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New Protocols for Secure Equality Test and Comparison

Geoffroy Couteau

Published Jan 1, 2016• 2 citations
OpenAlex

Abstract

Protocols for securely comparing private values are among the most fundamental building blocks of multiparty computation. introduced by Yao under the name millionaire’s problem, they have found numerous applications in a variety of privacy-preserving protocols; however, due to their inherent non-arithmetic structure, existing construction often remain an important bottleneck in large-scale secure protocols.

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Secure comparison problem, also known as Yao's Millionaires' problem, was introduced by Andrew Yao in 1982. It is a fundamental problem in secure multi-party computation. In this problem, two millionaires are interested in determining the richer one between them without revealing their actual wealth. Yao's millionaires' problem is a classic and fundamental problem in cryptography. The design of secure and efficient solutions to this problem provides effective building blocks for secure multi-party computation. However, only a few of the solutions in the literature have succeeded in resisting attacks of malicious adversaries, and none of these solutions has been proven secure in malicious model under ideal/real simulation paradigm. In this paper, we propose two secure solutions to Yao's millionaires' problem in the malicious model. One solution has full simulation security, and the other solution achieves onesided simulation security. Both protocols are only based on symmetric cryptography. Experimental results indicate that our protocols can securely solve Yao's millionaires' problem with high efficiency and scalability. Furthermore, our solutions show better performance than the state-of-the-art solutions in terms of complexity and security. Specifically, our solutions only require O(|U|) symmetric operations at most to achieve simulation-based security against malicious adversaries, where U denotes the universal set and |U| denotes the size of U.

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Protocols for securely comparing private values are among the most fundamental building blocks of multiparty computation. introduced by Yao under the name millionaire’s problem, they have found numerous applications in a variety of privacy-preserving protocols; however, due to their inherent non-arithmetic structure, existing construction often remain an important bottleneck in large-scale secure protocols.
Yao's classical millionaires' problem is about securely determining whether x>y, given two input values x, y, which are held as private inputs by two parties, respectively. The output which is result of comparison becomes known to both parties. In this paper we consider a variant of comparison problem in which the inputs x, y are encrypted and the actual values are not known to the parties. Our first solution deals with single comparison; however, in many applications, we encounter situations where it is necessary to make multiple comparisons to find the maximum among several encrypted data, so we make a modification to our first protocol to solve the multiple comparisons problem. Such a secure comparison is an important building block for applications like privacy preserving data mining and secure business. Our second protocol is based on Homomorphic encryption which achieves very low communication and computational complexities. Also our protocols can be performed in constant rounds and do not use general circuit evaluation techniques so they are more efficient than circuit based ones but not general. Implementation is easy and fast.
In this paper, we present a protocol for generalized secure comparison problem. Yao's millionaire problem is for comparing the wealth of two parties by preserving their privacy. Ifnnnparties want to compare their wealth by using Yao's protocol, it should be run$n(n-1)2times;iftheirwealthintervalisaslargeasN,thecomplexityofYao′sprotocolfor2 times; if their wealth interval is as large as N, the complexity of Yao's protocol for2times;iftheirwealthintervalisaslargeasN,thecomplexityofYao′sprotocolfornpartiesisinorderofN.parties is in order of N.partiesisinorderofN.\mathbf{n}^{2}, \mathbf{i}.\mathbf{e}...\mathbf{O}\ (\mathbf{N}.\mathbf{n}^{2})$. In this paper, we present a generalized secure comparison protocol, which need not to be run by every two parties separately. We use an easy knapsack problem for distinguishing parties' indices. Our protocol computation and communication complexities are bounded by 0 (n).
Multi-party computation is receiving more and more attention as its application in more areas prove promising. In this research, our focus is on secure two-party computation. In particular, we propose non-interactive constructions for securely computing private equality testing and greater-than testing protocols. Our first construction is a private equality testing (PET) protocol. What distinguishes our construction from the state of the art is that it is single-round and secure against malicious adversaries. Our second construction is a private greater-than testing (PGT) protocol (i.e. the Yao's Millionaires problem) which is also single-round but only secure in the semi-honest model. Our protocols are based on the Peikert-Vaikuntanathan-Waters maliciously secure oblivious transfer and a collision resistant hash function. We formally prove that the PET protocol and the PGT protocol provide computational security. In this research, we developed our protocol for PET and run experiments to test it. The results provide evidence of efficiency of our protocol.
Secure comparison problem, also known as Yao's Millionaires' problem, was introduced by Andrew Yao in 1982. It is a fundamental problem in secure multi-party computation. In this problem, two millionaires are interested in determining the richer one between them without revealing their actual wealth. Yao's millionaires' problem is a classic and fundamental problem in cryptography. The design of secure and efficient solutions to this problem provides effective building blocks for secure multi-party computation. However, only a few of the solutions in the literature have succeeded in resisting attacks of malicious adversaries, and none of these solutions has been proven secure in malicious model under ideal/real simulation paradigm. In this paper, we propose two secure solutions to Yao's millionaires' problem in the malicious model. One solution has full simulation security, and the other solution achieves onesided simulation security. Both protocols are only based on symmetric cryptography. Experimental results indicate that our protocols can securely solve Yao's millionaires' problem with high efficiency and scalability. Furthermore, our solutions show better performance than the state-of-the-art solutions in terms of complexity and security. Specifically, our solutions only require O(|U|) symmetric operations at most to achieve simulation-based security against malicious adversaries, where U denotes the universal set and |U| denotes the size of U.