The explosive growth of networked and internetworked computer systems during the past decade has brought about a need for increased protection mechanisms. This paper discusses three authentication protocols that incorporate the use of methods that present effective user authentication. The first two protocols have been previously discussed in the literature; the third protocol draws from the first two and others to produce an authentication scheme that provides both mutual authentication and secure key distribution which is easy to use, is compatible with present operating systems, is transparent across systems, and provides password file protection.