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);
}
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);
}
DH *
choose_dh(int min, int wantbits, int max)
{
FILE *f;
char line[2048];
int best, bestcount, which;
int linenum;
struct dhgroup dhg;
if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL &&
(f = fopen(_PATH_DH_PRIMES, "r")) == NULL) {
log("WARNING: %s does not exist, using old modulus", _PATH_DH_MODULI);
return (dh_new_group1());
}
linenum = 0;
best = bestcount = 0;
while (fgets(line, sizeof(line), f)) {
linenum++;
if (!parse_prime(linenum, line, &dhg))
continue;
BN_clear_free(dhg.g);
BN_clear_free(dhg.p);
if (dhg.size > max || dhg.size < min)
continue;
if ((dhg.size > wantbits && dhg.size < best) ||
(dhg.size > best && best < wantbits)) {
best = dhg.size;
bestcount = 0;
}
if (dhg.size == best)
bestcount++;
}
rewind(f);
if (bestcount == 0) {
fclose(f);
log("WARNING: no suitable primes in %s", _PATH_DH_PRIMES);
return (NULL);
}
linenum = 0;
which = arc4random() % bestcount;
while (fgets(line, sizeof(line), f)) {
if (!parse_prime(linenum, line, &dhg))
continue;
if ((dhg.size > max || dhg.size < min) ||
dhg.size != best ||
linenum++ != which) {
BN_clear_free(dhg.g);
BN_clear_free(dhg.p);
continue;
}
break;
}
fclose(f);
if (linenum != which+1)
fatal("WARNING: line %d disappeared in %s, giving up",
which, _PATH_DH_PRIMES);
return (dh_new_group(dhg.g, dhg.p));
}
