Reliable S-Box Hardware Implementation by Gate-Level Fault Masking Enhancement

With technology scaling, fault tolerance has become more essential for digital circuits. Some solutions, like all types of redundancies, have been proposed to increase the reliability of the systems. In this paper, we present a cost-aware algorithm to enhance the fault tolerance ability of combinational digital circuits. Proposed algorithm improves the circuit logical masking with minimum area overhead based on an improved version of genetic algorithm (GA). Given a set of potential gates that are more sensitive to fault occurrence, we first extract feasible functional redundant, ffr, between the source nodes and the potential gates' outputs that their improvement on logical masking be more than a pre-defined threshold and hold them in a library, Masking_Lib. Then, we have to find a set of minimum number of potential gates as a target to add appropriate ffr, so that the maximum improvement on logical masking with minimum area overhead is achieved. Since, finding a set of potential gates with their suitable ffrs to meet these objectives is an NP-hard problem, we formulize this, as an optimization problem and solve using GA. We introduce an efficient chromosome representation and an adaptive objective function along with the basic GA operators. Besides, we integrate an assimilation operator with GA in order to enhance its searching ability. Our approach is applied to composite field substitution box implementation (S-box) that forms the core building block of any hardware implementation of the Advanced Encryption Standard algorithm. The simulation and synthesis results have been reported to show the effectiveness of our approach. Through these results, it has been shown that our proposed algorithm provides reliable digital circuits based on different level of logical masking (from 25.58 to 52.15).