feat: added feature flag to enable blake2b hashing

common/djangoapps/util/memcache.py

@@ -7,6 +7,7 @@ so that we can cache any keys, not just ones that memcache would ordinarily acce
 import hashlib
 from urllib.parse import quote_plus
 
+from django.conf import settings
 from django.utils.encoding import smart_str
 
 
@@ -14,9 +15,12 @@ def fasthash(string):
     """
     Hashes `string` into a string representation of a 128-bit digest.
     """
-    md4 = hashlib.new("md4")
-    md4.update(string.encode('utf-8'))
-    return md4.hexdigest()
+    if settings.FEATURES.get("ENABLE_BLAKE2B_HASHING", False):
+        hash_obj = hashlib.new("blake2b", digest_size=16)
+    else:
+        hash_obj = hashlib.new("md4")
+    hash_obj.update(string.encode('utf-8'))
+    return hash_obj.hexdigest()
 
 
 def cleaned_string(val):

common/djangoapps/util/tests/test_memcache.py

@@ -3,11 +3,15 @@ Tests for memcache in util app
 """
 
 
+from django.conf import settings
 from django.core.cache import caches
-from django.test import TestCase
+from django.test import TestCase, override_settings
 
 from common.djangoapps.util.memcache import safe_key
 
+BLAKE2B_ENABLED_FEATURES = settings.FEATURES.copy()
+BLAKE2B_ENABLED_FEATURES["ENABLE_BLAKE2B_HASHING"] = True
+
 
 class MemcacheTest(TestCase):
     """
@@ -51,6 +55,20 @@ class MemcacheTest(TestCase):
             # The key should now be valid
             assert self._is_valid_key(key), f'Failed for key length {length}'
 
+    @override_settings(FEATURES=BLAKE2B_ENABLED_FEATURES)
+    def test_safe_key_long_with_blake2b_enabled(self):
+        # Choose lengths close to memcached's cutoff (250)
+        for length in [248, 249, 250, 251, 252]:
+
+            # Generate a key of that length
+            key = 'a' * length
+
+            # Make the key safe
+            key = safe_key(key, '', '')
+
+            # The key should now be valid
+            assert self._is_valid_key(key), f'Failed for key length {length}'
+
     def test_long_key_prefix_version(self):
 
         # Long key
@@ -65,6 +83,21 @@ class MemcacheTest(TestCase):
         key = safe_key('key', 'prefix', 'a' * 300)
         assert self._is_valid_key(key)
 
+    @override_settings(FEATURES=BLAKE2B_ENABLED_FEATURES)
+    def test_long_key_prefix_version_with_blake2b_enabled(self):
+
+        # Long key
+        key = safe_key('a' * 300, 'prefix', 'version')
+        assert self._is_valid_key(key)
+
+        # Long prefix
+        key = safe_key('key', 'a' * 300, 'version')
+        assert self._is_valid_key(key)
+
+        # Long version
+        key = safe_key('key', 'prefix', 'a' * 300)
+        assert self._is_valid_key(key)
+
     def test_safe_key_unicode(self):
 
         for unicode_char in self.UNICODE_CHAR_CODES: