A method of obscuring the input and output of a modular exponentiation function, including: receiving modular exponentiation parameters including an exponent e having N bits and a modulus m; generating randomly a pre-multiplier; calculating a post-multiplier based upon the pre-multiplier, exponent e, and modulus m; multiplying an input to the modular exponentiation function by the pre-multiplier; performing the modular exponentiation function; and multiplying the output of the modular exponentiation function by the post-multiplier, wherein multiplying an input to the modular exponentiation function by the pre-multiplier, performing the modular exponentiation function, and multiplying the output of the modular exponentiation function by the post-multiplier are split variable operations.