Which combination of authentication methods can provide two-factor authentication?

Two-factor authentication (2FA) enhances security by requiring two independent forms of verification before granting access. This can include something the user knows (like a password) and something the user has (like a security token). The combination of RADIUS and RSA SecurID perfectly embodies this principle.

RADIUS (Remote Authentication Dial-In User Service) is a networking protocol for user authentication, which operates by communicating with a central server. RSA SecurID is a widely recognized two-factor authentication mechanism that generates time-sensitive one-time passwords (OTPs) based on a user's assigned token. The interaction between RADIUS and RSA SecurID ensures that in addition to a password (something the user knows), the user must also provide the OTP from their RSA token (something the user has), thus fulfilling the requirements for two-factor authentication.

In contrast, options that do not include a dedicated second factor (like a physical token) either rely solely on single-factor authentication or are based on methods that do not complement each other in creating a robust two-factor authentication system. Therefore, the combination of RADIUS and RSA SecurID stands out as the most effective choice for implementing 2FA.