The S/Key protocol is a variation of a well-known Lamport’s one-time password protocol. The idea is.

The S/Key protocol is a variation of a well-known Lamport’s one-time password protocol. The idea is that a user U can efficiently derive a new password for each session, based on a master password PU . The n one-time passwords are derived recursively by applying for instance hash function f and the sequence of password is given as, f n (PU ) def. = f(· · ·(f | {z } n (PU ))· · ·)