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bazarr/libs/itsdangerous/signer.py
2019-12-02 22:46:54 +01:00

179 lines
6.2 KiB
Python

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