source: trunk/third/openssh/kexdh.c @ 18759

/*
 * Copyright (c) 2001 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"
RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $");

#include <openssl/crypto.h>
#include <openssl/bn.h>

#include "xmalloc.h"
#include "buffer.h"
#include "bufaux.h"
#include "key.h"
#include "kex.h"
#include "log.h"
#include "packet.h"
#include "dh.h"
#include "ssh2.h"
#include "monitor_wrap.h"

static u_char *
kex_dh_hash(
    char *client_version_string,
    char *server_version_string,
    char *ckexinit, int ckexinitlen,
    char *skexinit, int skexinitlen,
    u_char *serverhostkeyblob, int sbloblen,
    BIGNUM *client_dh_pub,
    BIGNUM *server_dh_pub,
    BIGNUM *shared_secret)
{
        Buffer b;
        static u_char digest[EVP_MAX_MD_SIZE];
        const EVP_MD *evp_md = EVP_sha1();
        EVP_MD_CTX md;

        buffer_init(&b);
        buffer_put_cstring(&b, client_version_string);
        buffer_put_cstring(&b, server_version_string);

        /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
        buffer_put_int(&b, ckexinitlen+1);
        buffer_put_char(&b, SSH2_MSG_KEXINIT);
        buffer_append(&b, ckexinit, ckexinitlen);
        buffer_put_int(&b, skexinitlen+1);
        buffer_put_char(&b, SSH2_MSG_KEXINIT);
        buffer_append(&b, skexinit, skexinitlen);

        buffer_put_string(&b, serverhostkeyblob, sbloblen);
        buffer_put_bignum2(&b, client_dh_pub);
        buffer_put_bignum2(&b, server_dh_pub);
        buffer_put_bignum2(&b, shared_secret);

#ifdef DEBUG_KEX
        buffer_dump(&b);
#endif
        EVP_DigestInit(&md, evp_md);
        EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
        EVP_DigestFinal(&md, digest, NULL);

        buffer_free(&b);

#ifdef DEBUG_KEX
        dump_digest("hash", digest, EVP_MD_size(evp_md));
#endif
        return digest;
}

/* client */

static void
kexdh_client(Kex *kex)
{
        BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
        DH *dh;
        Key *server_host_key;
        u_char *server_host_key_blob = NULL, *signature = NULL;
        u_char *kbuf, *hash;
        u_int klen, kout, slen, sbloblen;

        /* generate and send 'e', client DH public key */
        dh = dh_new_group1();
        dh_gen_key(dh, kex->we_need * 8);
        packet_start(SSH2_MSG_KEXDH_INIT);
        packet_put_bignum2(dh->pub_key);
        packet_send();

        debug("sending SSH2_MSG_KEXDH_INIT");
#ifdef DEBUG_KEXDH
        DHparams_print_fp(stderr, dh);
        fprintf(stderr, "pub= ");
        BN_print_fp(stderr, dh->pub_key);
        fprintf(stderr, "\n");
#endif

        debug("expecting SSH2_MSG_KEXDH_REPLY");
        packet_read_expect(SSH2_MSG_KEXDH_REPLY);

        /* key, cert */
        server_host_key_blob = packet_get_string(&sbloblen);
        server_host_key = key_from_blob(server_host_key_blob, sbloblen);
        if (server_host_key == NULL)
                fatal("cannot decode server_host_key_blob");
        if (server_host_key->type != kex->hostkey_type)
                fatal("type mismatch for decoded server_host_key_blob");
        if (kex->verify_host_key == NULL)
                fatal("cannot verify server_host_key");
        if (kex->verify_host_key(server_host_key) == -1)
                fatal("server_host_key verification failed");

        /* DH paramter f, server public DH key */
        if ((dh_server_pub = BN_new()) == NULL)
                fatal("dh_server_pub == NULL");
        packet_get_bignum2(dh_server_pub);

#ifdef DEBUG_KEXDH
        fprintf(stderr, "dh_server_pub= ");
        BN_print_fp(stderr, dh_server_pub);
        fprintf(stderr, "\n");
        debug("bits %d", BN_num_bits(dh_server_pub));
#endif

        /* signed H */
        signature = packet_get_string(&slen);
        packet_check_eom();

        if (!dh_pub_is_valid(dh, dh_server_pub))
                packet_disconnect("bad server public DH value");

        klen = DH_size(dh);
        kbuf = xmalloc(klen);
        kout = DH_compute_key(kbuf, dh_server_pub, dh);
#ifdef DEBUG_KEXDH
        dump_digest("shared secret", kbuf, kout);
#endif
        if ((shared_secret = BN_new()) == NULL)
                fatal("kexdh_client: BN_new failed");
        BN_bin2bn(kbuf, kout, shared_secret);
        memset(kbuf, 0, klen);
        xfree(kbuf);

        /* calc and verify H */
        hash = kex_dh_hash(
            kex->client_version_string,
            kex->server_version_string,
            buffer_ptr(&kex->my), buffer_len(&kex->my),
            buffer_ptr(&kex->peer), buffer_len(&kex->peer),
            server_host_key_blob, sbloblen,
            dh->pub_key,
            dh_server_pub,
            shared_secret
        );
        xfree(server_host_key_blob);
        BN_clear_free(dh_server_pub);
        DH_free(dh);

        if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
                fatal("key_verify failed for server_host_key");
        key_free(server_host_key);
        xfree(signature);

        /* save session id */
        if (kex->session_id == NULL) {
                kex->session_id_len = 20;
                kex->session_id = xmalloc(kex->session_id_len);
                memcpy(kex->session_id, hash, kex->session_id_len);
        }

        kex_derive_keys(kex, hash, shared_secret);
        BN_clear_free(shared_secret);
        kex_finish(kex);
}

/* server */

static void
kexdh_server(Kex *kex)
{
        BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
        DH *dh;
        Key *server_host_key;
        u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
        u_int sbloblen, klen, kout;
        u_int slen;

        /* generate server DH public key */
        dh = dh_new_group1();
        dh_gen_key(dh, kex->we_need * 8);

        debug("expecting SSH2_MSG_KEXDH_INIT");
        packet_read_expect(SSH2_MSG_KEXDH_INIT);

        if (kex->load_host_key == NULL)
                fatal("Cannot load hostkey");
        server_host_key = kex->load_host_key(kex->hostkey_type);
        if (server_host_key == NULL)
                fatal("Unsupported hostkey type %d", kex->hostkey_type);

        /* key, cert */
        if ((dh_client_pub = BN_new()) == NULL)
                fatal("dh_client_pub == NULL");
        packet_get_bignum2(dh_client_pub);
        packet_check_eom();

#ifdef DEBUG_KEXDH
        fprintf(stderr, "dh_client_pub= ");
        BN_print_fp(stderr, dh_client_pub);
        fprintf(stderr, "\n");
        debug("bits %d", BN_num_bits(dh_client_pub));
#endif

#ifdef DEBUG_KEXDH
        DHparams_print_fp(stderr, dh);
        fprintf(stderr, "pub= ");
        BN_print_fp(stderr, dh->pub_key);
        fprintf(stderr, "\n");
#endif
        if (!dh_pub_is_valid(dh, dh_client_pub))
                packet_disconnect("bad client public DH value");

        klen = DH_size(dh);
        kbuf = xmalloc(klen);
        kout = DH_compute_key(kbuf, dh_client_pub, dh);
#ifdef DEBUG_KEXDH
        dump_digest("shared secret", kbuf, kout);
#endif
        if ((shared_secret = BN_new()) == NULL)
                fatal("kexdh_server: BN_new failed");
        BN_bin2bn(kbuf, kout, shared_secret);
        memset(kbuf, 0, klen);
        xfree(kbuf);

        key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);

        /* calc H */
        hash = kex_dh_hash(
            kex->client_version_string,
            kex->server_version_string,
            buffer_ptr(&kex->peer), buffer_len(&kex->peer),
            buffer_ptr(&kex->my), buffer_len(&kex->my),
            server_host_key_blob, sbloblen,
            dh_client_pub,
            dh->pub_key,
            shared_secret
        );
        BN_clear_free(dh_client_pub);

        /* save session id := H */
        /* XXX hashlen depends on KEX */
        if (kex->session_id == NULL) {
                kex->session_id_len = 20;
                kex->session_id = xmalloc(kex->session_id_len);
                memcpy(kex->session_id, hash, kex->session_id_len);
        }

        /* sign H */
        /* XXX hashlen depends on KEX */
        PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20));

        /* destroy_sensitive_data(); */

        /* send server hostkey, DH pubkey 'f' and singed H */
        packet_start(SSH2_MSG_KEXDH_REPLY);
        packet_put_string(server_host_key_blob, sbloblen);
        packet_put_bignum2(dh->pub_key);        /* f */
        packet_put_string(signature, slen);
        packet_send();

        xfree(signature);
        xfree(server_host_key_blob);
        /* have keys, free DH */
        DH_free(dh);

        kex_derive_keys(kex, hash, shared_secret);
        BN_clear_free(shared_secret);
        kex_finish(kex);
}

void
kexdh(Kex *kex)
{
        if (kex->server)
                kexdh_server(kex);
        else
                kexdh_client(kex);
}