Method and apparatus for modular operation

Abstract

The modular operation apparatus of the present invention that enables to improve the tamper resistance to the side channel attacks includes an operator that carries out a Montgomery multiplication according to one of a first multiplicand and a second multiplicand, a multiplier, and a divisor, a first multiplicand register that stores an operation result of the Montgomery multiplication as the first multiplicand, a subtractor that subtracts the divisor from the operation result of the Montgomery multiplication, a second multiplicand register that stores a subtraction result of the subtractor as the second multiplicand, and a selector that outputs one of a value of the first multiplicand register and a value of the second multiplicand register according to a comparison result between the operation result of the Montgomery multiplication and the divisor.

Dependencies are inferred from the claim text.