ECDSA: Add mbedtls_ecdsa_can_do

include/mbedtls/ecdsa.h

@@ -125,6 +125,16 @@ typedef void mbedtls_ecdsa_restart_ctx;
 
 #endif /* MBEDTLS_ECP_RESTARTABLE */
 
+/**
+ * \brief          This function checks whether a given group can be used
+ *                 for ECDSA.
+ *
+ * \param gid      The ECP group ID to check.
+ *
+ * \return         \c 1 if the group can be used, \c 0 otherwise
+ */
+int mbedtls_ecdsa_can_do( mbedtls_ecp_group_id gid );
+
 /**
  * \brief           This function computes the ECDSA signature of a
  *                  previously-hashed message.
@@ -469,7 +479,6 @@ int mbedtls_ecdsa_read_signature_restartable( mbedtls_ecdsa_context *ctx,
                           const unsigned char *hash, size_t hlen,
                           const unsigned char *sig, size_t slen,
                           mbedtls_ecdsa_restart_ctx *rs_ctx );
-
 /**
  * \brief          This function generates an ECDSA keypair on the given curve.
  *

library/ecdsa.c

@@ -263,9 +263,7 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
     mbedtls_mpi *pk = &k, *pr = r;
 
     /* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
-    if( grp->id == MBEDTLS_ECP_DP_CURVE25519 ||
-        grp->id == MBEDTLS_ECP_DP_CURVE448 ||
-        grp->N.p == NULL )
+    if( !mbedtls_ecdsa_can_do( grp->id ) || grp->N.p == NULL )
         return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
 
     /* Make sure d is in range 1..n-1 */
@@ -380,6 +378,20 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
     return( ret );
 }
 
+int mbedtls_ecdsa_can_do( mbedtls_ecp_group_id gid )
+{
+    switch( gid )
+    {
+#ifdef MBEDTLS_ECP_DP_CURVE25519_ENABLED
+    case MBEDTLS_ECP_DP_CURVE25519: return 0;
+#endif
+#ifdef MBEDTLS_ECP_DP_CURVE448_ENABLED
+    case MBEDTLS_ECP_DP_CURVE448: return 0;
+#endif
+    default: return 1;
+    }
+}
+
 /*
  * Compute ECDSA signature of a hashed message
  */
@@ -504,7 +516,7 @@ static int ecdsa_verify_restartable( mbedtls_ecp_group *grp,
     mbedtls_mpi_init( &u1 ); mbedtls_mpi_init( &u2 );
 
     /* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
-    if( grp->N.p == NULL )
+    if( !mbedtls_ecdsa_can_do( grp->id ) || grp->N.p == NULL )
         return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
 
     ECDSA_RS_ENTER( ver );

programs/test/benchmark.c

@@ -835,6 +835,9 @@ int main( int argc, char *argv[] )
              curve_info->grp_id != MBEDTLS_ECP_DP_NONE;
              curve_info++ )
         {
+            if( mbedtls_ecdsa_can_do( curve_info->grp_id ) == 0 )
+                continue;
+
             mbedtls_ecdsa_init( &ecdsa );
 
             if( mbedtls_ecdsa_genkey( &ecdsa, curve_info->grp_id, myrand, NULL ) != 0 )
@@ -854,6 +857,9 @@ int main( int argc, char *argv[] )
              curve_info->grp_id != MBEDTLS_ECP_DP_NONE;
              curve_info++ )
         {
+            if( mbedtls_ecdsa_can_do( curve_info->grp_id ) == 0 )
+                continue;
+
             mbedtls_ecdsa_init( &ecdsa );
 
             if( mbedtls_ecdsa_genkey( &ecdsa, curve_info->grp_id, myrand, NULL ) != 0 ||