A method is disclosed for protecting secret data, which is intended to be processed by an original function, from being deduced by a side-channel attack upon execution of the original function by an electronic computing device. The method includes creating hardware circuitry which replaces the original function with one or more pairs of replacement functions, by applying a predetermined masking algorithm which performs a recursive protection process. Further disclosed is an apparatus for protecting secret data, which is intended to be processed by an original function, from being deduced by a side-channel attack upon execution of the original function by an electronic computing device.