Parameter Space for the Architecture of FFT-Based Montgomery Modular Multiplication

Modular multiplication is the core operation in public-key cryptographic algorithms such as RSA and the Diffie-Hellman algorithm. The efficiency of the modular multiplier plays a crucial role in the performance of these cryptographic methods. In this paper, improvements to FFT-based Montgomery Modular Multiplication (FFTM3) using carry-save arithmetic and pre-computation techniques are presented. Moreover, pseudo-Fermat number transform is used to enrich the supported operand sizes for the FFTM3. The asymptotic complexity of our method is O(l log l log log l), which is the same as the Schonhage-Strassen multiplication algorithm (SSA). A systematic procedure to select suitable parameter set for the FFTM3 is provided. Prototypes of the improved FFTM3 multiplier with appropriate parameter sets are implemented on Xilinx Virtex-6 FPGA. Our method can perform 3,100-bit and 4,124-bit modular multiplications in 6.74 and 7.78 mu s, respectively. It offers better computation latency and area-latency product compared to the state-of-the-art methods for operand size of 3,072-bit and above.