Environmental requirements for authentication protocols

Most work on requirements in the area of authentication protocols has concentrated on identifying requirements for the protocol without much consideration of context. Little work has concentrated on assumptions about the environment, for example, the applications that make use of authenticated keys. We will show in this paper how the interaction between a protocol and its environment can have a major e ect on a protocol. Speci cally we will demonstrate a number of attacks on published and/or widely used protocols that are not feasible against the protocol running in isolation (even with multiple runs) but become feasible in some application environments. We will also discuss the tradeo between putting constraints on a protocol and putting constraints on the environment in which it operates

Discussing Anonymity Metrics for Mix Based Anonymity Approaches

Today the Chaumian Mix idea is not only an academic approach for anonymous communication, it is also a practical system with many variants used in real-world scenarios. It is therefore important to find an appropriate measure for the anonymity provided by these approaches. Many measurement approaches have been proposed that consider only the static state of the system without accounting for past and future information. Still other measurements evaluate only statistics. These measurements have in common that they do not measure when the anonymity function of the system is broken. Inspired by the idea of unicity distance in cryptography, and the mean time to failure in dependable systems, we believe that measuring the point at which the system fails to hide the relation between a sender and a receiver is a more appropriate measure of its anonymity. In this paper, we discuss our arguments with respect to existing measurement approaches