TOTP: Time-Based One-Time Password Algorithm

This document describes an extension of the One-Time Password (OTP) algorithm, namely the HMAC-based One-Time Password (HOTP) algorithm, as defined in RFC 4226, to support the time-based moving factor.The HOTP algorithm specifies an event-based OTP algorithm, where the moving factor is an event counter.The present work bases the moving factor on a time value.A time-based variant of the OTP algorithm provides short-lived OTP values, which are desirable for enhanced security.The proposed algorithm can be used across a wide range of network applications, from remote Virtual Private Network (VPN) access and Wi-Fi network logon to transaction-oriented Web applications.The authors believe that a common and shared algorithm will facilitate adoption of two-factor authentication on the Internet by enabling interoperability across commercial and open-source implementations.