diff --git a/src/protocol-detail/ndncert-common.cpp b/src/protocol-detail/ndncert-common.cpp
new file mode 100644
index 0000000..1915082
--- /dev/null
+++ b/src/protocol-detail/ndncert-common.cpp
@@ -0,0 +1,57 @@
+/* -*- 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 "ndncert-common.hpp"
+
+namespace ndn {
+namespace ndncert {
+
+const std::map<ErrorCode, std::string> errorCodeText = {
+  {ErrorCode::NO_ERROR,             "NO_ERROR"},
+  {ErrorCode::BAD_INTEREST_FORMAT,  "BAD_INTEREST_FORMAT"},
+  {ErrorCode::BAD_PARAMETER_FORMAT, "BAD_PARAMETER_FORMAT"},
+  {ErrorCode::BAD_SIGNATURE,        "BAD_SIGNATURE"},
+  {ErrorCode::INVALID_PARAMETER,    "INVALID_PARAMETER"},
+  {ErrorCode::NAME_NOT_ALLOWED,     "NAME_NOT_ALLOWED"},
+  {ErrorCode::BAD_VALIDITY_PERIOD,  "BAD_VALIDITY_PERIOD"},
+  {ErrorCode::OUT_OF_TRIES,         "OUT_OF_TRIES"},
+  {ErrorCode::OUT_OF_TIME,          "OUT_OF_TIME"},
+  {ErrorCode::NO_AVAILABLE_NAMES,   "NO_AVAILABLE_NAMES"}
+};
+
+const std::map<RequestType, std::string> requestTypeText = {
+  {RequestType::NEW, "New"},
+  {RequestType::RENEW, "Renew"},
+  {RequestType::REVOKE, "Revoke"},
+  {RequestType::NOTINITIALIZED, "Not Initialized"},
+};
+
+std::string errorCodeToString(ErrorCode code)
+{
+  return errorCodeText.at(code);
+}
+
+std::string requestTypeToString(RequestType type)
+{
+  return requestTypeText.at(type);
+}
+
+} // namespace ndncert
+} // namespace ndn