Which of the following is the MOST secure method of storing critical and sensitive system information (e.g., administrative passwords, trusted signing keys)?

Storing data both encrypted and offline in a physical safe provides layered security: strong encryption protects the data if the medium is stolen, while offline isolation removes it from any network-accessible system and eliminates remote attack vectors entirely. The physical access controls of a safe add a third layer, ensuring that compromising one control does not automatically expose the sensitive material.

ZIP password encryption historically uses weak algorithms such as ZipCrypto that are trivially crackable, and the file remains stored on a network-connected system where it is exposed to remote access or malware.

Full disk encryption protects data at rest on the physical drive, but when the system is running and the volume is unlocked, the contents are accessible to any process on the system including network-borne malware or an authenticated remote attacker.

An encrypted virtual disk is decrypted and mounted within a running, potentially network-connected operating system, leaving the contents vulnerable to memory scraping, privilege escalation, or remote exploitation while the disk is in use.