diff --git a/core/util/non-negative-integer.hpp b/core/util/non-negative-integer.hpp
new file mode 100644
index 0000000..eecef0f
--- /dev/null
+++ b/core/util/non-negative-integer.hpp
@@ -0,0 +1,31 @@
+/* -*- 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/>.
+ *
+ * See AUTHORS.md for complete list of nsl authors and contributors.
+ */
+
+#ifndef NSL_UTIL_NON_NEGATIVE_INTEGER_HPP
+#define NSL_UTIL_NON_NEGATIVE_INTEGER_HPP
+
+namespace nsl {
+
+typedef uint64_t NonNegativeInteger;
+
+} // namespace nsl
+
+#endif // NSL_UTIL_NON_NEGATIVE_INTEGER_HPP
diff --git a/core/util/timestamp.hpp b/core/util/timestamp.hpp
new file mode 100644
index 0000000..a955e1c
--- /dev/null
+++ b/core/util/timestamp.hpp
@@ -0,0 +1,31 @@
+/* -*- 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/>.
+ *
+ * See AUTHORS.md for complete list of nsl authors and contributors.
+ */
+
+#ifndef NSL_UTIL_TIMESTAMP_HPP
+#define NSL_UTIL_TIMESTAMP_HPP
+
+namespace nsl {
+
+typedef uint64_t Timestamp;
+
+} // namespace nsl
+
+#endif // NSL_UTIL_TIMESTAMP_HPP