Add support for an optional context parameter to TLS exporter

Allow an additional context value to be passed to TLS exporter as
specified in RFC 5705 section 4.

This does not yet implement it for the internal TLS implementation.
However, as currently nothing uses context yet, this will not break
anything right now. WolfSSL maintainers also stated that they are not
going to add context support yet, but would look into it if/when this is
required by a published draft or a standard.

Signed-off-by: Ervin Oro <ervin.oro@aalto.fi>

src/crypto/tls.h

@@ -370,15 +370,21 @@ int __must_check tls_connection_get_random(void *tls_ctx,
  * @tls_ctx: TLS context data from tls_init()
  * @conn: Connection context data from tls_connection_init()
  * @label: Label (e.g., description of the key) for PRF
+ * @context: Optional extra upper-layer context (max len 2^16)
+ * @context_len: The length of the context value
  * @out: Buffer for output data from TLS-PRF
  * @out_len: Length of the output buffer
  * Returns: 0 on success, -1 on failure
  *
- * Exports keying material using the mechanism described in RFC 5705.
+ * Exports keying material using the mechanism described in RFC 5705. If
+ * context is %NULL, context is not provided; otherwise, context is provided
+ * (including the case of empty context with context_len == 0).
  */
 int __must_check tls_connection_export_key(void *tls_ctx,
 					   struct tls_connection *conn,
 					   const char *label,
+					   const u8 *context,
+					   size_t context_len,
 					   u8 *out, size_t out_len);
 
 /**

src/crypto/tls_gnutls.c

@@ -898,14 +898,23 @@ int tls_connection_get_random(void *ssl_ctx, struct tls_connection *conn,
 
 
 int tls_connection_export_key(void *tls_ctx, struct tls_connection *conn,
-			      const char *label, u8 *out, size_t out_len)
+			      const char *label, const u8 *context,
+			      size_t context_len, u8 *out, size_t out_len)
 {
 	if (conn == NULL || conn->session == NULL)
 		return -1;
 
+#if GNUTLS_VERSION_NUMBER >= 0x030404
+	return gnutls_prf_rfc5705(conn->session, os_strlen(label), label,
+				  context_len, (const char *) context,
+				  out_len, (char *) out);
+#else /* 3.4.4 */
+	if (context)
+		return -1;
 	return gnutls_prf(conn->session, os_strlen(label), label,
 			  0 /* client_random first */, 0, NULL, out_len,
 			  (char *) out);
+#endif /* 3.4.4 */
 }
 
 

src/crypto/tls_internal.c

@@ -452,8 +452,11 @@ static int tls_connection_prf(void *tls_ctx, struct tls_connection *conn,
 
 
 int tls_connection_export_key(void *tls_ctx, struct tls_connection *conn,
-			      const char *label, u8 *out, size_t out_len)
+			      const char *label, const u8 *context,
+			      size_t context_len, u8 *out, size_t out_len)
 {
+	if (context)
+		return -1;
 	return tls_connection_prf(tls_ctx, conn, label, 0, 0, out, out_len);
 }
 

src/crypto/tls_none.c

@@ -94,7 +94,8 @@ int tls_connection_get_random(void *tls_ctx, struct tls_connection *conn,
 
 
 int tls_connection_export_key(void *tls_ctx, struct tls_connection *conn,
-			      const char *label, u8 *out, size_t out_len)
+			      const char *label, const u8 *context,
+			      size_t context_len, u8 *out, size_t out_len)
 {
 	return -1;
 }

src/crypto/tls_openssl.c

@@ -3908,11 +3908,13 @@ static int openssl_get_keyblock_size(SSL *ssl)
 
 
 int tls_connection_export_key(void *tls_ctx, struct tls_connection *conn,
-			      const char *label, u8 *out, size_t out_len)
+			      const char *label, const u8 *context,
+			      size_t context_len, u8 *out, size_t out_len)
 {
 	if (!conn ||
 	    SSL_export_keying_material(conn->ssl, out, out_len, label,
-				       os_strlen(label), NULL, 0, 0) != 1)
+				       os_strlen(label), context, context_len,
+				       context != NULL) != 1)
 		return -1;
 	return 0;
 }

src/crypto/tls_wolfssl.c

@@ -1973,8 +1973,11 @@ int tls_connection_get_random(void *ssl_ctx, struct tls_connection *conn,
 
 
 int tls_connection_export_key(void *tls_ctx, struct tls_connection *conn,
-			      const char *label, u8 *out, size_t out_len)
+			      const char *label, const u8 *context,
+			      size_t context_len, u8 *out, size_t out_len)
 {
+	if (context)
+		return -1;
 	if (!conn || wolfSSL_make_eap_keys(conn->ssl, out, out_len, label) != 0)
 		return -1;
 	return 0;

src/eap_peer/eap_peap.c

@@ -1084,6 +1084,7 @@ static struct wpabuf * eap_peap_process(struct eap_sm *sm, void *priv,
 				   "key derivation", label);
 			data->key_data =
 				eap_peer_tls_derive_key(sm, &data->ssl, label,
+							NULL, 0,
 							EAP_TLS_KEY_LEN +
 							EAP_EMSK_LEN);
 			if (data->key_data) {

src/eap_peer/eap_tls.c

@@ -198,6 +198,7 @@ static void eap_tls_success(struct eap_sm *sm, struct eap_tls_data *data,
 
 	eap_tls_free_key(data);
 	data->key_data = eap_peer_tls_derive_key(sm, &data->ssl, label,
+						 NULL, 0,
 						 EAP_TLS_KEY_LEN +
 						 EAP_EMSK_LEN);
 	if (data->key_data) {

src/eap_peer/eap_tls_common.c

@@ -349,6 +349,8 @@ void eap_peer_tls_ssl_deinit(struct eap_sm *sm, struct eap_ssl_data *data)
  * @sm: Pointer to EAP state machine allocated with eap_peer_sm_init()
  * @data: Data for TLS processing
  * @label: Label string for deriving the keys, e.g., "client EAP encryption"
+ * @context: Optional extra upper-layer context (max len 2^16)
+ * @context_len: The length of the context value
  * @len: Length of the key material to generate (usually 64 for MSK)
  * Returns: Pointer to allocated key on success or %NULL on failure
  *
@@ -357,9 +359,12 @@ void eap_peer_tls_ssl_deinit(struct eap_sm *sm, struct eap_ssl_data *data)
  * different label to bind the key usage into the generated material.
  *
  * The caller is responsible for freeing the returned buffer.
+ *
+ * Note: To provide the RFC 5705 context, the context variable must be non-NULL.
  */
 u8 * eap_peer_tls_derive_key(struct eap_sm *sm, struct eap_ssl_data *data,
-			     const char *label, size_t len)
+			     const char *label, const u8 *context,
+			     size_t context_len, size_t len)
 {
 	u8 *out;
 
@@ -367,8 +372,8 @@ u8 * eap_peer_tls_derive_key(struct eap_sm *sm, struct eap_ssl_data *data,
 	if (out == NULL)
 		return NULL;
 
-	if (tls_connection_export_key(data->ssl_ctx, data->conn, label, out,
+	if (tls_connection_export_key(data->ssl_ctx, data->conn, label,
-				      len)) {
+				      context, context_len, out, len)) {
 		os_free(out);
 		return NULL;
 	}
@@ -409,7 +414,7 @@ u8 * eap_peer_tls_derive_session_id(struct eap_sm *sm,
 		if (!id)
 			return NULL;
 		method_id = eap_peer_tls_derive_key(
-			sm, data, "EXPORTER_EAP_TLS_Method-Id", 64);
+			sm, data, "EXPORTER_EAP_TLS_Method-Id", NULL, 0, 64);
 		if (!method_id) {
 			os_free(id);
 			return NULL;

src/eap_peer/eap_tls_common.h

@@ -99,7 +99,8 @@ int eap_peer_tls_ssl_init(struct eap_sm *sm, struct eap_ssl_data *data,
 			  struct eap_peer_config *config, u8 eap_type);
 void eap_peer_tls_ssl_deinit(struct eap_sm *sm, struct eap_ssl_data *data);
 u8 * eap_peer_tls_derive_key(struct eap_sm *sm, struct eap_ssl_data *data,
-			     const char *label, size_t len);
+			     const char *label, const u8 *context,
+			     size_t context_len, size_t len);
 u8 * eap_peer_tls_derive_session_id(struct eap_sm *sm,
 				    struct eap_ssl_data *data, u8 eap_type,
 				    size_t *len);

src/eap_peer/eap_ttls.c

@@ -271,6 +271,7 @@ static int eap_ttls_v0_derive_key(struct eap_sm *sm,
 	eap_ttls_free_key(data);
 	data->key_data = eap_peer_tls_derive_key(sm, &data->ssl,
 						 "ttls keying material",
+						 NULL, 0,
 						 EAP_TLS_KEY_LEN +
 						 EAP_EMSK_LEN);
 	if (!data->key_data) {
@@ -303,7 +304,8 @@ static int eap_ttls_v0_derive_key(struct eap_sm *sm,
 static u8 * eap_ttls_implicit_challenge(struct eap_sm *sm,
 					struct eap_ttls_data *data, size_t len)
 {
-	return eap_peer_tls_derive_key(sm, &data->ssl, "ttls challenge", len);
+	return eap_peer_tls_derive_key(sm, &data->ssl, "ttls challenge",
+				       NULL, 0, len);
 }
 #endif /* CONFIG_FIPS */
 

src/eap_server/eap_server_peap.c

@@ -331,7 +331,7 @@ static int eap_peap_derive_cmk(struct eap_sm *sm, struct eap_peap_data *data)
 	 * phase 1 of PEAP (based on TLS).
 	 */
 	tk = eap_server_tls_derive_key(sm, &data->ssl, "client EAP encryption",
-				       EAP_TLS_KEY_LEN);
+				       NULL, 0, EAP_TLS_KEY_LEN);
 	if (tk == NULL)
 		return -1;
 	wpa_hexdump_key(MSG_DEBUG, "EAP-PEAP: TK", tk, 60);
@@ -1333,7 +1333,7 @@ static u8 * eap_peap_getKey(struct eap_sm *sm, void *priv, size_t *len)
 
 	/* TODO: PEAPv1 - different label in some cases */
 	eapKeyData = eap_server_tls_derive_key(sm, &data->ssl,
-					       "client EAP encryption",
+					       "client EAP encryption", NULL, 0,
 					       EAP_TLS_KEY_LEN + EAP_EMSK_LEN);
 	if (eapKeyData) {
 		os_memset(eapKeyData + EAP_TLS_KEY_LEN, 0, EAP_EMSK_LEN);
@@ -1363,7 +1363,7 @@ static u8 * eap_peap_get_emsk(struct eap_sm *sm, void *priv, size_t *len)
 
 	/* TODO: PEAPv1 - different label in some cases */
 	eapKeyData = eap_server_tls_derive_key(sm, &data->ssl,
-					       "client EAP encryption",
+					       "client EAP encryption", NULL, 0,
 					       EAP_TLS_KEY_LEN + EAP_EMSK_LEN);
 	if (eapKeyData) {
 		emsk = os_memdup(eapKeyData + EAP_TLS_KEY_LEN, EAP_EMSK_LEN);

src/eap_server/eap_server_tls.c

@@ -331,6 +331,7 @@ static u8 * eap_tls_getKey(struct eap_sm *sm, void *priv, size_t *len)
 	else
 		label = "client EAP encryption";
 	eapKeyData = eap_server_tls_derive_key(sm, &data->ssl, label,
+					       NULL, 0,
 					       EAP_TLS_KEY_LEN + EAP_EMSK_LEN);
 	if (eapKeyData) {
 		*len = EAP_TLS_KEY_LEN;
@@ -359,6 +360,7 @@ static u8 * eap_tls_get_emsk(struct eap_sm *sm, void *priv, size_t *len)
 	else
 		label = "client EAP encryption";
 	eapKeyData = eap_server_tls_derive_key(sm, &data->ssl, label,
+					       NULL, 0,
 					       EAP_TLS_KEY_LEN + EAP_EMSK_LEN);
 	if (eapKeyData) {
 		emsk = os_malloc(EAP_EMSK_LEN);

src/eap_server/eap_server_tls_common.c

@@ -107,7 +107,8 @@ void eap_server_tls_ssl_deinit(struct eap_sm *sm, struct eap_ssl_data *data)
 
 
 u8 * eap_server_tls_derive_key(struct eap_sm *sm, struct eap_ssl_data *data,
-			       const char *label, size_t len)
+			       const char *label, const u8 *context,
+			       size_t context_len, size_t len)
 {
 	u8 *out;
 
@@ -115,8 +116,8 @@ u8 * eap_server_tls_derive_key(struct eap_sm *sm, struct eap_ssl_data *data,
 	if (out == NULL)
 		return NULL;
 
-	if (tls_connection_export_key(sm->ssl_ctx, data->conn, label, out,
+	if (tls_connection_export_key(sm->ssl_ctx, data->conn, label,
-				      len)) {
+				      context, context_len, out, len)) {
 		os_free(out);
 		return NULL;
 	}
@@ -157,7 +158,7 @@ u8 * eap_server_tls_derive_session_id(struct eap_sm *sm,
 		if (!id)
 			return NULL;
 		method_id = eap_server_tls_derive_key(
-			sm, data, "EXPORTER_EAP_TLS_Method-Id", 64);
+			sm, data, "EXPORTER_EAP_TLS_Method-Id", NULL, 0, 64);
 		if (!method_id) {
 			os_free(id);
 			return NULL;

src/eap_server/eap_server_ttls.c

@@ -332,7 +332,7 @@ static u8 * eap_ttls_implicit_challenge(struct eap_sm *sm,
 					struct eap_ttls_data *data, size_t len)
 {
 	return eap_server_tls_derive_key(sm, &data->ssl, "ttls challenge",
-					 len);
+					 NULL, 0, len);
 }
 
 
@@ -1268,7 +1268,7 @@ static u8 * eap_ttls_getKey(struct eap_sm *sm, void *priv, size_t *len)
 		return NULL;
 
 	eapKeyData = eap_server_tls_derive_key(sm, &data->ssl,
-					       "ttls keying material",
+					       "ttls keying material", NULL, 0,
 					       EAP_TLS_KEY_LEN);
 	if (eapKeyData) {
 		*len = EAP_TLS_KEY_LEN;
@@ -1310,7 +1310,7 @@ static u8 * eap_ttls_get_emsk(struct eap_sm *sm, void *priv, size_t *len)
 		return NULL;
 
 	eapKeyData = eap_server_tls_derive_key(sm, &data->ssl,
-					       "ttls keying material",
+					       "ttls keying material", NULL, 0,
 					       EAP_TLS_KEY_LEN + EAP_EMSK_LEN);
 	if (eapKeyData) {
 		emsk = os_malloc(EAP_EMSK_LEN);

src/eap_server/eap_tls_common.h

@@ -78,7 +78,8 @@ int eap_server_tls_ssl_init(struct eap_sm *sm, struct eap_ssl_data *data,
 			    int verify_peer, int eap_type);
 void eap_server_tls_ssl_deinit(struct eap_sm *sm, struct eap_ssl_data *data);
 u8 * eap_server_tls_derive_key(struct eap_sm *sm, struct eap_ssl_data *data,
-			       const char *label, size_t len);
+			       const char *label, const u8 *context,
+			       size_t context_len, size_t len);
 u8 * eap_server_tls_derive_session_id(struct eap_sm *sm,
 				      struct eap_ssl_data *data, u8 eap_type,
 				      size_t *len);