In order to prevent the SPA (Simple Power Analysis) attack against modular exponentiation algorithms, a multiply-always implementation is generally used. Witteman et al. introduced in a new cross-correlation power analysis attack against the multiply-always implementation. The authors suggest two new algorithms, resistant to this attack and also to other known attacks; an alternative approach to exponentiation algorithms used in cryptography, which usually receive as an input some representation (e.g. binary) of the exponent. In their approach, both the exponent and the result are functions (not necessarily easily invertible) of the exponentiation algorithm input.