Three Factor Authentication

Multi-factor authentication (MFA) is a method of confirming a user's claimed identity in which a user is granted access only after successfully presenting 2 or more pieces of evidence (or factors) to an authentication mechanism: knowledge (something they and only they know), possession (something they and only they have), and inherence (something they and only they are).

Two-factor authentication (also known as 2FA) is a type (subset) of multi-factor authentication. It is a method of confirming a user's claimed identity by utilizing a combination of two different factors: 1) something they know, 2) something they have, or 3) something they are.

A good example of two-factor authentication is the withdrawing of money from a ATM; only the correct combination of a bank card (something that the user possesses) and a PIN (personal identification number, something that the user knows) allows the transaction to be carried out.

Two-step verification or two-step authentication is a method of confirming a user's claimed identity by utilizing something they know (password) and a second factor other than something they have or something they are. An example of a second step is the user repeating back something that was sent to them through an out-of-band mechanism. Or the second step might be a 6 digit number generated by an app that is common to the user and the authentication system.

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 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:

Knowledge factors are the most commonly used form of authentication. In this form, the user is required to prove knowledge of a secret in order to authenticate.

A password is a secret word or string of characters that is used for user authentication. This is the most commonly used mechanism of authentication. Many multi-factor authentication techniques rely on password as one factor of authentication. Variations include both longer ones formed from multiple words (a passphrase) and the shorter, purely numeric, personal identification number (PIN) commonly used for ATM access. Traditionally, passwords are expected to be memorized.

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