Abstract: “This memo describes a framework for simple caller authorization. It is a generalization of the RMX draft, which was designed to protect against e-mail fraud and spam. This new draft describes a general mechanism suitable for other protocols used in the Internet or other networks. It is designed to be simple and to not make use of any kind of secret, and to establish a cheap, robust, and lightweight authorization scheme. It is intended to be used for low security requirements.”
http://www.ietf.org/internet-drafts/draft-danisch-scaf-00.txt