ZweiFaktorAuth

ZweiFaktorAuth is a term describing two-factor authentication, a security measure that requires two independent credentials to verify a user's identity. Typically this combines something the user knows (a password) with something the user possesses (a token or device) or something the user is (a biometric trait).

Common implementations include time-based one-time passwords generated by authenticator apps, push-based approvals, and hardware security keys that support FIDO2/WebAuthn or U2F. SMS codes are also sometimes used but are generally less secure.

Standards such as TOTP (RFC 6238) and HOTP (RFC 4226) govern code-based methods, while FIDO2/WebAuthn provides phishing-resistant, public-key-based second factors. The choice of method affects usability, phishing resistance, and recovery options.

Security and policy considerations include the trade-off between convenience and protection, the need for backup/recovery options, and handling of device loss. 2FA reduces the risk of credential theft but is not immune to phishing or social engineering if weaker methods are used.