A system for authentication of network users which is operable in multiple modes, includes a plurality of user network stations and at least one sponsor network station representing a sponsor. Each network station represents a user associated with an asymmetric crypto-key having either a first or second number of private portions, the second number being greater than the first number. The one or more sponsor network stations receive authentication requests from the user network stations, determine the identity of a user associated with each of the received authentication requests, select from two or more available modes of operation based upon the determined identity. If operation in one mode is selected, the sponsor network station signs a particular received authentication request using one private portion of an asymmetric crypto-key having a first number of private portions. However, if another mode is selected, the sponsor network station signs that particular authentication request using one private portion of an asymmetric crypto-key having a second number of private portions.