[tls] Unify handling of ServerKeyExchange and ClientKeyExchange

Restructure the key exchange abstractions to provide a single method
to parse the suite-specific ServerKeyParams structure, with the
signature verification subsequently performed by the caller.

Reduce the suite-specific variation for ClientKeyExchange to a single
parameter that specifies the length of the initial length field, since
this is the only substantive difference between the various mechanisms
as far as the ClientKeyExchange record format is concerned.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/tls.h

@@ -48,6 +48,9 @@ struct tls_header {
 /** TLS version 1.2 */
 #define TLS_VERSION_TLS_1_2 0x0303
 
+/** TLS version 1.3 */
+#define TLS_VERSION_TLS_1_3 0x0304
+
 /** Change cipher content type */
 #define TLS_TYPE_CHANGE_CIPHER 20
 
@@ -192,27 +195,36 @@ enum tls_tx_pending {
 	TLS_TX_FINISHED = 0x0020,
 };
 
+/** TLS key exchange parameters */
+struct tls_key_exchange_parameters {
+	/** Length of parameters (excluding trailing signature) */
+	size_t len;
+	/** Partner key */
+	const void *partner;
+	/** Length of partner key */
+	size_t partner_len;
+};
+
 /** A TLS key exchange algorithm */
 struct tls_key_exchange_algorithm {
 	/** Algorithm name */
 	const char *name;
+	/** Fixed key exchange algorithm (if set) */
+	struct exchange_algorithm *exchange;
 	/**
-	 * Receive new Server Key Exchange record using ECDHE key exchange
+	 * Parse key exchange parameters from Server Key Exchange record
 	 *
 	 * @v tls		TLS connection
 	 * @v data		Server Key Exchange handshake record
 	 * @v len		Length of Server Key Exchange handshake record
+	 * @v params		Key exchange parameters to fill in
 	 * @ret rc		Return status code
 	 */
-	int ( * server ) ( struct tls_connection *tls, const void *data,
-			   size_t len );
-	/**
-	 * Transmit Client Key Exchange record
-	 *
-	 * @v tls		TLS connection
-	 * @ret rc		Return status code
-	 */
-	int ( * client ) ( struct tls_connection *tls );
+	int ( * parse ) ( struct tls_connection *tls,
+			  const void *data, size_t len,
+			  struct tls_key_exchange_parameters *params );
+	/** Length of length field in Client Key Exchange record */
+	uint8_t len_len;
 };
 
 /** A TLS cipher suite */
@@ -376,8 +388,6 @@ struct tls_key_schedule {
 	 * derivation.
 	 */
 	struct digest_algorithm *digest;
-	/** Key exchange algorithm */
-	struct exchange_algorithm *exchange;
 	/** Schedule holds secret key material
 	 *
 	 * This flag is set when shared secret key material is
@@ -548,6 +558,8 @@ struct tls_connection {
 
 	/** Protocol version */
 	uint16_t version;
+	/** Key exchange algorithm */
+	struct exchange_algorithm *exchange;
 	/** Secure renegotiation flag */
 	int secure_renegotiation;
 	/** Extended master secret flag */