Paper 1997/015

Optimistic fair Exchange of Digital Signatures

N. Asokan, V. Shoup, and M. Waidner


We present a new protocol that allows two players to exchange digital signatures (including RSA and DSS) over the Internet in a fair way, so that either each player gets the other's signature, or neither player does. One obvious application is where the signatures represent items of value, for example, an electronic check or airline ticket; the protocol can also be adapted to exchange encrypted data. The protocol relies on a trusted third party, but is "optimistic," in that the third party is only needed in cases where one player attempts to cheat or simply crashes. This is an important property, as it greatly reduces the load on the third party, which in particular facilitates a more robust and secure implementation of the third party.

Available format(s)
Publication info
Published elsewhere. Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive.
Contact author(s)
sho @ zurich ibm com
1997-12-05: received
Short URL
Creative Commons Attribution


      author = {N.  Asokan and V.  Shoup and M.  Waidner},
      title = {Optimistic fair Exchange of Digital Signatures},
      howpublished = {Cryptology ePrint Archive, Paper 1997/015},
      year = {1997},
      note = {\url{}},
      url = {}
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