Evaluating the Code Encryption Effects on Memory Fault Resilience

In most safety-critical systems, the robustness and the confidentiality of the application code are crucial. Such code is generally stored into Non-Volatile Memories (NVMs) that are prone to faults (e.g., due to radiation effects). Unfortunately, faults affecting the instruction code result very often into Silent Data Corruption (SDC). This condition lets faults remain undetected and it can lead to undesiderable errors that may compromise the system functionality. Thus, it is desirable that the system is able to detect faults affecting the code memory. To overcome this issue, designers often resort to expensive error detection/correction mechanisms. Furthermore, they also adopt memory encryption techniques to prevent unauthorized, hence malicious, access to the code or to protect it from any unauthorized copy. In this paper, we show that the presence of memory encryption alone is able to strongly reduce the probability of SDC, without the need of implementing expensive error detection. We have performed some experiments on the OpenRISC1200 microprocessor in order to evaluate the impact on reliability stemming from different encryption methods.