A CASTLE With TOWERs for Reliable, Secure Phase-Change Memory

The use of hardware encryption and new memory technologies such as phase change memory (PCM) are gaining popularity in a variety of server applications such as cloud systems. While PCM provides energy and density advantages over conventional DRAM memory, it faces endurance challenges. Such challenges are exacerbated when employing memory encryption as the stored data is essentially randomized, losing data similarity and reducing or eliminating the effectiveness of energy and endurance oriented encoding techniques. This results in increasing dynamic energy consumption and accelerated wear out. In this article, we propose CASTLE, a technique for in-memory encryption to leverage this encryption process to improve reliability in the presence of endurance faults. We also propose TOWERs for CASTLE that improve reliability as well as energy for encrypted data through a novel application of compression and encoding. CASTLE and TOWERs are compatible with error-correction codes (ECC) and error correction pointers (ECP), the standard for mitigating endurance faults in PCM. When combining CASTLE and TOWERS, we achieve an average lifetime improvement of over 45× compared to SECDED ECC, 7.1× compared to SECRET, and 3.6× compared to the leading partition-and-flip fault-tolerance approach (AEGIS) for the same area overhead.