International Association
for Cryptologic Research

Modular arithmetic used for cryptography includes modular adding, modular subtracting, modular multiplying, modular inverting, modular exponentiating etc. In this paper, the authors well analyze the bit complexity of a bitwise modular operation and the time complexity of a non-bitwise modular operation. Besides discuss the clock cycles for one bytewise modular operation utilizing directives from the ATmel 8-bit AVR instruction set. Last, reveal that the ratio of derivate numbers of clock cycles for two modular operations under different modulus lengths is almost a constant.