CID update to RFC 9146

The DTLS 1.2 CID specification has been published as RFC 9146. This PR updates the implementation to match the RFC content.

Signed-off-by: Hannes Tschofenig <hannes.tschofenig@arm.com>

include/mbedtls/check_config.h

@@ -839,6 +839,12 @@
 #error "MBEDTLS_SSL_CID_OUT_LEN_MAX too large (max 255)"
 #endif
 
+#if !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)            &&                 \
+    defined(MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT)
+#error "MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT defined, but not all prerequsites"
+#endif
+
+
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC) &&   \
     !defined(MBEDTLS_SSL_PROTO_TLS1_2)
 #error "MBEDTLS_SSL_ENCRYPT_THEN_MAC defined, but not all prerequisites"

include/mbedtls/mbedtls_config.h

@@ -1320,9 +1320,7 @@
 /**
  * \def MBEDTLS_SSL_DTLS_CONNECTION_ID
  *
- * Enable support for the DTLS Connection ID extension
- * (version draft-ietf-tls-dtls-connection-id-05,
- * https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05)
+ * Enable support for the DTLS Connection ID extension,
  * which allows to identify DTLS connections across changes
  * in the underlying transport.
  *
@@ -1331,10 +1329,6 @@
  * `mbedtls_ssl_conf_cid()`. See the corresponding documentation for
  * more information.
  *
- * \warning The Connection ID extension is still in draft state.
- *          We make no stability promises for the availability
- *          or the shape of the API controlled by this option.
- *
  * The maximum lengths of outgoing and incoming CIDs can be configured
  * through the options
  * - MBEDTLS_SSL_CID_OUT_LEN_MAX
@@ -1344,7 +1338,23 @@
  *
  * Uncomment to enable the Connection ID extension.
  */
-//#define MBEDTLS_SSL_DTLS_CONNECTION_ID
+#define MBEDTLS_SSL_DTLS_CONNECTION_ID
+
+
+/**
+ * \def MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT
+ *
+ * Defines whether RFC 9146 (default) or the legacy version
+ * (version draft-ietf-tls-dtls-connection-id-05,
+ * https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05)
+ * is used.
+ *
+ * Set the value to 0 for the standard version, and
+ * 1 for the legacy draft version.
+ *
+ * Requires: MBEDTLS_SSL_DTLS_CONNECTION_ID
+ */
+#define MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT 0
 
 /**
  * \def MBEDTLS_SSL_ASYNC_PRIVATE
@@ -3539,17 +3549,6 @@
 //#define MBEDTLS_PSK_MAX_LEN               32 /**< Max size of TLS pre-shared keys, in bytes (default 256 bits) */
 //#define MBEDTLS_SSL_COOKIE_TIMEOUT        60 /**< Default expiration delay of DTLS cookies, in seconds if HAVE_TIME, or in number of cookies issued */
 
-/** \def MBEDTLS_TLS_EXT_CID
- *
- * At the time of writing, the CID extension has not been assigned its
- * final value. Set this configuration option to make Mbed TLS use a
- * different value.
- *
- * A future minor revision of Mbed TLS may change the default value of
- * this option to match evolving standards and usage.
- */
-//#define MBEDTLS_TLS_EXT_CID                        254
-
 /**
  * Complete list of ciphersuites to use, in order of preference.
  *

include/mbedtls/ssl.h

@@ -401,7 +401,13 @@
 #define MBEDTLS_SSL_CID_TLS1_3_PADDING_GRANULARITY 16
 #endif
 
-/** \} name SECTION: Module settings */
+/*
+ * Default to standard CID mode
+ */
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID) && \
+    !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT)
+#define MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT 0
+#endif
 
 /*
  * Length of the verify data for secure renegotiation
@@ -571,15 +577,10 @@
 #define MBEDTLS_TLS_EXT_SIG_ALG_CERT                50 /* RFC 8446 TLS 1.3 */
 #define MBEDTLS_TLS_EXT_KEY_SHARE                   51 /* RFC 8446 TLS 1.3 */
 
-/* The value of the CID extension is still TBD as of
- * draft-ietf-tls-dtls-connection-id-05
- * (https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05).
- *
- * A future minor revision of Mbed TLS may change the default value of
- * this option to match evolving standards and usage.
- */
-#if !defined(MBEDTLS_TLS_EXT_CID)
-#define MBEDTLS_TLS_EXT_CID                        254 /* TBD */
+#if MBEDTLS_SSL_DTLS_CONNECTION_ID_COMPAT == 0
+#define MBEDTLS_TLS_EXT_CID                         54 /* RFC 9146 DTLS 1.2 CID */
+#else
+#define MBEDTLS_TLS_EXT_CID                        254 /* Pre-RFC 9146 DTLS 1.2 CID */
 #endif
 
 #define MBEDTLS_TLS_EXT_ECJPAKE_KKPP               256 /* experimental */
@@ -2003,8 +2004,9 @@ void mbedtls_ssl_set_bio( mbedtls_ssl_context *ssl,
  * \brief             Configure the use of the Connection ID (CID)
  *                    extension in the next handshake.
  *
- *                    Reference: draft-ietf-tls-dtls-connection-id-05
+ *                    Reference: RFC 9146 (or draft-ietf-tls-dtls-connection-id-05
  *                    https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-05
+ *                    for legacy version)
  *
  *                    The DTLS CID extension allows the reliable association of
  *                    DTLS records to DTLS connections across changes in the