MemJam: A False Dependency Attack against Constant-Time Crypto Implementations

TL;DR

MemJam introduces a novel side-channel attack exploiting false dependencies in memory read-after-write operations, successfully breaking constant-time cryptographic implementations and bypassing existing protections across modern Intel processors, including SGX enclaves.

Contribution

This work presents the first intra cache level timing attack applicable to all major Intel processors, demonstrating key recovery on constant-time AES and SM4 implementations, and bypassing existing protections.

Findings

Successfully recovered AES keys from constant-time implementations.

Demonstrated attack on SGX enclave encryption.

Outperformed CacheBleed by targeting newer processors.

Abstract

Cache attacks exploit memory access patterns of cryptographic implementations. Constant-Time implementation techniques have become an indispensable tool in fighting cache timing attacks. These techniques engineer the memory accesses of cryptographic operations to follow a uniform key independent pattern. However, the constant-time behavior is dependent on the underlying architecture, which can be highly complex and often incorporates unpublished features. CacheBleed attack targets cache bank conflicts and thereby invalidates the assumption that microarchitectural side-channel adversaries can only observe memory with cache line granularity. In this work, we propose MemJam, a side-channel attack that exploits false dependency of memory read-after-write and provides a high quality intra cache level timing channel. As a proof of concept, we demonstrate the first key recovery attacks on a constant-time implementation of AES, and a SM4 implementation with cache protection in the current Intel Integrated Performance Primitives (Intel IPP) cryptographic library. Further, we demonstrate the first intra cache level timing attack on SGX by reproducing the AES key recovery results on an enclave that performs encryption using the aforementioned constant-time implementation of AES. Our results show that we can not only use this side channel to efficiently attack memory dependent cryptographic operations but also to bypass proposed protections. Compared to CacheBleed, which is limited to older processor generations, MemJam is the first intra cache level attack applicable to all major Intel processors including the latest generations that support the SGX extension.