AlphaFL: Secure Aggregation with Malicious2 Security for Federated Learning against Dishonest Majority

Research output: Contribution to journalResearch articleContributedpeer-review

Contributors

  • Yufan Jiang - , Karlsruhe Institute of Technology (Author)
  • Maryam Zarezadeh - , Barkhausen Institut (Author)
  • Tianxiang Dai - , Lancaster University Leipzig (Author)
  • Stefan Köpsell - , Barkhausen Institut (Author)

Abstract

Federated learning (FL) proposes to train a global machine learning model across distributed datasets. However, the aggregation protocol as the core component in FL is vulnerable to well-studied attacks, such as inference attacks, poisoning attacks [71] and malicious participants who try to deviate from the protocol [24]. Therefore, it is crucial to achieve both malicious security and poisoning resilience from cryptographic and FL perspectives, respectively. Prior works either achieve incomplete malicious security [76], address issues by using expensive cryptographic tools [22, 59] or assume the availability of a clean dataset on the server side [32]. In this work, we propose AlphaFL, a two-server secure aggregation protocol achieving both malicious security in the universal composability (UC) framework [19] and poisoning resilience in FL (thus malicious2) against a dishonest majority. We design maliciously secure multi-party computation (MPC) protocols [24, 26, 48] and introduce an efficient input commitment protocol tolerating server-client collusion (dishonest majority). We also propose an efficient input commitment protocol for the non-collusion case (honest majority), which triples the efficiency in time and quadruples that in communication, compared to the state-of-the-art solution in MP-SPDZ [46]. To achieve poisoning resilience, we carry out 𝐿∞ and 𝐿2-Norm checks with a dynamic L_2-Norm bound by introducing a novel silent select protocol, which improves the runtime by at least two times compared to the classic select protocol. Combining these, AlphaFL achieves malicious2 security at a cost of 25% − 79% more runtime overhead than the state-of-the-art semi-malicious counterpart Elsa [76], with even less communication cost.

Details

Original languageEnglish
Pages (from-to)348-368
Number of pages21
JournalProceedings on privacy enhancing technologies : PoPETs
Volume2025
Issue number4
Publication statusPublished - Oct 2025
Peer-reviewedYes
Externally publishedYes

External IDs

ORCID /0000-0002-0466-562X/work/199216541
Mendeley 6163c8a6-35a0-385c-a517-0156d8f68a15
unpaywall 10.56553/popets-2025-0134