A Framework for Formal Analysis of Anonymous Communication Protocols

Abstract

Anonymity is the property of keeping secret the identity of the user performing a certain action. The need for anonymity may arise in a wide range of situations, like electronic voting, Web browsing, and so on. In order to verify the anonymity of security protocols, a framework for formal analysis of anonymous communication protocols is proposed. In this framework, we define operational semantics for security protocols using a labelled transition system; the transition relation is defined by the transition rules, which include create rule, send rule, and receive rule. In addition, the formal description of intruder model in this framework is given. The proposed intruder model specifies the capabilities of the intruder and is weaker than the Dolev–Yao model. Moreover, the concepts of mapping and trace equivalence are proposed; the sender anonymity is formally defined. To illustrate the applicability of proposed framework, we explore the use of probabilistic model checking tool PRISM to analyze the sender anonymity of Crowds protocol. The experimental results show the relationship between sender anonymity and the number of nodes, path reformulations, and forwarding probability, which provides a good way about how to protect the sender anonymity of anonymous communication protocols.