Butler Lampson, one of the pioneers in computer security, once wrote:
"What people want from computer security is to be as secure with computers as they are in the real world".
Increasingly, however, the "real world" is full of interconnected computers in critical roles. Accordingly, computer security becomes more essential but also harder to define and even harder to achieve.
This lecture is an introduction to some of the themes and techniques of computer security. It emphasizes security protocols. These play a well-established role in authentication in distributed sytems and related tasks; they have many other actual or imagined applications, for instance discouraging junk email ("spam"). Over time, useful methods have been developed for the design and analysis of security protocols. Advances in other parts of computer security, in particular those that touch system administrators and users, remain more sporadic and challenging