Enhancement of Hardware Security by Hamming-Ball Based State Assignment

Modern fault injection techniques allow an adversary to attack cryptographic devices by inducing errors of any multiplicity. The induced errors can affect any part of the circuit, including the Finite State Machine (FSM) that controls the execution of cryptographic algorithms. One of the most efficient countermeasures against these attacks is robust error detecting codes. Robust codes are usually designed under the assumption that the code words occur with equal probability. However, in most FSMs, some states (which are encoded as binary code words) are much more probable than others. In this paper, we show that when the probability distribution of the states is highly skewed, the state assignment, that is, the mapping between the states and the code words, determines the attack detection capability. A worst-case scenario is analyzed, and a method that allows the designer to avoid this scenario with a relatively low cost is presented. The proposed security-oriented method and random state assignment are analyzed with benchmark FSMs.