diff --git a/src/challenge-module.cpp b/src/challenge-module.cpp
new file mode 100644
index 0000000..2170c5f
--- /dev/null
+++ b/src/challenge-module.cpp
@@ -0,0 +1,125 @@
+/* -*- 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.
+ */
+
+#include "challenge-module.hpp"
+#include <random>
+
+namespace ndn {
+namespace ndncert {
+
+const std::string ChallengeModule::WAIT_SELECTION = "wait-selection";
+const std::string ChallengeModule::SUCCESS = "success";
+const std::string ChallengeModule::PENDING = "pending";
+
+ChallengeModule::ChallengeModule(const std::string& uniqueType)
+  : CHALLENGE_TYPE(uniqueType)
+{
+}
+
+unique_ptr<ChallengeModule>
+ChallengeModule::createChallengeModule(const std::string& canonicalName)
+{
+  ChallengeFactory& factory = getFactory();
+  auto i = factory.find(canonicalName);
+  return i == factory.end() ? nullptr : i->second();
+}
+
+JsonSection
+ChallengeModule::handleChallengeRequest(const Interest& interest, CertificateRequest& request)
+{
+  int pos = request.getCaName().size();
+  const Name& interestName = interest.getName();
+  std::string interestType = interestName.get(pos).toUri();
+  if (interestType == "_SELECT") {
+    return processSelectInterest(interest, request);
+  }
+  else if (interestType == "_VALIDATE"){
+    return processValidateInterest(interest, request);
+  }
+  else {
+    return processStatusInterest(interest, request);
+  }
+}
+
+std::list<std::string>
+ChallengeModule::getRequirementForSelect()
+{
+  return getSelectRequirements();
+}
+
+std::list<std::string>
+ChallengeModule::getRequirementForValidate(const std::string& status)
+{
+  return getValidateRequirements(status);
+}
+
+JsonSection
+ChallengeModule::genRequestChallengeInfo(const std::string& interestType, const std::string& status,
+                                         const std::list<std::string>& paramList)
+{
+  return genChallengeInfo(interestType, status, paramList);
+}
+
+JsonSection
+ChallengeModule::processStatusInterest(const Interest& interest, const CertificateRequest& request)
+{
+  // interest format: /CA/_STATUS/{"request-id":"id"}/<signature>
+  if (request.getStatus() == SUCCESS) {
+    Name downloadName = genDownloadName(request.getCaName(), request.getStatus());
+    return genResponseChallengeJson(request.getRequestId(), request.getChallengeType(),
+                                    SUCCESS, downloadName);
+  }
+  else
+    return genResponseChallengeJson(request.getRequestId(), request.getChallengeType(),
+                                    request.getStatus());
+}
+
+JsonSection
+ChallengeModule::getJsonFromNameComponent(const Name& name, int pos)
+{
+  std::string jsonString = encoding::readString(name.get(pos));
+  std::istringstream ss(jsonString);
+  JsonSection json;
+  boost::property_tree::json_parser::read_json(ss, json);
+  return json;
+}
+
+Name
+ChallengeModule::genDownloadName(const Name& caName, const std::string& requestId)
+{
+  JsonSection json;
+  json.put(JSON_REQUEST_ID, requestId);
+  std::stringstream ss;
+  boost::property_tree::write_json(ss, json);
+  Block jsonBlock = makeStringBlock(ndn::tlv::NameComponent, ss.str());
+  Name name = caName;
+  name.append("_DOWNLOAD").append(jsonBlock);
+  return name;
+}
+
+ChallengeModule::ChallengeFactory&
+ChallengeModule::getFactory()
+{
+  static ChallengeModule::ChallengeFactory factory;
+  return factory;
+}
+
+} // namespace ndncert
+} // namespace ndn