Check whether the TLS stack supports channel binding.

Add a runtime check per TLS stack which returns whether channel binding is
supported or not.

This fixes #270

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

Makefile.am

@@ -17,7 +17,9 @@ if TLS_WITH_GNUTLS
 SSL_CFLAGS = @gnutls_CFLAGS@
 SSL_LIBS = @gnutls_LIBS@
 else
-if !TLS_WITH_SCHANNEL
+if TLS_WITH_SCHANNEL
+SSL_CFLAGS = -DSTROPHE_TLS_SCHANNEL
+else
 SSL_CFLAGS = @openssl_CFLAGS@
 SSL_LIBS = @openssl_LIBS@
 endif

src/auth.c

@@ -602,8 +602,10 @@ static int _make_scram_init_msg(struct scram_user_data *scram)
         l = strophe_snprintf(message, message_len, "p=%s,,n=%s,r=%s",
                              binding_type, node, buf);
     } else {
-        l = strophe_snprintf(message, message_len, "%c,,n=%s,r=%s",
+        l = strophe_snprintf(
-                             is_secured ? 'y' : 'n', node, buf);
+            message, message_len, "%c,,n=%s,r=%s",
+            is_secured && tls_supports_channel_binding(conn->tls) ? 'y' : 'n',
+            node, buf);
     }
     if (l < 0 || (size_t)l >= message_len) {
         goto err_msg;

src/scram.c

@@ -93,12 +93,14 @@ const struct hash_alg scram_sha512_plus = {
  * https://datatracker.ietf.org/doc/html/draft-ietf-kitten-password-storage
  */
 const struct hash_alg *scram_algs[] = {
+#if !defined(STROPHE_TLS_SCHANNEL)
     /* *1 */
     &scram_sha512_plus,
     /* *1 */
     &scram_sha256_plus,
     /* *1 */
     &scram_sha1_plus,
+#endif
     /* *1 */
     &scram_sha512,
     /* *1 */

src/tls.h

@@ -45,6 +45,7 @@ unsigned int tls_id_on_xmppaddr_num(xmpp_conn_t *conn);
 
 xmpp_tlscert_t *tls_peer_cert(xmpp_conn_t *conn);
 int tls_set_credentials(tls_t *tls, const char *cafilename);
+int tls_supports_channel_binding(tls_t *tls);
 int tls_init_channel_binding(tls_t *tls,
                              const char **binding_prefix,
                              size_t *binding_prefix_len);

src/tls_dummy.c

@@ -75,6 +75,12 @@ int tls_set_credentials(tls_t *tls, const char *cafilename)
     return -1;
 }
 
+int tls_supports_channel_binding(tls_t *tls)
+{
+    UNUSED(tls);
+    return 0;
+}
+
 int tls_init_channel_binding(tls_t *tls,
                              const char **binding_prefix,
                              size_t *binding_prefix_len)

src/tls_gnutls.c

@@ -577,6 +577,20 @@ int tls_set_credentials(tls_t *tls, const char *cafilename)
     return err == GNUTLS_E_SUCCESS;
 }
 
+int tls_supports_channel_binding(tls_t *tls)
+{
+    switch (gnutls_protocol_get_version(tls->session)) {
+    case GNUTLS_SSL3:
+    case GNUTLS_TLS1_0:
+    case GNUTLS_TLS1_1:
+    case GNUTLS_TLS1_2:
+    case GNUTLS_TLS1_3:
+        return 1;
+    default:
+        return 0;
+    }
+}
+
 int tls_init_channel_binding(tls_t *tls,
                              const char **binding_prefix,
                              size_t *binding_prefix_len)

src/tls_openssl.c

@@ -793,6 +793,22 @@ int tls_set_credentials(tls_t *tls, const char *cafilename)
     return -1;
 }
 
+int tls_supports_channel_binding(tls_t *tls)
+{
+    switch (SSL_version(tls->ssl)) {
+    case SSL3_VERSION:
+    case TLS1_VERSION:
+    case TLS1_1_VERSION:
+    case TLS1_2_VERSION:
+#ifdef TLS1_3_VERSION
+    case TLS1_3_VERSION:
+#endif
+        return 1;
+    default:
+        return 0;
+    }
+}
+
 int tls_init_channel_binding(tls_t *tls,
                              const char **binding_prefix,
                              size_t *binding_prefix_len)

src/tls_schannel.c

@@ -237,6 +237,12 @@ int tls_set_credentials(tls_t *tls, const char *cafilename)
     return -1;
 }
 
+int tls_supports_channel_binding(tls_t *tls)
+{
+    UNUSED(tls);
+    return 0;
+}
+
 int tls_init_channel_binding(tls_t *tls,
                              const char **binding_prefix,
                              size_t *binding_prefix_len)