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

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. The contribution of this paper is to describe a new construction that combines the efficiency of Goyal's first proposal with a very simple weak black-box tracing mechanism. The proposed scheme is presented in the selective-ID model but readily extends to meet all ...

• Type: Conference
• Year: 2009
• Where: PKC
• Authors: Benoît Libert, Damien Vergnaud
• Keywords: Cryptography, PKC 2009, Weak Black-box Model, Weak Black-box Tracing, Well-formed Decryption Keys