Wide Mouth Frog

Wide Mouth Frog is a computer network authentication protocol designed for use on insecure networks (the Internet for example). It allows individuals communicating over a network to prove their identity to each other while also preventing evesdropping or replay attacks, and provides for detection of modification and the prevention of unauthorized reading.

The protocol can be specified as follows in security protocol notation, where Alice is authenticating herself to Bob using a server S:

The protocol has two major problems, the first is that all the clocks need to be kept in sync and secondly the server has access to all keys.

See also: Kerberos, Otway-Rees, Needham-Schroeder.