.. index:: single: otp_protocol
.. _otp_protocol/0:

.. rst-class:: right

**protocol**

``otp_protocol``
================

Protocol for HOTP and TOTP generation and verification as specified in RFC 4226 and RFC 6238.

| **Availability:** 
|    ``logtalk_load(otp(loader))``

| **Author:** Paulo Moura
| **Version:** 1:0:0
| **Date:** 2026-07-14

| **Compilation flags:**
|    ``static``


| **Dependencies:**
|   (none)


| **Remarks:**
|    (none)

| **Inherited public predicates:**
|    (none)

.. contents::
   :local:
   :backlinks: top

Public predicates
-----------------

.. index:: hotp/5
.. _otp_protocol/0::hotp/5:

``hotp/5``
^^^^^^^^^^

Computes an HOTP value for the given hash object, secret, moving counter, and number of digits. The secret can be either a raw byte list or a Base32 wrapper term of the form ``base32(atom(Atom))``, ``base32(chars(Chars))``, or ``base32(codes(Codes))``.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``hotp(Hash,Secret,Counter,Digits,OTP)``
| **Mode and number of proofs:**
|    ``hotp(+object_identifier,+term,+integer,+integer,--atom)`` - ``one``


------------

.. index:: totp/5
.. _otp_protocol/0::totp/5:

``totp/5``
^^^^^^^^^^

Computes a TOTP value using the standard 30-second time step and Unix epoch ``T0 = 0`` for the given hash object, secret, Unix time, and number of digits.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``totp(Hash,Secret,UnixTime,Digits,OTP)``
| **Mode and number of proofs:**
|    ``totp(+object_identifier,+term,+integer,+integer,--atom)`` - ``one``


------------

.. index:: hotp_verify/7
.. _otp_protocol/0::hotp_verify/7:

``hotp_verify/7``
^^^^^^^^^^^^^^^^^

Verifies an HOTP value by searching from the given counter through the bounded forward counter window. Returns the matched counter on success.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``hotp_verify(Hash,Secret,Counter,Window,Digits,OTP,MatchedCounter)``
| **Mode and number of proofs:**
|    ``hotp_verify(+object_identifier,+term,+integer,+integer,+integer,+atom,--integer)`` - ``zero_or_one_or_error``


------------

.. index:: totp_verify/7
.. _otp_protocol/0::totp_verify/7:

``totp_verify/7``
^^^^^^^^^^^^^^^^^

Verifies a TOTP value by searching within the bounded symmetric time-step window around the current time step. Returns the matched time step on success.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``totp_verify(Hash,Secret,UnixTime,Window,Digits,OTP,MatchedTimeStep)``
| **Mode and number of proofs:**
|    ``totp_verify(+object_identifier,+term,+integer,+integer,+integer,+atom,--integer)`` - ``zero_or_one_or_error``


------------

Protected predicates
--------------------

(none)

Private predicates
------------------

(none)

Operators
---------

(none)

.. seealso::

   :ref:`hmac_protocol <hmac_protocol/0>`