Which of the following commands would an administrator use to create an OpenSSH authentication key?

`sshd` is the OpenSSH daemon that listens for incoming SSH connections, not a key generation tool.

`ssh-agent` is a program that holds private keys used for public key authentication, allowing them to be used without re-entering passphrases, but it does not create the keys.

`ssh-keygen` is the standard OpenSSH command-line utility specifically designed to create, manage, and convert authentication keys (both public and private) for secure shell (SSH) connections. It supports various key types like RSA, DSA, ECDSA, and Ed25519.

`ssh-add` adds identity files (private keys) to the authentication agent (`ssh-agent`), it does not generate new keys.