2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/154669We propose a general way of constructing zero-knowledge authentication schemes from actions of a semigroup on a set, without exploiting any specific algebraic properties of the set acted upon. Then we give several concrete realizations of this general idea, and in particular, we describe several zero-knowledge authentication schemes where forgery (a.k.a. impersonation) is NP-hard. Computationally hard problems that can be employed in these realizations include (Sub)graph Isomorphism, Graph Colorability, Diophantine Problem, and many others.Cryptography and Security94A62, 68P25text