Paper 2003/015

A Universally Composable Cryptographic Library

Michael Backes, Birgit Pfitzmann, and Michael Waidner


Bridging the gap between formal methods and cryptography has recently received a lot of interest, i.e., investigating to what extent proofs of cryptographic protocols made with abstracted cryptographic operations are valid for real implementations. However, a major goal has not been achieved yet: a soundness proof for an abstract crypto-library as needed for the cryptographic protocols typically proved with formal methods, e.g., authentication and key exchange protocols. Prior work that directly justifies the typical Dolev-Yao abstraction is restricted to passive adversaries and certain protocol environments. Prior work starting from the cryptographic side entirely hides the cryptographic objects, so that the operations are not composable: While secure channels or signing of application data is modeled, one cannot encrypt a signature or sign a key. We make the major step towards this goal: We specify an abstract crypto-library that allows composed operations, define a cryptographic realization, and prove that the abstraction is sound for arbitrary active attacks in arbitrary reactive scenarios. The library currently contains public-key encryption and signatures, nonces, lists, and application data. The proof is a novel combination of a probabilistic, imperfect bisimulation with cryptographic reductions and static information-flow analysis.

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Publication info
Published elsewhere. Unknown where it was published
cryptographic protocolssecurity analysis of protocolscryptographically composable operators
Contact author(s)
mbc @ zurich ibm com
2003-01-24: received
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      author = {Michael Backes and Birgit Pfitzmann and Michael Waidner},
      title = {A Universally Composable Cryptographic Library},
      howpublished = {Cryptology ePrint Archive, Paper 2003/015},
      year = {2003},
      note = {\url{}},
      url = {}
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