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/*
* 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);
}
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