/* Validate KEX method name list */
int
kex_names_valid(const char *names)
{
char *s, *cp, *p;
if (names == NULL || strcmp(names, "") == 0)
return 0;
s = cp = xstrdup(names);
for ((p = strsep(&cp, ",")); p && *p != '\0';
(p = strsep(&cp, ","))) {
if (strcmp(p, KEX_DHGEX_SHA256) != 0 &&
strcmp(p, KEX_DHGEX_SHA1) != 0 &&
strcmp(p, KEX_DH14) != 0 &&
strcmp(p, KEX_DH1) != 0 &&
(strncmp(p, KEX_ECDH_SHA2_STEM,
sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 ||
kex_ecdh_name_to_nid(p) == -1)) {
error("Unsupported KEX algorithm \"%.100s\"", p);
xfree(s);
return 0;
}
}
debug3("kex names ok: [%s]", names);
xfree(s);
return 1;
}
const EVP_MD *
kex_ecdh_name_to_evpmd(const char *kexname)
{
int nid = kex_ecdh_name_to_nid(kexname);
if (nid == -1)
fatal("%s: unsupported ECDH curve \"%s\"", __func__, kexname);
return key_ec_nid_to_evpmd(nid);
}
void
kexecdh_server(Kex *kex)
{
EC_POINT *client_public;
EC_KEY *server_key;
const EC_GROUP *group;
BIGNUM *shared_secret;
Key *server_host_private, *server_host_public;
u_char *server_host_key_blob = NULL, *signature = NULL;
u_char *kbuf, *hash;
u_int klen, slen, sbloblen, hashlen;
int curve_nid;
if ((curve_nid = kex_ecdh_name_to_nid(kex->name)) == -1)
fatal("%s: unsupported ECDH curve \"%s\"", __func__, kex->name);
if ((server_key = EC_KEY_new_by_curve_name(curve_nid)) == NULL)
fatal("%s: EC_KEY_new_by_curve_name failed", __func__);
if (EC_KEY_generate_key(server_key) != 1)
fatal("%s: EC_KEY_generate_key failed", __func__);
group = EC_KEY_get0_group(server_key);
#ifdef DEBUG_KEXECDH
fputs("server private key:\n", stderr);
key_dump_ec_key(server_key);
#endif
if (kex->load_host_public_key == NULL ||
kex->load_host_private_key == NULL)
fatal("Cannot load hostkey");
server_host_public = kex->load_host_public_key(kex->hostkey_type);
if (server_host_public == NULL)
fatal("Unsupported hostkey type %d", kex->hostkey_type);
server_host_private = kex->load_host_private_key(kex->hostkey_type);
if (server_host_private == NULL)
fatal("Missing private key for hostkey type %d",
kex->hostkey_type);
debug("expecting SSH2_MSG_KEX_ECDH_INIT");
packet_read_expect(SSH2_MSG_KEX_ECDH_INIT);
if ((client_public = EC_POINT_new(group)) == NULL)
fatal("%s: EC_POINT_new failed", __func__);
packet_get_ecpoint(group, client_public);
packet_check_eom();
if (key_ec_validate_public(group, client_public) != 0)
fatal("%s: invalid client public key", __func__);
#ifdef DEBUG_KEXECDH
fputs("client public key:\n", stderr);
key_dump_ec_point(group, client_public);
#endif
/* Calculate shared_secret */
klen = (EC_GROUP_get_degree(group) + 7) / 8;
kbuf = xmalloc(klen);
if (ECDH_compute_key(kbuf, klen, client_public,
server_key, NULL) != (int)klen)
fatal("%s: ECDH_compute_key failed", __func__);
#ifdef DEBUG_KEXDH
dump_digest("shared secret", kbuf, klen);
#endif
if ((shared_secret = BN_new()) == NULL)
fatal("%s: BN_new failed", __func__);
if (BN_bin2bn(kbuf, klen, shared_secret) == NULL)
fatal("%s: BN_bin2bn failed", __func__);
memset(kbuf, 0, klen);
xfree(kbuf);
/* calc H */
key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
kex_ecdh_hash(
kex->evp_md,
group,
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,
client_public,
EC_KEY_get0_public_key(server_key),
shared_secret,
&hash, &hashlen
);
EC_POINT_clear_free(client_public);
/* save session id := H */
if (kex->session_id == NULL) {
kex->session_id_len = hashlen;
kex->session_id = xmalloc(kex->session_id_len);
memcpy(kex->session_id, hash, kex->session_id_len);
}
/* sign H */
if (PRIVSEP(key_sign(server_host_private, &signature, &slen,
hash, hashlen)) < 0)
fatal("kexdh_server: key_sign failed");
/* destroy_sensitive_data(); */
/* send server hostkey, ECDH pubkey 'Q_S' and signed H */
packet_start(SSH2_MSG_KEX_ECDH_REPLY);
packet_put_string(server_host_key_blob, sbloblen);
packet_put_ecpoint(group, EC_KEY_get0_public_key(server_key));
packet_put_string(signature, slen);
packet_send();
xfree(signature);
xfree(server_host_key_blob);
/* have keys, free server key */
EC_KEY_free(server_key);
kex_derive_keys(kex, hash, hashlen, shared_secret);
BN_clear_free(shared_secret);
kex_finish(kex);
}
