Dynamic Threshold Public-Key Encryption

  • Authors:
  • Cécile Delerablée;David Pointcheval

  • Affiliations:
  • Orange Labs, and ENS-CNRS-INRIA,;ENS-CNRS-INRIA,

  • Venue:
  • CRYPTO 2008 Proceedings of the 28th Annual conference on Cryptology: Advances in Cryptology
  • Year:
  • 2008

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Abstract

This paper deals with threshold public-key encryptionwhich allows a pool of players to decrypt a ciphertext if a given threshold of authorized players cooperate. We generalize this primitive to the dynamic setting, where any user can dynamicallyjoin the system, as a possible recipient; the sender can dynamicallychoose the authorized set of recipients, for each ciphertext; and the sender can dynamicallyset the threshold tfor decryption capability among the authorized set. We first give a formal security model, which includes strong robustness notions, and then we propose a candidate achieving all the above dynamic properties, that is semantically secure in the standard model, under a new non-interactive assumption, that fits into the general Diffie-Hellman exponent framework on groups with a bilinear map. It furthermore compares favorably with previous proposals, a.k.a.threshold broadcast encryption, since this is the first threshold public-key encryption, with dynamic authorized set of recipients and dynamic threshold that provides constant-size ciphertexts.