Editing Authenticator (section)

====ATM card====

To withdraw cash from an [[automated teller machine]] (ATM), a bank customer inserts an ATM card into a cash machine and types a Personal Identification Number (PIN). The input PIN is compared to the PIN stored on the card's chip. If the two match, the ATM withdrawal can proceed.

Note that an ATM withdrawal involves a memorized secret (i.e., a PIN) but the true value of the secret is not known to the ATM in advance. The machine blindly passes the input PIN to the card, which compares the customer's input to the secret PIN stored on the card's chip. If the two match, the card reports success to the ATM and the transaction continues.

An ATM card is an example of a multi-factor authenticator. The card itself is ''something that one has'' while the PIN stored on the card's chip is presumably ''something that one knows''. Presenting the card to the ATM and demonstrating knowledge of the PIN is a kind of multi-factor authentication.