How to Efficiently Evaluate RAM Programs with Malicious Security.

Secure 2-party computation (2PC) is becoming practical for some applications. However, most approaches 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 evaluation 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 similar to 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.