On the Trade-Offs in Oblivious Execution Techniques

To enable privacy-preserving computation on encrypted data, a class of techniques for input-oblivious execution have surfaced. The property of input-oblivious execution guarantees that an adversary observing the interaction of a program with the underlying system learns nothing about the sensitive input. To highlight the importance of oblivious execution, we demonstrate a concrete practical attack—called a logic-reuse attack—that leaks every byte of encrypted input if oblivious techniques are not used. Next, we study the efficacy of oblivious execution techniques and understand their limitations from a practical perspective. We manually transform 30 common Linux utilities by applying known oblivious execution techniques. As a positive result, we show that 6 utilities perform input-oblivious execution without modification, 11 utilities can be transformed with O(1) performance overhead and 11 other show O(N) overhead. As a negative result, we show that theoretical limitations of oblivious execution techniques do manifest in 2 real applications in our case studies incurring a performance cost of \(O(2^N)\) over non-oblivious execution.