Check that the cipher GCM receives is a 128-bit-based cipher
diff --git a/library/gcm.c b/library/gcm.c
index e041647..1dfc199 100644
--- a/library/gcm.c
+++ b/library/gcm.c
@@ -117,6 +117,9 @@
     if( cipher_info == NULL )
         return( POLARSSL_ERR_GCM_BAD_INPUT );
 
+    if( cipher_info->block_size != 16 )
+        return( POLARSSL_ERR_GCM_BAD_INPUT );
+
     if( ( ret = cipher_init_ctx( &ctx->cipher_ctx, cipher_info ) ) != 0 )
         return( ret );