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https://github.com/susam/mintotp
Minimal TOTP generator in 20 lines of Python
https://github.com/susam/mintotp
2fa cryptography hotp minimalist python3 security totp
Last synced: 14 days ago
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Minimal TOTP generator in 20 lines of Python
- Host: GitHub
- URL: https://github.com/susam/mintotp
- Owner: susam
- License: mit
- Created: 2019-08-08T14:40:10.000Z (over 5 years ago)
- Default Branch: main
- Last Pushed: 2024-01-21T01:42:02.000Z (10 months ago)
- Last Synced: 2024-10-01T08:48:28.909Z (about 1 month ago)
- Topics: 2fa, cryptography, hotp, minimalist, python3, security, totp
- Language: Python
- Homepage:
- Size: 39.1 KB
- Stars: 1,306
- Watchers: 21
- Forks: 90
- Open Issues: 3
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGES.md
- License: LICENSE.md
Awesome Lists containing this project
README
MinTOTP
=======
MinTOTP is a minimal TOTP generator written in Python.
[![View Source][Source SVG]][src]
[![PyPI Package][PyPI SVG]][pypi]
[![PyPI Hits][Hits SVG]][pypi]
[![MIT License][License SVG]][L]
[Source SVG]: https://img.shields.io/badge/view-source-brightgreen.svg
[src]: mintotp.py
[PyPI SVG]: https://img.shields.io/pypi/v/mintotp.svg
[Hits SVG]: https://img.shields.io/pypi/dm/mintotp
[License SVG]: https://img.shields.io/badge/license-MIT-blue.svg
Contents
--------
* [Introduction](#introduction)
* [Source Code](#source-code)
* [Install](#install)
* [From PyPI](#from-pypi)
* [From GitHub](#from-github)
* [Get Started](#get-started)
* [With Base32 Key](#with-base32-key)
* [With QR Code](#with-qr-code)
* [Protect Key with GPG](#protect-key-with-gpg)
* [Install GPG](#install-gpg)
* [Encrypt Base32 Key With GPG](#encrypt-base32-key-with-gpg)
* [Encrypt QR Code With GPG](#encrypt-qr-code-with-gpg)
* [Usage](#usage)
* [Multiple Keys](#multiple-keys)
* [Command Line Arguments](#command-line-arguments)
* [Tradeoff](#tradeoff)
* [Alternative: OATH Toolkit](#alternative-oath-toolkit)
* [Resources](#resources)
* [License](#license)
* [Thanks](#thanks)
Introduction
------------
TOTP stands for Time-Based One-Time Password. Many websites and services
require two-factor authentication (2FA) or multi-factor authentication
(MFA) where the user is required to present two or more pieces of
evidence:
- Something only the user knows, e.g., password, passphrase, etc.
- Something only the user has, e.g., hardware token, mobile phone, etc.
- Something only the user is, e.g., biometrics.
A TOTP value serves as the second factor, i.e., it proves that the user
has a device (e.g., mobile phone) that contains a TOTP
secret key from which the TOTP value is generated. Usually the service
provider that provides a user's account also issues a secret key encoded
either as a Base32 string or as a QR code. This secret key is added to
an authenticator app (e.g., Google Authenticator) on a mobile device.
The app can then generate TOTP values based on the current time.
By default, it generates a new TOTP value every 30 seconds.
MinTOTP is a Python tool that can be used to generate TOTP values from a
secret key. Additionally, it exposes its functionality as module-level
functions for Python developers. It can be used on any system with
Python 3.4 or later installed on it.
Source Code
-----------
At the heart of the TOTP algorithm lies the HOTP algorithm. HOTP stands
for HMAC-based One-Time Password. HMAC stands for Hash-based Message
Authentication Code. Here are the relevant RFCs to learn more about
these algorithms:
- [RFC 2104]: HMAC: Keyed-Hashing for Message Authentication
- [RFC 4226]: HOTP: An HMAC-Based One-Time Password Algorithm
- [RFC 6238]: TOTP: Time-Based One-Time Password Algorithm
[RFC 2104]: https://tools.ietf.org/html/rfc2104
[RFC 4226]: https://tools.ietf.org/html/rfc4226
[RFC 6238]: https://tools.ietf.org/html/rfc6238
The source code in [`mintotp.py`][src] generates TOTP values from a
secret key and current time. It's just 30 lines of code (actually 20
lines if we ignore the shebang and blank lines). There are no comments
in the code, so a brief description of the code is presented in this
section. Here is the entire code presented once again for convenience:
```python
#!/usr/bin/env python3
import base64
import hmac
import struct
import sys
import time
def hotp(key, counter, digits=6, digest='sha1'):
key = base64.b32decode(key.upper() + '=' * ((8 - len(key)) % 8))
counter = struct.pack('>Q', counter)
mac = hmac.new(key, counter, digest).digest()
offset = mac[-1] & 0x0f
binary = struct.unpack('>L', mac[offset:offset+4])[0] & 0x7fffffff
return str(binary)[-digits:].zfill(digits)
def totp(key, time_step=30, digits=6, digest='sha1'):
return hotp(key, int(time.time() / time_step), digits, digest)
def main():
args = [int(x) if x.isdigit() else x for x in sys.argv[1:]]
for key in sys.stdin:
print(totp(key.strip(), *args))
if __name__ == '__main__':
main()
```
In the code above, we use the `hmac` module available in the Python
standard library to implement HOTP. The implementation can be found in
the `hotp()` function. It is a pretty straightforward implementation of
[RFC 2104: Section 5: HOTP Algorithm][RFC 2104-5]. It takes a
Base32-encoded secret key and a counter as input. It returns a 6-digit
HOTP value as output.
The `totp()` function implements the TOTP algorithm. It is a thin
wrapper around the HOTP algorithm. The TOTP value is obtained by
invoking the HOTP function with the secret key and the number of time
intervals (30-second intervals by default) that have elapsed since Unix
epoch (1970-01-01 00:00:00 UTC).
[RFC 2104-5]: https://tools.ietf.org/html/rfc4226#section-5
Install
-------
MinTOTP requires Python 3.4 or later. If Python 3.4 or later is present
on your system, follow one of the two sections below to get MinTOTP on
your system.
### From PyPI
If you want to install the MinTOTP package from [PyPI][pypi] as a Python
module on your system, then follow the steps provided below. Doing so
makes MinTOTP available as the `mintotp` command that you can run on the
terminal. A module named `mintotp` also becomes available that you can
`import` in your own Python code.
1. Enter the following command to install MinTOTP on your system:
```shell
pip3 install mintotp
```
2. Test that MinTOTP works fine as a command:
```shell
mintotp <<< ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS
```
A 6-digit TOTP value should appear as the output.
3. Test that MinTOTP can be used as a library module:
```pycon
$ python3
>>> import mintotp
>>> mintotp.totp('ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS')
>>> mintotp.hotp('ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS', 42)
```
The `totp()` function call should return a 6-digit TOTP value based
on the current time. The `hotp()` call should return the following
HOTP value: `626854`.
### From GitHub
If you do not want to install MinTOTP to your system as a command but
you want to work with the [`mintotp.py`][src] source file directly
clone the GitHub repository of this project.
1. Clone GitHub repository of this project and enter its top-level
directory.
```shell
git clone https://github.com/susam/mintotp.git
cd mintotp
```
2. Test that [`mintotp.py`][src] works fine:
```shell
python3 mintotp.py <<< ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS
```
A 6-digit TOTP value should appear as the output.
3. Test that [`mintotp.py`][src] can be imported as a module:
```pycon
$ python3
>>> import mintotp
>>> mintotp.totp('ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS')
>>> mintotp.hotp('ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS', 42)
```
The `totp()` function call should return a 6-digit TOTP value based
on the current time. The `hotp()` call should return the following
HOTP value: `626854`.
All examples provided in the sections below assume that MinTOTP has been
installed from PyPI. If you choose to use MinTOTP from GitHub instead,
replace all occurrences of `mintotp` in the example commands below with
`python3 mintotp.py`.
Get Started
-----------
This section presents a few examples to quickly get started with
MinTOTP.
Note that this section uses a few example secret keys and QR codes. They
are merely examples that come with this project for you to quickly test
the program with. They should not be used for any real account that
requires TOTP-based two-factor authentication. Usually, the issuer of a
real account (such as an account on a website or an organization) would
also issue a secret key or a secret QR code to you which you must use to
generate TOTP values for the purpose of logging into that account.
### With Base32 Key
1. Enter this command:
```shell
mintotp <<< ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS
```
The output should be a 6-digit TOTP value.
2. Add the following key to a TOTP-based authenticator app:
```
ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS
```
For example, if you have Google Authenticator on your mobile phone,
open it, tap the button with plus sign, select "Enter a provided
key", enter any account name and "Time-based" and enter the
above key. Set the dropdown menu to "Time-based" and tap the "Add"
button. A 6-digit TOTP value should appear for the new key.
3. Run the command in step 1 again and verify that the TOTP value
printed by the Python program matches the TOTP value that appears in
the authenticator app.
### With QR Code
1. Install `zbarimg` to scan QR codes:
```shell
# On macOS
brew install zbar
# On Debian, Ubuntu, etc.
apt-get install zbar-tools
```
2. Download and save the following QR code on your system:\
[](secret1.png)\
The QR code above can also be found in this file:
[secret1.png](secret1.png).
3. Enter this command to read the data in the QR code:
```shell
zbarimg -q secret1.png
```
The output should be:
```
QR-Code:otpauth://totp/alice:bob?secret=ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS
```
Note that the secret key in the URI is the same as the secret key we
used in the previous sections.
4. Now enter this command to extract the secret key from the QR code
and feed it to MinTOTP.
```shell
zbarimg -q secret1.png | sed 's/.*secret=\([^&]*\).*/\1/' | mintotp
```
5. Scan the QR code shown above in step 3 with a TOTP-based
authenticator app. For example, if you have Google Authenticator on
your mobile phone, open it, tap the button with plus sign, select
"Scan a barcode", and scan the QR code shown above in step 3. A
6-digit TOTP value should appear for the new key.
6. Run the command in step 4 again and verify that the TOTP value
printed by MinTOTP matches the TOTP value that appears in the
authenticator app.
Protect Key with GPG
--------------------
The previous sections use an example key and QR code to show how this
tool works. If you use this tool to generate TOTP values from a real
secret key for a real account, you must encrypt your secret key to keep
it safe. The next two subsections explain how to protect the key with
GNU Privacy Guard (also known as GnuPG or GPG).
### Install GPG
1. Install GNU Privacy Guard:
```shell
# On macOS
brew install gnupg
# On Debian, Ubuntu, etc.
apt-get update
apt-get install gnupg
```
2. Enter the following command to ensure that GPG is installed.
```shell
gpg --version
```
If GPG is installed properly, the command above should print its
version, license details, and cipher details.
### Encrypt Base32 Key With GPG
The steps below show the usage of GPG to encrypt our example secret key.
You would have to replace this example secret key with a real secret key
that you want to use to generate TOTP values.
1. Encrypt the secret key using GPG. First enter this command:
```shell
gpg -c -o secret.gpg
```
Then enter a [strong passphrase] when it prompts for it. Re-enter
the passphrase to confirm it. Then paste the following key as input:
```
ZYTYYE5FOAGW5ML7LRWUL4WTZLNJAMZS
```
Press enter to end the line. Press ctrl +
d to end input. The encrypted secret key would be saved
in a file named `secret.gpg`.
2. Generate TOTP value from the encrypted key:
```shell
gpg -q -o - secret.gpg | mintotp
```
3. You can also generate TOTP value and copy it to system clipboard:
```shell
# On macOS
gpg -q -o - secret.gpg | mintotp | tr -d '\n' | pbcopy
# On Linux
gpg -q -o - secret.gpg | mintotp | tr -d '\n' | xclip
```
Now you can easily paste the TOTP value to any login form that
requires it. On Linux, of course, you need to have `xclip` installed
to use it. On Debian, Ubuntu, etc. it can be installed with the
`apt-get install xclip` command. To paste the value copied into the
clipboard by `xclip`, middle-click on your mouse.
4. In case you want to see the TOTP value on the terminal while it is
also copied to the system clipboard, use one of these commands:
```shell
# On macOS
gpg -q -o - secret.gpg | mintotp | tee /dev/stderr | tr -d '\n' | pbcopy
# On Linux
gpg -q -o - secret.gpg | mintotp | tee /dev/stderr | tr -d '\n' | xclip
```
[strong passphrase]: https://www.gnupg.org/faq/gnupg-faq.html#strong_passphrase
### Encrypt QR Code With GPG
The steps below show the usage of GPG to encrypt our example QR code.
You would have to replace the example QR code with a real QR code that
you want to use to generate TOTP values.
1. Encrypt the QR code using GPG. First enter this command:
```shell
gpg -c secret1.png
```
Then enter a [strong passphrase] when it prompts for it. Re-enter
the passphrase to confirm it. The encrypted QR code would be saved in
a file named `secret1.png.gpg`.
2. Delete the unencrypted QR code file securely:
```shell
# On macOS
rm -P secret1.png
# On Linux
shred -u secret1.png
```
3. Generate TOTP value from the encrypted QR code file:
```shell
zbarimg -q <(gpg -q -o - secret1.png.gpg) | sed 's/.*secret=\([^&]*\).*/\1/' | mintotp
```
4. You can also generate the TOTP value and copy it to system clipboard:
```shell
# On macOS
zbarimg -q <(gpg -q -o - secret1.png.gpg) | sed 's/.*secret=\([^&]*\).*/\1/' | mintotp | tr -d '\n' | pbcopy
# On Linux
zbarimg -q <(gpg -q -o - secret1.png.gpg) | sed 's/.*secret=\([^&]*\).*/\1/' | mintotp | tr -d '\n' | xclip
```
5. In case you want to see the TOTP value on the terminal while it is
also copied to the system clipboard, use one of these commands:
```shell
# On macOS
zbarimg -q <(gpg -q -o - secret1.png.gpg) | sed 's/.*secret=\([^&]*\).*/\1/' | mintotp | tee /dev/stderr | tr -d '\n' | pbcopy
# On Linux
zbarimg -q <(gpg -q -o - secret1.png.gpg) | sed 's/.*secret=\([^&]*\).*/\1/' | mintotp | tee /dev/stderr | tr -d '\n' | xclip
```
Usage
-----
### Multiple Keys
This tool accepts one or more Base32 secret keys as standard input. Each
key must occur in its own line.
1. Generate multiple TOTP values, one for each of multiple Base32 keys:
```shell
mintotp <.
Thanks
------
Thanks to [Prateek Nischal][PN] for getting me involved with TOTP. I
referred to his TOTP implementation at
[prateeknischal/qry/util/totp.py][PNTOTP] while writing my own.
[PN]: https://github.com/prateeknischal
[PNTOTP]: https://github.com/prateeknischal/qry/blob/master/util/totp.py