Reduce priority of 3DES ciphersuites

ChangeLog

@@ -2,6 +2,10 @@ mbed TLS ChangeLog (Sorted per branch, date)
 
 = mbed TLS 2.x.x branch released xxxx-xx-xx
 
+Features
+   * Add MBEDTLS_REMOVE_3DES_CIPHERSUITES to allow removing 3DES ciphersuites
+     from the default list (inactive by default).
+
 Bugfix
    * Fix a compilation issue with mbedtls_ecp_restart_ctx not being defined
      when MBEDTLS_ECP_ALT is defined. Reported by jwhui. Fixes #2242.
@@ -37,6 +41,7 @@ Changes
    * Ensure that ssl-opt.h can be run in OS X. #2029
    * Reduce the complexity of the timing tests. They were assuming more than the
      underlying OS actually guarantees.
+   * Ciphersuites based on 3DES now have the lowest priority by default.
 
 = mbed TLS 2.16.0 branch released 2018-12-21
 

include/mbedtls/config.h

@@ -686,6 +686,19 @@
  */
 #define MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 
+/**
+ * \def MBEDTLS_REMOVE_3DES_CIPHERSUITES
+ *
+ * Remove 3DES ciphersuites by default in SSL / TLS.
+ * This flag removes the ciphersuites based on 3DES from the default list as
+ * returned by mbedtls_ssl_list_ciphersuites(). However, it is still possible
+ * to enable (some of) them with mbedtls_ssl_conf_ciphersuites() by including
+ * them explicitly.
+ *
+ * Comment this macro to keep 3DES in the default ciphersuite list.
+ */
+#define MBEDTLS_REMOVE_3DES_CIPHERSUITES
+
 /**
  * \def MBEDTLS_ECP_DP_SECP192R1_ENABLED
  *

library/ssl_ciphersuites.c

@@ -43,11 +43,11 @@
 /*
  * Ordered from most preferred to least preferred in terms of security.
  *
- * Current rule (except rc4, weak and null which come last):
+ * Current rule (except RC4 and 3DES, weak and null which come last):
  * 1. By key exchange:
  *    Forward-secure non-PSK > forward-secure PSK > ECJPAKE > other non-PSK > other PSK
  * 2. By key length and cipher:
- *    ChaCha > AES-256 > Camellia-256 > ARIA-256 > AES-128 > Camellia-128 > ARIA-128 > 3DES
+ *    ChaCha > AES-256 > Camellia-256 > ARIA-256 > AES-128 > Camellia-128 > ARIA-128
  * 3. By cipher mode when relevant GCM > CCM > CBC > CCM_8
  * 4. By hash function used when relevant
  * 5. By key exchange/auth again: EC > non-EC
@@ -126,11 +126,6 @@ static const int ciphersuite_preference[] =
     MBEDTLS_TLS_ECDHE_RSA_WITH_ARIA_128_CBC_SHA256,
     MBEDTLS_TLS_DHE_RSA_WITH_ARIA_128_CBC_SHA256,
 
-    /* All remaining >= 128-bit ephemeral suites */
-    MBEDTLS_TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA,
-    MBEDTLS_TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA,
-    MBEDTLS_TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA,
-
     /* The PSK ephemeral suites */
     MBEDTLS_TLS_ECDHE_PSK_WITH_CHACHA20_POLY1305_SHA256,
     MBEDTLS_TLS_DHE_PSK_WITH_CHACHA20_POLY1305_SHA256,
@@ -162,9 +157,6 @@ static const int ciphersuite_preference[] =
     MBEDTLS_TLS_ECDHE_PSK_WITH_ARIA_128_CBC_SHA256,
     MBEDTLS_TLS_DHE_PSK_WITH_ARIA_128_CBC_SHA256,
 
-    MBEDTLS_TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA,
-    MBEDTLS_TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA,
-
     /* The ECJPAKE suite */
     MBEDTLS_TLS_ECJPAKE_WITH_AES_128_CCM_8,
 
@@ -228,11 +220,6 @@ static const int ciphersuite_preference[] =
     MBEDTLS_TLS_ECDH_RSA_WITH_ARIA_128_CBC_SHA256,
     MBEDTLS_TLS_RSA_WITH_ARIA_128_CBC_SHA256,
 
-    /* All remaining >= 128-bit suites */
-    MBEDTLS_TLS_RSA_WITH_3DES_EDE_CBC_SHA,
-    MBEDTLS_TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA,
-    MBEDTLS_TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA,
-
     /* The RSA PSK suites */
     MBEDTLS_TLS_RSA_PSK_WITH_CHACHA20_POLY1305_SHA256,
     MBEDTLS_TLS_RSA_PSK_WITH_AES_256_GCM_SHA384,
@@ -251,8 +238,6 @@ static const int ciphersuite_preference[] =
     MBEDTLS_TLS_RSA_PSK_WITH_ARIA_128_GCM_SHA256,
     MBEDTLS_TLS_RSA_PSK_WITH_ARIA_128_CBC_SHA256,
 
-    MBEDTLS_TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA,
-
     /* The PSK suites */
     MBEDTLS_TLS_PSK_WITH_CHACHA20_POLY1305_SHA256,
     MBEDTLS_TLS_PSK_WITH_AES_256_GCM_SHA384,
@@ -275,6 +260,16 @@ static const int ciphersuite_preference[] =
     MBEDTLS_TLS_PSK_WITH_ARIA_128_GCM_SHA256,
     MBEDTLS_TLS_PSK_WITH_ARIA_128_CBC_SHA256,
 
+    /* 3DES suites */
+    MBEDTLS_TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_RSA_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA,
+    MBEDTLS_TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA,
     MBEDTLS_TLS_PSK_WITH_3DES_EDE_CBC_SHA,
 
     /* RC4 suites */
@@ -2187,6 +2182,26 @@ const int *mbedtls_ssl_list_ciphersuites( void )
 static int supported_ciphersuites[MAX_CIPHERSUITES];
 static int supported_init = 0;
 
+static int ciphersuite_is_removed( const mbedtls_ssl_ciphersuite_t *cs_info )
+{
+    (void)cs_info;
+
+#if defined(MBEDTLS_REMOVE_ARC4_CIPHERSUITES)
+    if( cs_info->cipher == MBEDTLS_CIPHER_ARC4_128 )
+        return( 1 );
+#endif /* MBEDTLS_REMOVE_ARC4_CIPHERSUITES */
+
+#if defined(MBEDTLS_REMOVE_3DES_CIPHERSUITES)
+    if( cs_info->cipher == MBEDTLS_CIPHER_DES_EDE3_ECB ||
+        cs_info->cipher == MBEDTLS_CIPHER_DES_EDE3_CBC )
+    {
+        return( 1 );
+    }
+#endif /* MBEDTLS_REMOVE_3DES_CIPHERSUITES */
+
+    return( 0 );
+}
+
 const int *mbedtls_ssl_list_ciphersuites( void )
 {
     /*
@@ -2202,15 +2217,13 @@ const int *mbedtls_ssl_list_ciphersuites( void )
              *p != 0 && q < supported_ciphersuites + MAX_CIPHERSUITES - 1;
              p++ )
         {
-#if defined(MBEDTLS_REMOVE_ARC4_CIPHERSUITES)
             const mbedtls_ssl_ciphersuite_t *cs_info;
             if( ( cs_info = mbedtls_ssl_ciphersuite_from_id( *p ) ) != NULL &&
-                cs_info->cipher != MBEDTLS_CIPHER_ARC4_128 )
+                !ciphersuite_is_removed( cs_info ) )
-#else
+            {
-            if( mbedtls_ssl_ciphersuite_from_id( *p ) != NULL )
-#endif
                 *(q++) = *p;
             }
+        }
         *q = 0;
 
         supported_init = 1;

library/version_features.c

@@ -300,6 +300,9 @@ static const char *features[] = {
 #if defined(MBEDTLS_REMOVE_ARC4_CIPHERSUITES)
     "MBEDTLS_REMOVE_ARC4_CIPHERSUITES",
 #endif /* MBEDTLS_REMOVE_ARC4_CIPHERSUITES */
+#if defined(MBEDTLS_REMOVE_3DES_CIPHERSUITES)
+    "MBEDTLS_REMOVE_3DES_CIPHERSUITES",
+#endif /* MBEDTLS_REMOVE_3DES_CIPHERSUITES */
 #if defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED)
     "MBEDTLS_ECP_DP_SECP192R1_ENABLED",
 #endif /* MBEDTLS_ECP_DP_SECP192R1_ENABLED */

scripts/config.pl

@@ -29,6 +29,7 @@
 #   MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
 #   MBEDTLS_NO_PLATFORM_ENTROPY
 #   MBEDTLS_REMOVE_ARC4_CIPHERSUITES
+#   MBEDTLS_REMOVE_3DES_CIPHERSUITES
 #   MBEDTLS_SSL_HW_RECORD_ACCEL
 #   MBEDTLS_RSA_NO_CRT
 #   MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3
@@ -89,6 +90,7 @@ MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
 MBEDTLS_NO_PLATFORM_ENTROPY
 MBEDTLS_RSA_NO_CRT
 MBEDTLS_REMOVE_ARC4_CIPHERSUITES
+MBEDTLS_REMOVE_3DES_CIPHERSUITES
 MBEDTLS_SSL_HW_RECORD_ACCEL
 MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3
 MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION