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

crypto/cup_openssl.cc

+// 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"
+
+using base::StringPiece;
+
+namespace crypto {
+
+size_t ClientUpdateProtocol::LoadPublicKey(const StringPiece& public_key) {
+  NOTIMPLEMENTED();
+  return 0;
+}
+
+bool ClientUpdateProtocol::EncryptKeySource(
+    const std::vector<uint8>& key_source) {
+  NOTIMPLEMENTED();
+  return false;
+}
+
+}  // namespace crypto
+