When using ssh, which of the following can an administrator do to recover a lost passphrase for a DSA or RSA authentication key?

The `ssh-keygen` command can change an existing passphrase (if the old one is known) or generate a new key pair, but it cannot recover a lost passphrase.

There is no standard `ssh --recover` command available for passphrase recovery.

SSH key passphrases are used to encrypt the private key, making it unreadable without the passphrase. This is a one-way cryptographic process; if the passphrase is lost, the private key becomes permanently unusable, and there is no method to recover the original passphrase or decrypt the key.

GnuPG (gpg) is a different encryption system for PGP-compatible keys and files, not designed for decrypting SSH private keys.

There is no `ssh --decrypt` command; SSH client tools do not offer a facility to decrypt private keys without their passphrase.