3 files changed, 62 insertions, 4 deletions
diff --git a/django/conf/global_settings.py b/django/conf/global_settings.py
index 42df4b601a..aa67e48bcd 100644
--- a/django/conf/global_settings.py
+++ b/django/conf/global_settings.py
@@ -515,6 +515,7 @@ PASSWORD_RESET_TIMEOUT_DAYS = 3
 PASSWORD_HASHERS = (
     'django.contrib.auth.hashers.PBKDF2PasswordHasher',
     'django.contrib.auth.hashers.PBKDF2SHA1PasswordHasher',
+    'django.contrib.auth.hashers.BCryptSHA256PasswordHasher',
     'django.contrib.auth.hashers.BCryptPasswordHasher',
     'django.contrib.auth.hashers.SHA1PasswordHasher',
     'django.contrib.auth.hashers.MD5PasswordHasher',
diff --git a/django/contrib/auth/hashers.py b/django/contrib/auth/hashers.py
index 480fde69ce..092cccedde 100644
--- a/django/contrib/auth/hashers.py
+++ b/django/contrib/auth/hashers.py
@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 import base64
+import binascii
 import hashlib
 
 from django.dispatch import receiver
@@ -257,7 +258,7 @@ class PBKDF2SHA1PasswordHasher(PBKDF2PasswordHasher):
     digest = hashlib.sha1
 
 
-class BCryptPasswordHasher(BasePasswordHasher):
+class BCryptSHA256PasswordHasher(BasePasswordHasher):
     """
     Secure password hashing using the bcrypt algorithm (recommended)
 
@@ -266,7 +267,8 @@ class BCryptPasswordHasher(BasePasswordHasher):
     this library depends on native C code and might cause portability
     issues.
     """
-    algorithm = "bcrypt"
+    algorithm = "bcrypt_sha256"
+    digest = hashlib.sha256
     library = ("py-bcrypt", "bcrypt")
     rounds = 12
 
@@ -278,14 +280,34 @@ class BCryptPasswordHasher(BasePasswordHasher):
         bcrypt = self._load_library()
         # Need to reevaluate the force_bytes call once bcrypt is supported on
         # Python 3
-        data = bcrypt.hashpw(force_bytes(password), salt)
+
+        # Hash the password prior to using bcrypt to prevent password truncation
+        #   See: https://code.djangoproject.com/ticket/20138
+        if self.digest is not None:
+            # We use binascii.hexlify here because Python3 decided that a hex encoded
+            #   bytestring is somehow a unicode.
+            password = binascii.hexlify(self.digest(force_bytes(password)).digest())
+        else:
+            password = force_bytes(password)
+
+        data = bcrypt.hashpw(password, salt)
         return "%s$%s" % (self.algorithm, data)
 
     def verify(self, password, encoded):
         algorithm, data = encoded.split('$', 1)
         assert algorithm == self.algorithm
         bcrypt = self._load_library()
-        return constant_time_compare(data, bcrypt.hashpw(force_bytes(password), data))
+
+        # Hash the password prior to using bcrypt to prevent password truncation
+        #   See: https://code.djangoproject.com/ticket/20138
+        if self.digest is not None:
+            # We use binascii.hexlify here because Python3 decided that a hex encoded
+            #   bytestring is somehow a unicode.
+            password = binascii.hexlify(self.digest(force_bytes(password)).digest())
+        else:
+            password = force_bytes(password)
+
+        return constant_time_compare(data, bcrypt.hashpw(password, data))
 
     def safe_summary(self, encoded):
         algorithm, empty, algostr, work_factor, data = encoded.split('$', 4)
@@ -299,6 +321,25 @@ class BCryptPasswordHasher(BasePasswordHasher):
         ])
 
 
+class BCryptPasswordHasher(BCryptSHA256PasswordHasher):
+    """
+    Secure password hashing using the bcrypt algorithm
+
+    This is considered by many to be the most secure algorithm but you
+    must first install the py-bcrypt library.  Please be warned that
+    this library depends on native C code and might cause portability
+    issues.
+
+    This hasher does not first hash the password which means it is subject to
+    the 72 character bcrypt password truncation, most use cases should prefer
+    the BCryptSha512PasswordHasher.
+
+    See: https://code.djangoproject.com/ticket/20138
+    """
+    algorithm = "bcrypt"
+    digest = None
+
+
 class SHA1PasswordHasher(BasePasswordHasher):
     """
     The SHA1 password hashing algorithm (not recommended)
diff --git a/django/contrib/auth/tests/hashers.py b/django/contrib/auth/tests/hashers.py
index 2b2243cb0c..9253fcbc43 100644
--- a/django/contrib/auth/tests/hashers.py
+++ b/django/contrib/auth/tests/hashers.py
@@ -93,6 +93,22 @@ class TestUtilsHashPass(unittest.TestCase):
         self.assertEqual(identify_hasher(encoded).algorithm, "crypt")
 
     @skipUnless(bcrypt, "py-bcrypt not installed")
+    def test_bcrypt_sha256(self):
+        encoded = make_password('lètmein', hasher='bcrypt_sha256')
+        self.assertTrue(is_password_usable(encoded))
+        self.assertTrue(encoded.startswith('bcrypt_sha256$'))
+        self.assertTrue(check_password('lètmein', encoded))
+        self.assertFalse(check_password('lètmeinz', encoded))
+        self.assertEqual(identify_hasher(encoded).algorithm, "bcrypt_sha256")
+
+        # Verify that password truncation no longer works
+        password = ('VSK0UYV6FFQVZ0KG88DYN9WADAADZO1CTSIVDJUNZSUML6IBX7LN7ZS3R5'
+                    'JGB3RGZ7VI7G7DJQ9NI8BQFSRPTG6UWTTVESA5ZPUN')
+        encoded = make_password(password, hasher='bcrypt_sha256')
+        self.assertTrue(check_password(password, encoded))
+        self.assertFalse(check_password(password[:72], encoded))
+
+    @skipUnless(bcrypt, "py-bcrypt not installed")
     def test_bcrypt(self):
         encoded = make_password('lètmein', hasher='bcrypt')
         self.assertTrue(is_password_usable(encoded))