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Towards Black-Box Accountable Authority IBE with Short Ciphertexts and Private Keys

Benoît Libert 1 Damien Vergnaud 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 : At Crypto'07, Goyal introduced the concept of Accountable Authority Identity-Based Encryption as a convenient tool to reduce the amount of trust in authorities in Identity-Based Encryption. In this model, if the Private Key Generator (PKG) maliciously re-distributes users' decryption keys, it runs the risk of being caught and prosecuted. Goyal proposed two constructions: the first one is efficient but can only trace well-formed decryption keys to their source; the second one allows tracing obfuscated decryption boxes in a model (called weak black-box model) where cheating authorities have no decryption oracle. The latter scheme is unfortunately far less efficient in terms of decryption cost and ciphertext size. In this work, we propose a new construction that combines the efficiency of Goyal's first proposal with a very simple weak black-box tracing mechanism. Our scheme is described in the selective-ID model but readily extends to meet all security properties in the adaptive-ID sense, which is not known to be true for prior black-box schemes.
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Submitted on : Thursday, January 29, 2009 - 11:13:02 AM
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Benoît Libert, Damien Vergnaud. Towards Black-Box Accountable Authority IBE with Short Ciphertexts and Private Keys. 12th International Conference on Practice and Theory in Public-Key Cryptography - PKC 2009, 2009, Irvine, United States. pp.235-255. ⟨inria-00356999⟩

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