TAPAS实现高效双服务器隐私聚合,通信量与数据维度无关。
TAPAS: Efficient Two-Server Asymmetric Private Aggregation Beyond Prio(+)
- 一服务器处理高维计算,另一服务器轻量辅助,实现计算不对称
- 通信开销不随输入维度增加,支持千万级参数场景
- 基于格密码的后量子安全,可识别恶意行为者
隐私保护聚合是分布式学习和遥测系统的核心技术,能在不暴露个体记录的前提下训练模型。现有双服务器协议(如Prio)虽能防止单方获知用户数据,但存在服务器负载对称、通信量随客户端输入维度 $L$ 增长的问题。现代学习任务中 $L$ 可达数百万至数千万参数。本文提出 TAPAS,一种新型双服务器非对称隐私聚合方案:(i) 无需可信设置或预处理;(ii) 服务端通信量独立于 $L$;(iii) 基于标准格假设(LWE、SIS)提供后量子安全;(iv) 支持可识别中止和全恶意安全。核心设计为有意的不对称:一个服务器承担 $O(L)$ 的聚合与验证工作,另一服务器作为轻量级协作者,计算量与 $L$ 无关。该设计降低总成本,使次服务器可在普通硬件运行,并强化服务器间不共谋假设。主要贡献之一是构建了一套新的高效格基零知识证明,在双服务器场景首次实现隐私性与正确性结合可识别中止。
原文摘要 · Abstract (English)
Privacy-preserving aggregation is a cornerstone for AI systems that learn from distributed data without exposing individual records, especially in federated learning and telemetry. Existing two-server protocols (e.g., Prio and successors) set a practical baseline by validating inputs while preventing any single party from learning users' values, but they impose symmetric costs on both servers and communication that scales with the per-client input dimension $L$. Modern learning tasks routinely involve dimensionalities $L$ in the tens to hundreds of millions of model parameters. We present TAPAS, a two-server asymmetric private aggregation scheme that addresses these limitations along four dimensions: (i) no trusted setup or preprocessing, (ii) server-side communication that is independent of $L$ (iii) post-quantum security based solely on standard lattice assumptions (LWE, SIS), and (iv) stronger robustness with identifiable abort and full malicious security for the servers. A key design choice is intentional asymmetry: one server bears the $O(L)$ aggregation and verification work, while the other operates as a lightweight facilitator with computation independent of $L$. This reduces total cost, enables the secondary server to run on commodity hardware, and strengthens the non-collusion assumption of the servers. One of our main contributions is a suite of new and efficient lattice-based zero-knowledge proofs; to our knowledge, we are the first to establish privacy and correctness with identifiable abort in the two-server setting.
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