diff --git a/src/challenge-module.hpp b/src/challenge-module.hpp
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+++ b/src/challenge-module.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2017, Regents of the University of California.
+ *
+ * This file is part of ndncert, a certificate management system based on NDN.
+ *
+ * ndncert 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.
+ *
+ * ndncert 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 copies of the GNU General Public License along with
+ * ndncert, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndncert authors and contributors.
+ */
+
+#ifndef NDNCERT_CHALLENGE_MODULE_HPP
+#define NDNCERT_CHALLENGE_MODULE_HPP
+
+#include "ndncert-common.hpp"
+#include "certificate-request.hpp"
+#include "json-helper.hpp"
+
+namespace ndn {
+namespace ndncert {
+
+class ChallengeModule : noncopyable
+{
+public:
+  /**
+   * @brief Error that can be thrown from ChallengeModule
+   *
+   * ChallengeModule should throw Error to notice CA there's an Error. In this case, CA will
+   * generate an Error JSON file back to end entity.
+   */
+  class Error : public std::runtime_error
+  {
+  public:
+    using std::runtime_error::runtime_error;
+  };
+
+public:
+  ChallengeModule(const std::string& uniqueType);
+
+  template<class ChallengeType>
+  static void
+  registerChallengeModule(const std::string& typeName)
+  {
+    ChallengeFactory& factory = getFactory();
+    BOOST_ASSERT(factory.count(typeName) == 0);
+    factory[typeName] = [] { return make_unique<ChallengeType>(); };
+  }
+
+  static unique_ptr<ChallengeModule>
+  createChallengeModule(const std::string& ChallengeType);
+
+  /**
+   * @brief Handle the challenge related interest and update certificate request.
+   * @note Should be used by CA Module
+   * @note Signature of interest should already be validated by CA Module
+   *
+   * When CA receives a SELECT or a VALIDATE or a STATUS interest, CA should invoke the function
+   * to enable selected challenge to go on the verification process.
+   *
+   * @param interest The request interest packet
+   * @param request The CertificateRequest instance
+   * @return the JSON file as the response data content
+   */
+  JsonSection
+  handleChallengeRequest(const Interest& interest, CertificateRequest& request);
+
+  /**
+   * @brief Get requirements for requester before sending SELECT interest.
+   * @note Should be used by Client Module
+   *
+   * Before requester sends a USE interest, client should invoke the function to
+   * get input instruction and expose the instruction to requester.
+   *
+   * Every item in the return list requires a input from requester. The item itself is
+   * an instruction for requester.
+   *
+   * @return the input instruction for requester
+   */
+  std::list<std::string>
+  getRequirementForSelect();
+
+  /**
+   * @brief Get requirements for requester before sending VALIDATE interest.
+   * @note Should be used by Client Module
+   *
+   * Before requester sends a POLL interest, client should invoke the function to
+   * get input instruction and expose the instruction to requester.
+   *
+   * Every item in the return list requires a input from requester. The item itself is
+   * an instruction for requester.
+   *
+   * @param status of the challenge
+   * @return the input instruction for requester
+   */
+  std::list<std::string>
+  getRequirementForValidate(const std::string& status);
+
+  /**
+   * @brief Generate ChallengeInfo part for SELECT and VALIDATE interest.
+   * @note Should be used by Client Module
+   *
+   * After requester provides required information, client should invoke the function to
+   * generate the ChallengeInfo part of the interest.
+   *
+   * @param interestType of the request
+   * @param status of the challenge
+   * @param paramList contains all the input from requester
+   * @return the JSON file of ChallengeInfo
+   */
+  JsonSection
+  genRequestChallengeInfo(const std::string& interestType, const std::string& status,
+                          const std::list<std::string>& paramList);
+
+PUBLIC_WITH_TESTS_ELSE_PROTECTED:
+  virtual JsonSection
+  processSelectInterest(const Interest& interest, CertificateRequest& request) = 0;
+
+  virtual JsonSection
+  processValidateInterest(const Interest& interest, CertificateRequest& request) = 0;
+
+  virtual std::list<std::string>
+  getSelectRequirements() = 0;
+
+  virtual std::list<std::string>
+  getValidateRequirements(const std::string& status) = 0;
+
+  virtual JsonSection
+  genChallengeInfo(const std::string& interestType, const std::string& status,
+                   const std::list<std::string>& paramList) = 0;
+
+  virtual JsonSection
+  processStatusInterest(const Interest& interest, const CertificateRequest& request);
+
+  static JsonSection
+  getJsonFromNameComponent(const Name& name, int pos);
+
+  static Name
+  genDownloadName(const Name& caName, const std::string& requestId);
+
+public:
+  const std::string CHALLENGE_TYPE;
+  static const std::string WAIT_SELECTION;
+  static const std::string SUCCESS;
+  static const std::string PENDING;
+
+private:
+  typedef function<unique_ptr<ChallengeModule> ()> ChallengeCreateFunc;
+  typedef std::map<std::string, ChallengeCreateFunc> ChallengeFactory;
+
+  static ChallengeFactory&
+  getFactory();
+};
+
+#define NDNCERT_REGISTER_CHALLENGE(C, T)                           \
+static class NdnCert ## C ## ChallengeRegistrationClass            \
+{                                                                  \
+public:                                                            \
+  NdnCert ## C ## ChallengeRegistrationClass()                     \
+  {                                                                \
+    ::ndn::ndncert::ChallengeModule::registerChallengeModule<C>(T);\
+  }                                                                \
+} g_NdnCert ## C ## ChallengeRegistrationVariable
+
+} // namespace ndncert
+} // namespace ndn
+
+#endif // NDNCERT_CHALLENGE_MODULE_HPP