SRAM has no chill: exploiting power domain separation to steal on-chip secrets

The abundance of embedded systems and smart devices increases the risk of physical memory disclosure attacks. One such classic noninvasive attack exploits dynamic RAM's temperature-dependent ability to retain information across power cycles-known as a cold boot attack. When exposed to low temperatures, DRAM cells preserve their state for a short time without power, mimicking nonvolatile memories in that time frame. Attackers exploit this physical phenomenon to gain access to a system's secrets, leading to data theft from encrypted storage. To prevent cold boot attacks, programmers hide secrets on-chip in Static Random-Access Memory (SRAM); by construction, on-chip SRAM is isolated from external probing and has little intrinsic capacitance, making it robust against cold boot attacks.

While it is the case that SRAM protects against traditional cold boot attacks, we show that there is another way to retain information in on-chip SRAM across power cycles and software changes. This paper presents Volt Boot, an attack that demonstrates a vulnerability of on-chip volatile memories due to the physical separation common to modern system-on-chip power distribution networks. Volt Boot leverages asymmetrical power states (e.g., on vs. off) to force SRAM state retention across power cycles, eliminating the need for traditional cold boot attack enablers, such as low-temperature or intrinsic data retention time. Using several modern ARM Cortex-A devices, we demonstrate the effectiveness of the attack in caches, registers, and iRAMs. Unlike other forms of SRAM data retention attacks, Volt Boot retrieves data with 100% accuracy-without any complex post-processing.