Flexible NTT/iNTT Accelerator Based on Montgomery Reduction

As the importance of data grows, so does the significance of homomorphic encryption(HE), which enables direct computations on encrypted data. However, HE presents a major challenge, with computational overhead increasing compared to plaintext operations. To address this, we developed a hardware accelerator for NTT and iNTT, which are commonly used in HE and contribute to this overhead. The accelerator implements modular arithmetic using Montgomery reduction, and pipelining is applied to improve throughput. Additionally, a mode-switching feature is introduced, allowing both NTT and iNTT operations to be performed on a single circuit. The accelerator is also designed to operate flexibly across various cryptographic strength parameters ( $\boldsymbol{N}$ -values). The proposed accelerator achieved an average speedup of approximately 4.24 times compared to software, demonstrating its effectiveness in reducing computation time in HE systems.