Since Power Analysis on smart cards was introduced by Paul Kocher [7], many countermeasures have been proposed to protect implementations of cryptographic algorithms. In this paper we propose a new protection principle: the transformed masking method. We apply this method to protect two of the most popular block ciphers: DES and the AES Rijndael. To this end we introduce some transformed S-boxes for DES and a new masking method and its applications to the non-linear part of Rijndael.