diff --git a/src/challenge-module/challenge-private-key.cpp b/src/challenge-module/challenge-private-key.cpp
new file mode 100644
index 0000000..0b77af9
--- /dev/null
+++ b/src/challenge-module/challenge-private-key.cpp
@@ -0,0 +1,135 @@
+/*
+ * Copyright (c) 2017-2020, 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-private-key.hpp"
+
+#include <iostream>
+#include <ndn-cxx/security/verification-helpers.hpp>
+#include <ndn-cxx/util/io.hpp>
+
+#include "../logging.hpp"
+
+namespace ndn {
+namespace ndncert {
+
+_LOG_INIT(ndncert.ChallengePrivateKey);
+
+NDNCERT_REGISTER_CHALLENGE(ChallengePrivateKey, "Private");
+
+const std::string ChallengePrivateKey::FAILURE_INVALID_REQUEST_TYPE = "failure-invalid-request-type";
+const std::string ChallengePrivateKey::FAILURE_INVALID_FORMAT_SELF_SIGNED = "failure-cannot-parse-self-signed";
+const std::string ChallengePrivateKey::FAILURE_INVALID_CREDENTIAL = "failure-invalid-credential";
+const std::string ChallengePrivateKey::JSON_PROOF_OF_PRIVATE_KEY = "proof-of-private-key";
+
+ChallengePrivateKey::ChallengePrivateKey()
+    : ChallengeModule("PrivateKey")
+{
+}
+
+// For CA
+void
+ChallengePrivateKey::handleChallengeRequest(const Block& params, CertificateRequest& request)
+{
+  if (request.m_requestType == REQUEST_TYPE_NEW) {
+      _LOG_TRACE("Cannot use this private key challenge for new certificate request");
+      request.m_status = STATUS_FAILURE;
+      request.m_challengeStatus = FAILURE_INVALID_REQUEST_TYPE;
+      updateRequestOnChallengeEnd(request);
+  }
+  params.parse();
+  shared_ptr<security::v2::Certificate> selfSigned;
+  auto& elements = params.elements();
+  for (size_t i = 0; i < elements.size(); i++) {
+    if (elements[i].type() == tlv_parameter_key) {
+      if (readString(elements[i]) == JSON_PROOF_OF_PRIVATE_KEY) {
+        std::istringstream ss(readString(params.elements()[i + 1]));
+        selfSigned = io::load<security::v2::Certificate>(ss);
+        if (selfSigned == nullptr) {
+          _LOG_ERROR("Cannot load credential parameter: cert");
+          request.m_status = STATUS_FAILURE;
+          request.m_challengeStatus = FAILURE_INVALID_FORMAT_SELF_SIGNED;
+          updateRequestOnChallengeEnd(request);
+          return;
+        }
+      }
+      else {
+        continue;
+      }
+    }
+  }
+
+  // verify the credential and the self-signed cert
+  if (security::verifySignature(*selfSigned, request.m_cert) &&
+    readString(selfSigned->getContent()) == request.m_requestId) {
+    request.m_status = STATUS_PENDING;
+    request.m_challengeStatus = CHALLENGE_STATUS_SUCCESS;
+    updateRequestOnChallengeEnd(request);
+    return;
+  }
+
+  _LOG_TRACE("Cannot verify the credential + self-signed Data + data content");
+  request.m_status = STATUS_FAILURE;
+  request.m_challengeStatus = FAILURE_INVALID_CREDENTIAL;
+  updateRequestOnChallengeEnd(request);
+}
+
+// For Client
+JsonSection
+ChallengePrivateKey::getRequirementForChallenge(int status, const std::string& challengeStatus)
+{
+  JsonSection result;
+  if (status == STATUS_BEFORE_CHALLENGE && challengeStatus == "") {
+    result.put(JSON_PROOF_OF_PRIVATE_KEY, "Please_copy_key_signed_request_id_data_here");
+  }
+  else {
+    _LOG_ERROR("Client's status and challenge status are wrong");
+  }
+  return result;
+}
+
+JsonSection
+ChallengePrivateKey::genChallengeRequestJson(int status, const std::string& challengeStatus, const JsonSection& params)
+{
+  JsonSection result;
+  if (status == STATUS_BEFORE_CHALLENGE && challengeStatus == "") {
+    result.put(JSON_PROOF_OF_PRIVATE_KEY, params.get(JSON_PROOF_OF_PRIVATE_KEY, ""));
+  }
+  else {
+    _LOG_ERROR("Client's status and challenge status are wrong");
+  }
+  return result;
+}
+
+Block
+ChallengePrivateKey::genChallengeRequestTLV(int status, const std::string& challengeStatus, const JsonSection& params)
+{
+  Block request = makeEmptyBlock(tlv_encrypted_payload);
+  if (status == STATUS_BEFORE_CHALLENGE && challengeStatus == "") {
+    request.push_back(makeStringBlock(tlv_selected_challenge, CHALLENGE_TYPE));
+    request.push_back(makeStringBlock(tlv_parameter_key, JSON_PROOF_OF_PRIVATE_KEY));
+    request.push_back(makeStringBlock(tlv_parameter_value, params.get(JSON_PROOF_OF_PRIVATE_KEY, "")));
+  }
+  else {
+    _LOG_ERROR("Client's status and challenge status are wrong");
+  }
+  request.encode();
+  return request;
+}
+}  // namespace ndncert
+}  // namespace ndn