Abstract
Security protocols are designed to meet particular security properties. In order to analyse such protocols formally, it is necessary to provide a formal definition of the property that they are intended to provide. This paper is concerned with the property of anonymity. It proposes a definition of anonymity within the CSP notation, discusses the approach taken by CSP to anonymity with respect to different viewpoints, and illustrates this approach on some toy examples, and then applies it to a machine-assisted analysis of the dining cryptographers example and some variants.