From ca3df803c9afd04d7dee612e0bf321cc62cf900f Mon Sep 17 00:00:00 2001
From: Michael Merickel <michael@merickel.org>
Date: Sun, 4 Nov 2012 12:34:22 -0600
Subject: emit a warning if a user is using the default hashalg to AuthTkt

---
 CHANGES.txt                          |  9 +++++++++
 TODO.txt                             |  3 +++
 pyramid/authentication.py            | 17 ++++++++++++++++-
 pyramid/tests/test_authentication.py |  9 +++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index b3733a787..43a910f96 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -48,6 +48,15 @@ Bug Fixes
   attribute of the request.  It no longer fails in this case.  See
   https://github.com/Pylons/pyramid/issues/700
 
+Deprecations
+------------
+
+- ``pyramid.authentication.AuthTktAuthenticationPolicy`` will emit a warning
+  if an application is using the policy without explicitly setting the
+  ``hashalg``. This is because the default is "md5" which is considered
+  insecure. If you really want "md5" then you must specify it explicitly to
+  get rid of the warning.
+
 Internals
 ---------
 
diff --git a/TODO.txt b/TODO.txt
index ac5738244..af164adc9 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -141,6 +141,9 @@ Future
 
 - 1.6: Remove IContextURL and TraversalContextURL.
 
+- 1.7: Change ``pyramid.authentication.AuthTktAuthenticationPolicy`` default
+  ``hashalg`` to ``sha512``.
+
 Probably Bad Ideas
 ------------------
 
diff --git a/pyramid/authentication.py b/pyramid/authentication.py
index dbca68a11..0a406e370 100644
--- a/pyramid/authentication.py
+++ b/pyramid/authentication.py
@@ -6,6 +6,7 @@ import base64
 import datetime
 import re
 import time as time_mod
+import warnings
 
 from zope.interface import implementer
 
@@ -405,6 +406,8 @@ class RemoteUserAuthenticationPolicy(CallbackAuthenticationPolicy):
         be done somewhere else or in a subclass."""
         return []
 
+_marker = object()
+
 @implementer(IAuthenticationPolicy)
 class AuthTktAuthenticationPolicy(CallbackAuthenticationPolicy):
     """A :app:`Pyramid` :term:`authentication policy` which
@@ -549,8 +552,20 @@ class AuthTktAuthenticationPolicy(CallbackAuthenticationPolicy):
                  http_only=False,
                  wild_domain=True,
                  debug=False,
-                 hashalg='md5',
+                 hashalg=_marker
                  ):
+        if hashalg is _marker:
+            hashalg = 'md5'
+            warnings.warn('The MD5 hash function is known to have collisions. '
+                          'We recommend instead that you update your code to '
+                          'use the SHA512 algorithm by setting '
+                          'hashalg=\'sha512\'. If you accept these risks '
+                          'and want to continue using MD5, explicitly set '
+                          'the hashalg=\'md5\' in your authentication policy. '
+                          'The default algorithm used in this policy is '
+                          'likely to change in the future.',
+                          DeprecationWarning,
+                          stacklevel=2)
         self.cookie = AuthTktCookieHelper(
             secret,
             cookie_name=cookie_name,
diff --git a/pyramid/tests/test_authentication.py b/pyramid/tests/test_authentication.py
index 2d69173fa..123e4f9f5 100644
--- a/pyramid/tests/test_authentication.py
+++ b/pyramid/tests/test_authentication.py
@@ -1,4 +1,5 @@
 import unittest
+import warnings
 from pyramid import testing
 from pyramid.compat import (
     text_,
@@ -440,6 +441,14 @@ class TestAuthTktAuthenticationPolicy(unittest.TestCase):
         inst.cookie = DummyCookieHelper(cookieidentity)
         return inst
 
+    def setUp(self):
+        self.warnings = warnings.catch_warnings()
+        self.warnings.__enter__()
+        warnings.simplefilter('ignore', DeprecationWarning)
+
+    def tearDown(self):
+        self.warnings.__exit__(None, None, None)
+
     def test_allargs(self):
         # pass all known args
         inst = self._getTargetClass()(
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