Multi-factor authentication

Multi-factor authentication (MFA; two-factor authentication, or 2FA) is an electronic authentication method in which a user is granted access to a website or application only after successfully presenting two or more distinct types of evidence (or factors) to an authentication mechanism. MFA protects personal data—which may include personal identification or financial assets—from being accessed by an unauthorized third party that may have been able to discover, for example, a single password.

Usage of MFA has increased in recent years. Security issues which can cause the bypass of MFA are fatigue attacks, phishing and SIM swapping.

Accounts with MFA enabled are significantly less likely to be compromised.

Authentication takes place when someone tries to log into a computer resource (such as a computer network, device, or application). The resource requires the user to supply the identity by which the user is known to the resource, along with evidence of the authenticity of the user's claim to that identity. Simple authentication requires only one such piece of evidence (factor), typically a password, or occasionally multiple pieces of evidence all of the same type, as with a credit card number and a card verification code (CVC). For additional security, the resource may require more than one factor—multi-factor authentication, or two-factor authentication in cases where exactly two types of evidence are to be supplied.

The use of multiple authentication factors to prove one's identity is based on the premise that an unauthorized actor is unlikely to be able to supply all of the factors required for access. If, in an authentication attempt, at least one of the components is missing or supplied incorrectly, the user's identity is not established with sufficient certainty and access to the asset (e.g., a building, or data) being protected by multi-factor authentication then remains blocked. The authentication factors of a multi-factor authentication scheme may include:

An example of two-factor authentication is the withdrawing of money from an ATM; only the correct combination of a physically present bank card (something the user possesses) and a PIN (something the user knows) allows the transaction to be carried out. Two other examples are to supplement a user-controlled password with a one-time password (OTP) or code generated or received by an authenticator (e.g. a security token or smartphone) that only the user possesses.

An authenticator app enables two-factor authentication in a different way, by showing a randomly generated and constantly refreshing code, rather than sending an SMS or using another method. This code is a Time-based one-time password (a TOTP), and the authenticator app contains the key material that allows the generation of these codes.

Knowledge factors ("something only the user knows") are a form of authentication. In this form, the user is required to prove knowledge of a secret in order to authenticate.