diff --git a/src/security/detail/openssl-helper.hpp b/src/security/detail/openssl-helper.hpp
new file mode 100644
index 0000000..e9e5900
--- /dev/null
+++ b/src/security/detail/openssl-helper.hpp
@@ -0,0 +1,39 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2016 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#ifndef NDN_CXX_SECURITY_DETAIL_OPENSSL_HELPER_HPP
+#define NDN_CXX_SECURITY_DETAIL_OPENSSL_HELPER_HPP
+
+#include "../security-common.hpp"
+#include "openssl.hpp"
+
+namespace ndn {
+namespace security {
+namespace detail {
+
+const EVP_MD*
+toDigestEvpMd(DigestAlgorithm algo);
+
+} // namespace detail
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_CXX_SECURITY_DETAIL_OPENSSL_HELPER_HPP