Complexity of Anonymity for Security Protocols

Abstract

Anonymity, as an instance of information hiding, is one of the security properties intensively studied nowadays due to its applications to various fields such as e-voting, e-commerce, e-mail, e -cash, and so on. In this paper we study the decidability and complexity status of the anonymity property in security protocols. We show that anonymity is undecidable for unrestricted security protocols, is NEXPTIME-complete for bounded security protocols, and it is NP-complete for 1-session bounded security protocols. In order to reach these objectives, an epistemic language and logic to reason about anonymity properties for security protocols under an active intruder, are provided. Agent states are endowed with facts derived from actions performed by agents in protocol executions, and an inference system is provided. To define anonymity, an observational equivalence is used, which is shown to be decidable in deterministic polynomial time.

Compiling an Epistemic Logic for Multiagent Systems

“… at ARES 2011 conference, the main interest was related to the complementarity between the behavioral equivalence, defined in the referenced paper and the observational equivalence presented in Refs. and . This article answers the questions that were addressed there and to sum up the core of the epistemic logic used in Ref.…”

“…In Ref. , the structure of the local state of an agent was rigorously defined for the case of reasoning about security protocols. Even if here we will not followed the same level of specification as in Ref.…”

“…Elaborating on the results presented in Refs. and , we distinguish between introspective equivalence and extrospective equivalence and analyze the relation between them, thus answering (we hope) to the questions raised at the ASRES 2011 conference. By considering costs associated with actions, we also introduce bounded variants of the two types of equivalence.…”

“…. Tiplea et al . make the first step toward defining a local state equivalence based on formula derivation in a formally defined local state structure.…”

“…, even if the concepts are differently defined, observational equivalence is presented as a sort of behavioral equivalence so, to avoid any confusion; here we introduce introspective equivalence referring to the meaning presented in Ref. and extrospective equivalence referring to presented in Ref. .…”