Use standard binascii

One of the local functions was reimplementing hexlify. Unfortunately
it was also not py3 compatible.

Change-Id: Ib653c960de4dd7494a193525b7b80281616f3007

anchor/X509/message_digest.py

@@ -15,6 +15,8 @@ from __future__ import absolute_import
 
 from cryptography.hazmat.backends.openssl import backend
 
+import binascii
+
 
 class MessageDigestError(Exception):
     def __init__(self, what):
@@ -67,13 +69,6 @@ class MessageDigest(object):
             self._lib.EVP_MD_CTX_cleanup(self.ctx)
             self._lib.EVP_MD_CTX_destroy(self.ctx)
 
-    def _octx_to_num(self, x):
-        v = 0L
-        lx = len(x)
-        for i in range(lx):
-            v = v + ord(x[i]) * (256L ** (lx - i - 1))
-        return v
-
     def update(self, data):
         """Add more data to the digest."""
 
@@ -95,4 +90,4 @@ class MessageDigest(object):
             raise MessageDigestError(
                 "Failed to get message digest.")  # pragma: no cover
         digest = self._ffi.string(data)
-        return hex(self._octx_to_num(digest))[2:-1].upper()
+        return binascii.hexlify(digest).decode('ascii').upper()

tests/X509/test_message_digest.py

@@ -20,7 +20,7 @@ from anchor.X509 import message_digest
 
 
 class TestMessageDigest(unittest.TestCase):
-    data = "this is test data to test with"
+    data = b"this is test data to test with"
 
     def setUp(self):
         super(TestMessageDigest, self).setUp()