From Substitution Box to Threshold

With the escalating demand for lightweight ciphers as well as side channel protected implementation of those ciphers in recent times, this work focuses on two related aspects. First, we present a tool for automating the task of finding a Threshold Implementation (TI) of a given Substitution Box (SBox). Our tool returns ‘with decomposition’ and ‘without decomposition’ based TI. The ‘with decomposition’ based implementation returns a combinational SBox; whereas we get a sequential SBox from the ‘without decomposition’ based implementation. Despite being high in demand, it appears that this kind of tool has been missing so far. In the process, we report new decomposition for the PRESENT SBox (improving from Poschmann et al.’s JoC’11 paper) and that of the GIFT SBox (improving from Jati et al.’s TIFS’20 paper). Second, we show an algorithmic approach where a given cipher implementation can be tweaked (without altering the cipher specification) so that its TI cost can be significantly reduced. We take the PRESENT cipher as our case study (our methodology can be applied to other ciphers as well). Indeed, we show over 31% reduction in area and over 52% reduction in depth compared to the basic threshold implementation.