What is HMAC-Based One-Time Password (HOTP)?

A HMAC-based One-Time Password (HOTP) is a password that makes use of a one-time password (OTP) algorithm leveraging Hash-Based Message Authentication Code (HMAC). HOTPs, like Time-based One-Time Passwords (TOTPs), are used as a security measure for specialized authentication methods such as two-factor authentication (2FA). The HOTP mechanism uses a hash-generated one-time password that allows users to securely log in to various websites often through their mobile phone using an authentication application.