Attaining GOD Beyond Honest Majority with Friends and Foes

Hegde, A and Koti, N and Kukkala, VB and Patil, S and Patra, A and Paul, P (2022) Attaining GOD Beyond Honest Majority with Friends and Foes. In: 8th International Conference on the Theory and Application of Cryptology and Information Security, ASIACRYPT 2022, 5 - 9 December 2022, Taipei, pp. 556-587.

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Abstract

In the classical notion of multiparty computation (MPC), an honest party learning private inputs of others, either as a part of protocol specification or due to a malicious party’s unspecified messages, is not considered a potential breach. Several works in the literature exploit this seemingly minor loophole to achieve the strongest security of guaranteed output delivery via a trusted third party, which nullifies the purpose of MPC. Alon et al. (CRYPTO 2020) presented the notion of Friends and Foes (FaF ) security, which accounts for such undesired leakage towards honest parties by modelling them as semi-honest (friends) who do not collude with malicious parties (foes). With real-world applications in mind, it’s more realistic to assume parties are semi-honest rather than completely honest, hence it is imperative to design efficient protocols conforming to the FaF security model. Our contributions are not only motivated by the practical viewpoint, but also consider the theoretical aspects of FaF security. We prove the necessity of semi-honest oblivious transfer for FaF -secure protocols with optimal resiliency. On the practical side, we present QuadSquad, a ring-based 4PC protocol, which achieves fairness and GOD in the FaF model, with an optimal corruption of 1 malicious and 1 semi-honest party. QuadSquad is, to the best of our knowledge, the first practically efficient FaF secure protocol with optimal resiliency. Its performance is comparable to the state-of-the-art dishonest majority protocols while improving the security guarantee from abort to fairness and GOD. Further, QuadSquad elevates the security by tackling a stronger adversarial model over the state-of-the-art honest-majority protocols, while offering a comparable performance for the input-dependent computation. We corroborate these claims by benchmarking the performance of QuadSquad. We consider the application of liquidity matching that deals with sensitive financial transaction data, where FaF security is apt. We design a range of FaF secure building blocks to securely realize liquidity matching as well as other popular applications such as privacy-preserving machine learning. Inclusion of these blocks makes QuadSquad a comprehensive framework.

Item Type:	Conference Paper
Publication:	Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Publisher:	Springer Science and Business Media Deutschland GmbH
Additional Information:	The copyright for this article belongs to Springer Science and Business Media Deutschland GmbH.
Keywords:	Computation theory; Privacy-preserving techniques; Sensitive data, Friend and foe; Matchings; Multiparty computation; Oblivious transfer; Performance; Protocol specifications; Secure protocols; State of the art; Strong securities; Trusted third parties, Benchmarking
Department/Centre:	Division of Electrical Sciences > Computer Science & Automation
Date Deposited:	27 Mar 2023 08:35
Last Modified:	27 Mar 2023 08:35
URI:	https://eprints.iisc.ac.in/id/eprint/81204

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