static const SSL_CIPHER *choose_tls13_cipher(
const SSL *ssl, const SSL_CLIENT_HELLO *client_hello) {
if (client_hello->cipher_suites_len % 2 != 0) {
return NULL;
}
CBS cipher_suites;
CBS_init(&cipher_suites, client_hello->cipher_suites,
client_hello->cipher_suites_len);
const int aes_is_fine = EVP_has_aes_hardware();
const uint16_t version = ssl3_protocol_version(ssl);
const SSL_CIPHER *best = NULL;
while (CBS_len(&cipher_suites) > 0) {
uint16_t cipher_suite;
if (!CBS_get_u16(&cipher_suites, &cipher_suite)) {
return NULL;
}
/* Limit to TLS 1.3 ciphers we know about. */
const SSL_CIPHER *candidate = SSL_get_cipher_by_value(cipher_suite);
if (candidate == NULL ||
SSL_CIPHER_get_min_version(candidate) > version ||
SSL_CIPHER_get_max_version(candidate) < version) {
continue;
}
/* TLS 1.3 removes legacy ciphers, so honor the client order, but prefer
* ChaCha20 if we do not have AES hardware. */
if (aes_is_fine) {
return candidate;
}
if (candidate->algorithm_enc == SSL_CHACHA20POLY1305) {
return candidate;
}
if (best == NULL) {
best = candidate;
}
}
return best;
}
static enum ssl_hs_wait_t do_process_server_hello(SSL *ssl, SSL_HANDSHAKE *hs) {
if (!tls13_check_message_type(ssl, SSL3_MT_SERVER_HELLO)) {
return ssl_hs_error;
}
CBS cbs, server_random, extensions;
uint16_t server_wire_version;
uint16_t cipher_suite;
CBS_init(&cbs, ssl->init_msg, ssl->init_num);
if (!CBS_get_u16(&cbs, &server_wire_version) ||
!CBS_get_bytes(&cbs, &server_random, SSL3_RANDOM_SIZE) ||
!CBS_get_u16(&cbs, &cipher_suite) ||
!CBS_get_u16_length_prefixed(&cbs, &extensions) ||
CBS_len(&cbs) != 0) {
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
return ssl_hs_error;
}
if (server_wire_version != ssl->version) {
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_VERSION_NUMBER);
return ssl_hs_error;
}
/* Parse out the extensions. */
int have_key_share = 0;
CBS key_share;
while (CBS_len(&extensions) != 0) {
uint16_t type;
CBS extension;
if (!CBS_get_u16(&extensions, &type) ||
!CBS_get_u16_length_prefixed(&extensions, &extension)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_PARSE_TLSEXT);
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
return ssl_hs_error;
}
switch (type) {
case TLSEXT_TYPE_key_share:
if (have_key_share) {
OPENSSL_PUT_ERROR(SSL, SSL_R_DUPLICATE_EXTENSION);
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
return ssl_hs_error;
}
key_share = extension;
have_key_share = 1;
break;
default:
OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNSUPPORTED_EXTENSION);
return ssl_hs_error;
}
}
assert(ssl->s3->have_version);
memcpy(ssl->s3->server_random, CBS_data(&server_random), SSL3_RANDOM_SIZE);
ssl->hit = 0;
if (!ssl_get_new_session(ssl, 0)) {
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
return ssl_hs_error;
}
const SSL_CIPHER *cipher = SSL_get_cipher_by_value(cipher_suite);
if (cipher == NULL) {
OPENSSL_PUT_ERROR(SSL, SSL_R_UNKNOWN_CIPHER_RETURNED);
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
return ssl_hs_error;
}
/* Check if the cipher is disabled. */
if ((cipher->algorithm_mkey & ssl->cert->mask_k) ||
(cipher->algorithm_auth & ssl->cert->mask_a) ||
SSL_CIPHER_get_min_version(cipher) > ssl3_protocol_version(ssl) ||
SSL_CIPHER_get_max_version(cipher) < ssl3_protocol_version(ssl) ||
!sk_SSL_CIPHER_find(ssl_get_ciphers_by_id(ssl), NULL, cipher)) {
OPENSSL_PUT_ERROR(SSL, SSL_R_WRONG_CIPHER_RETURNED);
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_ILLEGAL_PARAMETER);
return ssl_hs_error;
}
ssl->session->cipher = cipher;
ssl->s3->tmp.new_cipher = cipher;
/* The PRF hash is now known. Set up the key schedule. */
static const uint8_t kZeroes[EVP_MAX_MD_SIZE] = {0};
size_t hash_len =
EVP_MD_size(ssl_get_handshake_digest(ssl_get_algorithm_prf(ssl)));
if (!tls13_init_key_schedule(ssl, kZeroes, hash_len)) {
return ssl_hs_error;
}
/* Resolve PSK and incorporate it into the secret. */
if (cipher->algorithm_auth == SSL_aPSK) {
/* TODO(davidben): Support PSK. */
OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
return ssl_hs_error;
} else if (!tls13_advance_key_schedule(ssl, kZeroes, hash_len)) {
return ssl_hs_error;
}
/* Resolve ECDHE and incorporate it into the secret. */
if (cipher->algorithm_mkey == SSL_kECDHE) {
if (!have_key_share) {
OPENSSL_PUT_ERROR(SSL, SSL_R_MISSING_KEY_SHARE);
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_MISSING_EXTENSION);
return ssl_hs_error;
}
uint8_t *dhe_secret;
size_t dhe_secret_len;
uint8_t alert = SSL_AD_DECODE_ERROR;
if (!ext_key_share_parse_serverhello(ssl, &dhe_secret, &dhe_secret_len,
&alert, &key_share)) {
ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
return ssl_hs_error;
}
int ok = tls13_advance_key_schedule(ssl, dhe_secret, dhe_secret_len);
OPENSSL_free(dhe_secret);
if (!ok) {
return ssl_hs_error;
}
} else {
if (have_key_share) {
OPENSSL_PUT_ERROR(SSL, SSL_R_UNEXPECTED_EXTENSION);
ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_UNSUPPORTED_EXTENSION);
return ssl_hs_error;
}
if (!tls13_advance_key_schedule(ssl, kZeroes, hash_len)) {
return ssl_hs_error;
}
}
/* If there was no HelloRetryRequest, the version negotiation logic has
* already hashed the message. */
if (ssl->s3->hs->retry_group != 0 &&
!ssl->method->hash_current_message(ssl)) {
return ssl_hs_error;
}
if (!tls13_set_handshake_traffic(ssl)) {
return ssl_hs_error;
}
hs->state = state_process_encrypted_extensions;
return ssl_hs_read_message;
}
const SSL_CIPHER *ssl3_choose_cipher(
SSL *ssl, const struct ssl_early_callback_ctx *client_hello,
const struct ssl_cipher_preference_list_st *server_pref) {
const SSL_CIPHER *c, *ret = NULL;
STACK_OF(SSL_CIPHER) *srvr = server_pref->ciphers, *prio, *allow;
int ok;
size_t cipher_index;
uint32_t alg_k, alg_a, mask_k, mask_a;
/* in_group_flags will either be NULL, or will point to an array of bytes
* which indicate equal-preference groups in the |prio| stack. See the
* comment about |in_group_flags| in the |ssl_cipher_preference_list_st|
* struct. */
const uint8_t *in_group_flags;
/* group_min contains the minimal index so far found in a group, or -1 if no
* such value exists yet. */
int group_min = -1;
STACK_OF(SSL_CIPHER) *clnt = ssl_parse_client_cipher_list(client_hello);
if (clnt == NULL) {
return NULL;
}
if (ssl->options & SSL_OP_CIPHER_SERVER_PREFERENCE) {
prio = srvr;
in_group_flags = server_pref->in_group_flags;
allow = clnt;
} else {
prio = clnt;
in_group_flags = NULL;
allow = srvr;
}
ssl_get_compatible_server_ciphers(ssl, &mask_k, &mask_a);
for (size_t i = 0; i < sk_SSL_CIPHER_num(prio); i++) {
c = sk_SSL_CIPHER_value(prio, i);
ok = 1;
/* Check the TLS version. */
if (SSL_CIPHER_get_min_version(c) > ssl3_protocol_version(ssl) ||
SSL_CIPHER_get_max_version(c) < ssl3_protocol_version(ssl)) {
ok = 0;
}
alg_k = c->algorithm_mkey;
alg_a = c->algorithm_auth;
ok = ok && (alg_k & mask_k) && (alg_a & mask_a);
if (ok && sk_SSL_CIPHER_find(allow, &cipher_index, c)) {
if (in_group_flags != NULL && in_group_flags[i] == 1) {
/* This element of |prio| is in a group. Update the minimum index found
* so far and continue looking. */
if (group_min == -1 || (size_t)group_min > cipher_index) {
group_min = cipher_index;
}
} else {
if (group_min != -1 && (size_t)group_min < cipher_index) {
cipher_index = group_min;
}
ret = sk_SSL_CIPHER_value(allow, cipher_index);
break;
}
}
if (in_group_flags != NULL && in_group_flags[i] == 0 && group_min != -1) {
/* We are about to leave a group, but we found a match in it, so that's
* our answer. */
ret = sk_SSL_CIPHER_value(allow, group_min);
break;
}
}
sk_SSL_CIPHER_free(clnt);
return ret;
}
