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Reference.org
HMAC-based one-time password
open-in-new
<p>HMAC-based one-time password (HOTP) is a <a href="/facts/One-time_password/4u0a4vgk">one-time password</a> (OTP) algorithm based on <a href="/facts/HMAC/Qy9WD4V9">HMAC</a>. It is a cornerstone of the <a href="/facts/Initiative_for_Open_Authentication/hv5DsP8c">Initiative for Open Authentication</a> (OATH). </p><p>HOTP was published as an informational <a href="/facts/IETF/tIcCsFhX">IETF</a> <a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://www.rfc-editor.org/rfc/rfc4226">4226</a> in December 2005, documenting the algorithm along with a Java implementation. Since then, the algorithm has been adopted by many companies worldwide (see below). The HOTP algorithm is a freely available <a href="/facts/Open_standard/RGvhGQVI">open standard</a>. </p>