Verisign, Inc. Ecole Normale Superieure Portwise, Inc. Symantec Corp. Diversinet Corp. This document describes an algorithm for challenge-response authentication developed by the Initiative for Open Authentication (OATH). The specified mechanisms leverage the HMAC-based One-Time Password (HOTP) algorithm and offer one-way and mutual authentication, and electronic signature capabilities. This document is not an Internet Standards Track specification; it is published for informational purposes.