Security-enhanced mailing lists

The Computer Center at the Technical University of Berlin (PRZ) has developed a security-enhanced mail exploder. It uses the well-known technology of public key cryptography to improve confidentiality and authenticity of a mailing list. One of the design goals was ease of use. No participant of a secure mailing list needs to know a public key of any other member; all a sender has to know is the public key of the mailing list. In this scheme PRZ gets the clear text of the message before it is distributed to the members of the mailing list. This article discusses several possibilities to improve the confidentiality by omitting the clear text phase. The goal is for PRZ to be able to forward the mail but not read it.