The correct option is Security keys for the highest level of protection on GitHub Enterprise.

Security keys use FIDO2 and WebAuthn with hardware backed credentials that bind authentication to the real GitHub origin, so a phishing site cannot replay or proxy the sign in. They perform a challenge and response using private keys that never leave the device and they require an explicit user touch or presence, which stops credential theft and common code relay attacks.

GitHub supports Security keys for two factor authentication and treats them as the most secure choice for administrators who need strong, phishing resistant protection.

The SMS authentication option is vulnerable to SIM swapping and message interception and GitHub has been phasing out SMS authentication for new two factor enrollments, so it is neither robust nor phishing resistant.

The TOTP option relies on codes that users can be tricked into entering on a fake site because it does not validate the website origin, so it is phishable and weaker than Security keys.

The SSH keys option secures Git operations over SSH, which does not serve as a second factor for signing in to the GitHub web interface, so it does not meet the requirement.

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