180 lines
6.2 KiB
Python
180 lines
6.2 KiB
Python
import hashlib
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import hmac
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from ._compat import constant_time_compare
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from .encoding import _base64_alphabet
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from .encoding import base64_decode
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from .encoding import base64_encode
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from .encoding import want_bytes
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from .exc import BadSignature
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class SigningAlgorithm(object):
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"""Subclasses must implement :meth:`get_signature` to provide
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signature generation functionality.
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"""
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def get_signature(self, key, value):
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"""Returns the signature for the given key and value."""
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raise NotImplementedError()
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def verify_signature(self, key, value, sig):
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"""Verifies the given signature matches the expected
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signature.
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"""
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return constant_time_compare(sig, self.get_signature(key, value))
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class NoneAlgorithm(SigningAlgorithm):
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"""Provides an algorithm that does not perform any signing and
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returns an empty signature.
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"""
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def get_signature(self, key, value):
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return b""
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class HMACAlgorithm(SigningAlgorithm):
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"""Provides signature generation using HMACs."""
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#: The digest method to use with the MAC algorithm. This defaults to
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#: SHA1, but can be changed to any other function in the hashlib
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#: module.
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default_digest_method = staticmethod(hashlib.sha1)
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def __init__(self, digest_method=None):
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if digest_method is None:
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digest_method = self.default_digest_method
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self.digest_method = digest_method
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def get_signature(self, key, value):
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mac = hmac.new(key, msg=value, digestmod=self.digest_method)
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return mac.digest()
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class Signer(object):
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"""This class can sign and unsign bytes, validating the signature
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provided.
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Salt can be used to namespace the hash, so that a signed string is
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only valid for a given namespace. Leaving this at the default value
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or re-using a salt value across different parts of your application
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where the same signed value in one part can mean something different
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in another part is a security risk.
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See :ref:`the-salt` for an example of what the salt is doing and how
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you can utilize it.
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.. versionadded:: 0.14
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``key_derivation`` and ``digest_method`` were added as arguments
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to the class constructor.
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.. versionadded:: 0.18
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``algorithm`` was added as an argument to the class constructor.
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"""
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#: The digest method to use for the signer. This defaults to
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#: SHA1 but can be changed to any other function in the hashlib
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#: module.
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#:
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#: .. versionadded:: 0.14
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default_digest_method = staticmethod(hashlib.sha1)
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#: Controls how the key is derived. The default is Django-style
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#: concatenation. Possible values are ``concat``, ``django-concat``
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#: and ``hmac``. This is used for deriving a key from the secret key
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#: with an added salt.
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#:
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#: .. versionadded:: 0.14
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default_key_derivation = "django-concat"
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def __init__(
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self,
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secret_key,
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salt=None,
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sep=".",
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key_derivation=None,
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digest_method=None,
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algorithm=None,
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):
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self.secret_key = want_bytes(secret_key)
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self.sep = want_bytes(sep)
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if self.sep in _base64_alphabet:
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raise ValueError(
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"The given separator cannot be used because it may be"
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" contained in the signature itself. Alphanumeric"
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" characters and `-_=` must not be used."
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)
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self.salt = "itsdangerous.Signer" if salt is None else salt
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if key_derivation is None:
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key_derivation = self.default_key_derivation
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self.key_derivation = key_derivation
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if digest_method is None:
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digest_method = self.default_digest_method
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self.digest_method = digest_method
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if algorithm is None:
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algorithm = HMACAlgorithm(self.digest_method)
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self.algorithm = algorithm
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def derive_key(self):
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"""This method is called to derive the key. The default key
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derivation choices can be overridden here. Key derivation is not
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intended to be used as a security method to make a complex key
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out of a short password. Instead you should use large random
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secret keys.
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"""
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salt = want_bytes(self.salt)
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if self.key_derivation == "concat":
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return self.digest_method(salt + self.secret_key).digest()
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elif self.key_derivation == "django-concat":
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return self.digest_method(salt + b"signer" + self.secret_key).digest()
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elif self.key_derivation == "hmac":
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mac = hmac.new(self.secret_key, digestmod=self.digest_method)
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mac.update(salt)
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return mac.digest()
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elif self.key_derivation == "none":
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return self.secret_key
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else:
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raise TypeError("Unknown key derivation method")
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def get_signature(self, value):
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"""Returns the signature for the given value."""
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value = want_bytes(value)
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key = self.derive_key()
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sig = self.algorithm.get_signature(key, value)
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return base64_encode(sig)
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def sign(self, value):
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"""Signs the given string."""
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return want_bytes(value) + want_bytes(self.sep) + self.get_signature(value)
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def verify_signature(self, value, sig):
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"""Verifies the signature for the given value."""
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key = self.derive_key()
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try:
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sig = base64_decode(sig)
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except Exception:
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return False
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return self.algorithm.verify_signature(key, value, sig)
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def unsign(self, signed_value):
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"""Unsigns the given string."""
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signed_value = want_bytes(signed_value)
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sep = want_bytes(self.sep)
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if sep not in signed_value:
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raise BadSignature("No %r found in value" % self.sep)
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value, sig = signed_value.rsplit(sep, 1)
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if self.verify_signature(value, sig):
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return value
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raise BadSignature("Signature %r does not match" % sig, payload=value)
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def validate(self, signed_value):
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"""Only validates the given signed value. Returns ``True`` if
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the signature exists and is valid.
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"""
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try:
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self.unsign(signed_value)
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return True
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except BadSignature:
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return False
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