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Accountability: Definition and Relationship to Verifiability (BibTeX)

  author      = {Ralf K{\"u}sters and Tomasz Truderung and Andreas Vogt},
  title       = {{Accountability: Definition and Relationship to Verifiability}},
  booktitle   = {Proceedings of the 17th ACM Conference on Computer and Communications Security (CCS 2010)},
  year        = 2010,
  pages       = {526--535},
  publisher   = {ACM Press},
  abstract    = {Many cryptographic tasks and protocols, such as non-repudiation, contract-signing, voting, auction, identity-based encryption, and certain forms of secure multi-party computation, involve the use of (semi-)trusted parties, such as notaries and authorities. It is crucial that such parties can be held accountable in case they misbehave as this is a strong incentive for such parties to follow the protocol.  Unfortunately, there does not exist a general and convincing definition of accountability that would allow to assess the level of accountability a protocol provides. In this paper, we therefore propose a new, widely applicable definition of accountability, with interpretations both in symbolic and computational models. Our definition reveals that accountability is closely related to verifiability, for which we also propose a new definition. We prove that verifiability can be interpreted as a restricted form of accountability. Our findings on verifiability are of independent interest. As a proof of concept, we apply our definitions to the analysis of protocols for three different tasks: contract-signing, voting, and auctions.  Our analysis unveils some subtleties and unexpected weaknesses, showing in one case that the protocol is unusable in practice.  However, for this protocol we propose a fix to establish a reasonable level of accountability.}