Merging and extending the PGP and PEM trust models-the ICE-TEL trust model

The ICE-TEL project is a pan-European project which is building an Internet X.509-based certification infrastructure throughout Europe plus several secure applications that will use it. This article describes the trust model being implemented by the project. A trust model specifies the means by which a user may build trust in the assertion that a remote user is really who he purports to be (authentication) and that he does in fact, have a right to access the service or information he is requesting (authorization). The ICE-TEL trust model is based on a merging of and extensions to the existing pretty good privacy (PGP) web of trust and privacy-enhanced mail (PEM) hierarchy of trust models, and is called a web of hierarchies trust model. The web of hierarchies model has significant advantages over both previous models, and these are highlighted. The article further describes the way the trust model is enforced through some of the new extensions in the X.509 V3 certificates, and gives examples of its use in different scenarios.