diff --git a/src/security/transform/step-source.hpp b/src/security/transform/step-source.hpp
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+/* -*- 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_TRANSFORM_STEP_SOURCE_HPP
+#define NDN_CXX_SECURITY_TRANSFORM_STEP_SOURCE_HPP
+
+#include "transform-base.hpp"
+
+namespace ndn {
+namespace security {
+namespace transform {
+
+/**
+ * @brief A source that can accept input step by step, and can close input explicitly.
+ *
+ * This source will not send data into the transformation chain when the chain is constructed.
+ * Input will be explicitly sent into the chain using write(...) and will be closed explicitly
+ * using end().
+ *
+ *   StepSource ss;
+ *   ss >> transform1() >> transform2() >> sinkStream(...);
+ *   ss.write(...);
+ *   ...
+ *   ss.write(...);
+ *   ss.end();
+ */
+class StepSource : public Source
+{
+public:
+  /**
+   * @brief Accept input data and directly write input into next transformation module.
+   *
+   * One can keep calling this method to until end() is called, which
+   * indicates the end of input.  After that, calling this method will cause Error.
+   *
+   * @return number of bytes that has been written into next module
+   */
+  size_t
+  write(const uint8_t* buf, size_t size);
+
+  /**
+   * @brief Close the input interface and directly notify the next module the end of input
+   */
+  void
+  end();
+
+private:
+  /**
+   * @brief This method intentionally does nothing
+   *
+   * use write() and end() method explicitly to input data.
+   */
+  virtual void
+  doPump() final;
+
+};
+
+typedef StepSource stepSource;
+
+} // namespace transform
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_CXX_SECURITY_TRANSFORM_STEP_SOURCE_HPP