Adaptively Secure Distributed Broadcast Encryption with Linear-Size Public Parameters

2025-05-23

AI Summary

Existing distributed broadcast encryption (DBE) schemes suffer from two major bottlenecks: security relies on strong, non-standard *q*-type assumptions, and public parameter size grows quadratically in the number of users. This work presents the first adaptively secure DBE scheme based on static assumptions—specifically, in composite-order bilinear groups. Our construction achieves linear public parameter size in the number of users, while ciphertexts and private keys are both constant-sized. The scheme supports user-autonomous key generation and dynamic subset broadcasting, enhanced by a practical distributed key generation protocol. Security is rigorously proven in the standard model, without random oracles. Compared to prior *q*-type or quadratic-parameter constructions, our scheme delivers a substantial breakthrough in both efficiency and security, bridging a long-standing gap between theoretical feasibility and practical deployability.

Technology Category

• Search and Optimization: Distributed Search
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Machine Learning: Privacy

Application Category

• Security and Privacy: Large-scale security measurements
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• User Modeling, Personalization and Recommendation: User privacy protection in personalized systems

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.

Problem

• Achieving adaptive security in distributed broadcast encryption
• Reducing public parameters to linear size in DBE
• Eliminating reliance on q-Type assumptions for security

Innovation

• Adaptively secure DBE under static assumptions
• Linear-size public parameters in DBE
• Constant-size ciphertexts and private keys