diff --git a/core/leaf.cpp b/core/leaf.cpp
new file mode 100644
index 0000000..33ee527
--- /dev/null
+++ b/core/leaf.cpp
@@ -0,0 +1,40 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014,  Regents of the University of California
+ *
+ * This file is part of NSL (NDN Signature Logger).
+ * See AUTHORS.md for complete list of NSL authors and contributors.
+ *
+ * NSL is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * NSL 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * NSL, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @author Peizhen Guo <patrick.guopz@gmail.com>
+ */
+#include "leaf.hpp"
+
+namespace nsl{
+
+ndn::ConstBufferPtr
+Leaf::getData() const
+{
+  return m_data;
+}
+
+
+
+void
+Leaf::computeHash()
+{
+  ndn::ConstBufferPtr digest = ndn::crypto::sha256(m_data->buf(), m_data->size());
+  this->setHash(digest);
+}
+
+} // namespace nsl