winscp/source/putty/ssh1login.c

/*
 * Packet protocol layer for the SSH-1 login phase (combining what
 * SSH-2 would think of as key exchange and user authentication).
 */

#include <assert.h>

#include "putty.h"
#include "ssh.h"
#include "sshbpp.h"
#include "sshppl.h"
#include "sshcr.h"

struct ssh1_login_state {
    int crState;

    PacketProtocolLayer *successor_layer;

    Conf *conf;

    char *savedhost;
    int savedport;
    int try_agent_auth;

    int remote_protoflags;
    int local_protoflags;
    unsigned char session_key[32];
    char *username;
    agent_pending_query *auth_agent_query;

    int len;
    unsigned char *rsabuf;
    unsigned long supported_ciphers_mask, supported_auths_mask;
    int tried_publickey, tried_agent;
    int tis_auth_refused, ccard_auth_refused;
    unsigned char cookie[8];
    unsigned char session_id[16];
    int cipher_type;
    strbuf *publickey_blob;
    char *publickey_comment;
    int privatekey_available, privatekey_encrypted;
    prompts_t *cur_prompt;
    int userpass_ret;
    char c;
    int pwpkt_type;
    void *agent_response_to_free;
    ptrlen agent_response;
    BinarySource asrc[1];          /* response from SSH agent */
    int keyi, nkeys;
    int authed;
    struct RSAKey key;
    Bignum challenge;
    ptrlen comment;
    int dlgret;
    Filename *keyfile;
    struct RSAKey servkey, hostkey;
    int want_user_input;

    PacketProtocolLayer ppl;
};

static void ssh1_login_free(PacketProtocolLayer *); 
static void ssh1_login_process_queue(PacketProtocolLayer *);
static void ssh1_login_dialog_callback(void *, int);
static void ssh1_login_special_cmd(PacketProtocolLayer *ppl,
                                   SessionSpecialCode code, int arg);
static int ssh1_login_want_user_input(PacketProtocolLayer *ppl);
static void ssh1_login_got_user_input(PacketProtocolLayer *ppl);
static void ssh1_login_reconfigure(PacketProtocolLayer *ppl, Conf *conf);

static const struct PacketProtocolLayerVtable ssh1_login_vtable = {
    ssh1_login_free,
    ssh1_login_process_queue,
    ssh1_common_get_specials,
    ssh1_login_special_cmd,
    ssh1_login_want_user_input,
    ssh1_login_got_user_input,
    ssh1_login_reconfigure,
    NULL /* no layer names in SSH-1 */,
};

static void ssh1_login_agent_query(struct ssh1_login_state *s, strbuf *req);
static void ssh1_login_agent_callback(void *loginv, void *reply, int replylen);

PacketProtocolLayer *ssh1_login_new(
    Conf *conf, const char *host, int port,
    PacketProtocolLayer *successor_layer)
{
    struct ssh1_login_state *s = snew(struct ssh1_login_state);
    memset(s, 0, sizeof(*s));
    s->ppl.vt = &ssh1_login_vtable;

    s->conf = conf_copy(conf);
    s->savedhost = dupstr(host);
    s->savedport = port;
    s->successor_layer = successor_layer;
    return &s->ppl;
}

static void ssh1_login_free(PacketProtocolLayer *ppl)
{
    struct ssh1_login_state *s =
        container_of(ppl, struct ssh1_login_state, ppl);

    if (s->successor_layer)
        ssh_ppl_free(s->successor_layer);

    conf_free(s->conf);
    sfree(s->savedhost);
    sfree(s->rsabuf);
    sfree(s->username);
    if (s->publickey_blob)
        strbuf_free(s->publickey_blob);
    sfree(s->publickey_comment);
    if (s->cur_prompt)
        free_prompts(s->cur_prompt);
    sfree(s->agent_response_to_free);
    if (s->auth_agent_query)
        agent_cancel_query(s->auth_agent_query);
    sfree(s);
}

int ssh1_common_filter_queue(PacketProtocolLayer *ppl)
{
    PktIn *pktin;
    ptrlen msg;

    while ((pktin = pq_peek(ppl->in_pq)) != NULL) {
        switch (pktin->type) {
          case SSH1_MSG_DISCONNECT:
            msg = get_string(pktin);
            ssh_remote_error(ppl->ssh,
                             "Server sent disconnect message:\n\"%.*s\"",
                             PTRLEN_PRINTF(msg));
            pq_pop(ppl->in_pq);
            return TRUE;               /* indicate that we've been freed */

          case SSH1_MSG_DEBUG:
            msg = get_string(pktin);
            ppl_logevent(("Remote debug message: %.*s", PTRLEN_PRINTF(msg)));
            pq_pop(ppl->in_pq);
            break;

          case SSH1_MSG_IGNORE:
            /* Do nothing, because we're ignoring it! Duhh. */
            pq_pop(ppl->in_pq);
            break;

          default:
            return FALSE;
        }
    }

    return FALSE;
}

static int ssh1_login_filter_queue(struct ssh1_login_state *s)
{
    return ssh1_common_filter_queue(&s->ppl);
}

static PktIn *ssh1_login_pop(struct ssh1_login_state *s)
{
    if (ssh1_login_filter_queue(s))
        return NULL;
    return pq_pop(s->ppl.in_pq);
}

static void ssh1_login_process_queue(PacketProtocolLayer *ppl)
{
    struct ssh1_login_state *s =
        container_of(ppl, struct ssh1_login_state, ppl);
    PktIn *pktin;
    PktOut *pkt;
    int i;

    /* Filter centrally handled messages off the front of the queue on
     * every entry to this coroutine, no matter where we're resuming
     * from, even if we're _not_ looping on pq_pop. That way we can
     * still proactively handle those messages even if we're waiting
     * for a user response. */
    if (ssh1_login_filter_queue(s))
        return;

    crBegin(s->crState);

    crMaybeWaitUntilV((pktin = ssh1_login_pop(s)) != NULL);

    if (pktin->type != SSH1_SMSG_PUBLIC_KEY) {
        ssh_proto_error(s->ppl.ssh, "Public key packet not received");
        return;
    }

    ppl_logevent(("Received public keys"));

    {
        ptrlen pl = get_data(pktin, 8);
        memcpy(s->cookie, pl.ptr, pl.len);
    }

    get_rsa_ssh1_pub(pktin, &s->servkey, RSA_SSH1_EXPONENT_FIRST);
    get_rsa_ssh1_pub(pktin, &s->hostkey, RSA_SSH1_EXPONENT_FIRST);

    s->hostkey.comment = NULL; /* avoid confusing rsa_ssh1_fingerprint */

    /*
     * Log the host key fingerprint.
     */
    if (!get_err(pktin)) {
        char *fingerprint = rsa_ssh1_fingerprint(&s->hostkey);
        ppl_logevent(("Host key fingerprint is:"));
        ppl_logevent(("      %s", fingerprint));
        sfree(fingerprint);
    }

    s->remote_protoflags = get_uint32(pktin);
    s->supported_ciphers_mask = get_uint32(pktin);
    s->supported_auths_mask = get_uint32(pktin);

    if (get_err(pktin)) {
        ssh_proto_error(s->ppl.ssh, "Bad SSH-1 public key packet");
        return;
    }

    if ((s->ppl.remote_bugs & BUG_CHOKES_ON_RSA))
        s->supported_auths_mask &= ~(1 << SSH1_AUTH_RSA);

    s->local_protoflags =
        s->remote_protoflags & SSH1_PROTOFLAGS_SUPPORTED;
    s->local_protoflags |= SSH1_PROTOFLAG_SCREEN_NUMBER;

    {
        struct MD5Context md5c;

        MD5Init(&md5c);
        for (i = (bignum_bitcount(s->hostkey.modulus) + 7) / 8; i-- ;)
            put_byte(&md5c, bignum_byte(s->hostkey.modulus, i));
        for (i = (bignum_bitcount(s->servkey.modulus) + 7) / 8; i-- ;)
            put_byte(&md5c, bignum_byte(s->servkey.modulus, i));
        put_data(&md5c, s->cookie, 8);
        MD5Final(s->session_id, &md5c);
    }

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

    /*
     * Verify that the `bits' and `bytes' parameters match.
     */
    if (s->hostkey.bits > s->hostkey.bytes * 8 ||
        s->servkey.bits > s->servkey.bytes * 8) {
        ssh_proto_error(s->ppl.ssh, "SSH-1 public keys were badly formatted");
        return;
    }

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

    s->rsabuf = snewn(s->len, unsigned char);

    /*
     * Verify the host key.
     */
    {
        /*
         * First format the key into a string.
         */
        int len = rsastr_len(&s->hostkey);
        char *fingerprint;
        char *keystr = snewn(len, char);
        rsastr_fmt(keystr, &s->hostkey);
        fingerprint = rsa_ssh1_fingerprint(&s->hostkey);

        /* First check against manually configured host keys. */
        s->dlgret = verify_ssh_manual_host_key(s->conf, fingerprint, NULL);
        sfree(fingerprint);
        if (s->dlgret == 0) {          /* did not match */
            sfree(keystr);
            ssh_proto_error(s->ppl.ssh, "Host key did not appear in manually "
                            "configured list");
            return;
        } else if (s->dlgret < 0) { /* none configured; use standard handling */
            s->dlgret = seat_verify_ssh_host_key(
                s->ppl.seat, s->savedhost, s->savedport,
                "rsa", keystr, fingerprint, ssh1_login_dialog_callback, s);
            sfree(keystr);
#ifdef FUZZING
            s->dlgret = 1;
#endif
            crMaybeWaitUntilV(s->dlgret >= 0);

            if (s->dlgret == 0) {
                ssh_user_close(s->ppl.ssh,
                               "User aborted at host key verification");
                return;
            }
        } else {
            sfree(keystr);
        }
    }

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

    {
        struct RSAKey *smaller = (s->hostkey.bytes > s->servkey.bytes ?
                                  &s->servkey : &s->hostkey);
        struct RSAKey *larger = (s->hostkey.bytes > s->servkey.bytes ?
                                 &s->hostkey : &s->servkey);

        if (!rsa_ssh1_encrypt(s->rsabuf, 32, smaller) ||
            !rsa_ssh1_encrypt(s->rsabuf, smaller->bytes, larger)) {
            ssh_proto_error(s->ppl.ssh, "SSH-1 public key encryptions failed "
                            "due to bad formatting");
            return;
        }
    }

    ppl_logevent(("Encrypted session key"));

    {
        int cipher_chosen = 0, warn = 0;
        const char *cipher_string = NULL;
        int i;
	for (i = 0; !cipher_chosen && i < CIPHER_MAX; i++) {
	    int next_cipher = conf_get_int_int(
                s->conf, CONF_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. */
                ppl_logevent(("AES not supported in SSH-1, 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) {
                ssh_proto_error(s->ppl.ssh, "Server violates SSH-1 protocol "
                                "by not supporting 3DES encryption");
            } else {
                /* shouldn't happen */
                ssh_sw_abort(s->ppl.ssh, "No supported ciphers found");
            }
            return;
        }

        /* Warn about chosen cipher if necessary. */
        if (warn) {
            s->dlgret = seat_confirm_weak_crypto_primitive(
                s->ppl.seat, "cipher", cipher_string,
                ssh1_login_dialog_callback, s);
            crMaybeWaitUntilV(s->dlgret >= 0);
            if (s->dlgret == 0) {
                ssh_user_close(s->ppl.ssh, "User aborted at cipher warning");
                return;
            }
        }
    }

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

    pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_CMSG_SESSION_KEY);
    put_byte(pkt, s->cipher_type);
    put_data(pkt, s->cookie, 8);
    put_uint16(pkt, s->len * 8);
    put_data(pkt, s->rsabuf, s->len);
    put_uint32(pkt, s->local_protoflags);
    pq_push(s->ppl.out_pq, pkt);

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

    sfree(s->rsabuf);
    s->rsabuf = NULL;

    /*
     * Force the BPP to synchronously marshal all packets up to and
     * including the SESSION_KEY into wire format, before we turn on
     * crypto.
     */
    ssh_bpp_handle_output(s->ppl.bpp);

    {
        const struct ssh1_cipheralg *cipher =
            (s->cipher_type == SSH_CIPHER_BLOWFISH ? &ssh1_blowfish :
             s->cipher_type == SSH_CIPHER_DES ? &ssh1_des : &ssh1_3des);
        ssh1_bpp_new_cipher(s->ppl.bpp, cipher, s->session_key);
    }

    if (s->servkey.modulus) {
        sfree(s->servkey.modulus);
        s->servkey.modulus = NULL;
    }
    if (s->servkey.exponent) {
        sfree(s->servkey.exponent);
        s->servkey.exponent = NULL;
    }
    if (s->hostkey.modulus) {
        sfree(s->hostkey.modulus);
        s->hostkey.modulus = NULL;
    }
    if (s->hostkey.exponent) {
        sfree(s->hostkey.exponent);
        s->hostkey.exponent = NULL;
    }
    crMaybeWaitUntilV((pktin = ssh1_login_pop(s)) != NULL);

    if (pktin->type != SSH1_SMSG_SUCCESS) {
        ssh_proto_error(s->ppl.ssh, "Encryption not successfully enabled");
        return;
    }

    ppl_logevent(("Successfully started encryption"));

    if ((s->username = get_remote_username(s->conf)) == NULL) {
        s->cur_prompt = new_prompts();
        s->cur_prompt->to_server = TRUE;
        s->cur_prompt->name = dupstr("SSH login name");
        add_prompt(s->cur_prompt, dupstr("login as: "), TRUE);
        s->userpass_ret = seat_get_userpass_input(
            s->ppl.seat, s->cur_prompt, NULL);
        while (1) {
            while (s->userpass_ret < 0 &&
                   bufchain_size(s->ppl.user_input) > 0)
                s->userpass_ret = seat_get_userpass_input(
                    s->ppl.seat, s->cur_prompt, s->ppl.user_input);

            if (s->userpass_ret >= 0)
                break;

            s->want_user_input = TRUE;
            crReturnV;
            s->want_user_input = FALSE;
        }
        if (!s->userpass_ret) {
            /*
             * Failed to get a username. Terminate.
             */
            ssh_user_close(s->ppl.ssh, "No username provided");
            return;
        }
        s->username = dupstr(s->cur_prompt->prompts[0]->result);
        free_prompts(s->cur_prompt);
        s->cur_prompt = NULL;
    }

    pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_CMSG_USER);
    put_stringz(pkt, s->username);
    pq_push(s->ppl.out_pq, pkt);

    ppl_logevent(("Sent username \"%s\"", s->username));
    if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE))
        ppl_printf(("Sent username \"%s\"\r\n", s->username));

    crMaybeWaitUntilV((pktin = ssh1_login_pop(s)) != NULL);

    if (!(s->supported_auths_mask & (1 << SSH1_AUTH_RSA))) {
        /* We must not attempt PK auth. Pretend we've already tried it. */
        s->tried_publickey = s->tried_agent = TRUE;
    } else {
        s->tried_publickey = s->tried_agent = FALSE;
    }
    s->tis_auth_refused = s->ccard_auth_refused = FALSE;

    /*
     * Load the public half of any configured keyfile for later use.
     */
    s->keyfile = conf_get_filename(s->conf, CONF_keyfile);
    if (!filename_is_null(s->keyfile)) {
        int keytype;
        ppl_logevent(("Reading key file \"%.150s\"",
                      filename_to_str(s->keyfile)));
        keytype = key_type(s->keyfile);
        if (keytype == SSH_KEYTYPE_SSH1 ||
            keytype == SSH_KEYTYPE_SSH1_PUBLIC) {
            const char *error;
            s->publickey_blob = strbuf_new();
            if (rsa_ssh1_loadpub(s->keyfile,
                                 BinarySink_UPCAST(s->publickey_blob),
                                 &s->publickey_comment, &error)) {
                s->privatekey_available = (keytype == SSH_KEYTYPE_SSH1);
                if (!s->privatekey_available)
                    ppl_logevent(("Key file contains public key only"));
                s->privatekey_encrypted = rsa_ssh1_encrypted(s->keyfile, NULL);
            } else {
                ppl_logevent(("Unable to load key (%s)", error));
                ppl_printf(("Unable to load key file \"%s\" (%s)\r\n",
                            filename_to_str(s->keyfile), error));

                strbuf_free(s->publickey_blob);
                s->publickey_blob = NULL;
            }
        } else {
            ppl_logevent(("Unable to use this key file (%s)",
                          key_type_to_str(keytype)));
            ppl_printf(("Unable to use key file \"%s\" (%s)\r\n",
                        filename_to_str(s->keyfile),
                        key_type_to_str(keytype)));
        }
    }

    /* Check whether we're configured to try Pageant, and also whether
     * it's available. */
    s->try_agent_auth = (conf_get_int(s->conf, CONF_tryagent) &&
                         agent_exists());

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

        if (s->try_agent_auth && !s->tried_agent) {
            /*
             * Attempt RSA authentication using Pageant.
             */
            s->authed = FALSE;
            s->tried_agent = 1;
            ppl_logevent(("Pageant is running. Requesting keys."));

            /* Request the keys held by the agent. */
            {
                strbuf *request = strbuf_new_for_agent_query();
                put_byte(request, SSH1_AGENTC_REQUEST_RSA_IDENTITIES);
                ssh1_login_agent_query(s, request);
                strbuf_free(request);
                crMaybeWaitUntilV(!s->auth_agent_query);
            }
            BinarySource_BARE_INIT(
                s->asrc, s->agent_response.ptr, s->agent_response.len);

            get_uint32(s->asrc); /* skip length field */
            if (get_byte(s->asrc) == SSH1_AGENT_RSA_IDENTITIES_ANSWER) {
                s->nkeys = toint(get_uint32(s->asrc));
                if (s->nkeys < 0) {
                    ppl_logevent(("Pageant reported negative key count %d",
                                  s->nkeys));
                    s->nkeys = 0;
                }
                ppl_logevent(("Pageant has %d SSH-1 keys", s->nkeys));
                for (s->keyi = 0; s->keyi < s->nkeys; s->keyi++) {
                    size_t start, end;
                    start = s->asrc->pos;
                    get_rsa_ssh1_pub(s->asrc, &s->key,
                                     RSA_SSH1_EXPONENT_FIRST);
                    end = s->asrc->pos;
                    s->comment = get_string(s->asrc);
                    if (get_err(s->asrc)) {
                        ppl_logevent(("Pageant key list packet was truncated"));
                        break;
                    }
                    if (s->publickey_blob) {
                        ptrlen keystr = make_ptrlen(
                            (const char *)s->asrc->data + start, end - start);

                        if (keystr.len == s->publickey_blob->len &&
                            !memcmp(keystr.ptr, s->publickey_blob->s,
                                    s->publickey_blob->len)) {
                            ppl_logevent(("Pageant key #%d matches "
                                          "configured key file", s->keyi));
                            s->tried_publickey = 1;
                        } else
                            /* Skip non-configured key */
                            continue;
                    }
                    ppl_logevent(("Trying Pageant key #%d", s->keyi));
                    pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_CMSG_AUTH_RSA);
                    put_mp_ssh1(pkt, s->key.modulus);
                    pq_push(s->ppl.out_pq, pkt);
                    crMaybeWaitUntilV((pktin = ssh1_login_pop(s))
                                      != NULL);
                    if (pktin->type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
                        ppl_logevent(("Key refused"));
                        continue;
                    }
                    ppl_logevent(("Received RSA challenge"));
                    s->challenge = get_mp_ssh1(pktin);
                    if (get_err(pktin)) {
                        freebn(s->challenge);
                        ssh_proto_error(s->ppl.ssh, "Server's RSA challenge "
                                        "was badly formatted");
                        return;
                    }

                    {
                        strbuf *agentreq;
                        const char *ret;

                        agentreq = strbuf_new_for_agent_query();
                        put_byte(agentreq, SSH1_AGENTC_RSA_CHALLENGE);
                        put_uint32(agentreq, bignum_bitcount(s->key.modulus));
                        put_mp_ssh1(agentreq, s->key.exponent);
                        put_mp_ssh1(agentreq, s->key.modulus);
                        put_mp_ssh1(agentreq, s->challenge);
                        put_data(agentreq, s->session_id, 16);
                        put_uint32(agentreq, 1);    /* response format */
                        ssh1_login_agent_query(s, agentreq);
                        strbuf_free(agentreq);
                        crMaybeWaitUntilV(!s->auth_agent_query);

                        ret = s->agent_response.ptr;
                        if (ret) {
                            if (s->agent_response.len >= 5+16 &&
                                ret[4] == SSH1_AGENT_RSA_RESPONSE) {
                                ppl_logevent(("Sending Pageant's response"));
                                pkt = ssh_bpp_new_pktout(
                                    s->ppl.bpp, SSH1_CMSG_AUTH_RSA_RESPONSE);
                                put_data(pkt, ret + 5, 16);
                                pq_push(s->ppl.out_pq, pkt);
                                sfree((char *)ret);
                                crMaybeWaitUntilV(
                                    (pktin = ssh1_login_pop(s))
                                    != NULL);
                                if (pktin->type == SSH1_SMSG_SUCCESS) {
                                    ppl_logevent(("Pageant's response "
                                                  "accepted"));
                                    if (flags & FLAG_VERBOSE) {
                                        ppl_printf(("Authenticated using RSA "
                                                    "key \"%.*s\" from "
                                                    "agent\r\n", PTRLEN_PRINTF(
                                                        s->comment)));
                                    }
                                    s->authed = TRUE;
                                } else
                                    ppl_logevent(("Pageant's response not "
                                                  "accepted"));
                            } else {
                                ppl_logevent(("Pageant failed to answer "
                                              "challenge"));
                                sfree((char *)ret);
                            }
                        } else {
                            ppl_logevent(("No reply received from Pageant"));
                        }
                    }
                    freebn(s->key.exponent);
                    freebn(s->key.modulus);
                    freebn(s->challenge);
                    if (s->authed)
                        break;
                }
                sfree(s->agent_response_to_free);
                s->agent_response_to_free = NULL;
                if (s->publickey_blob && !s->tried_publickey)
                    ppl_logevent(("Configured key file not in Pageant"));
            } else {
                ppl_logevent(("Failed to get reply from Pageant"));
            }
            if (s->authed)
                break;
        }
        if (s->publickey_blob && s->privatekey_available &&
            !s->tried_publickey) {
            /*
             * Try public key authentication with the specified
             * key file.
             */
            int got_passphrase; /* need not be kept over crReturn */
            if (flags & FLAG_VERBOSE)
                ppl_printf(("Trying public key authentication.\r\n"));
            ppl_logevent(("Trying public key \"%s\"",
                          filename_to_str(s->keyfile)));
            s->tried_publickey = 1;
            got_passphrase = FALSE;
            while (!got_passphrase) {
                /*
                 * Get a passphrase, if necessary.
                 */
                int retd;
                char *passphrase = NULL;    /* only written after crReturn */
                const char *error;
                if (!s->privatekey_encrypted) {
                    if (flags & FLAG_VERBOSE)
                        ppl_printf(("No passphrase required.\r\n"));
                    passphrase = NULL;
                } else {
                    s->cur_prompt = new_prompts(s->ppl.seat);
                    s->cur_prompt->to_server = FALSE;
                    s->cur_prompt->name = dupstr("SSH key passphrase");
                    add_prompt(s->cur_prompt,
                               dupprintf("Passphrase for key \"%.100s\": ",
                                         s->publickey_comment), FALSE);
                    s->userpass_ret = seat_get_userpass_input(
                        s->ppl.seat, s->cur_prompt, NULL);
                    while (1) {
                        while (s->userpass_ret < 0 &&
                               bufchain_size(s->ppl.user_input) > 0)
                            s->userpass_ret = seat_get_userpass_input(
                                s->ppl.seat, s->cur_prompt, s->ppl.user_input);

                        if (s->userpass_ret >= 0)
                            break;

                        s->want_user_input = TRUE;
                        crReturnV;
                        s->want_user_input = FALSE;
                    }
                    if (!s->userpass_ret) {
                        /* Failed to get a passphrase. Terminate. */
                        ssh_user_close(s->ppl.ssh,
                                       "User aborted at passphrase prompt");
                        return;
                    }
                    passphrase = dupstr(s->cur_prompt->prompts[0]->result);
                    free_prompts(s->cur_prompt);
                    s->cur_prompt = NULL;
                }
                /*
                 * Try decrypting key with passphrase.
                 */
                retd = rsa_ssh1_loadkey(
                    s->keyfile, &s->key, passphrase, &error);
                if (passphrase) {
                    smemclr(passphrase, strlen(passphrase));
                    sfree(passphrase);
                }
                if (retd == 1) {
                    /* Correct passphrase. */
                    got_passphrase = TRUE;
                } else if (retd == 0) {
                    ppl_printf(("Couldn't load private key from %s (%s).\r\n",
                                filename_to_str(s->keyfile), error));
                    got_passphrase = FALSE;
                    break;             /* go and try something else */
                } else if (retd == -1) {
                    ppl_printf(("Wrong passphrase.\r\n"));
                    got_passphrase = FALSE;
                    /* and try again */
                } else {
                    assert(0 && "unexpected return from rsa_ssh1_loadkey()");
                    got_passphrase = FALSE;   /* placate optimisers */
                }
            }

            if (got_passphrase) {

                /*
                 * Send a public key attempt.
                 */
                pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_CMSG_AUTH_RSA);
                put_mp_ssh1(pkt, s->key.modulus);
                pq_push(s->ppl.out_pq, pkt);

                crMaybeWaitUntilV((pktin = ssh1_login_pop(s))
                                  != NULL);
                if (pktin->type == SSH1_SMSG_FAILURE) {
                    ppl_printf(("Server refused our public key.\r\n"));
                    continue;          /* go and try something else */
                }
                if (pktin->type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
                    ssh_proto_error(s->ppl.ssh, "Received unexpected packet"
                                    " in response to offer of public key, "
                                    "type %d (%s)", pktin->type,
                                    ssh1_pkt_type(pktin->type));
                    return;
                }

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

                    challenge = get_mp_ssh1(pktin);
                    if (get_err(pktin)) {
                        freebn(challenge);
                        ssh_proto_error(s->ppl.ssh, "Server's RSA challenge "
                                        "was badly formatted");
                        return;
                    }
                    response = rsa_ssh1_decrypt(challenge, &s->key);
                    freebn(s->key.private_exponent);/* burn the evidence */

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

                    {
                        struct MD5Context md5c;
                        MD5Init(&md5c);
                        put_data(&md5c, buffer, 32);
                        put_data(&md5c, s->session_id, 16);
                        MD5Final(buffer, &md5c);
                    }

                    pkt = ssh_bpp_new_pktout(
                        s->ppl.bpp, SSH1_CMSG_AUTH_RSA_RESPONSE);
                    put_data(pkt, buffer, 16);
                    pq_push(s->ppl.out_pq, pkt);

                    freebn(challenge);
                    freebn(response);
                }

                crMaybeWaitUntilV((pktin = ssh1_login_pop(s))
                                  != NULL);
                if (pktin->type == SSH1_SMSG_FAILURE) {
                    if (flags & FLAG_VERBOSE)
                        ppl_printf(("Failed to authenticate with"
                                    " our public key.\r\n"));
                    continue;          /* go and try something else */
                } else if (pktin->type != SSH1_SMSG_SUCCESS) {
                    ssh_proto_error(s->ppl.ssh, "Received unexpected packet"
                                    " in response to RSA authentication, "
                                    "type %d (%s)", pktin->type,
                                    ssh1_pkt_type(pktin->type));
                    return;
                }

                break;                 /* we're through! */
            }

        }

        /*
         * Otherwise, try various forms of password-like authentication.
         */
        s->cur_prompt = new_prompts(s->ppl.seat);

        if (conf_get_int(s->conf, CONF_try_tis_auth) &&
            (s->supported_auths_mask & (1 << SSH1_AUTH_TIS)) &&
            !s->tis_auth_refused) {
            s->pwpkt_type = SSH1_CMSG_AUTH_TIS_RESPONSE;
            ppl_logevent(("Requested TIS authentication"));
            pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_CMSG_AUTH_TIS);
            pq_push(s->ppl.out_pq, pkt);
            crMaybeWaitUntilV((pktin = ssh1_login_pop(s)) != NULL);
            if (pktin->type == SSH1_SMSG_FAILURE) {
                ppl_logevent(("TIS authentication declined"));
                if (flags & FLAG_INTERACTIVE)
                    ppl_printf(("TIS authentication refused.\r\n"));
                s->tis_auth_refused = 1;
                continue;
            } else if (pktin->type == SSH1_SMSG_AUTH_TIS_CHALLENGE) {
                ptrlen challenge;
                char *instr_suf, *prompt;

                challenge = get_string(pktin);
                if (get_err(pktin)) {
                    ssh_proto_error(s->ppl.ssh, "TIS challenge packet was "
                                    "badly formed");
                    return;
                }
                ppl_logevent(("Received TIS challenge"));
                s->cur_prompt->to_server = TRUE;
                s->cur_prompt->name = dupstr("SSH TIS authentication");
                /* Prompt heuristic comes from OpenSSH */
                if (memchr(challenge.ptr, '\n', challenge.len)) {
                    instr_suf = dupstr("");
                    prompt = mkstr(challenge);
                } else {
                    instr_suf = mkstr(challenge);
                    prompt = dupstr("Response: ");
                }
                s->cur_prompt->instruction =
                    dupprintf("Using TIS authentication.%s%s",
                              (*instr_suf) ? "\n" : "",
                              instr_suf);
                s->cur_prompt->instr_reqd = TRUE;
                add_prompt(s->cur_prompt, prompt, FALSE);
                sfree(instr_suf);
            } else {
                ssh_proto_error(s->ppl.ssh, "Received unexpected packet"
                                " in response to TIS authentication, "
                                "type %d (%s)", pktin->type,
                                ssh1_pkt_type(pktin->type));
                return;
            }
        }
        if (conf_get_int(s->conf, CONF_try_tis_auth) &&
            (s->supported_auths_mask & (1 << SSH1_AUTH_CCARD)) &&
            !s->ccard_auth_refused) {
            s->pwpkt_type = SSH1_CMSG_AUTH_CCARD_RESPONSE;
            ppl_logevent(("Requested CryptoCard authentication"));
            pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_CMSG_AUTH_CCARD);
            pq_push(s->ppl.out_pq, pkt);
            crMaybeWaitUntilV((pktin = ssh1_login_pop(s)) != NULL);
            if (pktin->type == SSH1_SMSG_FAILURE) {
                ppl_logevent(("CryptoCard authentication declined"));
                ppl_printf(("CryptoCard authentication refused.\r\n"));
                s->ccard_auth_refused = 1;
                continue;
            } else if (pktin->type == SSH1_SMSG_AUTH_CCARD_CHALLENGE) {
                ptrlen challenge;
                char *instr_suf, *prompt;

                challenge = get_string(pktin);
                if (get_err(pktin)) {
                    ssh_proto_error(s->ppl.ssh, "CryptoCard challenge packet "
                                    "was badly formed");
                    return;
                }
                ppl_logevent(("Received CryptoCard challenge"));
                s->cur_prompt->to_server = TRUE;
                s->cur_prompt->name = dupstr("SSH CryptoCard authentication");
                s->cur_prompt->name_reqd = FALSE;
                /* Prompt heuristic comes from OpenSSH */
                if (memchr(challenge.ptr, '\n', challenge.len)) {
                    instr_suf = dupstr("");
                    prompt = mkstr(challenge);
                } else {
                    instr_suf = mkstr(challenge);
                    prompt = dupstr("Response: ");
                }
                s->cur_prompt->instruction =
                    dupprintf("Using CryptoCard authentication.%s%s",
                              (*instr_suf) ? "\n" : "",
                              instr_suf);
                s->cur_prompt->instr_reqd = TRUE;
                add_prompt(s->cur_prompt, prompt, FALSE);
                sfree(instr_suf);
            } else {
                ssh_proto_error(s->ppl.ssh, "Received unexpected packet"
                                " in response to TIS authentication, "
                                "type %d (%s)", pktin->type,
                                ssh1_pkt_type(pktin->type));
                return;
            }
        }
        if (s->pwpkt_type == SSH1_CMSG_AUTH_PASSWORD) {
            if ((s->supported_auths_mask & (1 << SSH1_AUTH_PASSWORD)) == 0) {
                ssh_sw_abort(s->ppl.ssh, "No supported authentication methods "
                             "available");
                return;
            }
            s->cur_prompt->to_server = TRUE;
            s->cur_prompt->name = dupstr("SSH password");
            add_prompt(s->cur_prompt, dupprintf("%s@%s's password: ",
                                                s->username, s->savedhost),
                       FALSE);
        }

        /*
         * Show password prompt, having first obtained it via a TIS
         * or CryptoCard exchange if we're doing TIS or CryptoCard
         * authentication.
         */
        s->userpass_ret = seat_get_userpass_input(
            s->ppl.seat, s->cur_prompt, NULL);
        while (1) {
            while (s->userpass_ret < 0 &&
                   bufchain_size(s->ppl.user_input) > 0)
                s->userpass_ret = seat_get_userpass_input(
                    s->ppl.seat, s->cur_prompt, s->ppl.user_input);

            if (s->userpass_ret >= 0)
                break;

            s->want_user_input = TRUE;
            crReturnV;
            s->want_user_input = FALSE;
        }
        if (!s->userpass_ret) {
            /*
             * Failed to get a password (for example
             * because one was supplied on the command line
             * which has already failed to work). Terminate.
             */
            ssh_user_close(s->ppl.ssh, "User aborted at password prompt");
            return;
        }

        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 can't deal with SSH1_MSG_IGNORE, at
             * least in this context. 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.
             * 
             * A few servers can deal with neither SSH1_MSG_IGNORE
             * here _nor_ a padded password string.
             * For these servers we are left with no defences
             * against password length sniffing.
             */
            if (!(s->ppl.remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE) &&
                !(s->ppl.remote_bugs & BUG_NEEDS_SSH1_PLAIN_PASSWORD)) {
                /*
                 * The server can deal with SSH1_MSG_IGNORE, so
                 * we can use the primary defence.
                 */
                int bottom, top, pwlen, i;

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

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

                for (i = bottom; i <= top; i++) {
                    if (i == pwlen) {
                        pkt = ssh_bpp_new_pktout(s->ppl.bpp, s->pwpkt_type);
                        put_stringz(pkt, s->cur_prompt->prompts[0]->result);
                        pq_push(s->ppl.out_pq, pkt);
                    } else {
                        int j;
                        strbuf *random_data = strbuf_new();
                        for (j = 0; j < i; j++)
                            put_byte(random_data, random_byte());

                        pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_MSG_IGNORE);
                        put_stringsb(pkt, random_data);
                        pq_push(s->ppl.out_pq, pkt);
                    }
                }
                ppl_logevent(("Sending password with camouflage packets"));
            } 
            else if (!(s->ppl.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.
                 */
                strbuf *padded_pw = strbuf_new();

                ppl_logevent(("Sending length-padded password"));
                pkt = ssh_bpp_new_pktout(s->ppl.bpp, s->pwpkt_type);
                put_asciz(padded_pw, s->cur_prompt->prompts[0]->result);
                do {
                    put_byte(padded_pw, random_byte());
                } while (padded_pw->len % 64 != 0);
                put_stringsb(pkt, padded_pw);
                pq_push(s->ppl.out_pq, pkt);
            } else {
                /*
                 * The server is believed unable to cope with
                 * any of our password camouflage methods.
                 */
                ppl_logevent(("Sending unpadded password"));
                pkt = ssh_bpp_new_pktout(s->ppl.bpp, s->pwpkt_type);
                put_stringz(pkt, s->cur_prompt->prompts[0]->result);
                pq_push(s->ppl.out_pq, pkt);
            }
        } else {
            pkt = ssh_bpp_new_pktout(s->ppl.bpp, s->pwpkt_type);
            put_stringz(pkt, s->cur_prompt->prompts[0]->result);
            pq_push(s->ppl.out_pq, pkt);
        }
        ppl_logevent(("Sent password"));
        free_prompts(s->cur_prompt);
        s->cur_prompt = NULL;
        crMaybeWaitUntilV((pktin = ssh1_login_pop(s)) != NULL);
        if (pktin->type == SSH1_SMSG_FAILURE) {
            if (flags & FLAG_VERBOSE)
                ppl_printf(("Access denied\r\n"));
            ppl_logevent(("Authentication refused"));
        } else if (pktin->type != SSH1_SMSG_SUCCESS) {
            ssh_proto_error(s->ppl.ssh, "Received unexpected packet"
                            " in response to password authentication, type %d "
                            "(%s)", pktin->type, ssh1_pkt_type(pktin->type));
            return;
        }
    }

    ppl_logevent(("Authentication successful"));

    if (conf_get_int(s->conf, CONF_compression)) {
        ppl_logevent(("Requesting compression"));
        pkt = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_CMSG_REQUEST_COMPRESSION);
        put_uint32(pkt, 6);         /* gzip compression level */
        pq_push(s->ppl.out_pq, pkt);
        crMaybeWaitUntilV((pktin = ssh1_login_pop(s)) != NULL);
	if (pktin->type == SSH1_SMSG_SUCCESS) {
            /*
             * We don't have to actually do anything here: the SSH-1
             * BPP will take care of automatically starting the
             * compression, by recognising our outgoing request packet
             * and the success response. (Horrible, but it's the
             * easiest way to avoid race conditions if other packets
             * cross in transit.)
             */
	} else if (pktin->type == SSH1_SMSG_FAILURE) {
            ppl_logevent(("Server refused to enable compression"));
	    ppl_printf(("Server refused to compress\r\n"));
        } else {
            ssh_proto_error(s->ppl.ssh, "Received unexpected packet"
                            " in response to compression request, type %d "
                            "(%s)", pktin->type, ssh1_pkt_type(pktin->type));
            return;
	}
    }

    ssh1_connection_set_local_protoflags(
        s->successor_layer, s->local_protoflags);
    {
        PacketProtocolLayer *successor = s->successor_layer;
        s->successor_layer = NULL;     /* avoid freeing it ourself */
        ssh_ppl_replace(&s->ppl, successor);
        return;   /* we've just freed s, so avoid even touching s->crState */
    }

    crFinishV;
}

static void ssh1_login_dialog_callback(void *loginv, int ret)
{
    struct ssh1_login_state *s = (struct ssh1_login_state *)loginv;
    s->dlgret = ret;
    ssh_ppl_process_queue(&s->ppl);
}

static void ssh1_login_agent_query(struct ssh1_login_state *s, strbuf *req)
{
    void *response;
    int response_len;

    sfree(s->agent_response_to_free);
    s->agent_response_to_free = NULL;

    s->auth_agent_query = agent_query(req, &response, &response_len,
                                      ssh1_login_agent_callback, s);
    if (!s->auth_agent_query)
        ssh1_login_agent_callback(s, response, response_len);
}

static void ssh1_login_agent_callback(void *loginv, void *reply, int replylen)
{
    struct ssh1_login_state *s = (struct ssh1_login_state *)loginv;

    s->auth_agent_query = NULL;
    s->agent_response_to_free = reply;
    s->agent_response = make_ptrlen(reply, replylen);

    queue_idempotent_callback(&s->ppl.ic_process_queue);
}

static void ssh1_login_special_cmd(PacketProtocolLayer *ppl,
                                   SessionSpecialCode code, int arg)
{
    struct ssh1_login_state *s =
        container_of(ppl, struct ssh1_login_state, ppl);
    PktOut *pktout;

    if (code == SS_PING || code == SS_NOP) {
        if (!(s->ppl.remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE)) {
            pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH1_MSG_IGNORE);
            put_stringz(pktout, "");
            pq_push(s->ppl.out_pq, pktout);
        }
    }
}

static int ssh1_login_want_user_input(PacketProtocolLayer *ppl)
{
    struct ssh1_login_state *s =
        container_of(ppl, struct ssh1_login_state, ppl);
    return s->want_user_input;
}

static void ssh1_login_got_user_input(PacketProtocolLayer *ppl)
{
    struct ssh1_login_state *s =
        container_of(ppl, struct ssh1_login_state, ppl);
    if (s->want_user_input)
        queue_idempotent_callback(&s->ppl.ic_process_queue);
}

static void ssh1_login_reconfigure(PacketProtocolLayer *ppl, Conf *conf)
{
    struct ssh1_login_state *s =
        container_of(ppl, struct ssh1_login_state, ppl);
    ssh_ppl_reconfigure(s->successor_layer, conf);
}