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

TL;DR

This paper introduces a new accountable authority identity-based encryption scheme that combines efficiency with simple black-box tracing, extending security to adaptive identity models.

Contribution

It presents a novel IBE construction that merges Goyal's efficient scheme with a straightforward black-box tracing method, achieving adaptive security.

Findings

Efficient scheme with black-box traceability

Extends security to adaptive-ID model

Simple construction suitable for practical use

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.