diff --git a/src/interval.hpp b/src/interval.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014-2015,  Regents of the University of California
+ *
+ * This file is part of ndn-group-encrypt (Group-based Encryption Protocol for NDN).
+ * See AUTHORS.md for complete list of ndn-group-encrypt authors and contributors.
+ *
+ * ndn-group-encrypt 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.
+ *
+ * ndn-group-encrypt 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
+ * ndn-group-encrypt, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @author Zhiyi Zhang <dreamerbarrychang@gmail.com>
+ */
+
+#ifndef NDN_GEP_INTERVAL_HPP
+#define NDN_GEP_INTERVAL_HPP
+
+#include "common.hpp"
+
+#include <boost/date_time/posix_time/posix_time.hpp>
+
+namespace ndn {
+namespace gep {
+
+typedef boost::posix_time::ptime TimeStamp;
+
+///@brief Interval define a time duration which contains a start timestamp and an end timestamp
+class Interval
+{
+public:
+  class Error : public std::runtime_error
+  {
+  public:
+    explicit
+    Error(const std::string& what)
+      : std::runtime_error(what)
+    {
+    }
+  };
+
+public:
+  /**
+   * @brief Construction to create an object
+   *
+   * @parameter isValid If isValid is true, the created interval is an empty interval
+   */
+  explicit
+  Interval(bool isValid = false);
+
+  Interval(const TimeStamp& startTime,
+           const TimeStamp& endTime);
+
+  /**
+   * @brief Check if the timestamp tp is in the interval
+   * @pre this->isValid() == true
+   *
+   * @parameter tp A timestamp
+   */
+  bool
+  covers(const TimeStamp& tp) const;
+
+  /**
+   * @brief Get the intersection interval of two intervals
+   * @pre this->isValid() == true && interval.isValid() == true
+   *
+   * Two intervals should all be valid but they can be empty
+   */
+  Interval&
+  operator &&(const Interval& interval);
+
+  /**
+   * @brief Get the union set interval of two intervals
+   * @pre this->isValid() == true && interval.isValid() == true
+   *
+   * Two intervals should all be valid but they can be empty
+   */
+  Interval&
+  operator ||(const Interval& interval);
+
+  const TimeStamp&
+  getStartTime() const
+  {
+    BOOST_ASSERT(isValid());
+    return m_startTime;
+  }
+
+  const TimeStamp&
+  getEndTime() const
+  {
+    BOOST_ASSERT(isValid());
+    return m_endTime;
+  }
+
+  bool
+  isValid() const
+  {
+    return m_isValid;
+  }
+
+  bool
+  isEmpty() const
+  {
+    BOOST_ASSERT(isValid());
+    return m_startTime == m_endTime;
+  }
+
+private:
+  TimeStamp m_startTime;
+  TimeStamp m_endTime;
+
+  bool m_isValid;
+};
+
+} // namespace gep
+} // namespace ndn
+
+#endif // NDN_GEP_INTERVAL_HPP