OATH one-time password tool.


Generate TOTP token (behaves like Google Authenticator)

$ oathtool --totp --base32 "[secret]"

Generate a TOTP token for a specific time
$ oathtool --totp --now "[2004-02-29 16:21:42]" --base32 "[secret]"

Validate a TOTP token
$ oathtool --totp --base32 "[secret]" "[token]"


oathtool [OPTIONS]... [KEY [OTP]]...


oathtool 2.6.6

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


use event-based HOTP mode (default=on)


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

-b, --base32

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

-c, --counter=COUNTER

HOTP counter value

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


-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)


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), 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) 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:

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 $


Report bugs to: oathtool home page: <>
General help using GNU software: <>


Copyright © 2009-2021 Simon Josefsson. License GPLv3+: GNU GPL version 3 or later <>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.


Written by Simon Josefsson.

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