Efficient Modular Polynomial Multiplier for NTT Accelerator of Crystals-Kyber

This paper presents a hardware design that efficiently performs the number theoretic transform (NTT) for lattice-based cryptography. First, we propose an efficient modular multiplication method for lattice-based cryptography defined over Proth numbers. The proposed method is based on a K-RED technique specific to Proth numbers. In particular, we divide the intermediate result into the sign bit and the other absolute value bits and handle them separately to significantly reduce implementation costs. Then, we show a butterfly unit datapath of NTT and inverse INTT equipped with the proposed modular multiplier. We apply the proposed NTT accelerator to Crystals-Kyber, which is lattice-based cryptography, and evaluate its performance on Xilinx Artix-7. The results show that the proposed NTT accelerators achieve up-to 3% and 33% higher area-time efficiency in terms of LUTs and FFs, respectively, than conventional best methods. In addition, the low-latency version of the proposed NTT accelerators achieves a 18% lower-latency with an area-time efficiency (in terms of LUTs, FFs, and DSPs) than the existing fastest method.