explicit display (password, PIN, key)
implicit display (non-repeat identifier)
Multi parametric identification.
Cyber identities are most easy to fake, one is rarely too sure of the identity of his conversation partner.
Identities are determined based on:
Determination of identity is probabilistic: happens when the probability to be wrong is sufficiently small (never zero).
It's good practice to employ a mutual identification procedure, to insure each of the identity of the other.