There is provided a modular multiplication device for performing a multiplication of a first multiplicand and a second multiplicand modulo a given modulus, each of the multiplicand comprising a given number of digits, each digit having a given word size. The modular multiplication device comprises: a multiplier for multiplying at least one digit of the first multiplicand with the second multiplicand to produce a multiplier output; a modular reduction unit configured to reduce a quantity derived from the multiplier output by the product of an extended modulus and an integer coefficient, the extended modulus being the product of the given modulus with an extension parameter, which provides a reduction output, the reduction output being a positive integer strictly smaller than the extended modulus, wherein the modular multiplication device further comprises a selection unit configured to select the extension parameter such that the time taken for the device to perform the multiplication is independent from the multiplicands.

Various embodiments relate to a method, system, and non-transitory machine-readable medium encoded with instructions for execution by a processor for performing modular exponentiation, the non-transitory machine-readable medium including: instructions for iteratively calculating a modular exponentiation, b.sup.d mod n, including: instructions for squaring a working value, c; and instructions for conditionally multiplying the working value, c, by a base value, b, dependent on a bit of an exponent, d, including: instructions for unconditionally multiplying the working value, c, by a lookup table entry associated with the base value.