Cryptographic signing¶

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')[código-fonte]¶

sign(value)[código-fonte]¶

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

unsign(value, max_age=None)[código-fonte]¶

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)[código-fonte]¶

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)[código-fonte]¶

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