Montgomery Modular Multiplication on Reconfigurable Hardware: Systolic versus Multiplexed Implementation

Abstract

This paper describes a comparison of two Montgomery modular multiplication architectures: a systolic and a multiplexed. Both implementations target FPGA devices. The modular multiplication is employed in modular exponentiation processes, which are the most important operations of some public-key cryptographic algorithms, including the most popular of them, the RSA. The proposed systolic architecture presents a high-radix implementation with a one-dimensional array of Processing Elements. The multiplexed implementation is a new alternative and is composed of multiplier blocks in parallel with the new simplified Processing Elements, and it provides a pipelined operation mode. We compare the time × area efficiency for both architectures as well as an RSA application. The systolic implementation can run the 1024 bits RSA decryption process in just 3.23 ms, and the multiplexed architecture executes the same operation in 4.36 ms, but the second approach saves up to 28% of logical resources. These results are competitive with the state-of-the-art performance.