OpenSSH Service Must Use Passcode for Their Private Keys

Description

Verify the SSH private key files have a passcode. For each private key stored on the system, use the following command:

$ sudo ssh-keygen -y -f /path/to/file

If the contents of the key are displayed, without asking a passphrase this is a finding.

Rationale

If an unauthorized user obtains access to a private key without a passcode, that user would have unauthorized access to any system where the associated public key has been installed.