diff --git a/src/detail/challenge-encoder.cpp b/src/detail/challenge-encoder.cpp
new file mode 100644
index 0000000..658cbd8
--- /dev/null
+++ b/src/detail/challenge-encoder.cpp
@@ -0,0 +1,63 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * 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-encoder.hpp"
+
+namespace ndn {
+namespace ndncert {
+
+Block
+ChallengeEncoder::encodeDataContent(const CaState& request)
+{
+  Block response = makeEmptyBlock(tlv::EncryptedPayload);
+  response.push_back(makeNonNegativeIntegerBlock(tlv::Status, static_cast<size_t>(request.m_status)));
+  if (request.m_challengeState) {
+    response.push_back(makeStringBlock(tlv::ChallengeStatus, request.m_challengeState->m_challengeStatus));
+    response.push_back(
+        makeNonNegativeIntegerBlock(tlv::RemainingTries, request.m_challengeState->m_remainingTries));
+    response.push_back(
+        makeNonNegativeIntegerBlock(tlv::RemainingTime, request.m_challengeState->m_remainingTime.count()));
+  }
+  response.encode();
+  return response;
+}
+
+void
+ChallengeEncoder::decodeDataContent(const Block& data, RequesterState& state)
+{
+  data.parse();
+  state.m_status = static_cast<Status>(readNonNegativeInteger(data.get(tlv::Status)));
+  if (data.find(tlv::ChallengeStatus) != data.elements_end()) {
+    state.m_challengeStatus = readString(data.get(tlv::ChallengeStatus));
+  }
+  if (data.find(tlv::RemainingTries) != data.elements_end()) {
+    state.m_remainingTries = readNonNegativeInteger(data.get(tlv::RemainingTries));
+  }
+  if (data.find(tlv::RemainingTime) != data.elements_end()) {
+    state.m_freshBefore = time::system_clock::now() + time::seconds(readNonNegativeInteger(data.get(tlv::RemainingTime)));
+  }
+  if (data.find(tlv::IssuedCertName) != data.elements_end()) {
+    Block issuedCertNameBlock = data.get(tlv::IssuedCertName);
+    state.m_issuedCertName = Name(issuedCertNameBlock.blockFromValue());
+  }
+}
+
+} // namespace ndncert
+} // namespace ndn