Parameterised anonymity

We introduce the notion of parameterised anonymity, to formalize the anonymity property of protocols with an arbitrary number of participants. This definition is an extension of the well known CSP anonymity formalization of Schneider and Sidiropoulos [18]. Using recently developed invariant techniques for solving parameterised boolean equation systems, we then show that the Dining Cryptographers protocol guarantees parameterised anonymity with respect to outside observers. We also argue that although the question whether a protocol guarantees parameterised anonymity is in general undecidable, there are practical subclasses where anonymity can be decided for any group of processes