST);
                  ssh2_pkt_addstring(ssh, "tcpip-forward");
                  ssh2_pkt_addbool(ssh, 1);/* want reply */
                  if (*saddr)
                      ssh2_pkt_addstring(ssh, saddr);
                  if (ssh->cfg.rport_acceptall)
                      ssh2_pkt_addstring(ssh, "0.0.0.0");
                  else
                      ssh2_pkt_addstring(ssh, "127.0.0.1");
                  ssh2_pkt_adduint32(ssh, sport);
                  ssh2_pkt_send(ssh);

                  do {
                      crWaitUntilV(ispkt);
                      if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
                        unsigned i = ssh_pkt_getuint32(ssh);
                        struct ssh_channel *c;
                        c = find234(ssh->channels, &i, ssh_channelfind);
                        if (!c)
                            continue;/* nonexistent channel */
                        c->v.v2.remwindow += ssh_pkt_getuint32(ssh);
                      }
                  } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

                  if (ssh->pktin.type != SSH2_MSG_REQUEST_SUCCESS) {
                      if (ssh->pktin.type != SSH2_MSG_REQUEST_FAILURE) {
                        bombout(("Unexpected response to port "
                               "forwarding request: packet type %d",
                               ssh->pktin.type));
                        crStopV;
                      }
                      logevent("Server refused this port forwarding");
                  } else {
                      logevent("Remote port forwarding enabled");
                  }
                }
            }
          }
      }
    }

    /*
     * Potentially enable agent forwarding.
     */
    if (ssh->cfg.agentfwd && agent_exists()) {
      logevent("Requesting OpenSSH-style agent forwarding");
      ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
      ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
      ssh2_pkt_addstring(ssh, "auth-agent-req@openssh.com");
      ssh2_pkt_addbool(ssh, 1);            /* want reply */
      ssh2_pkt_send(ssh);

      do {
          crWaitUntilV(ispkt);
          if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */
            c->v.v2.remwindow += ssh_pkt_getuint32(ssh);
          }
      } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

      if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
          if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
            bombout(("Unexpected response to agent forwarding request:"
                   " packet type %d", ssh->pktin.type));
            crStopV;
          }
          logevent("Agent forwarding refused");
      } else {
          logevent("Agent forwarding enabled");
          ssh->agentfwd_enabled = TRUE;
      }
    }

    /*
     * Now allocate a pty for the session.
     */
    if (!ssh->cfg.nopty) {
      /* Unpick the terminal-speed string. */
      /* XXX perhaps we should allow no speeds to be sent. */
        ssh->ospeed = 38400; ssh->ispeed = 38400; /* last-resort defaults */
      sscanf(ssh->cfg.termspeed, "%d,%d", &ssh->ospeed, &ssh->ispeed);
      /* Build the pty request. */
      ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
      ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);     /* recipient channel */
      ssh2_pkt_addstring(ssh, "pty-req");
      ssh2_pkt_addbool(ssh, 1);            /* want reply */
      ssh2_pkt_addstring(ssh, ssh->cfg.termtype);
      ssh2_pkt_adduint32(ssh, ssh->term_width);
      ssh2_pkt_adduint32(ssh, ssh->term_height);
      ssh2_pkt_adduint32(ssh, 0);          /* pixel width */
      ssh2_pkt_adduint32(ssh, 0);          /* pixel height */
      ssh2_pkt_addstring_start(ssh);
      ssh2_pkt_addbyte(ssh, 128);          /* TTY_OP_ISPEED */
      ssh2_pkt_adduint32(ssh, ssh->ispeed);
      ssh2_pkt_addbyte(ssh, 129);          /* TTY_OP_OSPEED */
      ssh2_pkt_adduint32(ssh, ssh->ospeed);
      ssh2_pkt_addstring_data(ssh, "\0", 1); /* TTY_OP_END */
      ssh2_pkt_send(ssh);
      ssh->state = SSH_STATE_INTERMED;

      do {
          crWaitUntilV(ispkt);
          if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */
            c->v.v2.remwindow += ssh_pkt_getuint32(ssh);
          }
      } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);

      if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
          if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
            bombout(("Unexpected response to pty request:"
                   " packet type %d", ssh->pktin.type));
            crStopV;
          }
          c_write_str(ssh, "Server refused to allocate pty\r\n");
          ssh->editing = ssh->echoing = 1;
      } else {
          logeventf(ssh, "Allocated pty (ospeed %dbps, ispeed %dbps)",
                  ssh->ospeed, ssh->ispeed);
      }
    } else {
      ssh->editing = ssh->echoing = 1;
    }

    /*
     * Start a shell or a remote command. We may have to attempt
     * this twice if the config data has provided a second choice
     * of command.
     */
    while (1) {
      int subsys;
      char *cmd;

      if (ssh->fallback_cmd) {
          subsys = ssh->cfg.ssh_subsys2;
          cmd = ssh->cfg.remote_cmd_ptr2;
      } else {
          subsys = ssh->cfg.ssh_subsys;
          cmd = ssh->cfg.remote_cmd_ptr;
      }

      ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
      ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);     /* recipient channel */
      if (subsys) {
          ssh2_pkt_addstring(ssh, "subsystem");
          ssh2_pkt_addbool(ssh, 1);        /* want reply */
          ssh2_pkt_addstring(ssh, cmd);
      } else if (*cmd) {
          ssh2_pkt_addstring(ssh, "exec");
          ssh2_pkt_addbool(ssh, 1);        /* want reply */
          ssh2_pkt_addstring(ssh, cmd);
      } else {
          ssh2_pkt_addstring(ssh, "shell");
          ssh2_pkt_addbool(ssh, 1);        /* want reply */
      }
      ssh2_pkt_send(ssh);
      do {
          crWaitUntilV(ispkt);
          if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */
            c->v.v2.remwindow += ssh_pkt_getuint32(ssh);
          }
      } while (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST);
      if (ssh->pktin.type != SSH2_MSG_CHANNEL_SUCCESS) {
          if (ssh->pktin.type != SSH2_MSG_CHANNEL_FAILURE) {
            bombout(("Unexpected response to shell/command request:"
                   " packet type %d", ssh->pktin.type));
            crStopV;
          }
          /*
           * We failed to start the command. If this is the
           * fallback command, we really are finished; if it's
           * not, and if the fallback command exists, try falling
           * back to it before complaining.
           */
          if (!ssh->fallback_cmd && ssh->cfg.remote_cmd_ptr2 != NULL) {
            logevent("Primary command failed; attempting fallback");
            ssh->fallback_cmd = TRUE;
            continue;
          }
          bombout(("Server refused to start a shell/command"));
          crStopV;
      } else {
          logevent("Started a shell/command");
      }
      break;
    }

    ssh->state = SSH_STATE_SESSION;
    if (ssh->size_needed)
      ssh_size(ssh, ssh->term_width, ssh->term_height);
    if (ssh->eof_needed)
      ssh_special(ssh, TS_EOF);

    /*
     * Transfer data!
     */
    if (ssh->ldisc)
      ldisc_send(ssh->ldisc, NULL, 0, 0);/* cause ldisc to notice changes */
    ssh->send_ok = 1;
    while (1) {
      crReturnV;
      s->try_send = FALSE;
      if (ispkt) {
          if (ssh->pktin.type == SSH2_MSG_CHANNEL_DATA ||
            ssh->pktin.type == SSH2_MSG_CHANNEL_EXTENDED_DATA) {
            char *data;
            int length;
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */
            if (ssh->pktin.type == SSH2_MSG_CHANNEL_EXTENDED_DATA &&
                ssh_pkt_getuint32(ssh) != SSH2_EXTENDED_DATA_STDERR)
                continue;            /* extended but not stderr */
            ssh_pkt_getstring(ssh, &data, &length);
            if (data) {
                int bufsize = 0;
                c->v.v2.locwindow -= length;
                switch (c->type) {
                  case CHAN_MAINSESSION:
                  bufsize =
                      from_backend(ssh->frontend, ssh->pktin.type ==
                               SSH2_MSG_CHANNEL_EXTENDED_DATA,
                               data, length);
                  break;
                  case CHAN_X11:
                  bufsize = x11_send(c->u.x11.s, data, length);
                  break;
                  case CHAN_SOCKDATA:
                  bufsize = pfd_send(c->u.pfd.s, data, length);
                  break;
                  case CHAN_AGENT:
                  while (length > 0) {
                      if (c->u.a.lensofar < 4) {
                        int l = min(4 - c->u.a.lensofar, length);
                        memcpy(c->u.a.msglen + c->u.a.lensofar,
                               data, l);
                        data += l;
                        length -= l;
                        c->u.a.lensofar += l;
                      }
                      if (c->u.a.lensofar == 4) {
                        c->u.a.totallen =
                            4 + GET_32BIT(c->u.a.msglen);
                        c->u.a.message = snewn(c->u.a.totallen,
                                           unsigned char);
                        memcpy(c->u.a.message, c->u.a.msglen, 4);
                      }
                      if (c->u.a.lensofar >= 4 && length > 0) {
                        int l =
                            min(c->u.a.totallen - c->u.a.lensofar,
                              length);
                        memcpy(c->u.a.message + c->u.a.lensofar,
                               data, l);
                        data += l;
                        length -= l;
                        c->u.a.lensofar += l;
                      }
                      if (c->u.a.lensofar == c->u.a.totallen) {
                        void *reply;
                        int replylen;
                        if (agent_query(c->u.a.message,
                                    c->u.a.totallen,
                                    &reply, &replylen,
                                    ssh_agentf_callback, c))
                            ssh_agentf_callback(c, reply, replylen);
                        sfree(c->u.a.message);
                        c->u.a.lensofar = 0;
                      }
                  }
                  bufsize = 0;
                  break;
                }
                /*
                 * If we are not buffering too much data,
                 * enlarge the window again at the remote side.
                 */
                if (bufsize < OUR_V2_WINSIZE)
                  ssh2_set_window(c, OUR_V2_WINSIZE - bufsize);
            }
          } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_EOF) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;

            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */

            if (c->type == CHAN_X11) {
                /*
                 * Remote EOF on an X11 channel means we should
                 * wrap up and close the channel ourselves.
                 */
                x11_close(c->u.x11.s);
                sshfwd_close(c);
            } else if (c->type == CHAN_AGENT) {
                sshfwd_close(c);
            } else if (c->type == CHAN_SOCKDATA) {
                pfd_close(c->u.pfd.s);
                sshfwd_close(c);
            }
          } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_CLOSE) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;

            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c || ((int)c->remoteid) == -1) {
                bombout(("Received CHANNEL_CLOSE for %s channel %d\n",
                       c ? "half-open" : "nonexistent", i));
                crStopV;
            }
            /* Do pre-close processing on the channel. */
            switch (c->type) {
              case CHAN_MAINSESSION:
                break;         /* nothing to see here, move along */
              case CHAN_X11:
                if (c->u.x11.s != NULL)
                  x11_close(c->u.x11.s);
                sshfwd_close(c);
                break;
              case CHAN_AGENT:
                sshfwd_close(c);
                break;
              case CHAN_SOCKDATA:
                if (c->u.pfd.s != NULL)
                  pfd_close(c->u.pfd.s);
                sshfwd_close(c);
                break;
            }
            if (c->closes == 0) {
                ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_CLOSE);
                ssh2_pkt_adduint32(ssh, c->remoteid);
                ssh2_pkt_send(ssh);
            }
            del234(ssh->channels, c);
            bufchain_clear(&c->v.v2.outbuffer);
            sfree(c);

            /*
             * See if that was the last channel left open.
             */
            if (count234(ssh->channels) == 0) {
                logevent("All channels closed. Disconnecting");
#if 0
                    /*
                     * We used to send SSH_MSG_DISCONNECT here,
                     * because I'd believed that _every_ conforming
                     * SSH2 connection had to end with a disconnect
                     * being sent by at least one side; apparently
                     * I was wrong and it's perfectly OK to
                     * unceremoniously slam the connection shut
                     * when you're done, and indeed OpenSSH feels
                     * this is more polite than sending a
                     * DISCONNECT. So now we don't.
                     */
                ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
                ssh2_pkt_adduint32(ssh, SSH2_DISCONNECT_BY_APPLICATION);
                ssh2_pkt_addstring(ssh, "All open channels closed");
                ssh2_pkt_addstring(ssh, "en");  /* language tag */
                ssh2_pkt_send(ssh);
#endif
                    ssh_closing((Plug)ssh, NULL, 0, 0);
                crStopV;
            }
            continue;          /* remote sends close; ignore (FIXME) */
          } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c || c->closes)
                continue;            /* nonexistent or closing channel */
            c->v.v2.remwindow += ssh_pkt_getuint32(ssh);
            s->try_send = TRUE;
          } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */
            if (c->type != CHAN_SOCKDATA_DORMANT)
                continue;            /* dunno why they're confirming this */
            c->remoteid = ssh_pkt_getuint32(ssh);
            c->type = CHAN_SOCKDATA;
            c->v.v2.remwindow = ssh_pkt_getuint32(ssh);
            c->v.v2.remmaxpkt = ssh_pkt_getuint32(ssh);
            if (c->u.pfd.s)
                pfd_confirm(c->u.pfd.s);
            if (c->closes) {
                /*
                 * We have a pending close on this channel,
                 * which we decided on before the server acked
                 * the channel open. So now we know the
                 * remoteid, we can close it again.
                 */
                ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_CLOSE);
                ssh2_pkt_adduint32(ssh, c->remoteid);
                ssh2_pkt_send(ssh);
            }
          } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_OPEN_FAILURE) {
            unsigned i = ssh_pkt_getuint32(ssh);
            struct ssh_channel *c;
            c = find234(ssh->channels, &i, ssh_channelfind);
            if (!c)
                continue;            /* nonexistent channel */
            if (c->type != CHAN_SOCKDATA_DORMANT)
                continue;            /* dunno why they're failing this */

            logevent("Forwarded connection refused by server");

            pfd_close(c->u.pfd.s);

            del234(ssh->channels, c);
            sfree(c);
          } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_REQUEST) {
            unsigned localid;
            char *type;
            int typelen, want_reply;
            struct ssh_channel *c;

            localid = ssh_pkt_getuint32(ssh);
            ssh_pkt_getstring(ssh, &type, &typelen);
            want_reply = ssh2_pkt_getbool(ssh);

            /*
             * First, check that the channel exists. Otherwise,
             * we can instantly disconnect with a rude message.
             */
            c = find234(ssh->channels, &localid, ssh_channelfind);
            if (!c) {
                char buf[80];
                sprintf(buf, "Received channel request for nonexistent"
                      " channel %d", localid);
                logevent(buf);
                ssh2_pkt_init(ssh, SSH2_MSG_DISCONNECT);
                ssh2_pkt_adduint32(ssh, SSH2_DISCONNECT_BY_APPLICATION);
                ssh2_pkt_addstring(ssh, buf);
                ssh2_pkt_addstring(ssh, "en");  /* language tag */
                ssh2_pkt_send(ssh);
                connection_fatal(ssh->frontend, "%s", buf);
                    ssh_closing((Plug)ssh, NULL, 0, 0);
                crStopV;
            }

            /*
             * Having got the channel number, we now look at
             * the request type string to see if it's something
             * we recognise.
             */
            if (typelen == 11 && !memcmp(type, "exit-status", 11) &&
                c == ssh->mainchan) {
                /* We recognise "exit-status" on the primary channel. */
                char buf[100];
                ssh->exitcode = ssh_pkt_getuint32(ssh);
                sprintf(buf, "Server sent command exit status %d",
                      ssh->exitcode);
                logevent(buf);
                if (want_reply) {
                  ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_SUCCESS);
                  ssh2_pkt_adduint32(ssh, c->remoteid);
                  ssh2_pkt_send(ssh);
                }
            } else {
                /*
                 * This is a channel request we don't know
                 * about, so we now either ignore the request
                 * or respond with CHANNEL_FAILURE, depending
                 * on want_reply.
                 */
                if (want_reply) {
                  ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_FAILURE);
                  ssh2_pkt_adduint32(ssh, c->remoteid);
                  ssh2_pkt_send(ssh);
                }
            }
          } else if (ssh->pktin.type == SSH2_MSG_GLOBAL_REQUEST) {
            char *type;
            int typelen, want_reply;

            ssh_pkt_getstring(ssh, &type, &typelen);
            want_reply = ssh2_pkt_getbool(ssh);

                /*
                 * We currently don't support any global requests
                 * at all, so we either ignore the request or
                 * respond with REQUEST_FAILURE, depending on
                 * want_reply.
                 */
                if (want_reply) {
                    ssh2_pkt_init(ssh, SSH2_MSG_REQUEST_FAILURE);
                    ssh2_pkt_send(ssh);
            }
          } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_OPEN) {
            char *type;
            int typelen;
            char *peeraddr;
            int peeraddrlen;
            int peerport;
            char *error = NULL;
            struct ssh_channel *c;
            unsigned remid, winsize, pktsize;
            ssh_pkt_getstring(ssh, &type, &typelen);
            c = snew(struct ssh_channel);
            c->ssh = ssh;

            remid = ssh_pkt_getuint32(ssh);
            winsize = ssh_pkt_getuint32(ssh);
            pktsize = ssh_pkt_getuint32(ssh);

            if (typelen == 3 && !memcmp(type, "x11", 3)) {
                char *addrstr;

                    ssh_pkt_getstring(ssh, &peeraddr, &peeraddrlen);
                addrstr = snewn(peeraddrlen+1, char);
                memcpy(addrstr, peeraddr, peeraddrlen);
                peeraddr[peeraddrlen] = '\0';
                    peerport = ssh_pkt_getuint32(ssh);

                if (!ssh->X11_fwd_enabled)
                  error = "X11 forwarding is not enabled";
                else if (x11_init(&c->u.x11.s, ssh->cfg.x11_display, c,
                              ssh->x11auth, addrstr, peerport,
                              &ssh->cfg) != NULL) {
                  error = "Unable to open an X11 connection";
                } else {
                  c->type = CHAN_X11;
                }

                sfree(addrstr);
            } else if (typelen == 15 &&
                     !memcmp(type, "forwarded-tcpip", 15)) {
                struct ssh_rportfwd pf, *realpf;
                char *dummy;
                int dummylen;
                ssh_pkt_getstring(ssh, &dummy, &dummylen);/* skip address */
                pf.sport = ssh_pkt_getuint32(ssh);
                    ssh_pkt_getstring(ssh, &peeraddr, &peeraddrlen);
                    peerport = ssh_pkt_getuint32(ssh);
                realpf = find234(ssh->rportfwds, &pf, NULL);
                if (realpf == NULL) {
                  error = "Remote port is not recognised";
                } else {
                  const char *e = pfd_newconnect(&c->u.pfd.s,
                                           realpf->dhost,
                                           realpf->dport, c,
                                           &ssh->cfg);
                  logeventf(ssh, "Received remote port open request"
                          " for %s:%d", realpf->dhost, realpf->dport);
                  if (e != NULL) {
                      logeventf(ssh, "Port open failed: %s", e);
                      error = "Port open failed";
                  } else {
                      logevent("Forwarded port opened successfully");
                      c->type = CHAN_SOCKDATA;
                  }
                }
            } else if (typelen == 22 &&
                     !memcmp(type, "auth-agent@openssh.com", 3)) {
                if (!ssh->agentfwd_enabled)
                  error = "Agent forwarding is not enabled";
                else {
                  c->type = CHAN_AGENT;   /* identify channel type */
                  c->u.a.lensofar = 0;
                }
            } else {
                error = "Unsupported channel type requested";
            }

            c->remoteid = remid;
            if (error) {
                ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN_FAILURE);
                ssh2_pkt_adduint32(ssh, c->remoteid);
                ssh2_pkt_adduint32(ssh, SSH2_OPEN_CONNECT_FAILED);
                ssh2_pkt_addstring(ssh, error);
                ssh2_pkt_addstring(ssh, "en");  /* language tag */
                ssh2_pkt_send(ssh);
                sfree(c);
            } else {
                c->localid = alloc_channel_id(ssh);
                c->closes = 0;
                c->v.v2.locwindow = OUR_V2_WINSIZE;
                c->v.v2.remwindow = winsize;
                c->v.v2.remmaxpkt = pktsize;
                bufchain_init(&c->v.v2.outbuffer);
                add234(ssh->channels, c);
                ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
                ssh2_pkt_adduint32(ssh, c->remoteid);
                ssh2_pkt_adduint32(ssh, c->localid);
                ssh2_pkt_adduint32(ssh, c->v.v2.locwindow);
                ssh2_pkt_adduint32(ssh, 0x4000UL);    /* our max pkt size */
                ssh2_pkt_send(ssh);
            }
          } else {
            bombout(("Strange packet received: type %d", ssh->pktin.type));
            crStopV;
          }
      } else {
          /*
           * We have spare data. Add it to the channel buffer.
           */
          ssh2_add_channel_data(ssh->mainchan, (char *)in, inlen);
          s->try_send = TRUE;
      }
      if (s->try_send) {
          int i;
          struct ssh_channel *c;
          /*
           * Try to send data on all channels if we can.
           */
          for (i = 0; NULL != (c = index234(ssh->channels, i)); i++) {
            int bufsize;
            if (c->closes)
                continue;            /* don't send on closing channels */
            bufsize = ssh2_try_send(c);
            if (bufsize == 0) {
                switch (c->type) {
                  case CHAN_MAINSESSION:
                  /* stdin need not receive an unthrottle
                   * notification since it will be polled */
                  break;
                  case CHAN_X11:
                  x11_unthrottle(c->u.x11.s);
                  break;
                  case CHAN_AGENT:
                  /* agent sockets are request/response and need no
                   * buffer management */
                  break;
                  case CHAN_SOCKDATA:
                  pfd_unthrottle(c->u.pfd.s);
                  break;
                }
            }
          }
      }
    }

    crFinishV;
}

/*
 * Handle the top-level SSH2 protocol.
 */
static void ssh2_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt)
{
    if (do_ssh2_transport(ssh, in, inlen, ispkt) == 0)
      return;
    do_ssh2_authconn(ssh, in, inlen, ispkt);
}

/*
 * Called to set up the connection.
 *
 * Returns an error message, or NULL on success.
 */
static const char *ssh_init(void *frontend_handle, void **backend_handle,
                      Config *cfg,
                      char *host, int port, char **realhost, int nodelay,
                      int keepalive)
{
    const char *p;
    Ssh ssh;

    ssh = snew(struct ssh_tag);
    ssh->cfg = *cfg;                 /* STRUCTURE COPY */
    ssh->version = 0;                /* when not ready yet */
    ssh->s = NULL;
    ssh->cipher = NULL;
    ssh->v1_cipher_ctx = NULL;
    ssh->crcda_ctx = NULL;
    ssh->cscipher = NULL;
    ssh->cs_cipher_ctx = NULL;
    ssh->sccipher = NULL;
    ssh->sc_cipher_ctx = NULL;
    ssh->csmac = NULL;
    ssh->cs_mac_ctx = NULL;
    ssh->scmac = NULL;
    ssh->sc_mac_ctx = NULL;
    ssh->cscomp = NULL;
    ssh->cs_comp_ctx = NULL;
    ssh->sccomp = NULL;
    ssh->sc_comp_ctx = NULL;
    ssh->kex = NULL;
    ssh->kex_ctx = NULL;
    ssh->hostkey = NULL;
    ssh->exitcode = -1;
    ssh->state = SSH_STATE_PREPACKET;
    ssh->size_needed = FALSE;
    ssh->eof_needed = FALSE;
    ssh->ldisc = NULL;
    ssh->logctx = NULL;
    {
      static const struct Packet empty = { 0, 0, NULL, NULL, 0 };
      ssh->pktin = ssh->pktout = empty;
    }
    ssh->deferred_send_data = NULL;
    ssh->deferred_len = 0;
    ssh->deferred_size = 0;
    ssh->fallback_cmd = 0;
    ssh->pkt_ctx = 0;
    ssh->x11auth = NULL;
    ssh->v1_compressing = FALSE;
    ssh->v2_outgoing_sequence = 0;
    ssh->ssh1_rdpkt_crstate = 0;
    ssh->ssh2_rdpkt_crstate = 0;
    ssh->do_ssh_init_crstate = 0;
    ssh->ssh_gotdata_crstate = 0;
    ssh->ssh1_protocol_crstate = 0;
    ssh->do_ssh1_login_crstate = 0;
    ssh->do_ssh2_transport_crstate = 0;
    ssh->do_ssh2_authconn_crstate = 0;
    ssh->do_ssh_init_state = NULL;
    ssh->do_ssh1_login_state = NULL;
    ssh->do_ssh2_transport_state = NULL;
    ssh->do_ssh2_authconn_state = NULL;
    ssh->mainchan = NULL;
    ssh->throttled_all = 0;
    ssh->v1_stdout_throttling = 0;

    *backend_handle = ssh;

#ifdef MSCRYPTOAPI
    if (crypto_startup() == 0)
      return "Microsoft high encryption pack not installed!";
#endif

    ssh->frontend = frontend_handle;
    ssh->term_width = ssh->cfg.width;
    ssh->term_height = ssh->cfg.height;

    ssh->channels = NULL;
    ssh->rportfwds = NULL;

    ssh->send_ok = 0;
    ssh->editing = 0;
    ssh->echoing = 0;
    ssh->v1_throttle_count = 0;
    ssh->overall_bufsize = 0;
    ssh->fallback_cmd = 0;

    ssh->protocol = NULL;

    p = connect_to_host(ssh, host, port, realhost, nodelay, keepalive);
    if (p != NULL)
      return p;

    return NULL;
}

static void ssh_free(void *handle)
{
    Ssh ssh = (Ssh) handle;
    struct ssh_channel *c;
    struct ssh_rportfwd *pf;

    if (ssh->v1_cipher_ctx)
      ssh->cipher->free_context(ssh->v1_cipher_ctx);
    if (ssh->cs_cipher_ctx)
      ssh->cscipher->free_context(ssh->cs_cipher_ctx);
    if (ssh->sc_cipher_ctx)
      ssh->sccipher->free_context(ssh->sc_cipher_ctx);
    if (ssh->cs_mac_ctx)
      ssh->csmac->free_context(ssh->cs_mac_ctx);
    if (ssh->sc_mac_ctx)
      ssh->scmac->free_context(ssh->sc_mac_ctx);
    if (ssh->cs_comp_ctx) {
      if (ssh->cscomp)
          ssh->cscomp->compress_cleanup(ssh->cs_comp_ctx);
      else
          zlib_compress_cleanup(ssh->cs_comp_ctx);
    }
    if (ssh->sc_comp_ctx) {
      if (ssh->sccomp)
          ssh->sccomp->decompress_cleanup(ssh->sc_comp_ctx);
      else
          zlib_decompress_cleanup(ssh->sc_comp_ctx);
    }
    if (ssh->kex_ctx)
      dh_cleanup(ssh->kex_ctx);
    sfree(ssh->savedhost);

    if (ssh->channels) {
      while ((c = delpos234(ssh->channels, 0)) != NULL) {
          switch (c->type) {
            case CHAN_X11:
            if (c->u.x11.s != NULL)
                x11_close(c->u.x11.s);
            break;
            case CHAN_SOCKDATA:
            if (c->u.pfd.s != NULL)
                pfd_close(c->u.pfd.s);
            break;
          }
          sfree(c);
      }
      freetree234(ssh->channels);
    }

    if (ssh->rportfwds) {
      while ((pf = delpos234(ssh->rportfwds, 0)) != NULL)
          sfree(pf);
      freetree234(ssh->rportfwds);
    }
    sfree(ssh->deferred_send_data);
    if (ssh->x11auth)
      x11_free_auth(ssh->x11auth);
    sfree(ssh->do_ssh_init_state);
    sfree(ssh->do_ssh1_login_state);
    sfree(ssh->do_ssh2_transport_state);
    sfree(ssh->do_ssh2_authconn_state);
    if (ssh->pktout.data) {
      sfree(ssh->pktout.data);
      ssh->pktout.data = NULL;
    }
    if (ssh->pktin.data) {
      sfree(ssh->pktin.data);
      ssh->pktin.data = NULL;
    }
    if (ssh->crcda_ctx) {
      crcda_free_context(ssh->crcda_ctx);
      ssh->crcda_ctx = NULL;
    }
    if (ssh->logctx) {
      log_free(ssh->logctx);
      ssh->logctx = NULL;
    }
    if (ssh->s)
      ssh_do_close(ssh);
    sfree(ssh);
}

/*
 * Reconfigure the SSH backend.
 * 
 * Currently, this function does nothing very useful. In future,
 * however, we could do some handy things with it. For example, we
 * could make the port forwarding configurer active in the Change
 * Settings box, and this routine could close down existing
 * forwardings and open up new ones in response to changes.
 */
static void ssh_reconfig(void *handle, Config *cfg)
{
    Ssh ssh = (Ssh) handle;
    ssh->cfg = *cfg;                 /* STRUCTURE COPY */
}

/*
 * Called to send data down the Telnet connection.
 */
static int ssh_send(void *handle, char *buf, int len)
{
    Ssh ssh = (Ssh) handle;

    if (ssh == NULL || ssh->s == NULL || ssh->protocol == NULL)
      return 0;

    ssh->protocol(ssh, (unsigned char *)buf, len, 0);

    return ssh_sendbuffer(ssh);
}

/*
 * Called to query the current amount of buffered stdin data.
 */
static int ssh_sendbuffer(void *handle)
{
    Ssh ssh = (Ssh) handle;
    int override_value;

    if (ssh == NULL || ssh->s == NULL || ssh->protocol == NULL)
      return 0;

    /*
     * If the SSH socket itself has backed up, add the total backup
     * size on that to any individual buffer on the stdin channel.
     */
    override_value = 0;
    if (ssh->throttled_all)
      override_value = ssh->overall_bufsize;

    if (ssh->version == 1) {
      return override_value;
    } else if (ssh->version == 2) {
      if (!ssh->mainchan || ssh->mainchan->closes > 0)
          return override_value;
      else
          return (override_value +
                bufchain_size(&ssh->mainchan->v.v2.outbuffer));
    }

    return 0;
}

/*
 * Called to set the size of the window from SSH's POV.
 */
static void ssh_size(void *handle, int width, int height)
{
    Ssh ssh = (Ssh) handle;

    ssh->term_width = width;
    ssh->term_height = height;

    switch (ssh->state) {
      case SSH_STATE_BEFORE_SIZE:
      case SSH_STATE_PREPACKET:
      case SSH_STATE_CLOSED:
      break;                         /* do nothing */
      case SSH_STATE_INTERMED:
      ssh->size_needed = TRUE;       /* buffer for later */
      break;
      case SSH_STATE_SESSION:
      if (!ssh->cfg.nopty) {
          if (ssh->version == 1) {
            send_packet(ssh, SSH1_CMSG_WINDOW_SIZE,
                      PKT_INT, ssh->term_height,
                      PKT_INT, ssh->term_width,
                      PKT_INT, 0, PKT_INT, 0, PKT_END);
          } else {
            ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
            ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
            ssh2_pkt_addstring(ssh, "window-change");
            ssh2_pkt_addbool(ssh, 0);
            ssh2_pkt_adduint32(ssh, ssh->term_width);
            ssh2_pkt_adduint32(ssh, ssh->term_height);
            ssh2_pkt_adduint32(ssh, 0);
            ssh2_pkt_adduint32(ssh, 0);
            ssh2_pkt_send(ssh);
          }
      }
      break;
    }
}

/*
 * Return a list of the special codes that make sense in this
 * protocol.
 */
static const struct telnet_special *ssh_get_specials(void *handle)
{
    Ssh ssh = (Ssh) handle;

    if (ssh->version == 1) {
      static const struct telnet_special ssh1_specials[] = {
          {"IGNORE message", TS_NOP},
          {NULL, 0}
      };
      return ssh1_specials;
    } else if (ssh->version == 2) {
      static const struct telnet_special ssh2_specials[] = {
          {"Break", TS_BRK},
          {"IGNORE message", TS_NOP},
          {NULL, 0}
      };
      return ssh2_specials;
    } else
      return NULL;
}

/*
 * Send Telnet special codes. TS_EOF is useful for `plink', so you
 * can send an EOF and collect resulting output (e.g. `plink
 * hostname sort').
 */
static void ssh_special(void *handle, Telnet_Special code)
{
    Ssh ssh = (Ssh) handle;

    if (code == TS_EOF) {
      if (ssh->state != SSH_STATE_SESSION) {
          /*
           * Buffer the EOF in case we are pre-SESSION, so we can
           * send it as soon as we reach SESSION.
           */
          if (code == TS_EOF)
            ssh->eof_needed = TRUE;
          return;
      }
      if (ssh->version == 1) {
          send_packet(ssh, SSH1_CMSG_EOF, PKT_END);
      } else {
          ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_EOF);
          ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
          ssh2_pkt_send(ssh);
      }
      logevent("Sent EOF message");
    } else if (code == TS_PING || code == TS_NOP) {
      if (ssh->state == SSH_STATE_CLOSED
          || ssh->state == SSH_STATE_PREPACKET) return;
      if (ssh->version == 1) {
          if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE))
            send_packet(ssh, SSH1_MSG_IGNORE, PKT_STR, "", PKT_END);
      } else {
          ssh2_pkt_init(ssh, SSH2_MSG_IGNORE);
          ssh2_pkt_addstring_start(ssh);
          ssh2_pkt_send(ssh);
      }
    } else if (code == TS_BRK) {
      if (ssh->state == SSH_STATE_CLOSED
          || ssh->state == SSH_STATE_PREPACKET) return;
      if (ssh->version == 1) {
          logevent("Unable to send BREAK signal in SSH1");
      } else {
          ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
          ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
          ssh2_pkt_addstring(ssh, "break");
          ssh2_pkt_addbool(ssh, 0);
          ssh2_pkt_adduint32(ssh, 0);   /* default break length */
          ssh2_pkt_send(ssh);
      }
    } else {
      /* do nothing */
    }
}

void *new_sock_channel(void *handle, Socket s)
{
    Ssh ssh = (Ssh) handle;
    struct ssh_channel *c;
    c = snew(struct ssh_channel);
    c->ssh = ssh;

    if (c) {
      c->remoteid = -1;        /* to be set when open confirmed */
      c->localid = alloc_channel_id(ssh);
      c->closes = 0;
      c->type = CHAN_SOCKDATA_DORMANT;/* identify channel type */
      c->u.pfd.s = s;
      bufchain_init(&c->v.v2.outbuffer);
      add234(ssh->channels, c);
    }
    return c;
}

/*
 * This is called when stdout/stderr (the entity to which
 * from_backend sends data) manages to clear some backlog.
 */
static void ssh_unthrottle(void *handle, int bufsize)
{
    Ssh ssh = (Ssh) handle;
    if (ssh->version == 1) {
      if (ssh->v1_stdout_throttling && bufsize < SSH1_BUFFER_LIMIT) {
          ssh->v1_stdout_throttling = 0;
          ssh1_throttle(ssh, -1);
      }
    } else {
      if (ssh->mainchan && ssh->mainchan->closes == 0)
          ssh2_set_window(ssh->mainchan, OUR_V2_WINSIZE - bufsize);
    }
}

void ssh_send_port_open(void *channel, char *hostname, int port, char *org)
{
    struct ssh_channel *c = (struct ssh_channel *)channel;
    Ssh ssh = c->ssh;

    logeventf(ssh, "Opening forwarded connection to %s:%d", hostname, port);

    if (ssh->version == 1) {
      send_packet(ssh, SSH1_MSG_PORT_OPEN,
                PKT_INT, c->localid,
                PKT_STR, hostname,
                PKT_INT, port,
                //PKT_STR, <org:orgport>,
                PKT_END);
    } else {
      ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN);
      ssh2_pkt_addstring(ssh, "direct-tcpip");
      ssh2_pkt_adduint32(ssh, c->localid);
      c->v.v2.locwindow = OUR_V2_WINSIZE;
      ssh2_pkt_adduint32(ssh, c->v.v2.locwindow);/* our window size */
      ssh2_pkt_adduint32(ssh, 0x4000UL);      /* our max pkt size */
      ssh2_pkt_addstring(ssh, hostname);
      ssh2_pkt_adduint32(ssh, port);
      /*
       * We make up values for the originator data; partly it's
       * too much hassle to keep track, and partly I'm not
       * convinced the server should be told details like that
       * about my local network configuration.
       */
      ssh2_pkt_addstring(ssh, "client-side-connection");
      ssh2_pkt_adduint32(ssh, 0);
      ssh2_pkt_send(ssh);
    }
}


static Socket ssh_socket(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->s;
}

static int ssh_sendok(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->send_ok;
}

static int ssh_ldisc(void *handle, int option)
{
    Ssh ssh = (Ssh) handle;
    if (option == LD_ECHO)
      return ssh->echoing;
    if (option == LD_EDIT)
      return ssh->editing;
    return FALSE;
}

static void ssh_provide_ldisc(void *handle, void *ldisc)
{
    Ssh ssh = (Ssh) handle;
    ssh->ldisc = ldisc;
}

static void ssh_provide_logctx(void *handle, void *logctx)
{
    Ssh ssh = (Ssh) handle;
    ssh->logctx = logctx;
}

static int ssh_return_exitcode(void *handle)
{
    Ssh ssh = (Ssh) handle;
    if (ssh->s != NULL)
        return -1;
    else
        return (ssh->exitcode >= 0 ? ssh->exitcode : 0);
}

/*
 * Gross hack: pscp will try to start SFTP but fall back to scp1 if
 * that fails. This variable is the means by which scp.c can reach
 * into the SSH code and find out which one it got.
 */
extern int ssh_fallback_cmd(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->fallback_cmd;
}

Backend ssh_backend = {
    ssh_init,
    ssh_free,
    ssh_reconfig,
    ssh_send,
    ssh_sendbuffer,
    ssh_size,
    ssh_special,
    ssh_get_specials,
    ssh_socket,
    ssh_return_exitcode,
    ssh_sendok,
    ssh_ldisc,
    ssh_provide_ldisc,
    ssh_provide_logctx,
    ssh_unthrottle,
    22
};

Generated by  Doxygen 1.6.0   Back to index