Fairly exchanging digital content is an everyday problem. A fair exchange scenario commonly involves Alice and Bob. Alice has something that Bob wants, and Bob has something that Alice wants. A fair exchange protocol guarantees that at the end either each of them obtains what (s)he wants, or neither of them does.

There has been a great deal of research on fairly exchanging two items. But when one considers peer-to-peer systems, efficiency and performance of the fair exchange protocol matters. In the past, we have created an efficient and scalable optimistic fair exchange protocol suitable for use in high-churn peer-to-peer file sharing systems. Currently, we are working on applying fair exchange protocols to other scenarios where needed. These scenarios include secure two-party or multi-party computation, as well as cloud storage systems.

Furthermore, while analyzing the limits of fair exchange protocols, we looked at distributing centralized parties, such as the trusted third party, the arbiter. Our results include impossibility cases and optimality proofs.

Related Publications:

  1. Alptekin Küpçü, “Incentivized Outsourced Computation Resistant to Malicious Contractors“, IEEE Transactions on Dependable and Secure Computing 14(6): 633 – 649, Nov 2017. (See also Cryptology ePrint Archive Report 2014/992).
  2. Handan Kılınç, Alptekin Küpçü, “Efficiently Making Secure Two-Party Computation Fair“, FC 2016. (See also Cryptology ePrint Archive Report2014/896).
  3. Alptekin Küpçü, Payman Mohassel, “Fast Optimistically Fair Cut-and-Choose 2PC“, FC 2016. (See also Cryptology ePrint Archive Report 2015/1209).
  4. Handan Kılınç, Alptekin Küpçü, “Optimally Efficient Multi-Party Fair Exchange and Fair Secure Multi-Party Computation“, CT-RSA 2015. (See also Cryptology ePrint Archive Report 2015/064).
  5. Alptekin Küpçü, Anna Lysyanskaya, “Usable Optimistic Fair Exchange“, Elsevier Computer Networks Journal, Volume 56, Issue 1, Pages 50–63, 12 January 2012, doi: 10.1016/j.comnet.2011.08.005.
  6. Alptekin Küpçü, “Distributing Trusted Third Parties“, ACM SIGACT News 44(2), pages 88-118, Distributed Computing Column, June 2013.
  7. Alptekin Küpçü, “Official Arbitration with Secure Cloud Storage Application“, The Computer Journal, 5 December 2013, doi: 10.1093/comjnl/bxt138. (See also Cryptology ePrint Archive Report 2012/276).
  8. Alptekin Küpçü, Anna Lysyanskaya, “Usable Optimistic Fair Exchange“, RSA 2010. [Eurocrypt 2008 Rump Session video presentation]
  9. Alptekin Küpçü, Anna Lysyanskaya, “Optimistic Fair Exchange with Multiple Arbiters“, ESORICS 2010.
  10. Alptekin Küpçü, Anna Lysyanskaya, “Brief Announcement: Impossibility Results for Optimistic Fair Exchange with Multiple Autonomous Arbiters“, PODC 2009.

Project Funding:

We are grateful for the support from TÜBİTAK and European Union COST Action IC1306.