Paper 2021/1145

Recurring Contingent Payment for Proofs of Retrievability

Aydin Abadi, Steven J. Murdoch, and Thomas Zacharias


Fair exchange protocols let two mutually distrusted parties exchange digital data in a way that neither can cheat. At CCS 2017, Campanelli et al. proposed two blockchain-based protocols for the fair exchange of digital coins and a certain service, i.e., “proofs of retrievability” (PoR), that take place between a buyer and seller. In this work, we identify two serious issues of these schemes; namely, (1) a malicious client can waste the seller’s resources, and (2) real-time leakage of information to non-participants in the exchange. To rectify the issues, we propose “recurring contingent PoR payment” (RC-PoR-P). It lets the fair exchange reoccur while ensuring that the seller’s resources are not wasted, and the parties’ privacy is preserved. We implemented the RC- PoR-P. Our cost analysis indicates that the RC-PoR-P is efficient. The RC-PoR-P is the first of its kind that offers all the above features.

Available format(s)
Cryptographic protocols
Publication info
Preprint. MINOR revision.
Proofs of RetrievabilityFair ExchangeBlockchainSmart contract
Contact author(s)
aydin abadi @ ucl ac uk
s murdoch @ ucl ac uk
thomas zacharias @ ed ac uk
2021-09-10: received
Short URL
Creative Commons Attribution


      author = {Aydin Abadi and Steven J.  Murdoch and Thomas Zacharias},
      title = {Recurring Contingent Payment for Proofs of Retrievability},
      howpublished = {Cryptology ePrint Archive, Paper 2021/1145},
      year = {2021},
      note = {\url{}},
      url = {}
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