Practical time capsule signatures in the standard model from bilinear maps

  • Authors:
  • Benoît Libert;Jean-Jacques Quisquater

  • Affiliations:
  • UCL, Microelectronics Laboratory, Crypto Group, Louvain-La-Neuve, Belgium;UCL, Microelectronics Laboratory, Crypto Group, Louvain-La-Neuve, Belgium

  • Venue:
  • Pairing'07 Proceedings of the First international conference on Pairing-Based Cryptography
  • Year:
  • 2007

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Abstract

At FC'05, Dodis and Yum introduced a new cryptographic tool called time capsule signature (TCS) which allows signers to generate "future signatures" that only become valid from a specific future time t (chosen at signature generation) when a trusted entity (called Time Server) discloses some trapdoor information for period t. In addition, time capsule signatures endow signers with the ability to make their signatures valid before the pre-determined time t. Full signatures that were completed by their original issuer should be indistinguishable from those that automatically became valid after the release of the timespecific trapdoor. Time capsule signatures were showed to be generically constructible from another primitive called identity-based trapdoor hardto-invert relation (ID-THIR). The only known instantiations of the latter either rely on the idealized random oracle model or are too inefficient for real-world applications. In this paper, we devise the first efficient IDTHIR (and thus TCS) construction which is secure in the standard model (i.e. without the random oracle heuristic).