Hardware-level memory encryption is designed to protect the contents of RAM from being read or stolen by an attacker who gains sufficient access (for example, through privileged malware, a hypervisor/host compromise, physical attacks like cold-boot techniques, or other memory-snooping methods). That maps directly to data in use, because "data in use" is the state where data is actively processed and often resides in memory during computation. The Study Guide explicitly defines the three data states and makes the connection to memory for data in use: "Data in use is data that is actively in use by a computer system. This includes the data stored in memory while processing takes place. An attacker with control of the system may be able to read the contents of memory and steal sensitive information." By contrast, data at rest focuses on storage media (disk, tape, cloud storage), data in transit focuses on network movement, and data sovereignty concerns jurisdiction/location requirements-none of which are directly addressed by encrypting RAM contents at the hardware level. Since the requirement is specifically
"hardware-level memory encryption," the targeted data state is unambiguously data in use.
References: Data state definitions-data in use includes data stored in memory while processing