International Association
for Cryptologic Research

The dual-execution protocol of Mohassel \\& Franklin (PKC 2006) is a highly efficient (each party garbling only one circuit) 2PC protocol that achieves malicious security apart from leaking an {\\em arbitrary, adversarially-chosen} predicate about the honest party\'s input. We present two practical and orthogonal approaches to improve the security of the dual-execution technique.

First, we show how to greatly restrict the predicate that an adversary can learn in the protocol, to a natural notion of ``only computation leaks\'\'-style leakage. Along the way, we identify a natural security property of garbled circuits called {\\em property-enforcing} that may be of independent interest.

Second, we address a complementary direction of reducing the probability that the leakage occurs. We propose a new dual-execution protocol --- with a very light cheating-detection phase and each party garbling $s+1$ circuits --- in which a cheating party learns a bit with probability only $2^{-s}$. Our concrete measurements show approximately $35\\%$ reduction in communication for the AES circuit, compared to the best combination of state of the art techniques for achieving the same security notion.

Combining the two results, we achieve a rich continuum of practical trade-offs between efficiency \\& security, connecting the covert, dual-execution and full-malicious guarantees.