International Association
for Cryptologic Research

Most implementations of Yao\'s garbled circuit approach for 2-party secure computation use the {\\em free-XOR} optimization of Kolesnikov \\& Schneider (ICALP 2008). We introduce an alternative technique called {\\em flexible-XOR} (fleXOR) that generalizes free-XOR and offers several advantages. First, fleXOR can be instantiated under a weaker hardness assumption on the underlying cipher/hash function (related-key security only, compared to related-key and circular security required for free-XOR) while maintaining most of the performance improvements that free-XOR offers. Alternatively, even though XOR gates are not always ``free\'\' in our approach, we show that the other (non-XOR) gates can be optimized more heavily than what is possible when using free-XOR. For many circuits of cryptographic interest, this can yield a significantly (over 30\\%) smaller garbled circuit than any other known techniques (including free-XOR) or their combinations.