## CryptoDB

### Paper: Accountability: Definition and Relationship to Verifiability

Authors: Ralf Küsters Tomasz Truderung Andreas Vogt URL: http://eprint.iacr.org/2010/236 Search ePrint Search Google 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.
##### BibTeX
@misc{eprint-2010-23137,
title={Accountability: Definition and Relationship to Verifiability},
booktitle={IACR Eprint archive},
keywords={cryptographic protocols / Accountability, Verifiability, Protocol Analysis, E-Voting, Auction, Contract Signing},
url={http://eprint.iacr.org/2010/236},
note={ kuesters@uni-trier.de 14726 received 27 Apr 2010},
author={Ralf Küsters and Tomasz Truderung and Andreas Vogt},
year=2010
}