Spectral arithmetic in Montgomery modular multiplication

Modular multiplication is considered to be the most computation-intensive operation for cryptographic algorithms involving large operands, such as RSA and Diffie–Hellman. Their key sizes have been increased significantly in recent decades to provide sufficient cryptographic strength. Thus, large integer modular multiplication algorithm with high efficiency is in demand. Montgomery modular multiplication (MMM) integrated by the spectral arithmetic can be a suitable solution. This is because MMM eliminates the time-consuming trail division, while the spectral arithmetic can speed up the integer multiplications from quadratic time to linearithmic time. This survey paper introduces the development of spectral-based MMM, as well as its two important properties: high parallelism and low complexity. Besides, different algorithms are explored to demonstrate how each of them benefits the modular multiplication. Moreover, we also compare these algorithms in terms of digit-level complexity and provide general ideas about algorithm selection when implementing modular multiplication with 1024-bit operand size and above.