TLS 1.3: SRV: Implement mbedtls_ssl_read_early_data()

include/mbedtls/ssl.h

@@ -90,8 +90,18 @@
 #define MBEDTLS_ERR_SSL_RECEIVED_NEW_SESSION_TICKET       -0x7B00
 /** Not possible to read early data */
 #define MBEDTLS_ERR_SSL_CANNOT_READ_EARLY_DATA            -0x7B80
+/**
+ * Early data has been received as part of an on-going handshake.
+ * This error code can be returned only on server side if and only if early
+ * data has been enabled by means of the mbedtls_ssl_conf_early_data() API.
+ * This error code can then be returned by mbedtls_ssl_handshake(),
+ * mbedtls_ssl_handshake_step(), mbedtls_ssl_read() or mbedtls_ssl_write() if
+ * early data has been received as part of the handshake sequence they
+ * triggered. To read the early data, call mbedtls_ssl_read_early_data().
+ */
+#define MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA               -0x7C00
 /** Not possible to write early data */
-#define MBEDTLS_ERR_SSL_CANNOT_WRITE_EARLY_DATA           -0x7C00
+#define MBEDTLS_ERR_SSL_CANNOT_WRITE_EARLY_DATA           -0x7C80
 /* Error space gap */
 /* Error space gap */
 /* Error space gap */
@@ -1644,6 +1654,18 @@ struct mbedtls_ssl_context {
      */
     mbedtls_ssl_protocol_version MBEDTLS_PRIVATE(tls_version);
 
+#if defined(MBEDTLS_SSL_EARLY_DATA) && defined(MBEDTLS_SSL_CLI_C)
+    /**
+     *  Status of the negotiation of the use of early data.
+     *  See the documentation of mbedtls_ssl_get_early_data_status() for more
+     *  information.
+     *
+     *  Reset to #MBEDTLS_SSL_EARLY_DATA_STATUS_NOT_SENT when the context is
+     *  reset.
+     */
+    int MBEDTLS_PRIVATE(early_data_status);
+#endif
+
     unsigned MBEDTLS_PRIVATE(badmac_seen);       /*!< records with a bad MAC received    */
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
@@ -1841,10 +1863,6 @@ struct mbedtls_ssl_context {
                                              *   and #MBEDTLS_SSL_CID_DISABLED. */
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
-#if defined(MBEDTLS_SSL_EARLY_DATA)
-    int MBEDTLS_PRIVATE(early_data_status);
-#endif /* MBEDTLS_SSL_EARLY_DATA && MBEDTLS_SSL_CLI_C */
-
     /** Callback to export key block and master secret                      */
     mbedtls_ssl_export_keys_t *MBEDTLS_PRIVATE(f_export_keys);
     void *MBEDTLS_PRIVATE(p_export_keys);            /*!< context for key export callback    */
@@ -1993,22 +2011,32 @@ void mbedtls_ssl_conf_transport(mbedtls_ssl_config *conf, int transport);
  */
 void mbedtls_ssl_conf_authmode(mbedtls_ssl_config *conf, int authmode);
 
-#if defined(MBEDTLS_SSL_PROTO_TLS1_3) && defined(MBEDTLS_SSL_EARLY_DATA)
+#if defined(MBEDTLS_SSL_EARLY_DATA)
 /**
  * \brief    Set the early data mode
  *           Default: disabled on server and client
  *
  * \param conf   The SSL configuration to use.
  * \param early_data_enabled can be:
  *
- *  MBEDTLS_SSL_EARLY_DATA_DISABLED:  early data functionality is disabled
- *                                    This is the default on client and server.
- *
- *  MBEDTLS_SSL_EARLY_DATA_ENABLED:  early data functionality is enabled and
- *                        may be negotiated in the handshake. Application using
- *                        early data functionality needs to be aware of the
- *                        lack of replay protection of the early data application
- *                        payloads.
+ *  MBEDTLS_SSL_EARLY_DATA_DISABLED:
+ *  Early data functionality is disabled. This is the default on client and
+ *  server.
+ *
+ *  MBEDTLS_SSL_EARLY_DATA_ENABLED:
+ *  Early data functionality is enabled and may be negotiated in the handshake.
+ *  Application using early data functionality needs to be aware that the
+ *  security properties for early data (also refered to as 0-RTT data) are
+ *  weaker than those for other kinds of TLS data. See the documentation of
+ *  mbedtls_ssl_write_early_data() and mbedtls_ssl_read_early_data() for more
+ *  information.
+ *  When early data functionality is enabled on server and only in that case,
+ *  the call to one of the APIs that trigger or resume an handshake sequence,
+ *  namely mbedtls_ssl_handshake(), mbedtls_ssl_handshake_step(),
+ *  mbedtls_ssl_read() or mbedtls_ssl_write() may return with the error code
+ *  MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA indicating that some early data have
+ *  been received. To read the early data, call mbedtls_ssl_read_early_data()
+ *  before calling the original function again.
  *
  * \warning This interface is experimental and may change without notice.
  *
@@ -2048,7 +2076,7 @@ void mbedtls_ssl_conf_max_early_data_size(
     mbedtls_ssl_config *conf, uint32_t max_early_data_size);
 #endif /* MBEDTLS_SSL_SRV_C */
 
-#endif /* MBEDTLS_SSL_PROTO_TLS1_3 && MBEDTLS_SSL_EARLY_DATA */
+#endif /* MBEDTLS_SSL_EARLY_DATA */
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
 /**
@@ -4733,6 +4761,13 @@ int mbedtls_ssl_get_session(const mbedtls_ssl_context *ssl,
  * \return         #MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED if DTLS is in use
  *                 and the client did not demonstrate reachability yet - in
  *                 this case you must stop using the context (see below).
+ * \return         #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA if early data, as
+ *                 defined in RFC 8446 (TLS 1.3 specification), has been
+ *                 received as part of the handshake. This is server specific
+ *                 and may occur only if the early data feature has been
+ *                 enabled on server (see mbedtls_ssl_conf_early_data()
+ *                 documentation). You must call mbedtls_ssl_read_early_data()
+ *                 to read the early data before resuming the handshake.
  * \return         Another SSL error code - in this case you must stop using
  *                 the context (see below).
  *
@@ -4741,7 +4776,8 @@ int mbedtls_ssl_get_session(const mbedtls_ssl_context *ssl,
  *                 #MBEDTLS_ERR_SSL_WANT_READ,
  *                 #MBEDTLS_ERR_SSL_WANT_WRITE,
  *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or
- *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS,
+ *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS or
+ *                 #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA,
  *                 you must stop using the SSL context for reading or writing,
  *                 and either free it or call \c mbedtls_ssl_session_reset()
  *                 on it before re-using it for a new connection; the current
@@ -4810,8 +4846,9 @@ static inline int mbedtls_ssl_is_handshake_over(mbedtls_ssl_context *ssl)
  *
  * \warning        If this function returns something other than \c 0,
  *                 #MBEDTLS_ERR_SSL_WANT_READ, #MBEDTLS_ERR_SSL_WANT_WRITE,
- *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or
- *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS, you must stop using
+ *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS,
+ *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS or
+ *                 #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA, you must stop using
  *                 the SSL context for reading or writing, and either free it
  *                 or call \c mbedtls_ssl_session_reset() on it before
  *                 re-using it for a new connection; the current connection
@@ -4879,6 +4916,13 @@ int mbedtls_ssl_renegotiate(mbedtls_ssl_context *ssl);
  * \return         #MBEDTLS_ERR_SSL_CLIENT_RECONNECT if we're at the server
  *                 side of a DTLS connection and the client is initiating a
  *                 new connection using the same source port. See below.
+ * \return         #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA if early data, as
+ *                 defined in RFC 8446 (TLS 1.3 specification), has been
+ *                 received as part of the handshake. This is server specific
+ *                 and may occur only if the early data feature has been
+ *                 enabled on server (see mbedtls_ssl_conf_early_data()
+ *                 documentation). You must call mbedtls_ssl_read_early_data()
+ *                 to read the early data before resuming the handshake.
  * \return         Another SSL error code - in this case you must stop using
  *                 the context (see below).
  *
@@ -4887,8 +4931,9 @@ int mbedtls_ssl_renegotiate(mbedtls_ssl_context *ssl);
  *                 #MBEDTLS_ERR_SSL_WANT_READ,
  *                 #MBEDTLS_ERR_SSL_WANT_WRITE,
  *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS,
- *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS or
- *                 #MBEDTLS_ERR_SSL_CLIENT_RECONNECT,
+ *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS,
+ *                 #MBEDTLS_ERR_SSL_CLIENT_RECONNECT or
+ *                 #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA,
  *                 you must stop using the SSL context for reading or writing,
  *                 and either free it or call \c mbedtls_ssl_session_reset()
  *                 on it before re-using it for a new connection; the current
@@ -4953,15 +4998,23 @@ int mbedtls_ssl_read(mbedtls_ssl_context *ssl, unsigned char *buf, size_t len);
  *                 operation is in progress (see mbedtls_ecp_set_max_ops()) -
  *                 in this case you must call this function again to complete
  *                 the handshake when you're done attending other tasks.
+ * \return         #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA if early data, as
+ *                 defined in RFC 8446 (TLS 1.3 specification), has been
+ *                 received as part of the handshake. This is server specific
+ *                 and may occur only if the early data feature has been
+ *                 enabled on server (see mbedtls_ssl_conf_early_data()
+ *                 documentation). You must call mbedtls_ssl_read_early_data()
+ *                 to read the early data before resuming the handshake.
  * \return         Another SSL error code - in this case you must stop using
  *                 the context (see below).
  *
  * \warning        If this function returns something other than
  *                 a non-negative value,
  *                 #MBEDTLS_ERR_SSL_WANT_READ,
  *                 #MBEDTLS_ERR_SSL_WANT_WRITE,
- *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS or
- *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS,
+ *                 #MBEDTLS_ERR_SSL_ASYNC_IN_PROGRESS,
+ *                 #MBEDTLS_ERR_SSL_CRYPTO_IN_PROGRESS or
+ *                 #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA,
  *                 you must stop using the SSL context for reading or writing,
  *                 and either free it or call \c mbedtls_ssl_session_reset()
  *                 on it before re-using it for a new connection; the current
@@ -5029,48 +5082,46 @@ int mbedtls_ssl_close_notify(mbedtls_ssl_context *ssl);
 
 #if defined(MBEDTLS_SSL_SRV_C)
 /**
- * \brief          Read at most 'len' application data bytes while performing
- *                 the handshake (early data).
- *
- * \note           This function behaves mainly as mbedtls_ssl_read(). The
- *                 specification of mbedtls_ssl_read() relevant to TLS 1.3
- *                 (thus not the parts specific to (D)TLS 1.2) applies to this
- *                 function and the present documentation is restricted to the
- *                 differences with mbedtls_ssl_read().
- *
- * \param ssl      SSL context
+ * \brief          Read at most 'len' bytes of early data
+ *
+ * \note           This API is server specific.
+ *
+ * \warning        Early data is defined in the TLS 1.3 specification, RFC 8446.
+ *                 IMPORTANT NOTE from section 2.3 of the specification:
+ *
+ *                 The security properties for 0-RTT data are weaker than
+ *                 those for other kinds of TLS data. Specifically:
+ *                 - This data is not forward secret, as it is encrypted
+ *                   solely under keys derived using the offered PSK.
+ *                 - There are no guarantees of non-replay between connections.
+ *                   Protection against replay for ordinary TLS 1.3 1-RTT data
+ *                   is provided via the server's Random value, but 0-RTT data
+ *                   does not depend on the ServerHello and therefore has
+ *                   weaker guarantees. This is especially relevant if the
+ *                   data is authenticated either with TLS client
+ *                   authentication or inside the application protocol. The
+ *                   same warnings apply to any use of the
+ *                   early_exporter_master_secret.
+ *
+ * \note           This function is used in conjunction with
+ *                 mbedtls_ssl_handshake(), mbedtls_ssl_handshake_step(),
+ *                 mbedtls_ssl_read() and mbedtls_ssl_write() to read early
+ *                 data when these functions return
+ *                 #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA.
+ *
+ * \param ssl      SSL context, it must have been initialized and set up.
  * \param buf      buffer that will hold the data
  * \param len      maximum number of bytes to read
  *
- * \return         One additional specific return value:
- *                 #MBEDTLS_ERR_SSL_CANNOT_READ_EARLY_DATA.
- *
- *                 #MBEDTLS_ERR_SSL_CANNOT_READ_EARLY_DATA is returned when it
- *                 is not possible to read early data for the SSL context
- *                 \p ssl.
- *
- *                 It may have been possible and it is not possible
- *                 anymore because the server received the End of Early Data
- *                 message or the maximum number of allowed early data for the
- *                 PSK in use has been reached.
- *
- *                 It may never have been possible and will never be possible
- *                 for the SSL context \p ssl because the use of early data
- *                 is disabled for that context or more generally the context
- *                 is not suitably configured to enable early data or the
- *                 client does not use early data or the first call to the
- *                 function was done while the handshake was already too
- *                 advanced to gather and accept early data.
- *
- *                 It is not possible to read early data for the SSL context
- *                 \p ssl but this does not preclude for using it with
- *                 mbedtls_ssl_write(), mbedtls_ssl_read() or
- *                 mbedtls_ssl_handshake().
- *
- * \note           When a server wants to retrieve early data, it is expected
- *                 that this function starts the handshake for the SSL context
- *                 \p ssl. But this is not mandatory.
- *
+ * \return         The (positive) number of bytes read if successful.
+ * \return         #MBEDTLS_ERR_SSL_BAD_INPUT_DATA if input data is invalid.
+ * \return         #MBEDTLS_ERR_SSL_CANNOT_READ_EARLY_DATA if it is not
+ *                 possible to read early data for the SSL context \p ssl. Note
+ *                 that this function is intended to be called for an SSL
+ *                 context \p ssl only after a call to mbedtls_ssl_handshake(),
+ *                 mbedtls_ssl_handshake_step(), mbedtls_ssl_read() or
+ *                 mbedtls_ssl_write() for \p ssl that has returned
+ *                 #MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA.
  */
 int mbedtls_ssl_read_early_data(mbedtls_ssl_context *ssl,
                                 unsigned char *buf, size_t len);

library/ssl_misc.h

@@ -650,6 +650,10 @@ struct mbedtls_ssl_handshake_params {
     /* Flag indicating if a CertificateRequest message has been sent
      * to the client or not. */
     uint8_t certificate_request_sent;
+#if defined(MBEDTLS_SSL_EARLY_DATA)
+    /* Flag indicating if the server has accepted early data or not. */
+    uint8_t early_data_accepted;
+#endif
 #endif /* MBEDTLS_SSL_SRV_C */
 
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
@@ -2130,12 +2134,6 @@ int mbedtls_ssl_tls13_write_early_data_ext(mbedtls_ssl_context *ssl,
                                            unsigned char *buf,
                                            const unsigned char *end,
                                            size_t *out_len);
-
-#if defined(MBEDTLS_SSL_SRV_C)
-#define MBEDTLS_SSL_EARLY_DATA_STATUS_NOT_RECEIVED \
-    MBEDTLS_SSL_EARLY_DATA_STATUS_NOT_SENT
-#endif /* MBEDTLS_SSL_SRV_C */
-
 #endif /* MBEDTLS_SSL_EARLY_DATA */
 
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */