RejSCore: Rejection Sampling Core for Multivariate-based Public key Cryptography

Post-quantum multivariate public key cryptography (MPKC) schemes resist quantum threats but require heavy operations, such as rejection sampling, which challenge resourcelimited devices. Prior hardware designs have addressed various aspects of MPKC signature generation. However, rejection sampling remains largely unexplored. This paper presents RejSCore, a lightweight hardware accelerator for rejection sampling in post-quantum cryptography. It targets the QRUOV scheme, which is a prominent candidate under the secondround of the National Institute of Standards and Technology (NIST) additional digital signature standardization process. The architecture includes an AES-CTR-128-based pseudorandom number generator. Moreover, a lightweight iterative method is employed in rejection sampling, offering reduced resource consumption and area overhead while slightly increasing latency. The performance of RejSCore is comprehensively evaluated on Artix-7 FPGAs and 65 nm CMOS technology using the Area-Delay Product (ADP) and Power-Delay Product (PDP). On Artix-7 and 65 nm CMOS, RejSCore achieves an area of 2042 slices and $464,866 \mu \mathrm{~m}^{2}$, with operating frequencies of 222 MHz and 565 MHz, respectively. Using the QR-UOV parameters for security level I ($q=127, v=156, m=54, l=3$), the core completes its operation in 8525 clock cycles. The ADP and PDP evaluations confirm RejSCore’s suitability for deployment in resource-constrained and security-critical environments.