---
name: "oathtool"
section: "1"
platform: "linux"
package: "oath-toolkit"
version: "2.6.15-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/oathtool"
---

# oathtool(1)

Open AuTHentication (OATH) one-time password tool

## NAME

oathtool - Open AuTHentication (OATH) one-time password tool

## SYNOPSIS

**oathtool** \[*OPTION*\]... \[*KEY* \[*OTP*\]\]...

## DESCRIPTION

Generate and validate OATH one-time passwords.  KEY and OTP is the string '-' to read from standard input, '@FILE' to read from indicated filename, or a hex encoded value (not recommended on multi-user systems).

- **-h**, **--help**

  Print help and exit

- **-V**, **--version**

  Print version and exit

- **--hotp**

  use event-based HOTP mode  (default=on)

- **--totp**\[=*MODE*\]

  use time-variant TOTP mode (values "SHA1", "SHA256", or "SHA512")  (default=\`SHA1')

- **-b**, **--base32**

  use base32 encoding of KEY instead of hex (default=off)

- **--hex**

  use hex encoding of KEY  (default=on)

- **-c**, **--counter**=*COUNTER*

  HOTP counter value

- **-s**, **--time-step-size**=*DURATION* TOTP time-step duration

  (default=\`30s')

- **-S**, **--start-time**=*TIME*

  when to start counting time steps for TOTP (default=\`1970-01-01 00:00:00 UTC')

- **-N**, **--now**=*TIME*

  use this time as current time for TOTP (default=\`now')

- **-d**, **--digits**=*DIGITS*

  number of digits in one-time password

- **-w**, **--window**=*WIDTH*

  number of additional OTPs to generate or validate against

- **-v**, **--verbose**

  explain what is being done  (default=off)

## EXAMPLES

To generate a time-based (TOTP) one-time password from a key protected by GnuPG:

  $ gpg --decrypt --quiet ~/.my-totp-secret.asc \| oathtool --totp -

How to create the encrypted file is outside of scope of this manual, see [gpg(1)](/gpg/1.md), however the following two commands may help you to encrypt the secret symmetrically (using a password) or asymmetrically (if you have created a private key), respectively.  You will need to provide the secret from the terminal after invoking the commands.

  $ gpg --symmetric \> ~/.my-totp-secret.asc\
   $ gpg --encrypt --default-recipient-self \> ~/.my-totp-secret.asc

For easier reading, the rest of this man page provides the KEY and OTP on the command line.  Keep in mind that this usage is not recommended since on most multi-user systems, command-line parameters of running processes can be seen by other users.

To generate the first event-based (HOTP) one-time password for an all-zero key:

   $ echo 00 \| oathtool -\
    328482\
    $

Sometime you want to generate more than a single OTP.  To generate 10 additional event-based one-time passwords, with the secret key used in the examples of RFC 4226, use the -w (--window) parameter:

   $ oathtool -w 10 3132333435363738393031323334353637383930\
    755224\
    287082\
    359152\
    969429\
    338314\
    254676\
    287922\
    162583\
    399871\
    520489\
    403154\
    $

In the last output, the counter for the first OTP was 0, the second OTP had a counter of 1, and so on up to 10.

In order to use keys encoded in Base32 instead of hex, you may provide the -b (--base32) parameter:

   $ oathtool --base32 -w 3 GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ\
    755224\
    287082\
    359152\
    969429\
    $

The tool ignore whitespace in base32 data and re-add padding if necessary, thus you may supply keys formatted like the one below.

   $ oathtool --base32 --totp "gr6d 5br7 25s6 vnck v4vl hlao re"\
    977872\
    $

To generate a particular OTP, use the -c (--counter) parameter to give the exact position directly:

   $ oathtool -c 5 3132333435363738393031323334353637383930\
    254676\
    $

To validate a HOTP one-time password supply the OTP last on the command line:

   $ oathtool -w 10 3132333435363738393031323334353637383930 969429\
    3\
    $

The output indicates the counter that was used.  It works by starting with counter 0 and increment until it founds a match (or not), within the supplied window of 10 OTPs.

The tool supports time-variant one-time passwords, in so called TOTP mode.  Usage is similar, but --totp needs to be provided:

   $ oathtool --totp 00\
    943388\
    $

Don't be alarmed if you do not get the same output, this is because the output depends on the current time.  To generate a TOTP for a particular fixed time use the -N (--now) parameter:

   $ oathtool --totp --now "2008-04-23 17:42:17 UTC" 00\
    974945\
    $

The format is a mostly free format human readable date string such as "Sun, 29 Feb 2004 16:21:42 -0800" or "2004-02-29 16:21:42" or even "next Thursday".  It is the same used as the --date parameter of the [date(1)](/date/1.md) tool.

The default MAC algorithm to use with TOTP is HMAC-SHA1 and this is what is usually used.  The tool supports two other MACs, namely the HMAC-SHA256 and HMAC-SHA512 as well.  To use either of these, qualify the --totp parameter with a value.  Use "SHA256" for HMAC-SHA256 and "SHA512" for HMAC-SHA512.  The following demonstrate generating one of the RFC 6238 test vectors.

   $ oathtool --totp=SHA256 --digits=8 --now "2009-02-13 23:31:30 UTC" 3132333435363738393031323334353637383930313233343536373839303132\
    91819424\
    $

You may generate several TOTPs by specifying the --window parameter, similar to how it works for HOTP.  The OTPs generated here will be for the initial time (normally current time) and then each following time step (e.g., 30 second window).

   $ oathtool --totp 00 -w5\
    815120\
    003818\
    814756\
    184042\
    582326\
    733842\
    $

You can validate a TOTP one-time password by supplying the secret and a window parameter (number of time steps before or after current time):

   $ oathtool --totp -w 5 00 \`oathtool --totp 00\`\
    0\
    $

Similar when generating TOTPs, you can use a -N (--now) parameter to specify the time to use instead of the current time:

  $ oathtool --totp --now="2005-03-18 01:58:29 UTC" -w 10000000 3132333435363738393031323334353637383930 89005924\
   4115227\
   $

The previous test uses values from the TOTP specification and will stress test the tool because the expected window is around 4 million time-steps.

There are two system parameters for TOTP: the time-step size and the time start.

By default the time-step size is 30 seconds, which means you get a new OTP every 30 seconds.  You may modify this with the -s (--time-step-size) parameter:

   $ oathtool --totp --time-step-size=45s 00\
    109841\
    $

The values are valid ISO-8601 durations, see: http://en.wikipedia.org/wiki/ISO\_8601#Durations

The time start is normally 1970-01-01 00:00:00 UTC but you may change it using the -S (--start-time):

   $ oathtool --totp --start-time "1980-01-01 00:00:00 UTC" 00\
    273884\
    $

To get more information about what the tool is using use the -v (--verbose) parameter.  Finally, to generate the last TOTP (for SHA-1) in the test vector table of RFC 6238 you can invoke the tool like this:

   $ oathtool --totp -v -N "2033-05-18 03:33:20 UTC" -d8 3132333435363738393031323334353637383930\
    Hex secret: 3132333435363738393031323334353637383930\
    Base32 secret: GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ\
    Digits: 8\
    Window size: 0\
    TOTP mode: SHA1\
    Step size (seconds): 30\
    Start time: 1970-01-01 00:00:00 UTC (0)\
    Time now: 2033-05-18 03:33:20 UTC (2000000000)\
    Counter: 0x3F940AA (66666666)

   69279037\
    $

## AUTHOR

Written by Simon Josefsson.

## REPORTING BUGS

Report bugs to: \<oath-toolkit-help@nongnu.org\>.\
 OATH Toolkit home page: \<https://oath-toolkit.codeberg.page/\>

## COPYRIGHT

Copyright © 2009-2026 Simon Josefsson. License GPLv3+: GNU GPL version 3 or later \<https://gnu.org/licenses/gpl.html\>.\
 This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.