Verifying Accountability for Unbounded Sets of Participants

TL;DR

This paper extends accountability verification methods to protocols with unbounded participants by combining formal definitions with automated analysis tools, enhancing flexibility and applicability.

Contribution

It introduces a general construction of verdict functions and verification conditions for accountability in unbounded participant protocols, integrated into the Tamarin verification tool.

Findings

Extended Tamarin to verify accountability in unbounded protocols

Achieved soundness and completeness in the verification process

Demonstrated increased flexibility over prior methods

Abstract

Little can be achieved in the design of security protocols without trusting at least some participants. This trust should be justified or, at the very least, subject to examination. One way to strengthen trustworthiness is to hold parties accountable for their actions, as this provides a strong incentive to refrain from malicious behavior. This has led to an increased interest in accountability in the design of security protocols. In this work, we combine the accountability definition of K\"unnemann, Esiyok, and Backes, with the notion of case tests to extend its applicability to protocols with unbounded sets of participants. We propose a general construction of verdict functions and a set of verification conditions that achieve soundness and completeness. Expressing the verification conditions in terms of trace properties allows us to extend Tamarin -- a protocol verification tool -- with the ability to analyze and verify accountability properties in a highly automated way. In contrast to prior work, our approach is significantly more flexible and applicable to a wider range of protocols.