`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: 2026-08-08

| 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

| Exceptions: | Hash, Secret, Counter, Window, Digits, or OTP is a variable or a partial list: | instantiation_error | Hash is not a supported OTP hash object: | domain_error(otp_hash,Hash) | Secret is neither a partial list nor a list: | type_error(list,Secret) | An element Byte of the Secret` list is neither a variable nor an integer: | type_error(integer,Byte) | An element Byte of the Secret list is an integer but not a valid byte: | domain_error(byte,Byte) | Secret is not a valid Base32 source: | domain_error(base32_source,Secret) | Counter or Window is neither a variable nor an integer: | type_error(integer,Integer) | Counter or Window is an integer but not a non-negative integer: | domain_error(non_negative_integer,Integer) | Digits is neither a variable nor an integer: | type_error(integer,Digits) | Digits is an integer but not a positive integer: | domain_error(positive_integer,Digits) | OTP neither a variable nor an atom: | type_error(atom,OTP) | OTP does not contain exactly Digits decimal digits: | domain_error(otp_value,OTP) | A searched counter exceeds the 64-bit HOTP moving-factor range: | domain_error(otp_moving_factor,Counter)

.. 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

| Exceptions: | Hash, Secret, UnixTime, Window, Digits, or OTP is a variable or a partial list: | instantiation_error | Hash is not a supported OTP hash object: | domain_error(otp_hash,Hash) | Secret is neither a partial list nor a list: | type_error(list,Secret) | An element Byte of the Secret` list is neither a variable nor an integer: | type_error(integer,Byte) | An element Byte of the Secret list is an integer but not a valid byte: | domain_error(byte,Byte) | Secret is not a valid Base32 source: | domain_error(base32_source,Secret) | UnixTime or Window is neither a variable nor an integer: | type_error(integer,Integer) | UnixTime or Window is an integer but not a non-negative integer: | domain_error(non_negative_integer,Integer) | Digits is neither a variable nor an integer: | type_error(integer,Digits) | Digits is an integer but not a positive integer: | domain_error(positive_integer,Digits) | OTP is neither a variable nor an atom: | type_error(atom,OTP) | OTP does not contain exactly Digits decimal digits: | domain_error(otp_value,OTP) | A searched time step exceeds the 64-bit HOTP moving-factor range: | domain_error(otp_moving_factor,TimeStep)

Protected predicates

(none)

Private predicates

(none)

Operators

(none)

.. seealso::

:ref:`hmac_protocol <hmac_protocol/0>`