Correct Answer: B
The CCST Cybersecurity Study Guide explains that hard disk encryption is a method used to protect data stored on a physical device from unauthorized access.
"Data at rest refers to data stored on a device, such as files on a hard drive, SSD, or removable media. Hard disk encryption protects data at rest by converting it into an unreadable format unless accessed with the correct decryption key." (CCST Cybersecurity, Essential Security Principles, Data States and Protection Methods section, Cisco Networking Academy) Data in process refers to data actively being handled by applications in memory (RAM), which is not the primary target of disk encryption.
Data in transit is protected via encryption methods such as TLS, not disk encryption.
Data in use is accessed and manipulated by programs in real-time, also not the primary scope of disk encryption.
Data at rest is the correct answer, as hard disk encryption directly safeguards stored files.