An administrator can prevent dictionary based attacks against an OpenSSH server by forcing keybased authentication with which TWO parameters in sshd_config?

Setting `PasswordAuthentication no` explicitly disables the use of passwords for authentication, thereby eliminating the attack vector for dictionary or brute-force password attempts.

`HostKey` specifies the path to the server's private host key, which is used to identify the server to clients, not to control user authentication methods.

`PrivatekeyAuthentication` is not a standard `sshd_config` parameter for controlling user authentication; `PubkeyAuthentication` is the correct directive for enabling key-based logins.

Setting `PubkeyAuthentication yes` (which is often the default or desired state) ensures that users must authenticate using SSH keys, which are much more resilient to dictionary attacks due to their complexity and cryptographic nature.

`ServerKey` is not a standard `sshd_config` parameter; `HostKey` is used for server key configuration.