HelloRetryRequest updates for draft-19

Draft-19 changes the HRR transcript hash so that the initial ClientHello
is replaced in the transcript with a special synthetic message_hash message
that just contains a hash of ClientHello1 as its message body.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2895)

include/openssl/ssl.h

@@ -2135,6 +2135,7 @@ int ERR_load_SSL_strings(void);
 # define SSL_F_ADD_KEY_SHARE                              512
 # define SSL_F_BYTES_TO_CIPHER_LIST                       519
 # define SSL_F_CHECK_SUITEB_CIPHER_LIST                   331
+# define SSL_F_CREATE_SYNTHETIC_MESSAGE_HASH              539
 # define SSL_F_CT_MOVE_SCTS                               345
 # define SSL_F_CT_STRICT                                  349
 # define SSL_F_D2I_SSL_SESSION                            103
@@ -2175,6 +2176,7 @@ int ERR_load_SSL_strings(void);
 # define SSL_F_OSSL_STATEM_SERVER_READ_TRANSITION         418
 # define SSL_F_PROCESS_KEY_SHARE_EXT                      439
 # define SSL_F_READ_STATE_MACHINE                         352
+# define SSL_F_SET_CLIENT_CIPHERSUITE                     540
 # define SSL_F_SSL3_CHANGE_CIPHER_STATE                   129
 # define SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM              130
 # define SSL_F_SSL3_CTRL                                  213
@@ -2464,6 +2466,7 @@ int ERR_load_SSL_strings(void);
 # define SSL_R_AT_LEAST_TLS_1_0_NEEDED_IN_FIPS_MODE       143
 # define SSL_R_AT_LEAST_TLS_1_2_NEEDED_IN_SUITEB_MODE     158
 # define SSL_R_BAD_CHANGE_CIPHER_SPEC                     103
+# define SSL_R_BAD_CIPHER                                 186
 # define SSL_R_BAD_DATA                                   390
 # define SSL_R_BAD_DATA_RETURNED_BY_CALLBACK              106
 # define SSL_R_BAD_DECOMPRESSION                          107

include/openssl/ssl3.h

@@ -295,6 +295,7 @@ extern "C" {
 # ifndef OPENSSL_NO_NEXTPROTONEG
 #  define SSL3_MT_NEXT_PROTO                     67
 # endif
+# define SSL3_MT_MESSAGE_HASH                    254
 # define DTLS1_MT_HELLO_VERIFY_REQUEST           3
 
 /* Dummy message type for handling CCS like a normal handshake message */

ssl/ssl_err.c

@@ -23,6 +23,8 @@ static ERR_STRING_DATA SSL_str_functs[] = {
     {ERR_FUNC(SSL_F_ADD_KEY_SHARE), "add_key_share"},
     {ERR_FUNC(SSL_F_BYTES_TO_CIPHER_LIST), "bytes_to_cipher_list"},
     {ERR_FUNC(SSL_F_CHECK_SUITEB_CIPHER_LIST), "check_suiteb_cipher_list"},
+    {ERR_FUNC(SSL_F_CREATE_SYNTHETIC_MESSAGE_HASH),
+     "create_synthetic_message_hash"},
     {ERR_FUNC(SSL_F_CT_MOVE_SCTS), "ct_move_scts"},
     {ERR_FUNC(SSL_F_CT_STRICT), "ct_strict"},
     {ERR_FUNC(SSL_F_D2I_SSL_SESSION), "d2i_SSL_SESSION"},
@@ -74,6 +76,7 @@ static ERR_STRING_DATA SSL_str_functs[] = {
      "ossl_statem_server_read_transition"},
     {ERR_FUNC(SSL_F_PROCESS_KEY_SHARE_EXT), "process_key_share_ext"},
     {ERR_FUNC(SSL_F_READ_STATE_MACHINE), "read_state_machine"},
+    {ERR_FUNC(SSL_F_SET_CLIENT_CIPHERSUITE), "set_client_ciphersuite"},
     {ERR_FUNC(SSL_F_SSL3_CHANGE_CIPHER_STATE), "ssl3_change_cipher_state"},
     {ERR_FUNC(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM),
      "ssl3_check_cert_and_algorithm"},
@@ -481,6 +484,7 @@ static ERR_STRING_DATA SSL_str_reasons[] = {
     {ERR_REASON(SSL_R_AT_LEAST_TLS_1_2_NEEDED_IN_SUITEB_MODE),
      "at least (D)TLS 1.2 needed in Suite B mode"},
     {ERR_REASON(SSL_R_BAD_CHANGE_CIPHER_SPEC), "bad change cipher spec"},
+    {ERR_REASON(SSL_R_BAD_CIPHER), "bad cipher"},
     {ERR_REASON(SSL_R_BAD_DATA), "bad data"},
     {ERR_REASON(SSL_R_BAD_DATA_RETURNED_BY_CALLBACK),
      "bad data returned by callback"},

ssl/statem/statem_clnt.c

@@ -1243,14 +1243,65 @@ MSG_PROCESS_RETURN dtls_process_hello_verify(SSL *s, PACKET *pkt)
     return MSG_PROCESS_ERROR;
 }
 
-MSG_PROCESS_RETURN tls_process_server_hello(SSL *s, PACKET *pkt)
+static int set_client_ciphersuite(SSL *s, const unsigned char *cipherchars)
 {
     STACK_OF(SSL_CIPHER) *sk;
     const SSL_CIPHER *c;
+    int i;
+
+    c = ssl_get_cipher_by_char(s, cipherchars, 0);
+    if (c == NULL) {
+        /* unknown cipher */
+        SSLerr(SSL_F_SET_CLIENT_CIPHERSUITE, SSL_R_UNKNOWN_CIPHER_RETURNED);
+        return 0;
+    }
+    /*
+     * If it is a disabled cipher we either didn't send it in client hello,
+     * or it's not allowed for the selected protocol. So we return an error.
+     */
+    if (ssl_cipher_disabled(s, c, SSL_SECOP_CIPHER_CHECK)) {
+        SSLerr(SSL_F_SET_CLIENT_CIPHERSUITE, SSL_R_WRONG_CIPHER_RETURNED);
+        return 0;
+    }
+
+    sk = ssl_get_ciphers_by_id(s);
+    i = sk_SSL_CIPHER_find(sk, c);
+    if (i < 0) {
+        /* we did not say we would use this cipher */
+        SSLerr(SSL_F_SET_CLIENT_CIPHERSUITE, SSL_R_WRONG_CIPHER_RETURNED);
+        return 0;
+    }
+
+    if (SSL_IS_TLS13(s) && s->s3->tmp.new_cipher != NULL
+            && s->s3->tmp.new_cipher->id != c->id) {
+        /* ServerHello selected a different ciphersuite to that in the HRR */
+        SSLerr(SSL_F_SET_CLIENT_CIPHERSUITE, SSL_R_WRONG_CIPHER_RETURNED);
+        return 0;
+    }
+
+    /*
+     * Depending on the session caching (internal/external), the cipher
+     * and/or cipher_id values may not be set. Make sure that cipher_id is
+     * set and use it for comparison.
+     */
+    if (s->session->cipher != NULL)
+        s->session->cipher_id = s->session->cipher->id;
+    if (s->hit && (s->session->cipher_id != c->id)) {
+        SSLerr(SSL_F_SET_CLIENT_CIPHERSUITE,
+               SSL_R_OLD_SESSION_CIPHER_NOT_RETURNED);
+        return 0;
+    }
+    s->s3->tmp.new_cipher = c;
+
+    return 1;
+}
+
+MSG_PROCESS_RETURN tls_process_server_hello(SSL *s, PACKET *pkt)
+{
     PACKET session_id, extpkt;
     size_t session_id_len;
     const unsigned char *cipherchars;
-    int i, al = SSL_AD_INTERNAL_ERROR;
+    int al = SSL_AD_INTERNAL_ERROR;
     unsigned int compression;
     unsigned int sversion;
     unsigned int context;
@@ -1437,53 +1488,17 @@ MSG_PROCESS_RETURN tls_process_server_hello(SSL *s, PACKET *pkt)
                SSL_R_SSL_SESSION_VERSION_MISMATCH);
         goto f_err;
     }
-
-    c = ssl_get_cipher_by_char(s, cipherchars, 0);
-    if (c == NULL) {
-        /* unknown cipher */
-        al = SSL_AD_ILLEGAL_PARAMETER;
-        SSLerr(SSL_F_TLS_PROCESS_SERVER_HELLO, SSL_R_UNKNOWN_CIPHER_RETURNED);
-        goto f_err;
-    }
     /*
      * Now that we know the version, update the check to see if it's an allowed
      * version.
      */
     s->s3->tmp.min_ver = s->version;
     s->s3->tmp.max_ver = s->version;
-    /*
-     * If it is a disabled cipher we either didn't send it in client hello,
-     * or it's not allowed for the selected protocol. So we return an error.
-     */
-    if (ssl_cipher_disabled(s, c, SSL_SECOP_CIPHER_CHECK)) {
-        al = SSL_AD_ILLEGAL_PARAMETER;
-        SSLerr(SSL_F_TLS_PROCESS_SERVER_HELLO, SSL_R_WRONG_CIPHER_RETURNED);
-        goto f_err;
-    }
 
-    sk = ssl_get_ciphers_by_id(s);
-    i = sk_SSL_CIPHER_find(sk, c);
-    if (i < 0) {
-        /* we did not say we would use this cipher */
+    if (!set_client_ciphersuite(s, cipherchars)) {
         al = SSL_AD_ILLEGAL_PARAMETER;
-        SSLerr(SSL_F_TLS_PROCESS_SERVER_HELLO, SSL_R_WRONG_CIPHER_RETURNED);
-        goto f_err;
-    }
-
-    /*
-     * Depending on the session caching (internal/external), the cipher
-     * and/or cipher_id values may not be set. Make sure that cipher_id is
-     * set and use it for comparison.
-     */
-    if (s->session->cipher)
-        s->session->cipher_id = s->session->cipher->id;
-    if (s->hit && (s->session->cipher_id != c->id)) {
-        al = SSL_AD_ILLEGAL_PARAMETER;
-        SSLerr(SSL_F_TLS_PROCESS_SERVER_HELLO,
-               SSL_R_OLD_SESSION_CIPHER_NOT_RETURNED);
         goto f_err;
     }
-    s->s3->tmp.new_cipher = c;
 
 #ifdef OPENSSL_NO_COMP
     if (compression != 0) {
@@ -1580,6 +1595,7 @@ static MSG_PROCESS_RETURN tls_process_hello_retry_request(SSL *s, PACKET *pkt)
 {
     unsigned int sversion;
     int errorcode;
+    const unsigned char *cipherchars;
     RAW_EXTENSION *extensions = NULL;
     int al;
     PACKET extpkt;
@@ -1600,6 +1616,17 @@ static MSG_PROCESS_RETURN tls_process_hello_retry_request(SSL *s, PACKET *pkt)
         goto f_err;
     }
 
+    if (!PACKET_get_bytes(pkt, &cipherchars, TLS_CIPHER_LEN)) {
+        SSLerr(SSL_F_TLS_PROCESS_HELLO_RETRY_REQUEST, SSL_R_LENGTH_MISMATCH);
+        al = SSL_AD_DECODE_ERROR;
+        goto f_err;
+    }
+
+    if (!set_client_ciphersuite(s, cipherchars)) {
+        al = SSL_AD_ILLEGAL_PARAMETER;
+        goto f_err;
+    }
+
     if (!PACKET_as_length_prefixed_2(pkt, &extpkt)) {
         al = SSL_AD_DECODE_ERROR;
         SSLerr(SSL_F_TLS_PROCESS_HELLO_RETRY_REQUEST, SSL_R_BAD_LENGTH);
@@ -1614,6 +1641,28 @@ static MSG_PROCESS_RETURN tls_process_hello_retry_request(SSL *s, PACKET *pkt)
 
     OPENSSL_free(extensions);
 
+    /*
+     * Re-initialise the Transcript Hash. We're going to prepopulate it with
+     * a synthetic message_hash in place of ClientHello1.
+     */
+    if (!create_synthetic_message_hash(s)) {
+        al = SSL_AD_INTERNAL_ERROR;
+        goto f_err;
+    }
+
+    /*
+     * Add this message to the Transcript Hash. Normally this is done
+     * automatically prior to the message processing stage. However due to the
+     * need to create the synthetic message hash, we defer that step until now
+     * for HRR messages.
+     */
+    if (!ssl3_finish_mac(s, (unsigned char *)s->init_buf->data,
+                                s->init_num + SSL3_HM_HEADER_LENGTH)) {
+        al = SSL_AD_INTERNAL_ERROR;
+        SSLerr(SSL_F_TLS_PROCESS_HELLO_RETRY_REQUEST, ERR_R_INTERNAL_ERROR);
+        goto f_err;
+    }
+
     return MSG_PROCESS_FINISHED_READING;
  f_err:
     ssl3_send_alert(s, SSL3_AL_FATAL, al);

ssl/statem/statem_lib.c

@@ -1149,7 +1149,12 @@ int tls_get_message_body(SSL *s, size_t *len)
             s->msg_callback(0, SSL2_VERSION, 0, s->init_buf->data,
                             (size_t)s->init_num, s, s->msg_callback_arg);
     } else {
-        if (!ssl3_finish_mac(s, (unsigned char *)s->init_buf->data,
+        /*
+         * We defer feeding in the HRR until later. We'll do it as part of
+         * processing the message
+         */
+        if (s->s3->tmp.message_type != SSL3_MT_HELLO_RETRY_REQUEST
+                && !ssl3_finish_mac(s, (unsigned char *)s->init_buf->data,
                                     s->init_num + SSL3_HM_HEADER_LENGTH)) {
             SSLerr(SSL_F_TLS_GET_MESSAGE_BODY, ERR_R_EVP_LIB);
             ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
@@ -1870,3 +1875,37 @@ int check_in_list(SSL *s, unsigned int group_id, const unsigned char *groups,
     return i < num_groups;
 }
 #endif
+
+/* Replace ClientHello1 in the transcript hash with a synthetic message */
+int create_synthetic_message_hash(SSL *s)
+{
+    unsigned char hashval[EVP_MAX_MD_SIZE];
+    size_t hashlen = 0;
+    unsigned char msghdr[SSL3_HM_HEADER_LENGTH] = {
+        SSL3_MT_MESSAGE_HASH,
+        0,
+        0,
+        0
+    };
+
+    /* Get the hash of the initial ClientHello */
+    if (!ssl3_digest_cached_records(s, 0)
+            || !ssl_handshake_hash(s, hashval, sizeof(hashval), &hashlen)) {
+        SSLerr(SSL_F_CREATE_SYNTHETIC_MESSAGE_HASH, ERR_R_INTERNAL_ERROR);
+        return 0;
+    }
+
+    /* Reinitialise the transcript hash */
+    if (!ssl3_init_finished_mac(s))
+        return 0;
+
+    /* Inject the synthetic message_hash message */
+    msghdr[SSL3_HM_HEADER_LENGTH - 1] = hashlen;
+    if (!ssl3_finish_mac(s, msghdr, SSL3_HM_HEADER_LENGTH)
+            || !ssl3_finish_mac(s, hashval, hashlen)) {
+        SSLerr(SSL_F_CREATE_SYNTHETIC_MESSAGE_HASH, ERR_R_INTERNAL_ERROR);
+        return 0;
+    }
+
+    return 1;
+}

ssl/statem/statem_locl.h

@@ -79,7 +79,7 @@ typedef int (*confunc_f) (SSL *s, WPACKET *pkt);
 
 int check_in_list(SSL *s, unsigned int group_id, const unsigned char *groups,
                   size_t num_groups, int checkallow);
-
+int create_synthetic_message_hash(SSL *s);
 /*
  * TLS/DTLS client state machine functions
  */

ssl/statem/statem_srvr.c

@@ -1975,6 +1975,16 @@ WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
                        SSL_R_NO_SHARED_CIPHER);
                 goto f_err;
             }
+            if (SSL_IS_TLS13(s) && s->s3->tmp.new_cipher != NULL
+                    && s->s3->tmp.new_cipher->id != cipher->id) {
+                /*
+                 * A previous HRR picked a different ciphersuite to the one we
+                 * just selected. Something must have changed.
+                 */
+                al = SSL_AD_ILLEGAL_PARAMETER;
+                SSLerr(SSL_F_TLS_POST_PROCESS_CLIENT_HELLO, SSL_R_BAD_CIPHER);
+                goto f_err;
+            }
             s->s3->tmp.new_cipher = cipher;
             if (!tls_choose_sigalg(s, &al))
                 goto f_err;
@@ -3662,17 +3672,18 @@ static int tls_construct_encrypted_extensions(SSL *s, WPACKET *pkt)
 static int tls_construct_hello_retry_request(SSL *s, WPACKET *pkt)
 {
     int al = SSL_AD_INTERNAL_ERROR;
+    size_t len = 0;
 
     /*
      * TODO(TLS1.3): Remove the DRAFT version before release
      * (should be s->version)
      */
     if (!WPACKET_put_bytes_u16(pkt, TLS1_3_VERSION_DRAFT)
+            || !s->method->put_cipher_by_char(s->s3->tmp.new_cipher, pkt, &len)
             || !tls_construct_extensions(s, pkt, EXT_TLS1_3_HELLO_RETRY_REQUEST,
                                          NULL, 0, &al)) {
         SSLerr(SSL_F_TLS_CONSTRUCT_HELLO_RETRY_REQUEST, ERR_R_INTERNAL_ERROR);
-        ssl3_send_alert(s, SSL3_AL_FATAL, al);
-        return 0;
+        goto err;
     }
 
     /* Ditch the session. We'll create a new one next time around */
@@ -3680,7 +3691,17 @@ static int tls_construct_hello_retry_request(SSL *s, WPACKET *pkt)
     s->session = NULL;
     s->hit = 0;
 
+    /*
+     * Re-initialise the Transcript Hash. We're going to prepopulate it with
+     * a synthetic message_hash in place of ClientHello1.
+     */
+    if (!create_synthetic_message_hash(s))
+        goto err;
+
     return 1;
+ err:
+    ssl3_send_alert(s, SSL3_AL_FATAL, al);
+    return 0;
 }
 
 MSG_PROCESS_RETURN tls_process_end_of_early_data(SSL *s, PACKET *pkt)

ssl/t1_trce.c

@@ -992,6 +992,29 @@ static int ssl_print_server_hello(BIO *bio, int indent,
     return 1;
 }
 
+static int ssl_print_hello_retry_request(BIO *bio, int indent,
+                                         const unsigned char *msg,
+                                         size_t msglen)
+{
+    unsigned int cs;
+
+    if (!ssl_print_version(bio, indent, "server_version", &msg, &msglen, NULL))
+        return 0;
+
+    cs = (msg[0] << 8) | msg[1];
+    BIO_indent(bio, indent, 80);
+    BIO_printf(bio, "cipher_suite {0x%02X, 0x%02X} %s\n",
+               msg[0], msg[1], ssl_trace_str(cs, ssl_ciphers_tbl));
+    msg += 2;
+    msglen -= 2;
+
+    if (!ssl_print_extensions(bio, indent, 1, SSL3_MT_HELLO_RETRY_REQUEST, &msg,
+                              &msglen))
+        return 0;
+
+    return 1;
+}
+
 static int ssl_get_keyex(const char **pname, SSL *ssl)
 {
     unsigned long alg_k = ssl->s3->tmp.new_cipher->algorithm_mkey;
@@ -1422,11 +1445,7 @@ static int ssl_print_handshake(BIO *bio, SSL *ssl, int server,
         break;
 
     case SSL3_MT_HELLO_RETRY_REQUEST:
-        if (!ssl_print_version(bio, indent + 2, "server_version", &msg, &msglen,
-                               NULL)
-                || !ssl_print_extensions(bio, indent + 2, 1,
-                                         SSL3_MT_HELLO_RETRY_REQUEST, &msg,
-                                         &msglen))
+        if (!ssl_print_hello_retry_request(bio, indent + 2, msg, msglen))
             return 0;
         break;
 

util/TLSProxy/HelloRetryRequest.pm

@@ -47,6 +47,9 @@ sub parse
         $server_version = TLSProxy::Record::VERS_TLS_1_3;
     }
 
+    my $ciphersuite = unpack('n', substr($self->data, $ptr));
+    $ptr += 2;
+
     my $extensions_len = unpack('n', substr($self->data, $ptr));
     if (!defined $extensions_len) {
         $extensions_len = 0;
@@ -75,6 +78,7 @@ sub parse
     }
 
     $self->server_version($server_version);
+    $self->ciphersuite($ciphersuite);
     $self->extension_data(\%extensions);
 
     print "    Extensions Len:".$extensions_len."\n";
@@ -100,6 +104,7 @@ sub set_message_contents
     }
 
     $data = pack('n', $self->server_version);
+    $data .= pack('n', $self->ciphersuite);
     $data .= pack('n', length($extensions));
     $data .= $extensions;
     $self->data($data);
@@ -114,6 +119,14 @@ sub server_version
     }
     return $self->{server_version};
 }
+sub ciphersuite
+{
+    my $self = shift;
+    if (@_) {
+      $self->{ciphersuite} = shift;
+    }
+    return $self->{ciphersuite};
+}
 sub extension_data
 {
     my $self = shift;