Ryan (PhD in mathematical physics from University of London) is with DERA from 1992 and will be leading an Information Assurance Group at SRI Cambridge from year 2000. He worked on cryptography and application of model-checking and CSP to security protocol analysis. His current interests include security impact of emerging, distributed computing technologies such as Java, mobile code and agents.

**Mathematical Models of Computer Security (MMCS): 6 hours.**

In these lectures I will describe the various mathematical techniques that have been used to specify, model and analyse computer security policies. In particular, I will concentrate on Multi-Level Security (MLS) policies and the notion of non-interference. The latter attempts to formalise the absence of information flow through a system and is thus central to the whole framework. The lectures will go to the state-of-the-art and conclude with outstanding issues and future directions.