Extending the RISC-V Instruction Set for Hardware Acceleration of the Post-Quantum Scheme LAC

The increasing effort in the development of quantum computers represents a high risk for communication systems due to their capability of breaking currently used public-key cryptography. LAC is a lattice-based public-key encryption scheme resistant to traditional and quantum attacks. It is characterized by small key sizes and low arithmetic complexity. Recent publications have shown practical post-quantum solutions through co-design techniques. However, for LAC only software implementations were explored. In this work, we propose an efficient, flexible and time-protected HW/SW co-design architecture for LAC. We present two contributions. First, we develop and integrate hardware accelerators for three LAC performance bottlenecks: the generation of polynomials, polynomial multiplication and error correction. The accelerators were designed to support all post-quantum security levels from 128 to 256-bits. Second, we develop tailored instruction set extensions for LAC on RISC-V and integrate the HW accelerators directly into a RISC-V core. The results show that our architecture for LAC with constant-time error correction improves the performance by a factor of 7.66 for LAC-128, 14.42 for LAC-192, and 13.36 for LAC-256, when compared to the unprotected reference implementation running on RISC-V. The increased performance comes at a cost of an increased resource consumption (32,617 LUTs, 11,019 registers, and two DSP slices).