Describes entity authentication mechanisms using zero-knowledge techniques: - mechanisms based on identities and providing unilateral authentication; - mechanisms based on integer factorization and providing unilateral authentication; - mechanisms based on discrete logarithms with respect to numbers that are either prime or composite, and providing unilateral authentication; - mechanisms based on asymmetric encryption systems and providing either unilateral authentication, or mutual authentication; - mechanisms based on discrete logarithms on elliptic curves and providing unilateral authentication.