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Dynamic Threshold Public-Key Encryption

Cécile Delerablée 1, 2, 3 David Pointcheval 2, 3
3 CASCADE - Construction and Analysis of Systems for Confidentiality and Authenticity of Data and Entities
DI-ENS - Département d'informatique de l'École normale supérieure, Inria Paris-Rocquencourt, CNRS - Centre National de la Recherche Scientifique : UMR 8548
Abstract : This paper deals with threshold public-key encryption which 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 dynamically join the system, as a possible recipient; the sender can dynamically choose the authorized set of recipients, for each ciphertext; and the sender can dynamically set the threshold t for 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.
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https://hal.inria.fr/inria-00419154
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Cécile Delerablée, David Pointcheval. Dynamic Threshold Public-Key Encryption. Advances in Cryptology -- Proceedings of CRYPTO '08, 2008, Santa-Barbara, Californie, United States. pp.317--334. ⟨inria-00419154⟩

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