Add NONCE_RANDOM_PREFIX_SIZE to constants

Add test for NONCE_RANDOM_PREFIX_SIZE constant

nkms/storage/constants.py

@@ -1 +1,5 @@
+# Number of random bytes to prefix before the counter
+NONCE_RANDOM_PREFIX_SIZE = 20
+
+# Size of the counter in bytes (4 = int)
 NONCE_COUNTER_BYTE_SIZE = 4

nkms/storage/header.py

@@ -1,6 +1,7 @@
 import msgpack
 import pathlib
 from nacl.utils import random
+from nkms.storage.constants import NONCE_RANDOM_PREFIX_SIZE
 
 
 class Header(object):
@@ -53,7 +54,7 @@ class Header(object):
         :rtype: Dict
         """
         if not nonce:
-            nonce = random(20)
+            nonce = random(NONCE_RANDOM_PREFIX_SIZE)
 
         return {
             'version': version,

tests/storage/test_constants.py

@@ -5,3 +5,4 @@ from nkms.storage import constants
 class TestConstants(unittest.TestCase):
     def test_constants(self):
         self.assertEqual(4, constants.NONCE_COUNTER_BYTE_SIZE)
+        self.assertEqual(20, constants.NONCE_RANDOM_PREFIX_SIZE)