How to Efficiently Evaluate RAM Programs with Malicious Security

Abstract

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.