diff --git a/src/challenge-module/challenge-email.hpp b/src/challenge-module/challenge-email.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_EMAIL_HPP
+#define NDNCERT_CHALLENGE_EMAIL_HPP
+
+#include "../challenge-module.hpp"
+#include <ndn-cxx/util/time.hpp>
+
+namespace ndn {
+namespace ndncert {
+
+/**
+ * @brief Provide Email based challenge
+ *
+ * @sa https://github.com/named-data/ndncert/wiki/NDN-Certificate-Management-Protocol
+ *
+ * The main process of this challenge module is:
+ *   1. Requester provides its email address.
+ *   2. The challenge module will send a verification code to this email address.
+ *   3. Requester provides the verification code to challenge module.
+ *
+ * There are several challenge status in EMAIL challenge:
+ *   NEED_CODE: When email address is provided and the verification code has been sent out.
+ *   WRONG_CODE: Wrong code but still within secret lifetime and within max try times.
+ *   FAILURE_INVALID_EMAIL: When the email is invalid.
+ *   FAILURE_TIMEOUT: When the secret lifetime expires.
+ *   FAILURE_MAXRETRY: When run out retry times.
+ */
+class ChallengeEmail : public ChallengeModule
+{
+public:
+  ChallengeEmail(const std::string& scriptPath = "send-mail.sh",
+                 const size_t& maxAttemptTimes = 3,
+                 const time::seconds secretLifetime = time::minutes(20));
+
+PUBLIC_WITH_TESTS_ELSE_PROTECTED:
+  JsonSection
+  processSelectInterest(const Interest& interest, CertificateRequest& request) override;
+
+  JsonSection
+  processValidateInterest(const Interest& interest, CertificateRequest& request) override;
+
+  std::list<std::string>
+  getSelectRequirements() override;
+
+  std::list<std::string>
+  getValidateRequirements(const std::string& status) override;
+
+  JsonSection
+  doGenSelectParamsJson(const std::string& status,
+                        const std::list<std::string>& paramList) override;
+
+  JsonSection
+  doGenValidateParamsJson(const std::string& status,
+                          const std::list<std::string>& paramList) override;
+
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  static bool
+  isValidEmailAddress(const std::string& emailAddress);
+
+  void
+  sendEmail(const std::string& emailAddress, const std::string& secret) const;
+
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  static std::tuple<time::system_clock::TimePoint, std::string, int>
+  parseStoredSecrets(const JsonSection& storedSecret);
+
+  static JsonSection
+  generateStoredSecrets(const time::system_clock::TimePoint& tp, const std::string& secretCode,
+                        int attempTimes);
+
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
+  static const std::string NEED_CODE;
+  static const std::string WRONG_CODE;
+  static const std::string FAILURE_INVALID_EMAIL;
+  static const std::string FAILURE_TIMEOUT;
+  static const std::string FAILURE_MAXRETRY;
+
+  static const std::string JSON_EMAIL;
+  static const std::string JSON_CODE_TP;
+  static const std::string JSON_CODE;
+  static const std::string JSON_ATTEMPT_TIMES;
+
+private:
+  std::string m_sendEmailScript;
+  int m_maxAttemptTimes;
+  time::seconds m_secretLifetime;
+};
+
+} // namespace ndncert
+} // namespace ndn
+
+#endif // NDNCERT_CHALLENGE_EMAIL_HPP