TOSS, for PKI-based authentication, must enforce authorized access to the corresponding private key.

If the private key is discovered, an attacker can use the key to authenticate as an authorized user and gain access to the network infrastructure.

The cornerstone of the PKI is the private key used to encrypt or digitally sign information.

If the private key is stolen, this will lead to the compromise of the authentication and non-repudiation gained through PKI because the attacker can use the private key to digitally sign documents and pretend to be the authorized user.

Both the holders of a digital certificate and the issuing authority must protect the computers, storage devices, or whatever they use to keep the private keys.

Verify the operating system, for PKI-based authentication, enforces authorized access to the corresponding private key.

If the system does not allow PKI authentication, this requirement is Not Applicable.

Verify the SSH private key files have a passphrase.

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, and use of un-passphrased SSH keys is not documented with the Information System Security Officer (ISSO), this is a finding.

Create a new private and public key pair that utilizes a passcode with the following command:

$ sudo ssh-keygen -n [passphrase]