Each year we have a theme, and each year people give talks about either the previous year’s theme or next year’s theme. This year the theme is discerning the protocol participants. There are usually several people who have an interest in a particular run of a protocol besides those who are actually sending and receiving the messages. When we come to do the proceedings we’ll try and pretend that everything that was said has something to do with this. Today we’re looking mainly at authentication. There are some people who are going to try to convince us that authentication is harmful, there are some who are going to talk about why authentication is a good thing that doesn’t actually involve knowing who people are in real life, there are some people who are going to argue that authentication doesn’t involve trusted third parties and that trusted third parties are actually bad for you, there are other people who will talk about why trusted third parties are jolly good things to have provided you don’t use them for any of the things that they’re usually sold to you for.