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_KEYLink 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.
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:GdMGD6HNQ_qdgxYP8yBZAdAIV1w'\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 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!")\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('my-other-secret')\n>>> value = signer.sign('My string')\n>>> value\n'My string:EkfQJafvGyiofrdGnuthdxImIJw'\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\nalphanumeric characters, hyphens, and underscores.
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:GdMGD6HNQ_qdgxYP8yBZAdAIV1w'\n>>> signer = Signer(salt='extra')\n>>> signer.sign('My string')\n'My string:Ee7vGi-ING6n02gkcJ-QLHg6vFw'\n>>> signer.unsign('My string:Ee7vGi-ING6n02gkcJ-QLHg6vFw')\n'My string'\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:1NMg5H:oPVuCqlJWmChm1rA2lyTUtelC-c'\n>>> signer.unsign(value)\n'hello'\n>>> signer.unsign(value, max_age=10)\n...\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.
If you wish to protect a list, tuple or dictionary you can do so using the\nsigning module’s dumps and loads functions. These imitate Python’s\npickle module, but use JSON serialization under the hood. JSON ensures that\neven if your SECRET_KEY is stolen an attacker will not be able\nto execute arbitrary commands by exploiting the pickle format:
>>> from django.core import signing\n>>> value = signing.dumps({"foo": "bar"})\n>>> value\n'eyJmb28iOiJiYXIifQ:1NMg1b:zGcDE4-TCkaeGzLeW9UQwZesciI'\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, sha1 signed base64 compressed JSON string. Serialized\nobject is signed using TimestampSigner.
Reverse of dumps(), raises BadSignature if signature fails.\nChecks max_age (in seconds) if given.