Conference Paper

A Cryptographic Model for Branching Time Security Properties - The Case of Contract Signing Protocols.

DOI: 10.1007/978-3-540-74835-9_28 Conference: Computer Security - ESORICS 2007, 12th European Symposium On Research In Computer Security, Dresden, Germany, September 24-26, 2007, Proceedings
Source: DBLP

ABSTRACT Some cryptographic tasks, such as contract signing and other related tasks, need to ensure complex, branching time security properties. When dening such properties one needs to deal with subtle problems regarding the scheduling of non-deterministic decisions, the delivery of messages sent on resilient (non-adversarially con- trolled) channels, fair executions (executions where no party, both honest and dishonest, is unreasonably precluded to perform its actions), and dening strategies of adversaries against all possible non-deterministic choices of parties and arbitrary delivery of messages via resilient channels. These problems are typically not addressed in crypto- graphic models and these models therefore do not sufce to formalize branching time properties, such as those required of contract signing protocols. In this paper, we develop a cryptographic model that deals with all of the above problems. One central feature of our model is a general denition of fair scheduling which not only formalizes fair scheduling of resilient channels but also fair scheduling of actions of honest and dishonest principals. Based on this model and the notion of fair scheduling, we provide a denition of a prominent branching time property of contract signing protocols, namely balance, and give the rst cryptographic proof that the Asokan-Shoup-Waidner two-party contract signing protocol is balanced.

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