LightHD: a lightweight and high-performance hardware accelerator of CRYSTALS-Dilithium

CRYSTALS-Dilithium serves as the foundation of the NIST-standardised PQC digital signature scheme, and has been declared as the first recommended digital signature algorithm. However, due to the computational complexity and intricate processing flow of CRYSTALS-Dilithium, two limitations are shown in existing methods: its applicability on resource-constrained devices is limited and the performance reported so far remains relatively low. This paper presents a lightweight yet high-performance hardware architecture that optimises the core computational units of CRYSTALS-Dilithium. First, an iterative dual-Keccak SHA-3 module is proposed, where two cores operate with a 26-cycle offset to accelerate processing without compromising frequency. In addition, the rejection sampler is streamlined by two compact registers for intermediate values and counters, improving efficiency when consuming interleaved SHA-3 outputs. Second, for small bit-width polynomials, we eliminate the first NTT stage via lookup tables and data regrouping, reducing NTT cycles by 11.7% with little hardware overhead. Further hardware savings are achieved by maximising IP core utilisation and simplifying input multiplexers. Furthermore, a compact scheduling strategy ensures that all intermediate storage fits within a single polynomial-sized memory block. On Xilinx Artix-7 FPGAs, the design reduces hardware overhead by 14.2% compared with state-of-the-art lightweight implementations. Across three security levels, KeyGen and Verify are 27.3% and 13.5% faster, respectively, than high-performance prior designs. At level 5, the best-case Sign latency is only 120 µs.