Paper 2012/462

Perfect Ambiguous Optimistic Fair Exchange

Yang Wang, Man Ho Au, and Willy Susilo

Abstract

Protocol for fair exchange of digital signatures is essential in many applications including contract signing, electronic commerce, or even peer-to-peer file sharing. In such a protocol, two parties, Alice and Bob, would like to exchange digital signatures on some messages in a fair way. It is known that a trusted arbitrator is necessary in the realization of such a protocol. We identify that in some scenarios, it is required that prior to the completion of the protocol, no observer should be able to tell whether Alice and Bob are conducting such an exchange. Consider the following scenario in which Apple engages Intel in an exchange protocol to sign a contract that terminates their OEM agreement. The information would be of value to a third party (such as the stock broker, or other OEM companies). If the protocol transcript can serve as an evidence that such a communication is in progress, any observer of this communication, including the employees of both companies, would be tempted to capture the transcript and sell it to outsiders. We introduce a new notion called \emph{perfect ambiguous optimistic fair exchange} (PAOFE), which is particularly suitable to the above scenario. PAOFE fulfils all traditional requirements of cryptographic fair exchange of digital signatures and, in addition, guarantees that the communication transcript cannot be used as a proof to convince others that the protocol is in progress. Specifically, we formalize the notion of PAOFE and present a rigorous security model in the multi-user setting under the chosen-key attack. We also present a generic construction of PAOFE from existing cryptographic primitives and prove that our proposal is secure with respect to our definition in the standard model.

Metadata
Available format(s)
PDF
Category
Public-key cryptography
Publication info
Published elsewhere. This is a full version of the paper that will appear in ICICS 2012
Keywords
signature scheme
Contact author(s)
wsusilo @ uow edu au
History
2012-08-14: received
Short URL
https://ia.cr/2012/462
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2012/462,
      author = {Yang Wang and Man Ho Au and Willy Susilo},
      title = {Perfect Ambiguous Optimistic Fair Exchange},
      howpublished = {Cryptology ePrint Archive, Paper 2012/462},
      year = {2012},
      note = {\url{https://eprint.iacr.org/2012/462}},
      url = {https://eprint.iacr.org/2012/462}
}
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