commit a709a0f2c62b89f11a1b277bbf13a5a2d85ce96b
author Ronald Cron <ronald.cron@arm.com> Tue Sep 27 16:46:11 2022 +0200
committer Ronald Cron <ronald.cron@arm.com> Tue Oct 25 19:05:26 2022 +0200
tree 727590a42b2973f3977db070991f1e24d98f1242
parent dd0c8f9c26b576464f72b080da7d922f2c2bce98

tls13: Declare PSK ephemeral key exchange mode first

In the PSK exchange modes extension declare first
PSK ephemeral if we support both PSK ephemeral
and PSK. This is aligned with our implementation
giving precedence to PSK ephemeral over pure PSK
and improve compatibility with GnuTLS.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>

library/ssl_tls13_client.c

diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 72f4857..ac19f63 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -648,14 +648,6 @@
      */
     p += 5;
 
-    if( mbedtls_ssl_conf_tls13_psk_enabled( ssl ) )
-    {
-        *p++ = MBEDTLS_SSL_TLS1_3_PSK_MODE_PURE;
-        ke_modes_len++;
-
-        MBEDTLS_SSL_DEBUG_MSG( 4, ( "Adding pure PSK key exchange mode" ) );
-    }
-
     if( mbedtls_ssl_conf_tls13_psk_ephemeral_enabled( ssl ) )
     {
         *p++ = MBEDTLS_SSL_TLS1_3_PSK_MODE_ECDHE;
@@ -664,6 +656,14 @@
         MBEDTLS_SSL_DEBUG_MSG( 4, ( "Adding PSK-ECDHE key exchange mode" ) );
     }
 
+    if( mbedtls_ssl_conf_tls13_psk_enabled( ssl ) )
+    {
+        *p++ = MBEDTLS_SSL_TLS1_3_PSK_MODE_PURE;
+        ke_modes_len++;
+
+        MBEDTLS_SSL_DEBUG_MSG( 4, ( "Adding pure PSK key exchange mode" ) );
+    }
+
     /* Now write the extension and ke_modes length */
     MBEDTLS_PUT_UINT16_BE( ke_modes_len + 1, buf, 2 );
     buf[4] = ke_modes_len;