An Improved S-Box of Lightweight Hash Function SPOGENT

The need for lightweight (that is, compact, low-power, low-energy) cryptographic hash functions has been repeatedly expressed by professionals, notably to implement cryptographic protocols in embedded system. Currently, SPONGENT is the most competitive lightweight hash function family. In this paper, we design a novel 4-bit S-box to improve the internal permutation of SPONGENT. The 4-bit S-box is designed by mathematical functions in finite fields. It includes power function as its core structure and outer affine transformation which has an involution matrix. Through calculating security indexes, it proves that the novel S-box has relatively high security levels as SPOGENT. Furthermore, the 4-bit S-box is very compact and has a smaller scale when implemented by hardware.