Per discussion, implement the Omaha Client Update Protocol (CUP) in src/crypto.

crypto/cup_openssl.cc

Index: crypto/cup_openssl.cc
===================================================================
--- crypto/cup_openssl.cc	(revision 0)
+++ crypto/cup_openssl.cc	(revision 0)
@@ -0,0 +1,22 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "crypto/cup.h"
+
+#include "base/logging.h"
+
+namespace crypto {
+
+size_t ClientUpdateProtocol::LoadPublicKey(const char* public_key) {
+  NOTIMPLEMENTED();
+  return 0;
+}
+
+bool ClientUpdateProtocol::EncryptSharedKey() {
+  NOTIMPLEMENTED();
+  return false;
+}
+
+}  // namespace crypto
+