Efficient Maliciously Secure Multiparty Computation for RAM

Sanjam Garg, Divya Gupta, Peihan Miao +1 more

Marcel Keller, Avishay Yanai

A crucial issue, that mostly affects the performance of actively secure computation of RAM programs, is the task of reading/writing from/to memory in a private and authenticated manner. Previous works in the active security and multiparty settings are based purely on the SPDZ (reactive) protocol, hence, memory accesses are treated just like any input to the computation. However, a garbled-circuit-based construction (such as BMR), which benefits from a lower round complexity, must resolve the issue of converting memory data bits to their corresponding wire keys and vice versa.

Arash Afshar, Zhangxiang Hu, Payman Mohassel +1 more

Secure 2-party computation (2PC) is becoming practical for some applications. However, most ap-proaches are limited by the fact that the desired functionality must be represented as a boolean circuit. In response, random-access machines (RAM programs) have recently been investigated as a promising alternative representation. In this work, we present the first practical protocols for evaluating RAM programs with security against malicious adversaries. A useful efficiency measure is to divide the cost of malicious-secure evalu-ation of f by the cost of semi-honest-secure evaluation of f. Our RAM protocols achieve ratios matching the state of the art for circuit-based 2PC. For statistical security 2−s, our protocol without preprocessing achieves a ratio of s; our online-offline protocol has a pre-processing phase and achieves online ratio ∼ 2s / log T, where T is the total execution time of the RAM program. To summarize, our solutions show that the “extra overhead ” of obtaining malicious security for RAM programs (beyond what is needed for circuits) is minimal and does not grow with the running time of the program. 1

Himanshu Tyagi, Shun Watanabe

Ivan Damgård, Yuval Ishai

顺东 LI, 文丽 WANG, 润萌 DU

Secure multiparty computation is a focus of the international cryptographic community. The millionaires problem is the most important problem in secure multiparty computation and is a building block for constructing other secure multiparty computation protocols. Several solutions are available to solve this problem, but except for protocols based on garbled circuits, the existing solutions based on public key cryptosystems are only secure in semihonest models. No solution based on a public key cryptosystem is secure against malicious adversaries. This state restricts the resolution of many secure multiparty computation problems in malicious scenarios. A solution that is secure in malicious models is highly applicable in practical application scenarios and is generally appealing. Therefore, the study of the solution to the millionaires problem in a malicious model is of great theoretical and practical significance. In this work, we propose a multiparty computation protocol for the millionaires problem that is secure in a semihonest model. The proposed protocol is simple and easily understandable. We analyze the possible malicious behaviors in this protocol and use zero-knowledge proof and cut-and-choose techniques to resist possible malicious behaviors and thereby convert the protocol into one that is secure in the malicious model. We prove that the proposed protocol is secure in the malicious model by using the well-accepted ideal-real paradigm. Theoretical efficiency analysis shows that the efficiency of our protocol is at least six times that of existing protocols.