refactor integer to bytes as utils.int_to_bytes

2 files changed, 14 insertions, 5 deletions

diff --git a/src/cryptography/utils.py b/src/cryptography/utils.py
index 24afe612..4ca4a7a2 100644
--- a/src/cryptography/utils.py
+++ b/src/cryptography/utils.py
@@ -5,6 +5,7 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
+import binascii
 import inspect
 import struct
 import sys
@@ -46,6 +47,18 @@ else:
         return result
 
 
+if hasattr(int, "to_bytes"):
+    int_to_bytes = int.to_bytes
+else:
+    def int_to_bytes(integer, byteorder, signed=False):
+        assert byteorder == 'big'
+        assert not signed
+
+        hex_string = '%x' % integer
+        n = len(hex_string)
+        return binascii.unhexlify(hex_string.zfill(n + (n & 1)))
+
+
 class InterfaceNotImplemented(Exception):
     pass
 
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index f54eccf4..3fff218a 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -5,7 +5,6 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
-import binascii
 import datetime
 import hashlib
 import ipaddress
@@ -699,10 +698,7 @@ class SubjectKeyIdentifier(object):
         for bit in spki.getComponentByName("subjectPublicKey"):
             bits = bits << 1 | bit
 
-        # convert the integer to bytes
-        hex_string = '%x' % bits
-        n = len(hex_string)
-        data = binascii.unhexlify(hex_string.zfill(n + (n & 1)))
+        data = utils.int_to_bytes(bits, "big")
         return cls(hashlib.sha1(data).digest())
 
     digest = utils.read_only_property("_digest")