Register leakage masking using Gray code

Since their introduction in 1996, the effectiveness of side channel attacks has been highly improved and many countermeasures have been invalidated. A very common countermeasure consists in randomizing sensitive variables of algorithms by masking techniques. In this paper, we propose a new way to apply this strategy to secure hardware implementations of block ciphers. The main advantage of the proposed solution is that the masked variables and the masking material can be manipulated simultaneously without leaking sensitive information in the Hamming distance model. Moreover, we show that the leaking information stays very limited when the deterministic part of the real leakage slightly deviates from the Hamming distance. Finally, we apply our method to protect an AES hardware implementation and we show that the performances are suitable for practical implementations.