Accelerating CRYSTALS-Kyber and Dilithium via a Single Montgomery Reduction ISE on RISC-V
Ryan Bevin, Ayesha Khalid, Malik Imran, Maire P. O'Neill · 2025
CRYSTALS family of Kyber key encapsulation mechanism and Dilithium digital signature algorithm are the first post quantum cryptography schemes standardized recently by the National Institute of Standards and Technology; numerous endeavours to accelerate them via instruction set extensions using the RISC-V instruction set architecture have been reported. Many of them focus on accelerating the costly Number Theoretic Transform and its inverse, either solely on CRYSTALS-Kyber or as part of greater lattice-based cryptography improvements. In this work, we demonstrate that by only one unified tightly coupled Instruction Set Extension for the Montgomery reduction operation, we improve the NTT/INTT cycle counts of CRYSTALS-Kyber by 1.69x/1.47x respectively and by 2.12x/2.36x in CRYSTALS-Dilithium respectively while costing a minimal additional hardware overhead on the Ibex RISC-V core implemented on an AMD Xilinx Artix-7 xc7a35tcsg324-1 device. Additionally, we also benchmark the NTT/INTT ISE in CRYSTALS-Kyber evaluating diminishing returns vs. the additional hardware cost induced.