Adaptively Secure Distributed Broadcast Encryption with Linear-Size Public Parameters
Kwangsu Lee
TL;DR
The paper addresses the challenge of distributed broadcast encryption with decentralized key generation by delivering a scheme that achieves constant-size ciphertexts and private keys alongside linear-size public parameters. It develops a semi-static DBE construction in composite-order bilinear groups and proves security under static assumptions, then leverages the Gentry–Waters transformation to obtain adaptive security. The work foregrounds Déjà Q style proofs to establish semi-static security and uses dual system encryption techniques to support the security claims. Practically, this yields an efficient, adaptively secure DBE with improved public-parameter size, offering potential advantages for decentralized environments such as blockchains, while remaining open to extension to prime-order groups.
Abstract
Distributed broadcast encryption (DBE) is a variant of broadcast encryption (BE) that can efficiently transmit a message to a subset of users, in which users independently generate user private keys and user public keys instead of a central trusted authority generating user keys. In this paper, we propose a DBE scheme with constant size ciphertexts, constant size private keys, and linear size public parameters, and prove the adaptive security of our DBE scheme under static assumptions in composite-order bilinear groups. The previous efficient DBE schemes with constant size ciphertexts and constant size private keys are proven secure under the $q$-Type assumption or have a drawback of having quadratic size public parameters. In contrast, our DBE scheme is the first DBE scheme with linear size public parameters proven adaptively secure under static assumptions in composite-order bilinear groups.