Recurring Contingent Service Payment

Abadi, A., Murdoch, S. J. and Zacharias, T. (2023) Recurring Contingent Service Payment. In: 2023 IEEE 8th European Symposium on Security and Privacy (EuroS&P), Delft, Netherlands, 3-7 July 2023, pp. 724-756. ISBN 9781665465120 (doi: 10.1109/eurosp57164.2023.00049)

Abstract

Fair exchange protocols let two mutually distrustful parties exchange digital data in a way that neither party can cheat. They have various applications such as the exchange of digital items, or the exchange of digital coins and digital services between a buyer/client and seller/server.In this work, we formally define and propose a generic blockchain-based construction called "Recurring Contingent Service Payment" (RC-S-P). It (i) lets a fair exchange of digital coins and verifiable service reoccur securely between clients and a server while ensuring that the server is paid if and only if it delivers a valid service, and (ii) ensures the parties’ privacy is preserved. RC-S-P supports arbitrary verifiable services, such as "Proofs of Retrievability" (PoR) or verifiable computation and imposes low on-chain over-heads. Our formal treatment and construction, for the first time, consider the setting where either client or server is malicious.We also present a concrete efficient instantiation of RC-S-P when the verifiable service is PoR. We implemented the concrete instantiation and analysed its cost. When it deals with a 4-GB outsourced file, a verifier can check a proof in only 90 milliseconds, and a dispute between a prover and verifier is resolved in 0.1 milliseconds.At CCS 2017, two blockchain-based protocols were proposed to support the fair exchange of digital coins and a certain verifiable service; namely, PoR. In this work, we show that these protocols (i) are susceptible to a free-riding attack which enables a client to receive the service without paying the server, and (ii) are not suitable for cases where parties’ privacy matters, e.g., when the server’s proof status or buyer’s file size must remain private from the public. RC-S-P simultaneously mitigates the above attack and preserves the parties’ privacy.

• Item Type: Conference Proceedings
• Additional Information: Aydin Abadi and Steven J. Murdoch were supported in part by REPHRAIN: The National Research Centre on Privacy, Harm Reduction and Adversarial Influence Online, under UKRI grant: EP/V011189/1. Steven J. Murdoch was also supported by The Royal Society under grant UF160505.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Zacharias, Dr Thomas
• Authors: Abadi, A., Murdoch, S. J., and Zacharias, T.
• College/School: College of Science and Engineering > School of Computing Science
• Publisher: IEEE
• ISBN: 9781665465120