Implementing a Persistent Key-Value Store in a Tamper-Resistant Device for SGX Enclave Applications

In confidential computing, it is not trivial to provide trusted persistent storage for trusted execution environments (TEEs). Conventional methods utilize the sealing function of TEEs, untrusted storage such as the operating system's file system, and a trusted monotonic counter. These methods have problems such as relying on local monotonic counters with short lifespans and uncertain resistance to shutdown attacks, or requiring complex distributed protocols. To address these problems, this paper proposes implementing persistent storage using a tamper-resistant device. The proposed method provides a persistent key-value store in a tamper-resistant device, thus avoiding complex distributed protocols. The proposed method uses log-structured file system technology on embedded Multi Media Card (eMMC), and achieves extended device lifespan and high resilience against shutdown attacks. As an application of the key-value store, the authors have implemented the basic functions of an electronic voting system that operates within an SGX enclave. This shows that the key-value store possesses sufficient functionality and useful performance.