# Documentação Django 5.2.8

# Cryptographic signing

The golden rule of web application security is to never trust data from untrusted sources. Sometimes it can be useful to pass data through an untrusted medium. Cryptographically signed values can be passed through an untrusted channel safe in the knowledge that any tampering will be detected.

Django provides both a low-level API for signing values and a high-level API for setting and reading signed cookies, one of the most common uses of signing in web applications.

Você também pode achar a assinatura útil para o seguinte:

- Gerar URLs do tipo “recuperar minha conta” para enviar a usuários que perderam suas senhas.

- Garantir que dados armazenados em campos hidden de formulários não foram alterados.

- Gerar URLs secretas de uso único para permitir acesso temporário a recursos protegidos, por exemplo um arquivo baixável pelo qual um usuário pagou.

## Protecting `SECRET_KEY` and `SECRET_KEY_FALLBACKS`

Quando você cria um novo projeto Django usando `startproject`, o arquivo `settings.py` é gerado automaticamente e recebe um valor aleatório para a `SECRET_KEY`. Esse valor é a chave para proteger dados assinados – Ela é vital para manter isso seguro, ou atacantes podem usá-la para gerar seus próprios valores assinados.

`SECRET_KEY_FALLBACKS` can be used to rotate secret keys. The values will not be used to sign data, but if specified, they will be used to validate signed data and must be kept secure.

## Utilizando a API de baixo nível

Django’s signing methods live in the `django.core.signing` module. To sign a value, first instantiate a `Signer` instance:

    >>> from django.core.signing import Signer
    >>> signer = Signer()
    >>> value = signer.sign("My string")
    >>> value
    'My string:v9G-nxfz3iQGTXrePqYPlGvH79WTcIgj1QIQSUODTW0'

The signature is appended to the end of the string, following the colon. You can retrieve the original value using the `unsign` method:

    >>> original = signer.unsign(value)
    >>> original
    'My string'

If you pass a non-string value to `sign`, the value will be forced to string before being signed, and the `unsign` result will give you that string value:

    >>> signed = signer.sign(2.5)
    >>> original = signer.unsign(signed)
    >>> original
    '2.5'

If you wish to protect a list, tuple, or dictionary you can do so using the `sign_object()` and `unsign_object()` methods:

    >>> signed_obj = signer.sign_object({"message": "Hello!"})
    >>> signed_obj
    'eyJtZXNzYWdlIjoiSGVsbG8hIn0:bzb48DBkB-bwLaCnUVB75r5VAPUEpzWJPrTb80JMIXM'
    >>> obj = signer.unsign_object(signed_obj)
    >>> obj
    {'message': 'Hello!'}

See Protegendo estruturas de dados complexas for more details.

If the signature or value have been altered in any way, a `django.core.signing.BadSignature` exception will be raised:

    >>> from django.core import signing
    >>> value += "m"
    >>> try:
    ...     original = signer.unsign(value)
    ... except signing.BadSignature:
    ...     print("Tampering detected!")
    ...

By default, the `Signer` class uses the `SECRET_KEY` setting to generate signatures. You can use a different secret by passing it to the `Signer` constructor:

    >>> signer = Signer(key="my-other-secret")
    >>> value = signer.sign("My string")
    >>> value
    'My string:o3DrrsT6JRB73t-HDymfDNbTSxfMlom2d8TiUlb1hWY'

class Signer(*, key=None, sep=':', salt=None, algorithm=None, fallback_keys=None)

  Returns a signer which uses `key` to generate signatures and `sep` to separate values. `sep` cannot be in the URL safe base64 alphabet. This alphabet contains alphanumeric characters, hyphens, and underscores. `algorithm` must be an algorithm supported by `hashlib`, it defaults to `'sha256'`. `fallback_keys` is a list of additional values used to validate signed data, defaults to `SECRET_KEY_FALLBACKS`.

### Usando o parâmetro `salt`

If you do not wish for every occurrence of a particular string to have the same signature hash, you can use the optional `salt` argument to the `Signer` class. Using a salt will seed the signing hash function with both the salt and your `SECRET_KEY`:

    >>> signer = Signer()
    >>> signer.sign("My string")
    'My string:v9G-nxfz3iQGTXrePqYPlGvH79WTcIgj1QIQSUODTW0'
    >>> signer.sign_object({"message": "Hello!"})
    'eyJtZXNzYWdlIjoiSGVsbG8hIn0:bzb48DBkB-bwLaCnUVB75r5VAPUEpzWJPrTb80JMIXM'
    >>> signer = Signer(salt="extra")
    >>> signer.sign("My string")
    'My string:YMD-FR6rof3heDkFRffdmG4pXbAZSOtb-aQxg3vmmfc'
    >>> signer.unsign("My string:YMD-FR6rof3heDkFRffdmG4pXbAZSOtb-aQxg3vmmfc")
    'My string'
    >>> signer.sign_object({"message": "Hello!"})
    'eyJtZXNzYWdlIjoiSGVsbG8hIn0:-UWSLCE-oUAHzhkHviYz3SOZYBjFKllEOyVZNuUtM-I'
    >>> signer.unsign_object(
    ...     "eyJtZXNzYWdlIjoiSGVsbG8hIn0:-UWSLCE-oUAHzhkHviYz3SOZYBjFKllEOyVZNuUtM-I"
    ... )
    {'message': 'Hello!'}

Using salt in this way puts the different signatures into different namespaces. A signature that comes from one namespace (a particular salt value) cannot be used to validate the same plaintext string in a different namespace that is using a different salt setting. The result is to prevent an attacker from using a signed string generated in one place in the code as input to another piece of code that is generating (and verifying) signatures using a different salt.

Ao contrário de sua `SECRET_KEY`, o seu argumento salt não precisa ser mantido em segredo.

### Verificando valores com timestamp

`TimestampSigner` is a subclass of `Signer` that appends a signed timestamp to the value. This allows you to confirm that a signed value was created within a specified period of time:

    >>> from datetime import timedelta
    >>> from django.core.signing import TimestampSigner
    >>> signer = TimestampSigner()
    >>> value = signer.sign("hello")
    >>> value
    'hello:1stLqR:_rvr4oXCgT4HyfwjXaU39QvTnuNuUthFRCzNOy4Hqt0'
    >>> signer.unsign(value)
    'hello'
    >>> signer.unsign(value, max_age=10)
    SignatureExpired: Signature age 15.5289158821 > 10 seconds
    >>> signer.unsign(value, max_age=20)
    'hello'
    >>> signer.unsign(value, max_age=timedelta(seconds=20))
    'hello'

class TimestampSigner(*, key=None, sep=':', salt=None, algorithm='sha256')
  sign(value)

    Assina um `value` e adiciona um rótulo com o horário atual nele.

  unsign(value, max_age=None)

    Checks if `value` was signed less than `max_age` seconds ago, otherwise raises `SignatureExpired`. The `max_age` parameter can accept an integer or a `datetime.timedelta` object.

  sign_object(obj, serializer=JSONSerializer, compress=False)

    Encode, optionally compress, append current timestamp, and sign complex data structure (e.g. list, tuple, or dictionary).

  unsign_object(signed_obj, serializer=JSONSerializer, max_age=None)

    Checks if `signed_obj` was signed less than `max_age` seconds ago, otherwise raises `SignatureExpired`. The `max_age` parameter can accept an integer or a `datetime.timedelta` object.

### Protegendo estruturas de dados complexas

If you wish to protect a list, tuple or dictionary you can do so using the `Signer.sign_object()` and `unsign_object()` methods, or signing module’s `dumps()` or `loads()` functions (which are shortcuts for `TimestampSigner(salt='django.core.signing').sign_object()/unsign_object()`). These use JSON serialization under the hood. JSON ensures that even if your `SECRET_KEY` is stolen an attacker will not be able to execute arbitrary commands by exploiting the pickle format:

    >>> from django.core import signing
    >>> signer = signing.TimestampSigner()
    >>> value = signer.sign_object({"foo": "bar"})
    >>> value
    'eyJmb28iOiJiYXIifQ:1stLrZ:_QiOBHafwucBF9FyAr54qEs84ZO1UdsO1XiTJCvvdno'
    >>> signer.unsign_object(value)
    {'foo': 'bar'}
    >>> value = signing.dumps({"foo": "bar"})
    >>> value
    'eyJmb28iOiJiYXIifQ:1stLsC:JItq2ZVjmAK6ivrWI-v1Gk1QVf2hOF52oaEqhZHca7I'
    >>> signing.loads(value)
    {'foo': 'bar'}

Because of the nature of JSON (there is no native distinction between lists and tuples) if you pass in a tuple, you will get a list from `signing.loads(object)`:

    >>> from django.core import signing
    >>> value = signing.dumps(("a", "b", "c"))
    >>> signing.loads(value)
    ['a', 'b', 'c']

dumps(obj, key=None, salt='django.core.signing', serializer=JSONSerializer, compress=False)

  Returns URL-safe, signed base64 compressed JSON string. Serialized object is signed using `TimestampSigner`.

loads(string, key=None, salt='django.core.signing', serializer=JSONSerializer, max_age=None, fallback_keys=None)

  Inverso da função `dumps()`, lança `BadSignature` se a assinatura falhar. Verifica o `max_age` (em segundos) se fornecido.