Avoid repeatedly scanning the list of extensions
[openssl.git] / ssl / statem / statem_srvr.c
index c8c0b8e17a596305b1ad47fb9cf8ff3a37631151..5aa395f4068aa8a0aaa55e5f467b4d6df41a1096 100644 (file)
@@ -61,6 +61,7 @@
 #include <openssl/bn.h>
 #include <openssl/md5.h>
 
+static int tls_construct_encrypted_extensions(SSL *s, WPACKET *pkt);
 static STACK_OF(SSL_CIPHER) *ssl_bytes_to_cipher_list(SSL *s,
                                                       PACKET *cipher_suites,
                                                       STACK_OF(SSL_CIPHER)
@@ -73,14 +74,18 @@ static STACK_OF(SSL_CIPHER) *ssl_bytes_to_cipher_list(SSL *s,
  * the client. The message type that the client has sent is provided in |mt|.
  * The current state is in |s->statem.hand_state|.
  *
- *  Valid return values are:
- *  1: Success (transition allowed)
- *  0: Error (transition not allowed)
+ * Return values are 1 for success (transition allowed) and  0 on error
+ * (transition not allowed)
  */
 static int ossl_statem_server13_read_transition(SSL *s, int mt)
 {
     OSSL_STATEM *st = &s->statem;
 
+    /*
+     * TODO(TLS1.3): This is still based on the TLSv1.2 state machine. Over time
+     * we will update this to look more like real TLSv1.3
+     */
+
     /*
      * Note: There is no case for TLS_ST_BEFORE because at that stage we have
      * not negotiated TLSv1.3 yet, so that case is handled by
@@ -90,15 +95,15 @@ static int ossl_statem_server13_read_transition(SSL *s, int mt)
     default:
         break;
 
-    case TLS_ST_SW_SRVR_DONE:
+    case TLS_ST_SW_FINISHED:
         if (s->s3->tmp.cert_request) {
             if (mt == SSL3_MT_CERTIFICATE) {
                 st->hand_state = TLS_ST_SR_CERT;
                 return 1;
             }
         } else {
-            if (mt == SSL3_MT_CHANGE_CIPHER_SPEC) {
-                st->hand_state = TLS_ST_SR_CHANGE;
+            if (mt == SSL3_MT_FINISHED) {
+                st->hand_state = TLS_ST_SR_FINISHED;
                 return 1;
             }
         }
@@ -106,8 +111,8 @@ static int ossl_statem_server13_read_transition(SSL *s, int mt)
 
     case TLS_ST_SR_CERT:
         if (s->session->peer == NULL) {
-            if (mt == SSL3_MT_CHANGE_CIPHER_SPEC) {
-                st->hand_state = TLS_ST_SR_CHANGE;
+            if (mt == SSL3_MT_FINISHED) {
+                st->hand_state = TLS_ST_SR_FINISHED;
                 return 1;
             }
         } else {
@@ -119,25 +124,11 @@ static int ossl_statem_server13_read_transition(SSL *s, int mt)
         break;
 
     case TLS_ST_SR_CERT_VRFY:
-        if (mt == SSL3_MT_CHANGE_CIPHER_SPEC) {
-            st->hand_state = TLS_ST_SR_CHANGE;
-            return 1;
-        }
-        break;
-
-    case TLS_ST_SR_CHANGE:
         if (mt == SSL3_MT_FINISHED) {
             st->hand_state = TLS_ST_SR_FINISHED;
             return 1;
         }
         break;
-
-    case TLS_ST_SW_FINISHED:
-        if (mt == SSL3_MT_CHANGE_CIPHER_SPEC) {
-            st->hand_state = TLS_ST_SR_CHANGE;
-            return 1;
-        }
-        break;
     }
 
     /* No valid transition found */
@@ -153,16 +144,18 @@ static int ossl_statem_server13_read_transition(SSL *s, int mt)
  * client. The message type that the client has sent is provided in |mt|. The
  * current state is in |s->statem.hand_state|.
  *
- *  Valid return values are:
- *  1: Success (transition allowed)
- *  0: Error (transition not allowed)
+ * Return values are 1 for success (transition allowed) and  0 on error
+ * (transition not allowed)
  */
 int ossl_statem_server_read_transition(SSL *s, int mt)
 {
     OSSL_STATEM *st = &s->statem;
 
-    if (s->method->version == TLS1_3_VERSION)
-        return ossl_statem_server13_read_transition(s, mt);
+    if (SSL_IS_TLS13(s)) {
+        if (!ossl_statem_server13_read_transition(s, mt))
+            goto err;
+        return 1;
+    }
 
     switch (st->hand_state) {
     default:
@@ -295,6 +288,7 @@ int ossl_statem_server_read_transition(SSL *s, int mt)
         break;
     }
 
+ err:
     /* No valid transition found */
     ssl3_send_alert(s, SSL3_AL_FATAL, SSL3_AD_UNEXPECTED_MESSAGE);
     SSLerr(SSL_F_OSSL_STATEM_SERVER_READ_TRANSITION, SSL_R_UNEXPECTED_MESSAGE);
@@ -390,16 +384,16 @@ static int send_certificate_request(SSL *s)
  * ossl_statem_server13_write_transition() works out what handshake state to
  * move to next when a TLSv1.3 server is writing messages to be sent to the
  * client.
- *
- * Return values:
- * WRITE_TRAN_ERROR - an error occurred
- * WRITE_TRAN_CONTINUE - Successful transition, more writing to be done
- * WRITE_TRAN_FINISHED - Successful transition, no more writing to be done
  */
 static WRITE_TRAN ossl_statem_server13_write_transition(SSL *s)
 {
     OSSL_STATEM *st = &s->statem;
 
+    /*
+     * TODO(TLS1.3): This is still based on the TLSv1.2 state machine. Over time
+     * we will update this to look more like real TLSv1.3
+     */
+
     /*
      * No case for TLS_ST_BEFORE, because at that stage we have not negotiated
      * TLSv1.3 yet, so that is handled by ossl_statem_server_write_transition()
@@ -415,61 +409,36 @@ static WRITE_TRAN ossl_statem_server13_write_transition(SSL *s)
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_SW_SRVR_HELLO:
-        if (s->hit) {
-            if (s->tlsext_ticket_expected)
-                st->hand_state = TLS_ST_SW_SESSION_TICKET;
-            else
-                st->hand_state = TLS_ST_SW_CHANGE;
-        } else {
-            st->hand_state = TLS_ST_SW_CERT;
-        }
+        st->hand_state = TLS_ST_SW_ENCRYPTED_EXTENSIONS;
         return WRITE_TRAN_CONTINUE;
 
-    case TLS_ST_SW_CERT:
-        if (s->tlsext_status_expected) {
-            st->hand_state = TLS_ST_SW_CERT_STATUS;
-            return WRITE_TRAN_CONTINUE;
-        }
-        /* Fall through */
-
-    case TLS_ST_SW_CERT_STATUS:
-        if (send_certificate_request(s)) {
+    case TLS_ST_SW_ENCRYPTED_EXTENSIONS:
+        if (s->hit)
+            st->hand_state = TLS_ST_SW_FINISHED;
+        else if (send_certificate_request(s))
             st->hand_state = TLS_ST_SW_CERT_REQ;
-            return WRITE_TRAN_CONTINUE;
-        }
-        /* Fall through */
+        else
+            st->hand_state = TLS_ST_SW_CERT;
 
-    case TLS_ST_SW_CERT_REQ:
-        st->hand_state = TLS_ST_SW_SRVR_DONE;
         return WRITE_TRAN_CONTINUE;
 
-    case TLS_ST_SW_SRVR_DONE:
-        return WRITE_TRAN_FINISHED;
-
-    case TLS_ST_SR_FINISHED:
-        if (s->hit) {
-            st->hand_state = TLS_ST_OK;
-            ossl_statem_set_in_init(s, 0);
-            return WRITE_TRAN_CONTINUE;
-        } else if (s->tlsext_ticket_expected) {
-            st->hand_state = TLS_ST_SW_SESSION_TICKET;
-        } else {
-            st->hand_state = TLS_ST_SW_CHANGE;
-        }
+    case TLS_ST_SW_CERT_REQ:
+        st->hand_state = TLS_ST_SW_CERT;
         return WRITE_TRAN_CONTINUE;
 
-    case TLS_ST_SW_SESSION_TICKET:
-        st->hand_state = TLS_ST_SW_CHANGE;
+    case TLS_ST_SW_CERT:
+            st->hand_state = s->tlsext_status_expected ? TLS_ST_SW_CERT_STATUS
+                                                       : TLS_ST_SW_FINISHED;
         return WRITE_TRAN_CONTINUE;
 
-    case TLS_ST_SW_CHANGE:
+    case TLS_ST_SW_CERT_STATUS:
         st->hand_state = TLS_ST_SW_FINISHED;
         return WRITE_TRAN_CONTINUE;
 
     case TLS_ST_SW_FINISHED:
-        if (s->hit) {
-            return WRITE_TRAN_FINISHED;
-        }
+        return WRITE_TRAN_FINISHED;
+
+    case TLS_ST_SR_FINISHED:
         st->hand_state = TLS_ST_OK;
         ossl_statem_set_in_init(s, 0);
         return WRITE_TRAN_CONTINUE;
@@ -479,11 +448,6 @@ static WRITE_TRAN ossl_statem_server13_write_transition(SSL *s)
 /*
  * ossl_statem_server_write_transition() works out what handshake state to move
  * to next when the server is writing messages to be sent to the client.
- *
- * Return values:
- * WRITE_TRAN_ERROR - an error occurred
- * WRITE_TRAN_CONTINUE - Successful transition, more writing to be done
- * WRITE_TRAN_FINISHED - Successful transition, no more writing to be done
  */
 WRITE_TRAN ossl_statem_server_write_transition(SSL *s)
 {
@@ -494,7 +458,7 @@ WRITE_TRAN ossl_statem_server_write_transition(SSL *s)
      * to negotiate yet, so we don't take this branch until later
      */
 
-    if (s->method->version == TLS1_3_VERSION)
+    if (SSL_IS_TLS13(s))
         return ossl_statem_server13_write_transition(s);
 
     switch (st->hand_state) {
@@ -750,6 +714,20 @@ WORK_STATE ossl_statem_server_post_work(SSL *s, WORK_STATE wst)
                      sizeof(sctpauthkey), sctpauthkey);
         }
 #endif
+        /*
+         * TODO(TLS1.3): This actually causes a problem. We don't yet know
+         * whether the next record we are going to receive is an unencrypted
+         * alert, or an encrypted handshake message. We're going to need
+         * something clever in the record layer for this.
+         */
+        if (SSL_IS_TLS13(s)) {
+            if (!s->method->ssl3_enc->setup_key_block(s)
+                || !s->method->ssl3_enc->change_cipher_state(s,
+                        SSL3_CC_HANDSHAKE | SSL3_CHANGE_CIPHER_SERVER_WRITE)
+                || !s->method->ssl3_enc->change_cipher_state(s,
+                        SSL3_CC_HANDSHAKE |SSL3_CHANGE_CIPHER_SERVER_READ))
+            return WORK_ERROR;
+        }
         break;
 
     case TLS_ST_SW_CHANGE:
@@ -792,6 +770,14 @@ WORK_STATE ossl_statem_server_post_work(SSL *s, WORK_STATE wst)
                      0, NULL);
         }
 #endif
+        if (SSL_IS_TLS13(s)) {
+            if (!s->method->ssl3_enc->generate_master_secret(s,
+                        s->session->master_key, s->handshake_secret, 0,
+                        &s->session->master_key_length)
+                || !s->method->ssl3_enc->change_cipher_state(s,
+                        SSL3_CC_APPLICATION | SSL3_CHANGE_CIPHER_SERVER_WRITE))
+            return WORK_ERROR;
+        }
         break;
     }
 
@@ -874,6 +860,11 @@ int ossl_statem_server_construct_message(SSL *s, WPACKET *pkt,
         *confunc = tls_construct_finished;
         *mt = SSL3_MT_FINISHED;
         break;
+
+    case TLS_ST_SW_ENCRYPTED_EXTENSIONS:
+        *confunc = tls_construct_encrypted_extensions;
+        *mt = SSL3_MT_ENCRYPTED_EXTENSIONS;
+        break;
     }
 
     return 1;
@@ -1011,7 +1002,7 @@ WORK_STATE ossl_statem_server_post_process_message(SSL *s, WORK_STATE wst)
 #endif
         return WORK_FINISHED_CONTINUE;
     }
-
+    return WORK_FINISHED_CONTINUE;
 }
 
 #ifndef OPENSSL_NO_SRP
@@ -1071,6 +1062,71 @@ int dtls_construct_hello_verify_request(SSL *s, WPACKET *pkt)
     return 1;
 }
 
+#ifndef OPENSSL_NO_EC
+/*-
+ * ssl_check_for_safari attempts to fingerprint Safari using OS X
+ * SecureTransport using the TLS extension block in |hello|.
+ * Safari, since 10.6, sends exactly these extensions, in this order:
+ *   SNI,
+ *   elliptic_curves
+ *   ec_point_formats
+ *
+ * We wish to fingerprint Safari because they broke ECDHE-ECDSA support in 10.8,
+ * but they advertise support. So enabling ECDHE-ECDSA ciphers breaks them.
+ * Sadly we cannot differentiate 10.6, 10.7 and 10.8.4 (which work), from
+ * 10.8..10.8.3 (which don't work).
+ */
+static void ssl_check_for_safari(SSL *s, const CLIENTHELLO_MSG *hello)
+{
+    unsigned int type;
+    PACKET sni, tmppkt;
+    size_t ext_len;
+
+    static const unsigned char kSafariExtensionsBlock[] = {
+        0x00, 0x0a,             /* elliptic_curves extension */
+        0x00, 0x08,             /* 8 bytes */
+        0x00, 0x06,             /* 6 bytes of curve ids */
+        0x00, 0x17,             /* P-256 */
+        0x00, 0x18,             /* P-384 */
+        0x00, 0x19,             /* P-521 */
+
+        0x00, 0x0b,             /* ec_point_formats */
+        0x00, 0x02,             /* 2 bytes */
+        0x01,                   /* 1 point format */
+        0x00,                   /* uncompressed */
+        /* The following is only present in TLS 1.2 */
+        0x00, 0x0d,             /* signature_algorithms */
+        0x00, 0x0c,             /* 12 bytes */
+        0x00, 0x0a,             /* 10 bytes */
+        0x05, 0x01,             /* SHA-384/RSA */
+        0x04, 0x01,             /* SHA-256/RSA */
+        0x02, 0x01,             /* SHA-1/RSA */
+        0x04, 0x03,             /* SHA-256/ECDSA */
+        0x02, 0x03,             /* SHA-1/ECDSA */
+    };
+
+    /* Length of the common prefix (first two extensions). */
+    static const size_t kSafariCommonExtensionsLength = 18;
+
+    tmppkt = hello->extensions;
+
+    if (!PACKET_forward(&tmppkt, 2)
+        || !PACKET_get_net_2(&tmppkt, &type)
+        || !PACKET_get_length_prefixed_2(&tmppkt, &sni)) {
+        return;
+    }
+
+    if (type != TLSEXT_TYPE_server_name)
+        return;
+
+    ext_len = TLS1_get_client_version(s) >= TLS1_2_VERSION ?
+        sizeof(kSafariExtensionsBlock) : kSafariCommonExtensionsLength;
+
+    s->s3->is_probably_safari = PACKET_equal(&tmppkt, kSafariExtensionsBlock,
+                                             ext_len);
+}
+#endif                          /* !OPENSSL_NO_EC */
+
 MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
 {
     int i, al = SSL_AD_INTERNAL_ERROR;
@@ -1258,8 +1314,8 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
 
     /* Preserve the raw extensions PACKET for later use */
     extensions = clienthello.extensions;
-    if (!tls_collect_extensions(&extensions, &clienthello.pre_proc_exts,
-                                  &clienthello.num_extensions, &al)) {
+    if (!tls_collect_extensions(s, &extensions, EXT_CLIENT_HELLO,
+                                &clienthello.pre_proc_exts, &al)) {
         /* SSLerr already been called */
         goto f_err;
     }
@@ -1344,9 +1400,9 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
     s->hit = 0;
 
     /* We need to do this before getting the session */
-    if (!tls_check_client_ems_support(s, &clienthello)) {
-        /* Only fails if the extension is malformed */
-        al = SSL_AD_DECODE_ERROR;
+    if (!tls_parse_extension(s, TLSEXT_IDX_extended_master_secret,
+                             EXT_CLIENT_HELLO,
+                             clienthello.pre_proc_exts, &al)) {
         SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_CLIENTHELLO_TLSEXT);
         goto f_err;
     }
@@ -1443,16 +1499,22 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         goto f_err;
     }
 
+#ifndef OPENSSL_NO_EC
+    if (s->options & SSL_OP_SAFARI_ECDHE_ECDSA_BUG)
+        ssl_check_for_safari(s, &clienthello);
+#endif                          /* !OPENSSL_NO_EC */
+
     /* TLS extensions */
-    if (!ssl_parse_clienthello_tlsext(s, &clienthello)) {
+    if (!tls_parse_all_extensions(s, EXT_CLIENT_HELLO,
+                                  clienthello.pre_proc_exts, &al)) {
         SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_PARSE_TLSEXT);
-        goto err;
+        goto f_err;
     }
 
     /* Check we've got a key_share for TLSv1.3 */
-    if (s->version == TLS1_3_VERSION && s->s3->peer_tmp == NULL && !s->hit) {
+    if (SSL_IS_TLS13(s) && s->s3->peer_tmp == NULL && !s->hit) {
         /* No suitable share */
-        /* TODO(1.3): Send a HelloRetryRequest */
+        /* TODO(TLS1.3): Send a HelloRetryRequest */
         al = SSL_AD_HANDSHAKE_FAILURE;
         SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_NO_SUITABLE_KEY_SHARE);
         goto f_err;
@@ -1630,6 +1692,54 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
     return MSG_PROCESS_ERROR;
 }
 
+/*
+ * Call the status request callback if needed. Upon success, returns 1.
+ * Upon failure, returns 0 and sets |al| to the appropriate fatal alert.
+ */
+static int tls_handle_status_request(SSL *s, int *al)
+{
+    s->tlsext_status_expected = 0;
+
+    /*
+     * If status request then ask callback what to do. Note: this must be
+     * called after servername callbacks in case the certificate has changed,
+     * and must be called after the cipher has been chosen because this may
+     * influence which certificate is sent
+     */
+    if ((s->tlsext_status_type != -1) && s->ctx && s->ctx->tlsext_status_cb) {
+        int ret;
+        CERT_PKEY *certpkey;
+        certpkey = ssl_get_server_send_pkey(s);
+        /* If no certificate can't return certificate status */
+        if (certpkey != NULL) {
+            /*
+             * Set current certificate to one we will use so SSL_get_certificate
+             * et al can pick it up.
+             */
+            s->cert->key = certpkey;
+            ret = s->ctx->tlsext_status_cb(s, s->ctx->tlsext_status_arg);
+            switch (ret) {
+                /* We don't want to send a status request response */
+            case SSL_TLSEXT_ERR_NOACK:
+                s->tlsext_status_expected = 0;
+                break;
+                /* status request response should be sent */
+            case SSL_TLSEXT_ERR_OK:
+                if (s->tlsext_ocsp_resp)
+                    s->tlsext_status_expected = 1;
+                break;
+                /* something bad happened */
+            case SSL_TLSEXT_ERR_ALERT_FATAL:
+            default:
+                *al = SSL_AD_INTERNAL_ERROR;
+                return 0;
+            }
+        }
+    }
+
+    return 1;
+}
+
 WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
 {
     int al = SSL_AD_HANDSHAKE_FAILURE;
@@ -1663,8 +1773,10 @@ WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
             s->s3->tmp.new_cipher = cipher;
             /* check whether we should disable session resumption */
             if (s->not_resumable_session_cb != NULL)
-                s->session->not_resumable = s->not_resumable_session_cb(s,
-                                                                        ((cipher->algorithm_mkey & (SSL_kDHE | SSL_kECDHE)) != 0));
+                s->session->not_resumable =
+                    s->not_resumable_session_cb(s, ((cipher->algorithm_mkey
+                                                    & (SSL_kDHE | SSL_kECDHE))
+                                                   != 0));
             if (s->session->not_resumable)
                 /* do not send a session ticket */
                 s->tlsext_ticket_expected = 0;
@@ -1692,13 +1804,14 @@ WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
          * s->s3->tmp.new_cipher- the new cipher to use.
          */
 
-        /* Handles TLS extensions that we couldn't check earlier */
-        if (s->version >= SSL3_VERSION) {
-            if (!ssl_check_clienthello_tlsext_late(s, &al)) {
-                SSLerr(SSL_F_TLS_POST_PROCESS_CLIENT_HELLO,
-                       SSL_R_CLIENTHELLO_TLSEXT);
-                goto f_err;
-            }
+        /*
+         * Call status_request callback if needed. Has to be done after the
+         * certificate callbacks etc above.
+         */
+        if (!tls_handle_status_request(s, &al)) {
+            SSLerr(SSL_F_TLS_POST_PROCESS_CLIENT_HELLO,
+                   SSL_R_CLIENTHELLO_TLSEXT);
+            goto f_err;
         }
 
         wst = WORK_MORE_B;
@@ -1792,18 +1905,27 @@ int tls_construct_server_hello(SSL *s, WPACKET *pkt)
         compm = s->s3->tmp.new_compression->id;
 #endif
 
-    if (!WPACKET_sub_memcpy_u8(pkt, s->session->session_id, sl)
+    if ((!SSL_IS_TLS13(s)
+                && !WPACKET_sub_memcpy_u8(pkt, s->session->session_id, sl))
             || !s->method->put_cipher_by_char(s->s3->tmp.new_cipher, pkt, &len)
-            || !WPACKET_put_bytes_u8(pkt, compm)
-            || !ssl_prepare_serverhello_tlsext(s)
-            || !ssl_add_serverhello_tlsext(s, pkt, &al)) {
+            || (!SSL_IS_TLS13(s)
+                && !WPACKET_put_bytes_u8(pkt, compm))
+               /*
+                * TODO(TLS1.3): For now we add all 1.2 and 1.3 extensions. Later
+                * we will do this based on the actual protocol
+                */
+            || !tls_construct_extensions(s, pkt,
+                                         EXT_TLS1_2_SERVER_HELLO
+                                         | EXT_TLS1_3_SERVER_HELLO
+                                         | EXT_TLS1_3_ENCRYPTED_EXTENSIONS
+                                         | EXT_TLS1_3_CERTIFICATE, &al)) {
         SSLerr(SSL_F_TLS_CONSTRUCT_SERVER_HELLO, ERR_R_INTERNAL_ERROR);
         goto err;
     }
 
     return 1;
  err:
-    ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+    ssl3_send_alert(s, SSL3_AL_FATAL, al);
     return 0;
 }
 
@@ -3123,7 +3245,7 @@ MSG_PROCESS_RETURN tls_process_client_certificate(SSL *s, PACKET *pkt)
      * Freeze the handshake buffer. For <TLS1.3 we do this after the CKE
      * message
      */
-    if (s->version == TLS1_3_VERSION && !ssl3_digest_cached_records(s, 1)) {
+    if (SSL_IS_TLS13(s) && !ssl3_digest_cached_records(s, 1)) {
         al = SSL_AD_INTERNAL_ERROR;
         SSLerr(SSL_F_TLS_PROCESS_CLIENT_CERTIFICATE, ERR_R_INTERNAL_ERROR);
         goto f_err;
@@ -3371,6 +3493,18 @@ MSG_PROCESS_RETURN tls_process_next_proto(SSL *s, PACKET *pkt)
 }
 #endif
 
+static int tls_construct_encrypted_extensions(SSL *s, WPACKET *pkt)
+{
+    /* TODO(TLS1.3): Zero length encrypted extensions message for now */
+    if (!WPACKET_put_bytes_u16(pkt, 0)) {
+        SSLerr(SSL_F_TLS_CONSTRUCT_ENCRYPTED_EXTENSIONS, ERR_R_INTERNAL_ERROR);
+        ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
+        return 0;
+    }
+
+    return 1;
+}
+
 #define SSLV2_CIPHER_LEN    3
 
 STACK_OF(SSL_CIPHER) *ssl_bytes_to_cipher_list(SSL *s,