build test

venv/lib/python3.7/site-packages/itsdangerous/signer.py

@@ -0,0 +1,179 @@
+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