Add injection of dummy's ChangeCipherSpec for middlebox compatibility

Signed-off-by: Ronald Cron <ronald.cron@arm.com>

include/mbedtls/ssl.h

@@ -641,6 +641,9 @@ typedef enum
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
     MBEDTLS_SSL_ENCRYPTED_EXTENSIONS,
     MBEDTLS_SSL_CLIENT_CERTIFICATE_VERIFY,
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+    MBEDTLS_SSL_CLIENT_CCS_AFTER_SERVER_FINISHED,
+#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
 }
 mbedtls_ssl_states;

library/ssl_misc.h

@@ -1676,6 +1676,12 @@ int mbedtls_ssl_tls13_process_certificate( mbedtls_ssl_context *ssl );
  */
 int mbedtls_ssl_tls13_process_certificate_verify( mbedtls_ssl_context *ssl );
 
+/*
+ * Write of dummy-CCS's for middlebox compatibility
+ */
+int mbedtls_ssl_tls13_write_change_cipher_spec( mbedtls_ssl_context *ssl );
+
+
 /*
  * Write TLS 1.3 handshake message tail
  */

library/ssl_tls13_client.c

@@ -723,8 +723,18 @@ static int ssl_tls13_write_client_hello_body( mbedtls_ssl_context *ssl,
      * ( also known as ossification ). Otherwise, it MUST be set as a zero-length
      * vector ( i.e., a zero-valued single byte length field ).
      */
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+    MBEDTLS_SSL_CHK_BUF_PTR( p, end, ssl->session_negotiate->id_len + 1 );
+    *p++ = (unsigned char)ssl->session_negotiate->id_len;
+    memcpy( p, ssl->session_negotiate->id, ssl->session_negotiate->id_len );
+    p += ssl->session_negotiate->id_len;
+
+    MBEDTLS_SSL_DEBUG_BUF( 3, "session id", ssl->session_negotiate->id,
+                              ssl->session_negotiate->id_len );
+#else
     MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 );
     *p++ = 0; /* session id length set to zero */
+#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
 
     /* Write cipher_suites */
     ret = ssl_tls13_write_client_hello_cipher_suites( ssl, p, end, &output_len );
@@ -843,6 +853,24 @@ static int ssl_tls13_prepare_client_hello( mbedtls_ssl_context *ssl )
         return( ret );
     }
 
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+    /*
+     * Create a session identifier for the purpose of middlebox compatibility
+     * only if one has not been created already.
+     */
+    if( ssl->session_negotiate->id_len == 0 )
+    {
+        /* Creating a session id with 32 byte length */
+        if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
+                                      ssl->session_negotiate->id, 32 ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "creating session id failed", ret );
+            return( ret );
+        }
+        ssl->session_negotiate->id_len = 32;
+    }
+#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
+
     return( 0 );
 }
 
@@ -1611,8 +1639,14 @@ static int ssl_tls13_process_server_finished( mbedtls_ssl_context *ssl )
     if( ret != 0 )
         return( ret );
 
-    mbedtls_ssl_set_outbound_transform( ssl, ssl->handshake->transform_handshake );
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+    mbedtls_ssl_handshake_set_state(
+        ssl,
+        MBEDTLS_SSL_CLIENT_CCS_AFTER_SERVER_FINISHED );
+#else
     mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_CLIENT_FINISHED );
+#endif
+
     return( 0 );
 }
 
@@ -1623,6 +1657,8 @@ static int ssl_tls13_write_client_finished( mbedtls_ssl_context *ssl )
 {
     int ret;
 
+    mbedtls_ssl_set_outbound_transform( ssl, ssl->handshake->transform_handshake );
+
     ret = mbedtls_ssl_tls13_write_finished_message( ssl );
     if( ret != 0 )
         return( ret );
@@ -1713,6 +1749,15 @@ int mbedtls_ssl_tls13_handshake_client_step( mbedtls_ssl_context *ssl )
             ret = ssl_tls13_handshake_wrapup( ssl );
             break;
 
+        /*
+         * Injection of dummy-CCS's for middlebox compatibility
+         */
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+        case MBEDTLS_SSL_CLIENT_CCS_AFTER_SERVER_FINISHED:
+            ret = mbedtls_ssl_tls13_write_change_cipher_spec( ssl );
+            break;
+#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
+
         default:
             MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid state %d", ssl->state ) );
             return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

library/ssl_tls13_generic.c

@@ -1148,6 +1148,76 @@ void mbedtls_ssl_tls13_handshake_wrapup( mbedtls_ssl_context *ssl )
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "<= handshake wrapup" ) );
 }
 
+/*
+ *
+ * STATE HANDLING: Write ChangeCipherSpec
+ *
+ */
+#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+
+static int ssl_tls13_write_change_cipher_spec_body( mbedtls_ssl_context *ssl,
+                                                    unsigned char *buf,
+                                                    unsigned char *end,
+                                                    size_t *olen )
+{
+    ((void) ssl);
+
+    MBEDTLS_SSL_CHK_BUF_PTR( buf, end, 1 );
+    buf[0] = 1;
+    *olen = 1;
+
+    return( 0 );
+}
+
+static int ssl_tls13_finalize_change_cipher_spec( mbedtls_ssl_context *ssl )
+{
+#if defined(MBEDTLS_SSL_SRV_C)
+    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
+        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
+    }
+#endif /* MBEDTLS_SSL_SRV_C */
+
+#if defined(MBEDTLS_SSL_CLI_C)
+    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
+    {
+        mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_CLIENT_FINISHED );
+    }
+#endif /* MBEDTLS_SSL_CLI_C */
+
+    return( 0 );
+}
+
+int mbedtls_ssl_tls13_write_change_cipher_spec( mbedtls_ssl_context *ssl )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write change cipher spec" ) );
+
+    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_flush_output( ssl ) );
+
+    /* Write CCS message */
+    MBEDTLS_SSL_PROC_CHK( ssl_tls13_write_change_cipher_spec_body(
+                              ssl, ssl->out_msg,
+                              ssl->out_msg + MBEDTLS_SSL_OUT_CONTENT_LEN,
+                              &ssl->out_msglen ) );
+
+    ssl->out_msgtype = MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC;
+
+    MBEDTLS_SSL_PROC_CHK( ssl_tls13_finalize_change_cipher_spec( ssl ) );
+
+    /* Dispatch message */
+    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_record( ssl, 1 ) );
+
+cleanup:
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write change cipher spec" ) );
+    return( ret );
+}
+
+#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
+
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
 
 #endif /* MBEDTLS_SSL_TLS_C */