[1.5.x] Fixed #18144 -- Added backwards compatibility with old unsalted MD5 passwords

Thanks apreobrazhensky at gmail.com for the report.
Backport of 63d6a50dd from master.

django/contrib/auth/hashers.py

@@ -132,7 +132,8 @@ def identify_hasher(encoded):
     get_hasher() to return hasher. Raises ValueError if
     algorithm cannot be identified, or if hasher is not loaded.
     """
-    if len(encoded) == 32 and '$' not in encoded:
+    if ((len(encoded) == 32 and '$' not in encoded) or
+            len(encoded) == 37 and encoded.startswith('md5$$')):
         algorithm = 'unsalted_md5'
     else:
         algorithm = encoded.split('$', 1)[0]
@@ -372,6 +373,8 @@ class UnsaltedMD5PasswordHasher(BasePasswordHasher):
         return hashlib.md5(force_bytes(password)).hexdigest()
 
     def verify(self, password, encoded):
+        if len(encoded) == 37 and encoded.startswith('md5$$'):
+            encoded = encoded[5:]
         encoded_2 = self.encode(password, '')
         return constant_time_compare(encoded, encoded_2)
 

django/contrib/auth/tests/hashers.py

@@ -66,6 +66,11 @@ class TestUtilsHashPass(unittest.TestCase):
         self.assertTrue(check_password('lètmein', encoded))
         self.assertFalse(check_password('lètmeinz', encoded))
         self.assertEqual(identify_hasher(encoded).algorithm, "unsalted_md5")
+        # Alternate unsalted syntax
+        alt_encoded = "md5$$%s" % encoded
+        self.assertTrue(is_password_usable(alt_encoded))
+        self.assertTrue(check_password('lètmein', alt_encoded))
+        self.assertFalse(check_password('lètmeinz', alt_encoded))
 
     @skipUnless(crypt, "no crypt module to generate password.")
     def test_crypt(self):