PyOTP - The Python One-Time Password Library
============================================

PyOTP is a Python library for generating and verifying one-time passwords. It can be used to implement two-factor (2FA)
or multi-factor (MFA) authentication methods in web applications and in other systems that require users to log in.

Open MFA standards are defined in `RFC 4226 <https://tools.ietf.org/html/rfc4226>`_ (HOTP: An HMAC-Based One-Time
Password Algorithm) and in `RFC 6238 <https://tools.ietf.org/html/rfc6238>`_ (TOTP: Time-Based One-Time Password
Algorithm). PyOTP implements server-side support for both of these standards. Client-side support can be enabled by
sending authentication codes to users over SMS or email (HOTP) or, for TOTP, by instructing users to use `Google
Authenticator <https://en.wikipedia.org/wiki/Google_Authenticator>`_, `Authy <https://www.authy.com/>`_, or another
compatible app. Users can set up auth tokens in their apps easily by using their phone camera to scan `otpauth://
<https://github.com/google/google-authenticator/wiki/Key-Uri-Format>`_ QR codes provided by PyOTP.

Implementers should read and follow the `HOTP security requirements <https://tools.ietf.org/html/rfc4226#section-7>`_
and `TOTP security considerations <https://tools.ietf.org/html/rfc6238#section-5>`_ sections of the relevant RFCs. At
minimum, application implementers should follow this checklist:

- Ensure transport confidentiality by using HTTPS
- Ensure HOTP/TOTP secret confidentiality by storing secrets in a controlled access database
- Deny replay attacks by rejecting one-time passwords that have been used by the client (this requires storing the most 
  recently authenticated timestamp, OTP, or hash of the OTP in your database, and rejecting the OTP when a match is seen)
- Throttle brute-force attacks against your application's login functionality
- When implementing a "green field" application, consider supporting
  `FIDO U2F <https://en.wikipedia.org/wiki/Universal_2nd_Factor>`_ in addition to HOTP/TOTP. U2F uses asymmetric
  cryptography to avoid using a shared secret design, which strengthens your MFA solution against server-side compromise.
  Hardware U2F also sequesters the client secret in a dedicated single-purpose device, which strengthens your clients
  against client-side compromise.

We also recommend that implementers read the
`OWASP Authentication Cheat Sheet <https://www.owasp.org/index.php/Authentication_Cheat_Sheet>`_ and
`NIST SP 800-63-3: Digital Authentication Guideline <https://pages.nist.gov/800-63-3/>`_ for a high level overview of
authentication best practices.

Quick overview of using One Time Passwords on your phone
--------------------------------------------------------

* OTPs involve a shared secret, stored both on the phone and the server
* OTPs can be generated on a phone without internet connectivity
* OTPs should always be used as a second factor of authentication (if your phone is lost, you account is still secured with a password)
* Google Authenticator and other OTP client apps allow you to store multiple OTP secrets and provision those using a QR Code

Installation
------------
::

    pip install pyotp

Usage
-----

Time-based OTPs
~~~~~~~~~~~~~~~
::

    totp = pyotp.TOTP('base32secret3232')
    totp.now() # => '492039'

    # OTP verified for current time
    totp.verify('492039') # => True
    time.sleep(30)
    totp.verify('492039') # => False

Counter-based OTPs
~~~~~~~~~~~~~~~~~~
::

    hotp = pyotp.HOTP('base32secret3232')
    hotp.at(0) # => '260182'
    hotp.at(1) # => '055283'
    hotp.at(1401) # => '316439'

    # OTP verified with a counter
    hotp.verify('316439', 1401) # => True
    hotp.verify('316439', 1402) # => False

Generating a base32 Secret Key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::

    pyotp.random_base32() # returns a 16 character base32 secret. Compatible with Google Authenticator and other OTP apps

Google Authenticator Compatible
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PyOTP works with the Google Authenticator iPhone and Android app, as well as other OTP apps like Authy. PyOTP includes the
ability to generate provisioning URIs for use with the QR Code scanner built into these MFA client apps::

    pyotp.totp.TOTP('JBSWY3DPEHPK3PXP').provisioning_uri("alice@google.com", issuer_name="Secure App")

    >>> 'otpauth://totp/Secure%20App:alice%40google.com?secret=JBSWY3DPEHPK3PXP&issuer=Secure%20App'

    pyotp.hotp.HOTP('JBSWY3DPEHPK3PXP').provisioning_uri("alice@google.com", initial_count=0, issuer_name="Secure App")

    >>> 'otpauth://hotp/Secure%20App:alice%40google.com?secret=JBSWY3DPEHPK3PXP&issuer=Secure%20App&counter=0'

This URL can then be rendered as a QR Code (for example, using https://github.com/neocotic/qrious) which can then be scanned
and added to the users list of OTP credentials.

Working example
~~~~~~~~~~~~~~~

Scan the following barcode with your phone's OTP app (e.g. Google Authenticator):

.. image:: http://chart.apis.google.com/chart?cht=qr&chs=250x250&chl=otpauth%3A%2F%2Ftotp%2Falice%40google.com%3Fsecret%3DJBSWY3DPEHPK3PXP

Now run the following and compare the output::

    import pyotp
    totp = pyotp.TOTP("JBSWY3DPEHPK3PXP")
    print("Current OTP:", totp.now())

Links
~~~~~

* `Project home page (GitHub) <https://github.com/pyotp/pyotp>`_
* `Documentation (Read the Docs) <https://pyotp.readthedocs.io/en/latest/>`_
* `Package distribution (PyPI) <https://pypi.python.org/pypi/pyotp>`_
* `Change log <https://github.com/pyotp/pyotp/blob/master/Changes.rst>`_
* `RFC 4226: HOTP: An HMAC-Based One-Time Password <https://tools.ietf.org/html/rfc4226>`_
* `RFC 6238: TOTP: Time-Based One-Time Password Algorithm <https://tools.ietf.org/html/rfc6238>`_
* `ROTP <https://github.com/mdp/rotp>`_ - Original Ruby OTP library by `Mark Percival <https://github.com/mdp>`_
* `OTPHP <https://github.com/lelag/otphp>`_ - PHP port of ROTP by `Le Lag <https://github.com/lelag>`_
* `OWASP Authentication Cheat Sheet <https://www.owasp.org/index.php/Authentication_Cheat_Sheet>`_
* `NIST SP 800-63-3: Digital Authentication Guideline <https://pages.nist.gov/800-63-3/>`_

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