Hash collision security issue

Lib/test/test_hash.py

 # test the invariant that
 #   iff a==b then hash(a)==hash(b)
 #
 # Also test that hash implementations are inherited as expected
 
+import datetime
+import os
+import struct
 import unittest
 from test import support
+from test.script_helper import assert_python_ok
 from collections import Hashable
+
+IS_64BIT = (struct.calcsize('l') == 8)
 
 
 class HashEqualityTestCase(unittest.TestCase):
 
     def same_hash(self, *objlist):
         # Hash each object given and fail if
         # the hash values are not all the same.
         hashed = list(map(hash, objlist))
         for h in hashed[1:]:
             if h != hashed[0]:
@@ skipping 92 matching lines @@
                        enumerate(range(10)),
                        iter(DefaultIterSeq()),
                        iter(lambda: 0, 0),
                       ]
 
     def test_hashes(self):
         _default_hash = object.__hash__
         for obj in self.hashes_to_check:
             self.assertEqual(hash(obj), _default_hash(obj))
 
+class HashRandomizationTests(unittest.TestCase):
+
+    # Each subclass should define a field "repr_", containing the repr() of
+    # an object to be tested
+
+    def get_hash_command(self, repr_):
+        return 'print(hash(%s))' % repr_
+
+    def get_hash(self, repr_, seed=None):
+        env = os.environ.copy()
+        env['__cleanenv'] = True  # signal to assert_python not to do a copy
+                                  # of os.environ on its own
+        if seed is not None:
+            env['PYTHONHASHSEED'] = str(seed)
+        else:
+            env.pop('PYTHONHASHSEED', None)
+        out = assert_python_ok(
+            '-c', self.get_hash_command(repr_),
+            **env)
+        stdout = out[1].strip()
+        return int(stdout)
+
+    def test_randomized_hash(self):
+        # two runs should return different hashes
+        run1 = self.get_hash(self.repr_, seed='random')
+        run2 = self.get_hash(self.repr_, seed='random')
+        self.assertNotEqual(run1, run2)
+
+class StringlikeHashRandomizationTests(HashRandomizationTests):
+    def test_null_hash(self):
+        # PYTHONHASHSEED=0 disables the randomized hash
+        if IS_64BIT:
+            known_hash_of_obj = 1453079729188098211
+        else:
+            known_hash_of_obj = -1600925533
+
+        # Randomization is disabled by default:
+        self.assertEqual(self.get_hash(self.repr_), known_hash_of_obj)
+
+        # It can also be disabled by setting the seed to 0:
+        self.assertEqual(self.get_hash(self.repr_, seed=0), known_hash_of_obj)
+
+    def test_fixed_hash(self):
+        # test a fixed seed for the randomized hash
+        # Note that all types share the same values:
+        if IS_64BIT:
+            h = -4410911502303878509
+        else:
+            h = -206076799
+        self.assertEqual(self.get_hash(self.repr_, seed=42), h)
+
+class StrHashRandomizationTests(StringlikeHashRandomizationTests):
+    repr_ = repr('abc')
+
+    def test_empty_string(self):
+        self.assertEqual(hash(""), 0)
+
+class BytesHashRandomizationTests(StringlikeHashRandomizationTests):
+    repr_ = repr(b'abc')
+
+    def test_empty_string(self):
+        self.assertEqual(hash(b""), 0)
+
+class DatetimeTests(HashRandomizationTests):
+    def get_hash_command(self, repr_):
+        return 'import datetime; print(hash(%s))' % repr_
+
+class DatetimeDateTests(DatetimeTests):
+    repr_ = repr(datetime.date(1066, 10, 14))
+
+class DatetimeDatetimeTests(DatetimeTests):
+    repr_ = repr(datetime.datetime(1, 2, 3, 4, 5, 6, 7))
+
+class DatetimeTimeTests(DatetimeTests):
+    repr_ = repr(datetime.time(0))
+
+
 def test_main():
     support.run_unittest(HashEqualityTestCase,
-                              HashInheritanceTestCase,
-                              HashBuiltinsTestCase)
+                         HashInheritanceTestCase,
+                         HashBuiltinsTestCase,
+                         StrHashRandomizationTests,
+                         BytesHashRandomizationTests,
+                         DatetimeDateTests,
+                         DatetimeDatetimeTests,
+                         DatetimeTimeTests)
 
 
 if __name__ == "__main__":
     test_main()