Paper 2001/055

Universally Composable Commitments

Ran Canetti and Marc Fischlin


We propose a new security measure for commitment protocols, called /universally composable/ (UC) Commitment. The measure guarantees that commitment protocols behave like an "ideal commitment service," even when concurrently composed with an arbitrary set of protocols. This is a strong guarantee: it implies that security is maintained even when an unbounded number of copies of the scheme are running concurrently, it implies non-malleability (not only with respect to other copies of the same protocol but even with respect to other protocols), it provides resilience to selective decommitment, and more. Unfortunately two-party UC commitment protocols do not exist in the plain model. However, we construct two-party UC commitment protocols, based on general complexity assumptions, in the /common reference string model/ where all parties have access to a common string taken from a predetermined distribution. The protocols are non-interactive, in the sense that both the commitment and the opening phases consist of a single message from the committer to the receiver.

Available format(s)
Publication info
Published elsewhere. extended abstract appears in Proceedings of Crypto 2001
commitment schemesconcurrent composition
Contact author(s)
marc @ mi informatik uni-frankfurt de
2001-07-10: received
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Creative Commons Attribution


      author = {Ran Canetti and Marc Fischlin},
      title = {Universally Composable Commitments},
      howpublished = {Cryptology ePrint Archive, Paper 2001/055},
      year = {2001},
      note = {\url{}},
      url = {}
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