Export provisioning sdk

Change-Id: I4d47d80444c9507f84896767dc676112ca11e901

provisioning_sdk/public/python/crypto_utility.py

@@ -0,0 +1,25 @@
+################################################################################
+# Copyright 2016 Google Inc.
+#
+# This software is licensed under the terms defined in the Widevine Master
+# License Agreement. For a copy of this agreement, please contact
+# widevine-licensing@google.com.
+################################################################################
+
+"""Utility functions for cryptography."""
+
+from cryptography.hazmat import backends
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import padding
+
+
+def VerifySignature(public_key, signature, data):
+  hash_algorithm = hashes.SHA1()
+  salt_len = 20
+
+  key = serialization.load_der_public_key(
+      public_key, backend=backends.default_backend())
+  key.verify(signature, data,
+             padding.PSS(padding.MGF1(hash_algorithm), salt_len),
+             hash_algorithm)