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. A way of strengthening trustworthiness is to
hold parties accountable for their actions, as this provides strong incentives
to refrain from malicious behavior. This has lead 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 which
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
wide range of protocols.Comment: 40 page
