| /* |
| * Copyright (c) 2000 Niels Provos. All rights reserved. |
| * 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: kexgex.c,v 1.12 2001/12/27 19:37:23 markus Exp $"); |
| |
| #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 "compat.h" |
| |
| static u_char * |
| kexgex_hash( |
| char *client_version_string, |
| char *server_version_string, |
| char *ckexinit, int ckexinitlen, |
| char *skexinit, int skexinitlen, |
| u_char *serverhostkeyblob, int sbloblen, |
| int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen, |
| BIGNUM *client_dh_pub, |
| BIGNUM *server_dh_pub, |
| BIGNUM *shared_secret) |
| { |
| Buffer b; |
| static u_char digest[EVP_MAX_MD_SIZE]; |
| 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); |
| if (min == -1 || max == -1) |
| buffer_put_int(&b, wantbits); |
| else { |
| buffer_put_int(&b, min); |
| buffer_put_int(&b, wantbits); |
| buffer_put_int(&b, max); |
| } |
| buffer_put_bignum2(&b, prime); |
| buffer_put_bignum2(&b, gen); |
| buffer_put_bignum2(&b, client_dh_pub); |
| buffer_put_bignum2(&b, server_dh_pub); |
| buffer_put_bignum2(&b, shared_secret); |
| |
| #ifdef DEBUG_KEXDH |
| 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_KEXDH |
| dump_digest("hash", digest, evp_md->md_size); |
| #endif |
| return digest; |
| } |
| |
| /* client */ |
| |
| static void |
| kexgex_client(Kex *kex) |
| { |
| BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; |
| BIGNUM *p = NULL, *g = NULL; |
| Key *server_host_key; |
| u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; |
| u_int klen, kout, slen, sbloblen; |
| int dlen, plen, min, max, nbits; |
| DH *dh; |
| |
| nbits = dh_estimate(kex->we_need * 8); |
| |
| if (datafellows & SSH_OLD_DHGEX) { |
| debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent"); |
| |
| /* Old GEX request */ |
| packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); |
| packet_put_int(nbits); |
| min = DH_GRP_MIN; |
| max = DH_GRP_MAX; |
| } else { |
| debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent"); |
| |
| /* New GEX request */ |
| min = DH_GRP_MIN; |
| max = DH_GRP_MAX; |
| packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); |
| packet_put_int(min); |
| packet_put_int(nbits); |
| packet_put_int(max); |
| } |
| #ifdef DEBUG_KEXDH |
| fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", |
| min, nbits, max); |
| #endif |
| packet_send(); |
| |
| debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); |
| packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_GROUP); |
| |
| if ((p = BN_new()) == NULL) |
| fatal("BN_new"); |
| packet_get_bignum2(p, &dlen); |
| if ((g = BN_new()) == NULL) |
| fatal("BN_new"); |
| packet_get_bignum2(g, &dlen); |
| packet_done(); |
| |
| if (BN_num_bits(p) < min || BN_num_bits(p) > max) |
| fatal("DH_GEX group out of range: %d !< %d !< %d", |
| min, BN_num_bits(p), max); |
| |
| dh = dh_new_group(g, p); |
| dh_gen_key(dh, kex->we_need * 8); |
| |
| #ifdef DEBUG_KEXDH |
| DHparams_print_fp(stderr, dh); |
| fprintf(stderr, "pub= "); |
| BN_print_fp(stderr, dh->pub_key); |
| fprintf(stderr, "\n"); |
| #endif |
| |
| debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); |
| /* generate and send 'e', client DH public key */ |
| packet_start(SSH2_MSG_KEX_DH_GEX_INIT); |
| packet_put_bignum2(dh->pub_key); |
| packet_send(); |
| |
| debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); |
| packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_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 (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, &dlen); |
| |
| #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_done(); |
| |
| 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("kexgex_client: BN_new failed"); |
| BN_bin2bn(kbuf, kout, shared_secret); |
| memset(kbuf, 0, klen); |
| xfree(kbuf); |
| |
| if (datafellows & SSH_OLD_DHGEX) |
| min = max = -1; |
| |
| /* calc and verify H */ |
| hash = kexgex_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, |
| min, nbits, max, |
| dh->p, dh->g, |
| dh->pub_key, |
| dh_server_pub, |
| shared_secret |
| ); |
| /* have keys, free DH */ |
| DH_free(dh); |
| xfree(server_host_key_blob); |
| BN_clear_free(dh_server_pub); |
| |
| 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 |
| kexgex_server(Kex *kex) |
| { |
| BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; |
| Key *server_host_key; |
| DH *dh = dh; |
| u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; |
| u_int sbloblen, klen, kout; |
| int min = -1, max = -1, nbits = -1, type, plen, dlen, slen; |
| |
| 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); |
| |
| type = packet_read(&plen); |
| switch (type) { |
| case SSH2_MSG_KEX_DH_GEX_REQUEST: |
| debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); |
| min = packet_get_int(); |
| nbits = packet_get_int(); |
| max = packet_get_int(); |
| min = MAX(DH_GRP_MIN, min); |
| max = MIN(DH_GRP_MAX, max); |
| break; |
| case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: |
| debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); |
| nbits = packet_get_int(); |
| min = DH_GRP_MIN; |
| max = DH_GRP_MAX; |
| /* unused for old GEX */ |
| break; |
| default: |
| fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); |
| } |
| packet_done(); |
| |
| if (max < min || nbits < min || max < nbits) |
| fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", |
| min, nbits, max); |
| |
| dh = choose_dh(min, nbits, max); |
| if (dh == NULL) |
| packet_disconnect("Protocol error: no matching DH grp found"); |
| |
| debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); |
| packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); |
| packet_put_bignum2(dh->p); |
| packet_put_bignum2(dh->g); |
| packet_send(); |
| |
| /* flush */ |
| packet_write_wait(); |
| |
| /* Compute our exchange value in parallel with the client */ |
| dh_gen_key(dh, kex->we_need * 8); |
| |
| debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); |
| packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT); |
| |
| /* key, cert */ |
| if ((dh_client_pub = BN_new()) == NULL) |
| fatal("dh_client_pub == NULL"); |
| packet_get_bignum2(dh_client_pub, &dlen); |
| |
| #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("kexgex_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); |
| |
| if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) |
| min = max = -1; |
| |
| /* calc H */ /* XXX depends on 'kex' */ |
| hash = kexgex_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, |
| min, nbits, max, |
| dh->p, dh->g, |
| 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 */ |
| key_sign(server_host_key, &signature, &slen, hash, 20); |
| |
| /* destroy_sensitive_data(); */ |
| |
| /* send server hostkey, DH pubkey 'f' and singed H */ |
| debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); |
| packet_start(SSH2_MSG_KEX_DH_GEX_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 |
| kexgex(Kex *kex) |
| { |
| if (kex->server) |
| kexgex_server(kex); |
| else |
| kexgex_client(kex); |
| } |