The module library requires the definition of a single routine: int pwcmp_check(const char* plain, const char* encod). Define this routine to return zero when the plaintext compares equal to the encoded text, and non-zero otherwise. The module library handles all startup, shutdown, and I/O conditions.
The module should try to avoid doing any more or less work when the comparison succeeds than when the comparison fails, to avoid timing-based attacks on other systems that use the module.