764 lines
27 KiB
Python
764 lines
27 KiB
Python
# -*- coding: utf-8 -*-
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"""
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itsdangerous
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~~~~~~~~~~~~
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A module that implements various functions to deal with untrusted
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sources. Mainly useful for web applications.
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:copyright: (c) 2011 by Armin Ronacher and the Django Software Foundation.
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:license: BSD, see LICENSE for more details.
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"""
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import sys
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import hmac
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import zlib
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import time
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import base64
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import hashlib
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import operator
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from datetime import datetime
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PY2 = sys.version_info[0] == 2
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if PY2:
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from itertools import izip
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text_type = unicode
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int_to_byte = chr
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else:
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from functools import reduce
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izip = zip
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text_type = str
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int_to_byte = operator.methodcaller('to_bytes', 1, 'big')
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try:
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import simplejson as json
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except ImportError:
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import json
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class _CompactJSON(object):
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"""Wrapper around simplejson that strips whitespace.
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"""
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def loads(self, payload):
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return json.loads(payload)
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def dumps(self, obj):
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return json.dumps(obj, separators=(',', ':'))
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compact_json = _CompactJSON()
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# 2011/01/01 in UTC
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EPOCH = 1293840000
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def want_bytes(s, encoding='utf-8', errors='strict'):
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if isinstance(s, text_type):
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s = s.encode(encoding, errors)
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return s
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def is_text_serializer(serializer):
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"""Checks wheather a serializer generates text or binary."""
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return isinstance(serializer.dumps({}), text_type)
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# Starting with 3.3 the standard library has a c-implementation for
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# constant time string compares.
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_builtin_constant_time_compare = getattr(hmac, 'compare_digest', None)
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def constant_time_compare(val1, val2):
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"""Returns True if the two strings are equal, False otherwise.
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The time taken is independent of the number of characters that match. Do
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not use this function for anything else than comparision with known
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length targets.
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This is should be implemented in C in order to get it completely right.
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"""
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if _builtin_constant_time_compare is not None:
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return _builtin_constant_time_compare(val1, val2)
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len_eq = len(val1) == len(val2)
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if len_eq:
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result = 0
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left = val1
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else:
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result = 1
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left = val2
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for x, y in izip(bytearray(left), bytearray(val2)):
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result |= x ^ y
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return result == 0
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class BadData(Exception):
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"""Raised if bad data of any sort was encountered. This is the
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base for all exceptions that itsdangerous is currently using.
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.. versionadded:: 0.15
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"""
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message = None
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def __init__(self, message):
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Exception.__init__(self, message)
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self.message = message
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def __str__(self):
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return text_type(self.message)
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if PY2:
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__unicode__ = __str__
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def __str__(self):
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return self.__unicode__().encode('utf-8')
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class BadPayload(BadData):
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"""This error is raised in situations when payload is loaded without
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checking the signature first and an exception happend as a result of
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that. The original exception that caused that will be stored on the
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exception as :attr:`original_error`.
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.. versionadded:: 0.15
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"""
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def __init__(self, message, original_error=None):
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BadData.__init__(self, message)
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#: If available, the error that indicates why the payload
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#: was not valid. This might be `None`.
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self.original_error = original_error
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class BadSignature(BadData):
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"""This error is raised if a signature does not match. As of
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itsdangerous 0.14 there are helpful attributes on the exception
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instances. You can also catch down the baseclass :exc:`BadData`.
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"""
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def __init__(self, message, payload=None):
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BadData.__init__(self, message)
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#: The payload that failed the signature test. In some
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#: situations you might still want to inspect this, even if
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#: you know it was tampered with.
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#:
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#: .. versionadded:: 0.14
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self.payload = payload
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class BadTimeSignature(BadSignature):
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"""Raised for time based signatures that fail. This is a subclass
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of :class:`BadSignature` so you can catch those down as well.
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"""
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def __init__(self, message, payload=None, date_signed=None):
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BadSignature.__init__(self, message, payload)
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#: If the signature expired this exposes the date of when the
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#: signature was created. This can be helpful in order to
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#: tell the user how long a link has been gone stale.
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#:
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#: .. versionadded:: 0.14
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self.date_signed = date_signed
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class SignatureExpired(BadTimeSignature):
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"""Signature timestamp is older than required max_age. This is a
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subclass of :exc:`BadTimeSignature` so you can use the baseclass for
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catching the error.
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"""
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def base64_encode(string):
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"""base64 encodes a single bytestring (and is tolerant to getting
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called with a unicode string).
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The resulting bytestring is safe for putting into URLs.
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"""
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string = want_bytes(string)
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return base64.urlsafe_b64encode(string).strip(b'=')
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def base64_decode(string):
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"""base64 decodes a single bytestring (and is tolerant to getting
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called with a unicode string).
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The result is also a bytestring.
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"""
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string = want_bytes(string, encoding='ascii', errors='ignore')
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return base64.urlsafe_b64decode(string + b'=' * (-len(string) % 4))
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def int_to_bytes(num):
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assert num >= 0
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rv = []
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while num:
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rv.append(int_to_byte(num & 0xff))
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num >>= 8
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return b''.join(reversed(rv))
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def bytes_to_int(bytestr):
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return reduce(lambda a, b: a << 8 | b, bytearray(bytestr), 0)
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class SigningAlgorithm(object):
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"""Subclasses of `SigningAlgorithm` have to implement `get_signature` to
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provide 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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class NoneAlgorithm(SigningAlgorithm):
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"""This class provides a 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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"""This class provides signature generation using HMACs."""
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#: The digest method to use with the MAC algorithm. This defaults to sha1
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#: but can be changed for any other function in the hashlib 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 bytes and unsign it and validate 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 only
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valid for a given namespace. Leaving this at the default value or re-using
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a salt value across different parts of your application where the same
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signed value in one part can mean something different in another part
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is a security risk.
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See :ref:`the-salt` for an example of what the salt is doing and how you
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can utilize it.
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.. versionadded:: 0.14
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`key_derivation` and `digest_method` were added as arguments to the
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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 sha1 but can
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#: be changed for any other function in the hashlib module.
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#:
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#: .. versionchanged:: 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__(self, secret_key, salt=None, sep='.', key_derivation=None,
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digest_method=None, algorithm=None):
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self.secret_key = want_bytes(secret_key)
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self.sep = sep
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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. If you're unhappy with
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the default key derivation choices you can override them here.
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Keep in mind that the key derivation in itsdangerous is not intended
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to be used as a security method to make a complex key out of a short
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password. Instead you should use large random 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' +
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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 value + want_bytes(self.sep) + self.get_signature(value)
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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 constant_time_compare(sig, self.get_signature(value)):
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return value
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raise BadSignature('Signature %r does not match' % sig,
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payload=value)
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def validate(self, signed_value):
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"""Just validates the given signed value. Returns `True` if the
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signature exists and is valid, `False` otherwise."""
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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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class TimestampSigner(Signer):
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"""Works like the regular :class:`Signer` but also records the time
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of the signing and can be used to expire signatures. The unsign
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method can rause a :exc:`SignatureExpired` method if the unsigning
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failed because the signature is expired. This exception is a subclass
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of :exc:`BadSignature`.
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"""
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def get_timestamp(self):
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"""Returns the current timestamp. This implementation returns the
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seconds since 1/1/2011. The function must return an integer.
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"""
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return int(time.time() - EPOCH)
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def timestamp_to_datetime(self, ts):
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"""Used to convert the timestamp from `get_timestamp` into a
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datetime object.
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"""
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return datetime.utcfromtimestamp(ts + EPOCH)
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def sign(self, value):
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"""Signs the given string and also attaches a time information."""
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value = want_bytes(value)
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timestamp = base64_encode(int_to_bytes(self.get_timestamp()))
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sep = want_bytes(self.sep)
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value = value + sep + timestamp
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return value + sep + self.get_signature(value)
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def unsign(self, value, max_age=None, return_timestamp=False):
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"""Works like the regular :meth:`~Signer.unsign` but can also
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validate the time. See the base docstring of the class for
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the general behavior. If `return_timestamp` is set to `True`
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the timestamp of the signature will be returned as naive
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:class:`datetime.datetime` object in UTC.
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"""
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try:
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result = Signer.unsign(self, value)
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sig_error = None
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except BadSignature as e:
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sig_error = e
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result = e.payload or b''
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sep = want_bytes(self.sep)
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# If there is no timestamp in the result there is something
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# seriously wrong. In case there was a signature error, we raise
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# that one directly, otherwise we have a weird situation in which
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# we shouldn't have come except someone uses a time-based serializer
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# on non-timestamp data, so catch that.
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if not sep in result:
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if sig_error:
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raise sig_error
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raise BadTimeSignature('timestamp missing', payload=result)
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value, timestamp = result.rsplit(sep, 1)
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try:
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timestamp = bytes_to_int(base64_decode(timestamp))
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except Exception:
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timestamp = None
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# Signature is *not* okay. Raise a proper error now that we have
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# split the value and the timestamp.
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if sig_error is not None:
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raise BadTimeSignature(text_type(sig_error), payload=value,
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date_signed=timestamp)
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# Signature was okay but the timestamp is actually not there or
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# malformed. Should not happen, but well. We handle it nonetheless
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if timestamp is None:
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raise BadTimeSignature('Malformed timestamp', payload=value)
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# Check timestamp is not older than max_age
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if max_age is not None:
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age = self.get_timestamp() - timestamp
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if age > max_age:
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raise SignatureExpired(
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'Signature age %s > %s seconds' % (age, max_age),
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payload=value,
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date_signed=self.timestamp_to_datetime(timestamp))
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if return_timestamp:
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return value, self.timestamp_to_datetime(timestamp)
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return value
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def validate(self, signed_value, max_age=None):
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"""Just validates the given signed value. Returns `True` if the
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signature exists and is valid, `False` otherwise."""
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try:
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self.unsign(signed_value, max_age=max_age)
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return True
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except BadSignature:
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return False
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|
|
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class Serializer(object):
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"""This class provides a serialization interface on top of the
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signer. It provides a similar API to json/pickle and other modules but is
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slightly differently structured internally. If you want to change the
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underlying implementation for parsing and loading you have to override the
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:meth:`load_payload` and :meth:`dump_payload` functions.
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This implementation uses simplejson if available for dumping and loading
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and will fall back to the standard library's json module if it's not
|
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available.
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Starting with 0.14 you do not need to subclass this class in order to
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switch out or customer the :class:`Signer`. You can instead also pass a
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different class to the constructor as well as keyword arguments as
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dictionary that should be forwarded::
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s = Serializer(signer_kwargs={'key_derivation': 'hmac'})
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.. versionchanged:: 0.14:
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The `signer` and `signer_kwargs` parameters were added to the
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constructor.
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"""
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#: If a serializer module or class is not passed to the constructor
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#: this one is picked up. This currently defaults to :mod:`json`.
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default_serializer = json
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#: The default :class:`Signer` class that is being used by this
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#: serializer.
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#:
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#: .. versionadded:: 0.14
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default_signer = Signer
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def __init__(self, secret_key, salt=b'itsdangerous', serializer=None,
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signer=None, signer_kwargs=None):
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self.secret_key = want_bytes(secret_key)
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self.salt = want_bytes(salt)
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if serializer is None:
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serializer = self.default_serializer
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self.serializer = serializer
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self.is_text_serializer = is_text_serializer(serializer)
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if signer is None:
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signer = self.default_signer
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self.signer = signer
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self.signer_kwargs = signer_kwargs or {}
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def load_payload(self, payload, serializer=None):
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"""Loads the encoded object. This function raises :class:`BadPayload`
|
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if the payload is not valid. The `serializer` parameter can be used to
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override the serializer stored on the class. The encoded payload is
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always byte based.
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"""
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if serializer is None:
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serializer = self.serializer
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is_text = self.is_text_serializer
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else:
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is_text = is_text_serializer(serializer)
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try:
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if is_text:
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payload = payload.decode('utf-8')
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return serializer.loads(payload)
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except Exception as e:
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raise BadPayload('Could not load the payload because an '
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'exception ocurred on unserializing the data',
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original_error=e)
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def dump_payload(self, obj):
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"""Dumps the encoded object. The return value is always a
|
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bytestring. If the internal serializer is text based the value
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will automatically be encoded to utf-8.
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"""
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return want_bytes(self.serializer.dumps(obj))
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|
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def make_signer(self, salt=None):
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"""A method that creates a new instance of the signer to be used.
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The default implementation uses the :class:`Signer` baseclass.
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"""
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if salt is None:
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salt = self.salt
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return self.signer(self.secret_key, salt=salt, **self.signer_kwargs)
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|
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def dumps(self, obj, salt=None):
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"""Returns a signed string serialized with the internal serializer.
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The return value can be either a byte or unicode string depending
|
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on the format of the internal serializer.
|
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"""
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payload = want_bytes(self.dump_payload(obj))
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rv = self.make_signer(salt).sign(payload)
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if self.is_text_serializer:
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rv = rv.decode('utf-8')
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return rv
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|
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def dump(self, obj, f, salt=None):
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|
"""Like :meth:`dumps` but dumps into a file. The file handle has
|
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to be compatible with what the internal serializer expects.
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"""
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|
f.write(self.dumps(obj, salt))
|
|
|
|
def loads(self, s, salt=None):
|
|
"""Reverse of :meth:`dumps`, raises :exc:`BadSignature` if the
|
|
signature validation fails.
|
|
"""
|
|
s = want_bytes(s)
|
|
return self.load_payload(self.make_signer(salt).unsign(s))
|
|
|
|
def load(self, f, salt=None):
|
|
"""Like :meth:`loads` but loads from a file."""
|
|
return self.loads(f.read(), salt)
|
|
|
|
def loads_unsafe(self, s, salt=None):
|
|
"""Like :meth:`loads` but without verifying the signature. This is
|
|
potentially very dangerous to use depending on how your serializer
|
|
works. The return value is ``(signature_okay, payload)`` instead of
|
|
just the payload. The first item will be a boolean that indicates
|
|
if the signature is okay (``True``) or if it failed. This function
|
|
never fails.
|
|
|
|
Use it for debugging only and if you know that your serializer module
|
|
is not exploitable (eg: do not use it with a pickle serializer).
|
|
|
|
.. versionadded:: 0.15
|
|
"""
|
|
return self._loads_unsafe_impl(s, salt)
|
|
|
|
def _loads_unsafe_impl(self, s, salt, load_kwargs=None,
|
|
load_payload_kwargs=None):
|
|
"""Lowlevel helper function to implement :meth:`loads_unsafe` in
|
|
serializer subclasses.
|
|
"""
|
|
try:
|
|
return True, self.loads(s, salt=salt, **(load_kwargs or {}))
|
|
except BadSignature as e:
|
|
if e.payload is None:
|
|
return False, None
|
|
try:
|
|
return False, self.load_payload(e.payload,
|
|
**(load_payload_kwargs or {}))
|
|
except BadPayload:
|
|
return False, None
|
|
|
|
def load_unsafe(self, f, *args, **kwargs):
|
|
"""Like :meth:`loads_unsafe` but loads from a file.
|
|
|
|
.. versionadded:: 0.15
|
|
"""
|
|
return self.loads_unsafe(f.read(), *args, **kwargs)
|
|
|
|
|
|
class TimedSerializer(Serializer):
|
|
"""Uses the :class:`TimestampSigner` instead of the default
|
|
:meth:`Signer`.
|
|
"""
|
|
|
|
default_signer = TimestampSigner
|
|
|
|
def loads(self, s, max_age=None, return_timestamp=False, salt=None):
|
|
"""Reverse of :meth:`dumps`, raises :exc:`BadSignature` if the
|
|
signature validation fails. If a `max_age` is provided it will
|
|
ensure the signature is not older than that time in seconds. In
|
|
case the signature is outdated, :exc:`SignatureExpired` is raised
|
|
which is a subclass of :exc:`BadSignature`. All arguments are
|
|
forwarded to the signer's :meth:`~TimestampSigner.unsign` method.
|
|
"""
|
|
base64d, timestamp = self.make_signer(salt) \
|
|
.unsign(s, max_age, return_timestamp=True)
|
|
payload = self.load_payload(base64d)
|
|
if return_timestamp:
|
|
return payload, timestamp
|
|
return payload
|
|
|
|
def loads_unsafe(self, s, max_age=None, salt=None):
|
|
load_kwargs = {'max_age': max_age}
|
|
load_payload_kwargs = {}
|
|
return self._loads_unsafe_impl(s, salt, load_kwargs, load_payload_kwargs)
|
|
|
|
|
|
class JSONWebSignatureSerializer(Serializer):
|
|
"""This serializer implements JSON Web Signature (JWS) support. Only
|
|
supports the JWS Compact Serialization.
|
|
"""
|
|
|
|
jws_algorithms = {
|
|
'HS256': HMACAlgorithm(hashlib.sha256),
|
|
'HS384': HMACAlgorithm(hashlib.sha384),
|
|
'HS512': HMACAlgorithm(hashlib.sha512),
|
|
'none': NoneAlgorithm(),
|
|
}
|
|
|
|
#: The default algorithm to use for signature generation
|
|
default_algorithm = 'HS256'
|
|
|
|
default_serializer = compact_json
|
|
|
|
def __init__(self, secret_key, salt=None, serializer=None,
|
|
signer=None, signer_kwargs=None, algorithm_name=None):
|
|
Serializer.__init__(self, secret_key, salt, serializer,
|
|
signer, signer_kwargs)
|
|
if algorithm_name is None:
|
|
algorithm_name = self.default_algorithm
|
|
self.algorithm_name = algorithm_name
|
|
self.algorithm = self.make_algorithm(algorithm_name)
|
|
|
|
def load_payload(self, payload, return_header=False):
|
|
payload = want_bytes(payload)
|
|
if b'.' not in payload:
|
|
raise BadPayload('No "." found in value')
|
|
base64d_header, base64d_payload = payload.split(b'.', 1)
|
|
try:
|
|
json_header = base64_decode(base64d_header)
|
|
json_payload = base64_decode(base64d_payload)
|
|
except Exception as e:
|
|
raise BadPayload('Could not base64 decode the payload because of '
|
|
'an exception', original_error=e)
|
|
header = Serializer.load_payload(self, json_header,
|
|
serializer=json)
|
|
if not isinstance(header, dict):
|
|
raise BadPayload('Header payload is not a JSON object')
|
|
payload = Serializer.load_payload(self, json_payload)
|
|
if return_header:
|
|
return payload, header
|
|
return payload
|
|
|
|
def dump_payload(self, header, obj):
|
|
base64d_header = base64_encode(self.serializer.dumps(header))
|
|
base64d_payload = base64_encode(self.serializer.dumps(obj))
|
|
return base64d_header + b'.' + base64d_payload
|
|
|
|
def make_algorithm(self, algorithm_name):
|
|
try:
|
|
return self.jws_algorithms[algorithm_name]
|
|
except KeyError:
|
|
raise NotImplementedError('Algorithm not supported')
|
|
|
|
def make_signer(self, salt=None, algorithm=None):
|
|
if salt is None:
|
|
salt = self.salt
|
|
key_derivation = 'none' if salt is None else None
|
|
if algorithm is None:
|
|
algorithm = self.algorithm
|
|
return self.signer(self.secret_key, salt=salt, sep='.',
|
|
key_derivation=key_derivation, algorithm=algorithm)
|
|
|
|
def make_header(self, header_fields):
|
|
header = header_fields.copy() if header_fields else {}
|
|
header['alg'] = self.algorithm_name
|
|
return header
|
|
|
|
def dumps(self, obj, salt=None, header_fields=None):
|
|
"""Like :meth:`~Serializer.dumps` but creates a JSON Web Signature. It
|
|
also allows for specifying additional fields to be included in the JWS
|
|
Header.
|
|
"""
|
|
header = self.make_header(header_fields)
|
|
signer = self.make_signer(salt, self.algorithm)
|
|
return signer.sign(self.dump_payload(header, obj))
|
|
|
|
def loads(self, s, salt=None, return_header=False):
|
|
"""Reverse of :meth:`dumps`. If requested via `return_header` it will
|
|
return a tuple of payload and header.
|
|
"""
|
|
payload, header = self.load_payload(
|
|
self.make_signer(salt, self.algorithm).unsign(want_bytes(s)),
|
|
return_header=True)
|
|
if header.get('alg') != self.algorithm_name:
|
|
raise BadSignature('Algorithm mismatch')
|
|
if return_header:
|
|
return payload, header
|
|
return payload
|
|
|
|
def loads_unsafe(self, s, salt=None, return_header=False):
|
|
kwargs = {'return_header': return_header}
|
|
return self._loads_unsafe_impl(s, salt, kwargs, kwargs)
|
|
|
|
|
|
class URLSafeSerializerMixin(object):
|
|
"""Mixed in with a regular serializer it will attempt to zlib compress
|
|
the string to make it shorter if necessary. It will also base64 encode
|
|
the string so that it can safely be placed in a URL.
|
|
"""
|
|
|
|
def load_payload(self, payload):
|
|
decompress = False
|
|
if payload.startswith(b'.'):
|
|
payload = payload[1:]
|
|
decompress = True
|
|
try:
|
|
json = base64_decode(payload)
|
|
except Exception as e:
|
|
raise BadPayload('Could not base64 decode the payload because of '
|
|
'an exception', original_error=e)
|
|
if decompress:
|
|
try:
|
|
json = zlib.decompress(json)
|
|
except Exception as e:
|
|
raise BadPayload('Could not zlib decompress the payload before '
|
|
'decoding the payload', original_error=e)
|
|
return super(URLSafeSerializerMixin, self).load_payload(json)
|
|
|
|
def dump_payload(self, obj):
|
|
json = super(URLSafeSerializerMixin, self).dump_payload(obj)
|
|
is_compressed = False
|
|
compressed = zlib.compress(json)
|
|
if len(compressed) < (len(json) - 1):
|
|
json = compressed
|
|
is_compressed = True
|
|
base64d = base64_encode(json)
|
|
if is_compressed:
|
|
base64d = b'.' + base64d
|
|
return base64d
|
|
|
|
|
|
class URLSafeSerializer(URLSafeSerializerMixin, Serializer):
|
|
"""Works like :class:`Serializer` but dumps and loads into a URL
|
|
safe string consisting of the upper and lowercase character of the
|
|
alphabet as well as ``'_'``, ``'-'`` and ``'.'``.
|
|
"""
|
|
default_serializer = compact_json
|
|
|
|
|
|
class URLSafeTimedSerializer(URLSafeSerializerMixin, TimedSerializer):
|
|
"""Works like :class:`TimedSerializer` but dumps and loads into a URL
|
|
safe string consisting of the upper and lowercase character of the
|
|
alphabet as well as ``'_'``, ``'-'`` and ``'.'``.
|
|
"""
|
|
default_serializer = compact_json
|