The golden rule of web application security is to never trust data from\nuntrusted sources. Sometimes it can be useful to pass data through an\nuntrusted medium. Cryptographically signed values can be passed through an\nuntrusted channel safe in the knowledge that any tampering will be detected.
\nDjango provides both a low-level API for signing values and a high-level API\nfor setting and reading signed cookies, one of the most common uses of\nsigning in web applications.
\nYou may also find signing useful for the following:
\nGenerating «recover my account» URLs for sending to users who have\nlost their password.
Ensuring data stored in hidden form fields has not been tampered with.
Generating one-time secret URLs for allowing temporary access to a\nprotected resource, for example a downloadable file that a user has\npaid for.
SECRET_KEY and SECRET_KEY_FALLBACKSLink to this heading#When you create a new Django project using startproject, the\nsettings.py file is generated automatically and gets a random\nSECRET_KEY value. This value is the key to securing signed\ndata – it is vital you keep this secure, or attackers could use it to\ngenerate their own signed values.
SECRET_KEY_FALLBACKS can be used to rotate secret keys. The\nvalues will not be used to sign data, but if specified, they will be used to\nvalidate signed data and must be kept secure.
Django’s signing methods live in the django.core.signing module.\nTo sign a value, first instantiate a Signer instance:
>>> from django.core.signing import Signer\n>>> signer = Signer()\n>>> value = signer.sign("My string")\n>>> value\n'My string:v9G-nxfz3iQGTXrePqYPlGvH79WTcIgj1QIQSUODTW0'\nThe signature is appended to the end of the string, following the colon.\nYou can retrieve the original value using the unsign method:
>>> original = signer.unsign(value)\n>>> original\n'My string'\nIf you pass a non-string value to sign, the value will be forced to string\nbefore being signed, and the unsign result will give you that string\nvalue:
>>> signed = signer.sign(2.5)\n>>> original = signer.unsign(signed)\n>>> original\n'2.5'\nIf you wish to protect a list, tuple, or dictionary you can do so using the\nsign_object() and unsign_object() methods:
>>> signed_obj = signer.sign_object({"message": "Hello!"})\n>>> signed_obj\n'eyJtZXNzYWdlIjoiSGVsbG8hIn0:bzb48DBkB-bwLaCnUVB75r5VAPUEpzWJPrTb80JMIXM'\n>>> obj = signer.unsign_object(signed_obj)\n>>> obj\n{'message': 'Hello!'}\nSee Protecting complex data structures for more details.
\nIf the signature or value have been altered in any way, a\ndjango.core.signing.BadSignature exception will be raised:
>>> from django.core import signing\n>>> value += "m"\n>>> try:\n... original = signer.unsign(value)\n... except signing.BadSignature:\n... print("Tampering detected!")\n...\nBy default, the Signer class uses the SECRET_KEY setting to\ngenerate signatures. You can use a different secret by passing it to the\nSigner constructor:
>>> signer = Signer(key="my-other-secret")\n>>> value = signer.sign("My string")\n>>> value\n'My string:o3DrrsT6JRB73t-HDymfDNbTSxfMlom2d8TiUlb1hWY'\nReturns a signer which uses key to generate signatures and sep to\nseparate values. sep cannot be in the URL safe base64 alphabet. This alphabet contains alphanumeric characters, hyphens,\nand underscores. algorithm must be an algorithm supported by\nhashlib, it defaults to 'sha256'. fallback_keys is a list\nof additional values used to validate signed data, defaults to\nSECRET_KEY_FALLBACKS.
salt argumentLink to this heading#If you do not wish for every occurrence of a particular string to have the same\nsignature hash, you can use the optional salt argument to the Signer\nclass. Using a salt will seed the signing hash function with both the salt and\nyour SECRET_KEY:
>>> signer = Signer()\n>>> signer.sign("My string")\n'My string:v9G-nxfz3iQGTXrePqYPlGvH79WTcIgj1QIQSUODTW0'\n>>> signer.sign_object({"message": "Hello!"})\n'eyJtZXNzYWdlIjoiSGVsbG8hIn0:bzb48DBkB-bwLaCnUVB75r5VAPUEpzWJPrTb80JMIXM'\n>>> signer = Signer(salt="extra")\n>>> signer.sign("My string")\n'My string:YMD-FR6rof3heDkFRffdmG4pXbAZSOtb-aQxg3vmmfc'\n>>> signer.unsign("My string:YMD-FR6rof3heDkFRffdmG4pXbAZSOtb-aQxg3vmmfc")\n'My string'\n>>> signer.sign_object({"message": "Hello!"})\n'eyJtZXNzYWdlIjoiSGVsbG8hIn0:-UWSLCE-oUAHzhkHviYz3SOZYBjFKllEOyVZNuUtM-I'\n>>> signer.unsign_object(\n... "eyJtZXNzYWdlIjoiSGVsbG8hIn0:-UWSLCE-oUAHzhkHviYz3SOZYBjFKllEOyVZNuUtM-I"\n... )\n{'message': 'Hello!'}\nUsing salt in this way puts the different signatures into different\nnamespaces. A signature that comes from one namespace (a particular salt\nvalue) cannot be used to validate the same plaintext string in a different\nnamespace that is using a different salt setting. The result is to prevent an\nattacker from using a signed string generated in one place in the code as input\nto another piece of code that is generating (and verifying) signatures using a\ndifferent salt.
\nUnlike your SECRET_KEY, your salt argument does not need to stay\nsecret.
TimestampSigner is a subclass of Signer that appends a signed\ntimestamp to the value. This allows you to confirm that a signed value was\ncreated within a specified period of time:
>>> from datetime import timedelta\n>>> from django.core.signing import TimestampSigner\n>>> signer = TimestampSigner()\n>>> value = signer.sign("hello")\n>>> value\n'hello:1stLqR:_rvr4oXCgT4HyfwjXaU39QvTnuNuUthFRCzNOy4Hqt0'\n>>> signer.unsign(value)\n'hello'\n>>> signer.unsign(value, max_age=10)\nSignatureExpired: Signature age 15.5289158821 > 10 seconds\n>>> signer.unsign(value, max_age=20)\n'hello'\n>>> signer.unsign(value, max_age=timedelta(seconds=20))\n'hello'\nSign value and append current timestamp to it.
Checks if value was signed less than max_age seconds ago,\notherwise raises SignatureExpired. The max_age parameter can\naccept an integer or a datetime.timedelta object.
Encode, optionally compress, append current timestamp, and sign complex\ndata structure (e.g. list, tuple, or dictionary).
\nChecks if signed_obj was signed less than max_age seconds ago,\notherwise raises SignatureExpired. The max_age parameter can\naccept an integer or a datetime.timedelta object.
If you wish to protect a list, tuple or dictionary you can do so using the\nSigner.sign_object() and unsign_object() methods, or signing module’s\ndumps() or loads() functions (which are shortcuts for\nTimestampSigner(salt='django.core.signing').sign_object()/unsign_object()).\nThese use JSON serialization under the hood. JSON ensures that even if your\nSECRET_KEY is stolen an attacker will not be able to execute\narbitrary commands by exploiting the pickle format:
>>> from django.core import signing\n>>> signer = signing.TimestampSigner()\n>>> value = signer.sign_object({"foo": "bar"})\n>>> value\n'eyJmb28iOiJiYXIifQ:1stLrZ:_QiOBHafwucBF9FyAr54qEs84ZO1UdsO1XiTJCvvdno'\n>>> signer.unsign_object(value)\n{'foo': 'bar'}\n>>> value = signing.dumps({"foo": "bar"})\n>>> value\n'eyJmb28iOiJiYXIifQ:1stLsC:JItq2ZVjmAK6ivrWI-v1Gk1QVf2hOF52oaEqhZHca7I'\n>>> signing.loads(value)\n{'foo': 'bar'}\nBecause of the nature of JSON (there is no native distinction between lists\nand tuples) if you pass in a tuple, you will get a list from\nsigning.loads(object):
>>> from django.core import signing\n>>> value = signing.dumps(("a", "b", "c"))\n>>> signing.loads(value)\n['a', 'b', 'c']\nReturns URL-safe, signed base64 compressed JSON string. Serialized object\nis signed using TimestampSigner.
Reverse of dumps(), raises BadSignature if signature fails.\nChecks max_age (in seconds) if given.