# Overview and Key Concepts

The django_otp package contains a framework for processing one-time passwords as well as support for several types of OTP devices. Support for additional devices is handled by plugins, distributed separately.

Adding two-factor authentication to your Django site involves four main tasks:

> 1. Installing the django-otp plugins you want to use.
> 2. Adding one or more OTP-enabled login views.
> 3. Restricting access to all or portions of your site based on whether users have been verified by a registered OTP device.
> 4. Providing mechanisms to register OTP devices to user accounts (or relying on the Django admin interface).

## Installation

Basic installation has only two steps:

> 1. Install `django_otp` and any plugins that you’d like to use. These are simply Django apps to be installed in the usual way.
> 2. Add `django_otp.middleware.OTPMiddleware` to `MIDDLEWARE`. It must be installed after `AuthenticationMiddleware`.

For example:

    INSTALLED_APPS = [
        'django.contrib.auth',
        'django.contrib.contenttypes',
        'django.contrib.sessions',
        'django.contrib.sites',
        'django.contrib.messages',
        'django.contrib.staticfiles',
        'django.contrib.admin',
        'django.contrib.admindocs',

        'django_otp',
        'django_otp.plugins.otp_totp',
        'django_otp.plugins.otp_hotp',
        'django_otp.plugins.otp_static',
    ]

    MIDDLEWARE = [
        'django.middleware.common.CommonMiddleware',
        'django.contrib.sessions.middleware.SessionMiddleware',
        'django.middleware.csrf.CsrfViewMiddleware',
        'django.contrib.auth.middleware.AuthenticationMiddleware',
        'django_otp.middleware.OTPMiddleware',
        'django.contrib.messages.middleware.MessageMiddleware',
    ]

The plugins contain models that must be migrated.

## Upgrading

Version 0.2.4 of django-otp introduced a South migration to the otp_totp plugin. Version 0.3.0 added Django 1.7 and South migrations to all apps. Care must be taken when upgrading in certain cases.

The recommended procedure is:

> 1. Upgrade django-otp to 0.2.7, as described below.
> 2. Upgrade Django to 1.7 or later.
> 3. Upgrade django-otp to the latest version.

django-otp 0.4 dropped support for Django < 1.7.

### Upgrading from 0.2.3 or Earlier

If you’re using django-otp <= 0.2.3, you need to convert otp_totp to South before going any further:

    pip install 'django-otp==0.2.7'
    python manage.py migrate otp_totp 0001 --fake
    python manage.py migrate otp_totp

If you’re not using South, you can run `python manage.py sql otp_totp` to see the definition of the new `last_t` field and then construct a suitable `ALTER TABLE` SQL statement for your database.

### Upgrading to Django 1.7+

Once you’ve upgraded django-otp to version 0.2.4 or later (up to 0.2.7), it’s safe to switch to Django 1.7 or later. You should not have South installed at this point, so any old migrations will simply be ignored.

Once on Django 1.7+, it’s safe to upgrade django-otp to 0.3 or later. All plugins with models have Django migrations, which will be ignored if the tables have already been created.

If you’re already on django-otp 0.3 or later when you move to Django 1.7+ (see below), you’ll want to make sure Django knows that all migrations have already been run:

    python manage.py migrate --fake <otp_plugin>
    ...

### Upgrading to 0.3.x with South

If you want to upgrade django-otp to 0.3.x under South, you’ll need to convert all of the remaining plugins. First make sure you’re running South 1.0, as earlier versions will not find the migrations. Then convert any plugin that you have installed:

    pip install 'django-otp>=0.3'
    python manage.py migrate otp_hotp 0001 --fake
    python manage.py migrate otp_static 0001 --fake
    python manage.py migrate otp_yubikey 0001 --fake
    python manage.py migrate otp_twilio 0001 --fake

## Authentication and Verification

In a normal Django deployment, the user associated with a request is either authenticated or not. With the introduction of two-factor authentication, the situation becomes a little more complicated: while it is certainly possible to design a site such that two factors are required for any authentication, that’s only one option. It’s entirely reasonable to allow users to log in with either one or two factors and grant then access accordingly.

In this documentation, a user that has passed Django’s authentication API is called authenticated. A user that has additionally been accepted by a registered OTP device is called verified. On an OTP-enabled Django site, there are thus three levels of authentication:

> - anonymous
> - authenticated
> - authenticated + verified

When planning your site, you’ll want to consider whether different views will require different levels of authentication. As a convenience, we provide the decorator `django_otp.decorators.otp_required()`, which is analogous to `login_required()`, but requires the user to be both authenticated and verified.

`OTPMiddleware` populates `request.user.otp_device` to the OTP device object that verified the current user (if any). As a convenience, it also adds `user.is_verified()` as a counterpart to `user.is_authenticated()`. It is not possible for a user to be verified without also being authenticated. [1]

## Plugins and Devices

A django-otp plugin is simply a Django app that contains one or more models that are subclassed from `django_otp.models.Device`. Each model class supports a single type of OTP device. Remember that when we use the term device in this context, we’re not necessarily referring to a physical device. At the code level, a device is a model object that can verify a particular type of OTP. For example, you might have a YubiKey that supports both the Yubico OTP algorithm and the HOTP standard: these would be represented as different devices and likely served by different plugins. A device that delivered HOTP values to a user by SMS would be a third device defined by another plugin.

OTP plugins are distributed as Django apps; to install a plugin, just add it to `INSTALLED_APPS` like any other. The order can be significant: any time we enumerate a user’s devices, such as when we ask the user which device they would like to authenticate with, we will present them according to the order in which the apps are installed.

OTP devices come in two general flavors: passive and interactive. A passive device is one that can accept a token from the user and verify it with no preparation. Examples include devices corresponding to dedicated hardware or smartphone apps that generate sequenced or time-based tokens. An interactive device needs to communicate something to the user before it can accept a token. Two common types are devices that use a challenge-response OTP algorithm and devices that deliver a token to the user through an independent channel, such as SMS.

Internally, device instances can be flagged as confirmed or unconfirmed. By default, devices are confirmed as soon as they are created, but a plugin or deployment that wishes to include a confirmation step can mark a device unconfirmed initially. Unconfirmed devices will be ignored by the high-level OTP APIs.

### Built-in Plugins

django-otp includes support for several standard device types. `HOTPDevice` and `TOTPDevice` handle standard OTP algorithms, which can be used with a variety of OTP generators. For example, it’s easy to pair these devices with Google Authenticator using the otpauth URL scheme. If you have the qrcode package installed, the admin interface will generate QR Codes for you.

#### HOTP Devices

HOTP is an algorithm that generates a pseudo-random sequence of codes based on an incrementing counter. Every time a prover generates a new code or a verifier verifies one, they increment their respective counters. This algorithm will fail if the prover generates too many codes without a successful verification.

If there is a failed attempt, this plugin will enforce an exponentially increasing delay before allowing verification to succeed (see `OTP_HOTP_THROTTLE_FACTOR`). The `verify_token()` method automatically applies this policy. For a better user experience, before calling `verify_token()` check whether verification is disabled by calling the `verify_is_allowed()` method.

class `django_otp.plugins.otp_hotp.models.``HOTPDevice`(*args, **kwargs)

  A generic HOTP `Device`. The model fields mostly correspond to the arguments to `django_otp.oath.hotp()`. They all have sensible defaults, including the key, which is randomly generated.

  `key`

    CharField: A hex-encoded secret key of up to 40 bytes. (Default: 20 random bytes)

  `digits`

    PositiveSmallIntegerField: The number of digits to expect from the token generator (6 or 8). (Default: 6)

  `tolerance`

    PositiveSmallIntegerField: The number of missed tokens to tolerate. (Default: 5)

  `counter`

    BigIntegerField: The next counter value to expect. (Initial: 0)

  exception `DoesNotExist`
  exception `MultipleObjectsReturned`
  `bin_key`

    The secret key as a binary string.

  `config_url`

    A URL for configuring Google Authenticator or similar.

    See https://github.com/google/google-authenticator/wiki/Key-Uri-Format. The issuer is taken from `OTP_HOTP_ISSUER`, if available.

  `verify_token`(token)

    Verifies a token. As a rule, the token should no longer be valid if this returns `True`.

    Parameters: | token (string) – The OTP token provided by the user.
    Return type: | bool

class `django_otp.plugins.otp_hotp.admin.``HOTPDeviceAdmin`(model, admin_site)

  `ModelAdmin` for `HOTPDevice`.

##### HOTP Settings

OTP_HOTP_ISSUER

Default: `None`

The `issuer` parameter for the otpauth URL generated by `config_url`. This can be a string or a callable to dynamically set the value.

OTP_HOTP_THROTTLE_FACTOR

Default: `1`

This controls the rate of throttling. The sequence of 1, 2, 4, 8… seconds is multiplied by this factor to define the delay imposed after 1, 2, 3, 4… successive failures. Set to `0` to disable throttling completely.

#### TOTP Devices

TOTP is an algorithm that generates a pseudo-random sequence of codes based on the current time. A typical implementation will change codes every 30 seconds, although this is configurable. This algorithm will fail if the prover and verifier have clocks that drift too far apart.

If there is a failed attempt, this plugin will enforce an exponentially increasing delay before allowing verification to succeed (see `OTP_TOTP_THROTTLE_FACTOR`). The `verify_token()` method automatically applies this policy. For a better user experience, before calling `verify_token()` check whether verification is disabled by calling the `verify_is_allowed()` method.

class `django_otp.plugins.otp_totp.models.``TOTPDevice`(*args, **kwargs)

  A generic TOTP `Device`. The model fields mostly correspond to the arguments to `django_otp.oath.totp()`. They all have sensible defaults, including the key, which is randomly generated.

  `key`

    CharField: A hex-encoded secret key of up to 40 bytes. (Default: 20 random bytes)

  `step`

    PositiveSmallIntegerField: The time step in seconds. (Default: 30)

  `t0`

    BigIntegerField: The Unix time at which to begin counting steps. (Default: 0)

  `digits`

    PositiveSmallIntegerField: The number of digits to expect in a token (6 or 8). (Default: 6)

  `tolerance`

    PositiveSmallIntegerField: The number of time steps in the past or future to allow. For example, if this is 1, we’ll accept any of three tokens: the current one, the previous one, and the next one. (Default: 1)

  `drift`

    SmallIntegerField: The number of time steps the prover is known to deviate from our clock. If `OTP_TOTP_SYNC` is `True`, we’ll update this any time we match a token that is not the current one. (Default: 0)

  `last_t`

    BigIntegerField: The time step of the last verified token. To avoid verifying the same token twice, this will be updated on each successful verification. Only tokens at a higher time step will be verified subsequently. (Default: -1)

  exception `DoesNotExist`
  exception `MultipleObjectsReturned`
  `bin_key`

    The secret key as a binary string.

  `config_url`

    A URL for configuring Google Authenticator or similar.

    See https://github.com/google/google-authenticator/wiki/Key-Uri-Format. The issuer is taken from `OTP_TOTP_ISSUER`, if available.

  `verify_token`(token)

    Verifies a token. As a rule, the token should no longer be valid if this returns `True`.

    Parameters: | token (string) – The OTP token provided by the user.
    Return type: | bool

class `django_otp.plugins.otp_totp.admin.``TOTPDeviceAdmin`(model, admin_site)

  `ModelAdmin` for `TOTPDevice`.

##### TOTP Settings

OTP_TOTP_ISSUER

Default: `None`

The `issuer` parameter for the otpauth URL generated by `config_url`. This can be a string or a callable to dynamically set the value.

OTP_TOTP_SYNC

Default: `True`

If true, then TOTP devices will keep track of the difference between the prover’s clock and our own. Any time a `TOTPDevice` matches a token in the past or future, it will update `drift` to the number of time steps that the two sides are out of sync. For subsequent tokens, we’ll slide the window of acceptable tokens by this number.

OTP_TOTP_THROTTLE_FACTOR

Default: `1`

This controls the rate of throttling. The sequence of 1, 2, 4, 8… seconds is multiplied by this factor to define the delay imposed after 1, 2, 3, 4… successive failures. Set to `0` to disable throttling completely.

#### Static Devices

class `django_otp.plugins.otp_static.models.``StaticDevice`(*args, **kwargs)

  A static `Device` simply consists of random tokens shared by the database and the user. These are frequently used as emergency tokens in case a user’s normal device is lost or unavailable. They can be consumed in any order; each token will be removed from the database as soon as it is used.

  This model has no fields of its own, but serves as a container for `StaticToken` objects.

  `token_set`

    The RelatedManager for our tokens.

  exception `DoesNotExist`
  exception `MultipleObjectsReturned`
  `verify_token`(token)

    Verifies a token. As a rule, the token should no longer be valid if this returns `True`.

    Parameters: | token (string) – The OTP token provided by the user.
    Return type: | bool

class `django_otp.plugins.otp_static.models.``StaticToken`(*args, **kwargs)

  A single token belonging to a `StaticDevice`.

  `device`

    ForeignKey: A foreign key to `StaticDevice`.

  `token`

    CharField: A random string up to 16 characters.

  exception `DoesNotExist`
  exception `MultipleObjectsReturned`
  static `random_token`()

    Returns a new random string that can be used as a static token.

    Return type: | bytes

class `django_otp.plugins.otp_static.admin.``StaticDeviceAdmin`(model, admin_site)

  `ModelAdmin` for `StaticDevice`.

##### addstatictoken

The static plugin also includes a management command called `addstatictoken`, which will add a single static token to any account. This is useful for bootstrapping and emergency access. Run `manage.py addstatictoken -h` for details.

#### Email Devices

class `django_otp.plugins.otp_email.models.``EmailDevice`(*args, **kwargs)

  A `Device` that delivers a token to the user’s registered email address (`user.email`). This is intended for demonstration purposes; if you allow users to reset their passwords via email, then this provides no security benefits.

  `key`

    CharField: A hex-encoded secret key of up to 40 bytes. (Default: 20 random bytes)

  exception `DoesNotExist`
  exception `MultipleObjectsReturned`
  `generate_challenge`()

    Generates a challenge value that the user will need to produce a token. This method is permitted to have side effects, such as transmitting information to the user through some other channel (email or SMS, perhaps). And, of course, some devices may need to commit the challenge to the database.

    Returns: | A message to the user. This should be a string that fits comfortably in the template `'OTP Challenge: {0}'`. This may return `None` if this device is not interactive.
    Return type: | string or `None`
    Raises: | Any `Exception` is permitted. Callers should trap `Exception` and report it to the user.

  `verify_token`(token)

    Verifies a token. As a rule, the token should no longer be valid if this returns `True`.

    Parameters: | token (string) – The OTP token provided by the user.
    Return type: | bool

class `django_otp.plugins.otp_email.admin.``EmailDeviceAdmin`(model, admin_site)

  `ModelAdmin` for `EmailDevice`.

### Other Plugins

The framework author also maintains a couple of other plugins for less common devices. Third-party plugins are not listed here.

> - django-otp-yubikey supports YubiKey USB devices.
> - django-otp-twilio supports delivering OTPs via Twilio’s SMS service.

## Settings

OTP_LOGIN_URL

Default: alias for `LOGIN_URL`

The URL where requests are redirected for two-factor authentication, especially when using the `otp_required()` decorator.

## Glossary

authenticated
  A user whose credentials have been accepted by Django’s authentication API is considered authenticated.
device
  A mechanism by which a user can acquire an OTP. This might correspond to a physical device dedicated to such a purpose, a virtual device such as a smart phone app, or even a set of stored single-use tokens.
OTP
  A one-time password. This is a generated value that a user can present as evidence of their identity. OTPs are only valid for a single use or, in some cases, for a strictly limited period of time.
prover
  An entity that is using an OTP to prove its identity. For example, a user who is providing an OTP token.
token
  An encoded OTP. Some OTPs consist of structured data, in which case they will be encoded into a printable string for transport.
two-factor authentication
  An authentication policy that requires a user to present two proofs of identity. The first is typically a password and the second is frequently tied to some physical device in the user’s possession.
verified
  A user whose credentials have been accepted by Django’s authentication API and also by a registered OTP device is considered verified.
verifier
  An entity that verifies tokens generated by a prover. For example, a web service that accepts OTPs as proof of identity.

Footnotes

[1] | If you’d like the second factor to persist across sessions, see django-agent-trust and django-otp-agents. The former deals with assigning trust to user agents (i.e. browsers) across sessions and the latter includes tools to use OTPs to establish that trust.