DR.SGX: Hardening SGX Enclaves against Cache Attacks with Data Location Randomization

Recent research has demonstrated that Intel's SGX is vulnerable to various software-based side-channel attacks. In particular, attacks that monitor CPU caches shared between the victim enclave and untrusted software enable accurate leakage of secret enclave data. Known defenses assume developer assistance, require hardware changes, impose high overhead, or prevent only some of the known attacks. In this paper we propose data location randomization as a novel defensive approach to address the threat of side-channel attacks. Our main goal is to break the link between the cache observations by the privileged adversary and the actual data accesses by the victim. We design and implement a compiler-based tool called DR.SGX that instruments enclave code such that data locations are permuted at the granularity of cache lines. We realize the permutation with the CPU's cryptographic hardware-acceleration units providing secure randomization. To prevent correlation of repeated memory accesses we continuously re-randomize all enclave data during execution. Our solution effectively protects many (but not all) enclaves from cache attacks and provides a complementary enclave hardening technique that is especially useful against unpredictable information leakage

Practical Frameworks For hh-Out-Of-nn Oblivious Transfer With Security Against Covert and Malicious Adversaries

We present two practical frameworks for $h$-out-of-$n$ oblivious transfer ($OT^{n}_{h}$). The first one is secure against covert adversaries who are not always willing to cheat at any price. The security is proven under the ideal/real simulation paradigm (call such security fully simulatable security). The second one is secure against malicious adversaries who are always willing to cheat. It provides fully simulatable security and privacy respectively for the sender and the receiver (call such security one-sided simulatable security). The two frameworks can be implemented from the decisional Diffie-Hellman (DDH) assumption, the decisional $N$-th residuosity assumption, the decisional quadratic residuosity assumption and so on. The DDH-based instantiation of our first framework costs the minimum communication rounds and the minimum computational overhead, compared with existing practical protocols for oblivious transfer with fully simulatable security against covert adversaries or malicious adversaries. Though our second framework is not efficient, compared with existing practical protocols with one-sided simulatable security against malicious adversaries. However, it first provides a way to deal with general $OT^{n}_{h}$ on this security level. What is more, its DDH-based instantiation is more efficient than the existing practical protocols for oblivious transfer with fully simulatable security against malicious adversaries