Using State Space Encoding To Counter Biased Fault Attacks on AES Countermeasures

Biased fault attacks such as the Differential Fault Intensity Analysis (DFIA) have been a major threat to cryptosystems in recent times. DFIA combines principles of side channel analysis and fault attacks to try and extract the key using faulty ciphertexts only. Biased fault attacks have also been shown to weaken traditional redundancy based countermeasures, such as Concurrent Error Detection (CED) techniques, that provide security against classical fault attacks such as Differential Fault Analysis (DFA). While these countermeasures are effective under the assumption that the adversary uses a uniform fault model, they are vulnerable to attacks using biased fault models. Till date, no effective countermeasure against such biased fault attacks has been reported in literature. In this work, we propose a countermeasure strategy that combines the principles of redundancy with that of fault space transformation to achieve security against both classical and biased fault attacks. The novelty in the proposed countermeasure lies in the concept of transforming the fault space, that reduces the probability that the adversary can bypass the redundant checks by introducing the same fault in the original and redundant computations. All claims have been validated via practical experiments on a SASEBO GII board.