Added fallback signers and switch back to sha1

Author: mitsuhiko

CHANGES.rst

@@ -1,8 +1,23 @@
+Version 1.1.0
+-------------
+
+Released 2018-10-26
+
+-   Change algorithm back to SHA-1
+-   Add support for fallback algorithm
+-   Changed capitalization of packages back to lowercase as the
+    change in capitalization broke some tooling.
+
 Version 1.0.0
 -------------
 
 Released 2018-10-18
 
+YANKED
+
+*Note*: this release was yanked from pypi because it changed the default
+algorithm to SHA-512.  This decision was reverted and it remains at SHA1.
+
 -   Drop support for Python 2.6 and 3.3.
 -   Refactor code from a single module to a package. Any object in the
     API docs is still importable from the top-level ``itsdangerous``

README.rst

@@ -19,7 +19,7 @@ Install and update using `pip`_:
 
 .. code-block:: text
 
-    pip install -U ItsDangerous
+    pip install -U itsdangerous
 
 .. _pip: https://pip.pypa.io/en/stable/quickstart/
 
@@ -33,13 +33,11 @@ name between web requests.
 .. code-block:: python
 
     from itsdangerous import URLSafeSerializer
-
     auth_s = URLSafeSerializer("secret key", "auth")
     token = auth_s.dumps({"id": 5, "name": "itsdangerous"})
 
     print(token)
-    # eyJpZCI6NSwibmFtZSI6Iml0c2Rhbmdlcm91cyJ9.AmSPrPa_iZ6q-ERXXdQxt6ce8NEqt
-    # 3i2Uke3sIRnDG0riZD6OoqckqC72VJ9SBIu-vAf_XlwNHnt7dLEClT0JA
+    # eyJpZCI6NSwibmFtZSI6Iml0c2Rhbmdlcm91cyJ9.6YP6T0BaO67XP--9UzTrmurXSmg
 
     data = auth_s.loads(token)
     print(data["name"])

docs/conf.py

@@ -6,7 +6,7 @@
 project = "It's Dangerous"
 copyright = "2011 Pallets Team"
 author = "Pallets Team"
-release, version = get_version("ItsDangerous")
+release, version = get_version("itsdangerous")
 
 # General --------------------------------------------------------------
 
@@ -22,7 +22,7 @@
     "project_links": [
         ProjectLink("Donate to Pallets", "https://palletsprojects.com/donate"),
         ProjectLink("Website", "https://palletsprojects.com/p/itsdangerous/"),
-        ProjectLink("PyPI releases", "https://pypi.org/project/ItsDangerous/"),
+        ProjectLink("PyPI releases", "https://pypi.org/project/itsdangerous/"),
         ProjectLink("Source Code", "https://github.com/pallets/itsdangerous/"),
         ProjectLink("Issue Tracker", "https://github.com/pallets/itsdangerous/issues/"),
     ]

docs/index.rst

@@ -30,7 +30,7 @@ Install and update using `pip`_:
 
 .. code-block:: text
 
-    pip install -U ItsDangerous
+    pip install -U itsdangerous
 
 .. _pip: https://pip.pypa.io/en/stable/quickstart/
 

setup.py

@@ -11,7 +11,7 @@
     version = re.search(r"__version__ = \"(.*?)\"", f.read()).group(1)
 
 setup(
-    name="ItsDangerous",
+    name="itsdangerous",
     version=version,
     url="https://palletsprojects.com/p/itsdangerous/",
     project_urls={

src/itsdangerous/serializer.py

@@ -32,9 +32,29 @@ class to the constructor as well as keyword arguments as a dict that
 
         s = Serializer(signer_kwargs={'key_derivation': 'hmac'})
 
+    Additionally as of 1.1 fallback signers can be defined by providing
+    a list as `fallback_signers`.  These are used for deserialization as a
+    fallback.  Each item can be one of the following:
+    a signer class (which is instantiated with `signer_kwargs`, salt and
+    secret key), a tuple `(signer_class, signer_kwargs)` or just `signer_kwargs`.
+    If kwargs are provided they need to be a dict.
+
+    For instance this is a serializer that supports deserialization that
+    supports both SHA1 and SHA512:
+
+    .. code-block:: python3
+
+        s = Serializer(
+            signer_kwargs={'digest_method': hashlib.sha512},
+            fallback_signers=[{'digest_method': hashlib.sha1}]
+        )
+
     .. versionchanged:: 0.14:
         The ``signer`` and ``signer_kwargs`` parameters were added to
         the constructor.
+
+    .. versionchanged:: 1.1:
+        Added support for `fallback_signers`.
     """
 
     #: If a serializer module or class is not passed to the constructor
@@ -55,6 +75,7 @@ def __init__(
         serializer_kwargs=None,
         signer=None,
         signer_kwargs=None,
+        fallback_signers=None,
     ):
         self.secret_key = want_bytes(secret_key)
         self.salt = want_bytes(salt)
@@ -66,6 +87,7 @@ def __init__(
             signer = self.default_signer
         self.signer = signer
         self.signer_kwargs = signer_kwargs or {}
+        self.fallback_signers = fallback_signers or ()
         self.serializer_kwargs = serializer_kwargs or {}
 
     def load_payload(self, payload, serializer=None):
@@ -106,6 +128,21 @@ def make_signer(self, salt=None):
             salt = self.salt
         return self.signer(self.secret_key, salt=salt, **self.signer_kwargs)
 
+    def iter_unsigners(self, salt=None):
+        """Iterates over all signers for unsigning."""
+        if salt is None:
+            salt = self.salt
+        yield self.make_signer(salt)
+        for fallback in self.fallback_signers:
+            if type(fallback) is dict:
+                kwargs = fallback
+                fallback = self.signer
+            elif type(fallback) is tuple:
+                fallback, kwargs = fallback
+            else:
+                kwargs = self.signer_kwargs
+            yield fallback(self.secret_key, salt=salt, **kwargs)
+
     def dumps(self, obj, salt=None):
         """Returns a signed string serialized with the internal
         serializer. The return value can be either a byte or unicode
@@ -128,7 +165,13 @@ def loads(self, s, salt=None):
         signature validation fails.
         """
         s = want_bytes(s)
-        return self.load_payload(self.make_signer(salt).unsign(s))
+        last_exception = None
+        for signer in self.iter_unsigners(salt):
+            try:
+                return self.load_payload(signer.unsign(s))
+            except BadSignature as err:
+                last_exception = err
+        raise last_exception
 
     def load(self, f, salt=None):
         """Like :meth:`loads` but loads from a file."""

src/itsdangerous/signer.py

@@ -38,12 +38,9 @@ class HMACAlgorithm(SigningAlgorithm):
     """Provides signature generation using HMACs."""
 
     #: The digest method to use with the MAC algorithm. This defaults to
-    #: SHA-512, but can be changed to any other function in the hashlib
+    #: SHA1, but can be changed to any other function in the hashlib
     #: module.
-    #:
-    #: .. versionchanged:: 1.0
-    #:     The default was changed from SHA-1 to SHA-512.
-    default_digest_method = staticmethod(hashlib.sha512)
+    default_digest_method = staticmethod(hashlib.sha1)
 
     def __init__(self, digest_method=None):
         if digest_method is None:
@@ -77,14 +74,11 @@ class Signer(object):
     """
 
     #: The digest method to use for the signer.  This defaults to
-    #: SHA-512 but can be changed to any other function in the hashlib
+    #: SHA1 but can be changed to any other function in the hashlib
     #: module.
     #:
-    #: .. versionchanged:: 1.0
-    #:     The default was changed from SHA-1 to SHA-512.
-    #:
     #: .. versionadded:: 0.14
-    default_digest_method = staticmethod(hashlib.sha512)
+    default_digest_method = staticmethod(hashlib.sha1)
 
     #: Controls how the key is derived. The default is Django-style
     #: concatenation. Possible values are ``concat``, ``django-concat``

src/itsdangerous/timed.py

@@ -123,13 +123,18 @@ def loads(self, s, max_age=None, return_timestamp=False, salt=None):
         raised. 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
+        s = want_bytes(s)
+        last_exception = None
+        for signer in self.iter_unsigners(salt):
+            try:
+                base64d, timestamp = signer.unsign(s, max_age, return_timestamp=True)
+                payload = self.load_payload(base64d)
+                if return_timestamp:
+                    return payload, timestamp
+                return payload
+            except BadSignature as err:
+                last_exception = err
+        raise last_exception
 
     def loads_unsafe(self, s, max_age=None, salt=None):
         load_kwargs = {"max_age": max_age}

tests/test_itsdangerous/test_serializer.py

@@ -1,3 +1,4 @@
+import hashlib
 import pickle
 from functools import partial
 from io import BytesIO
@@ -131,3 +132,36 @@ def test_serializer_kwargs(self, serializer_factory):
             return
 
         assert serializer.loads(serializer.dumps({(): 1})) == {}
+
+    def test_fallback_signers(self):
+        serializer = Serializer(
+            secret_key="foo", signer_kwargs={"digest_method": hashlib.sha512}
+        )
+        value = serializer.dumps([1, 2, 3])
+        fallback_serializer = Serializer(
+            secret_key="foo",
+            signer_kwargs={"digest_method": hashlib.sha1},
+            fallback_signers=[{"digest_method": hashlib.sha512}],
+        )
+        assert fallback_serializer.loads(value) == [1, 2, 3]
+
+    def test_digests(self):
+        default_value = Serializer(
+            secret_key="dev key", salt="dev salt", signer_kwargs={}
+        ).dumps([42])
+        sha1_value = Serializer(
+            secret_key="dev key",
+            salt="dev salt",
+            signer_kwargs={"digest_method": hashlib.sha1},
+        ).dumps([42])
+        sha512_value = Serializer(
+            secret_key="dev key",
+            salt="dev salt",
+            signer_kwargs={"digest_method": hashlib.sha512},
+        ).dumps([42])
+        assert default_value == sha1_value
+        assert sha1_value == "[42].-9cNi0CxsSB3hZPNCe9a2eEs1ZM"
+        assert sha512_value == (
+            "[42].MKCz_0nXQqv7wKpfHZcRtJRmpT2T5uvs9YQsJEhJimqxc"
+            "9bCLxG31QzS5uC8OVBI1i6jyOLAFNoKaF5ckO9L5Q"
+        )

tests/test_itsdangerous/test_timed.py

@@ -1,3 +1,4 @@
+import hashlib
 from datetime import datetime
 from datetime import timedelta
 from functools import partial
@@ -84,3 +85,15 @@ def test_max_age(self, serializer, value, ts, freeze):
     def test_return_payload(self, serializer, value, ts):
         signed = serializer.dumps(value)
         assert serializer.loads(signed, return_timestamp=True) == (value, ts)
+
+    def test_fallback_signers(self):
+        serializer = TimedSerializer(
+            secret_key="foo", signer_kwargs={"digest_method": hashlib.sha512}
+        )
+        value = serializer.dumps([1, 2, 3])
+        fallback_serializer = TimedSerializer(
+            secret_key="foo",
+            signer_kwargs={"digest_method": hashlib.sha1},
+            fallback_signers=[{"digest_method": hashlib.sha512}],
+        )
+        assert fallback_serializer.loads(value) == [1, 2, 3]