Paper 2026/478 Original: eprint.iacr.org/2026/478 ↗

A Hardware/Software Co-Optimization of HQC Using Tightly-Coupled Accelerators on a 32-bit Ibex Core

Abstract

We present Hardware/Software co-optimization of Hamming Quasi-Cyclic (HQC) enabled by tightly coupled accelerators implemented on a 32-bit Ibex RISC-V core. On the hardware side, we propose a unified multiplier capable of efficiently performing carryless multiplication for both polynomial multiplication over F_2[X]/(X^{n}−1) and multiplication over F_2^{8}. We also design a Keccak permutation accelerator to support efficient randomness sampling. On the software side, we identify the optimal combination of Toom–Cook and Karatsuba methods for efficient polynomial multiplication on the Ibex core and enhance its performance by minimizing the number of memory accesses during its execution.With our co-optimization strategies, our HQC implementation achieves a performance improvement of several tens of times over the reference implementation.