diff --git a/src/challenge-module/challenge-credential.cpp b/src/challenge-module/challenge-credential.cpp
index 839ccae..f5d7434 100644
--- a/src/challenge-module/challenge-credential.cpp
+++ b/src/challenge-module/challenge-credential.cpp
@@ -41,8 +41,9 @@
   if (configPath == "") {
     m_configFile = std::string(SYSCONFDIR) + "/ndncert/challenge-credential.conf";
   }
-  else
+  else {
     m_configFile = configPath;
+  }
 }
 
 void
@@ -65,9 +66,13 @@
   auto anchorList = config.get_child("anchor-list");
   auto it = anchorList.begin();
   for (; it != anchorList.end(); it++) {
-    std::istringstream ss(it->second.get<std::string>("certificate"));
-    security::v2::Certificate cert = *(io::load<security::v2::Certificate>(ss));
-    m_trustAnchors.push_back(cert);
+    std::istringstream ss(it->second.get("certificate", ""));
+    auto cert = io::load<security::v2::Certificate>(ss);
+    if (cert == nullptr) {
+      _LOG_ERROR("Cannot load the certificate from config file");
+      continue;
+    }
+    m_trustAnchors.push_back(*cert);
   }
 }
 
@@ -79,13 +84,10 @@
     parseConfigFile();
   }
   // load credential parameter
-  std::istringstream ss1(params.get<std::string>(JSON_CREDENTIAL_CERT));
-  security::v2::Certificate cert;
-  try {
-    cert = *(io::load<security::v2::Certificate>(ss1));
-  }
-  catch (const std::exception& e) {
-    _LOG_ERROR("Cannot load credential parameter: cert" << e.what());
+  std::istringstream ss1(params.get(JSON_CREDENTIAL_CERT, ""));
+  auto cert = io::load<security::v2::Certificate>(ss1);
+  if (cert == nullptr) {
+    _LOG_ERROR("Cannot load credential parameter: cert");
     request.m_status = STATUS_FAILURE;
     request.m_challengeStatus = FAILURE_INVALID_FORMAT_CREDENTIAL;
     updateRequestOnChallengeEnd(request);
@@ -94,13 +96,10 @@
   ss1.str("");
   ss1.clear();
   // load self-signed data
-  std::istringstream ss2(params.get<std::string>(JSON_CREDENTIAL_SELF));
-  Data self;
-  try {
-    self = *(io::load<Data>(ss2));
-  }
-  catch (const std::exception& e) {
-    _LOG_TRACE("Cannot load credential parameter: self-signed cert" << e.what());
+  std::istringstream ss2(params.get(JSON_CREDENTIAL_SELF, ""));
+  auto self = io::load<Data>(ss2);
+  if (self == nullptr) {
+    _LOG_TRACE("Cannot load credential parameter: self-signed cert");
     request.m_status = STATUS_FAILURE;
     request.m_challengeStatus = FAILURE_INVALID_FORMAT_SELF_SIGNED;
     updateRequestOnChallengeEnd(request);
@@ -110,11 +109,11 @@
   ss2.clear();
 
   // verify the credential and the self-signed cert
-  Name signingKeyName = cert.getSignature().getKeyLocator().getName();
+  Name signingKeyName = cert->getSignature().getKeyLocator().getName();
   for (auto anchor : m_trustAnchors) {
     if (anchor.getKeyName() == signingKeyName) {
-      if (security::verifySignature(cert, anchor) && security::verifySignature(self, cert)
-          && readString(self.getContent()) == request.m_requestId) {
+      if (security::verifySignature(*cert, anchor) && security::verifySignature(*self, *cert)
+          && readString(self->getContent()) == request.m_requestId) {
         request.m_status = STATUS_PENDING;
         request.m_challengeStatus = CHALLENGE_STATUS_SUCCESS;
         updateRequestOnChallengeEnd(request);
@@ -150,8 +149,8 @@
 {
   JsonSection result;
   if (status == STATUS_BEFORE_CHALLENGE && challengeStatus == "") {
-    result.put(JSON_CREDENTIAL_CERT, params.get<std::string>(JSON_CREDENTIAL_CERT, ""));
-    result.put(JSON_CREDENTIAL_SELF, params.get<std::string>(JSON_CREDENTIAL_SELF, ""));
+    result.put(JSON_CREDENTIAL_CERT, params.get(JSON_CREDENTIAL_CERT, ""));
+    result.put(JSON_CREDENTIAL_SELF, params.get(JSON_CREDENTIAL_SELF, ""));
   }
   else {
     _LOG_ERROR("Client's status and challenge status are wrong");
diff --git a/src/challenge-module/challenge-email.cpp b/src/challenge-module/challenge-email.cpp
index b22ec93..b9ca344 100644
--- a/src/challenge-module/challenge-email.cpp
+++ b/src/challenge-module/challenge-email.cpp
@@ -50,9 +50,10 @@
 void
 ChallengeEmail::handleChallengeRequest(const JsonSection& params, CertificateRequest& request)
 {
+  auto currentTime = time::system_clock::now();
   if (request.m_challengeStatus == "") {
     // for the first time, init the challenge
-    std::string emailAddress = params.get<std::string>(JSON_EMAIL);
+    std::string emailAddress = params.get(JSON_EMAIL, "");
     if (!isValidEmailAddress(emailAddress)) {
       request.m_status = STATUS_FAILURE;
       request.m_challengeStatus = FAILURE_INVALID_EMAIL;
@@ -79,7 +80,7 @@
     JsonSection secretJson;
     secretJson.add(JSON_CODE, emailCode);
     request.m_challengeSecrets = secretJson;
-    request.m_challengeTp = time::toIsoString(time::system_clock::now());
+    request.m_challengeTp = time::toIsoString(currentTime);
     request.m_remainingTime = m_secretLifetime.count();
     request.m_remainingTries = m_maxAttemptTimes;
     // send out the email
@@ -90,9 +91,9 @@
   else if (request.m_challengeStatus == NEED_CODE || request.m_challengeStatus == WRONG_CODE) {
     _LOG_TRACE("Challenge Interest arrives. Challenge Status: " << request.m_challengeStatus);
     // the incoming interest should bring the pin code
-    std::string givenCode = params.get<std::string>(JSON_CODE);
+    std::string givenCode = params.get(JSON_CODE, "");
     const auto realCode = request.m_challengeSecrets.get<std::string>(JSON_CODE);
-    if (time::system_clock::now() - time::fromIsoString(request.m_challengeTp) >= m_secretLifetime) {
+    if (currentTime - time::fromIsoString(request.m_challengeTp) >= m_secretLifetime) {
       // secret expires
       request.m_status = STATUS_FAILURE;
       request.m_challengeStatus = CHALLENGE_STATUS_FAILURE_TIMEOUT;
@@ -113,7 +114,7 @@
       if (request.m_remainingTries > 1) {
         request.m_challengeStatus = WRONG_CODE;
         request.m_remainingTries = request.m_remainingTries - 1;
-        auto remainTime = m_secretLifetime - (time::system_clock::now() - time::fromIsoString(request.m_challengeTp));
+        auto remainTime = m_secretLifetime - (currentTime - time::fromIsoString(request.m_challengeTp));
         request.m_remainingTime = remainTime.count();
         _LOG_TRACE("Secret code didn't match. Remaining Tries - 1.");
         return;
@@ -161,15 +162,15 @@
   JsonSection result;
   if (status == STATUS_BEFORE_CHALLENGE && challengeStatus == "") {
     result.put(JSON_CLIENT_SELECTED_CHALLENGE, CHALLENGE_TYPE);
-    result.put(JSON_EMAIL, params.get<std::string>(JSON_EMAIL, ""));
+    result.put(JSON_EMAIL, params.get(JSON_EMAIL, ""));
   }
   else if (status == STATUS_CHALLENGE && challengeStatus == NEED_CODE) {
     result.put(JSON_CLIENT_SELECTED_CHALLENGE, CHALLENGE_TYPE);
-    result.put(JSON_CODE, params.get<std::string>(JSON_CODE, ""));
+    result.put(JSON_CODE, params.get(JSON_CODE, ""));
   }
   else if (status == STATUS_CHALLENGE && challengeStatus == WRONG_CODE) {
     result.put(JSON_CLIENT_SELECTED_CHALLENGE, CHALLENGE_TYPE);
-    result.put(JSON_CODE, params.get<std::string>(JSON_CODE, ""));
+    result.put(JSON_CODE, params.get(JSON_CODE, ""));
   }
   else {
     _LOG_ERROR("Client's status and challenge status are wrong");
diff --git a/src/challenge-module/challenge-pin.cpp b/src/challenge-module/challenge-pin.cpp
index 9534b21..87f36cc 100644
--- a/src/challenge-module/challenge-pin.cpp
+++ b/src/challenge-module/challenge-pin.cpp
@@ -44,6 +44,7 @@
 void
 ChallengePin::handleChallengeRequest(const JsonSection& params, CertificateRequest& request)
 {
+  auto currentTime = time::system_clock::now();
   if (request.m_challengeStatus == "") {
     _LOG_TRACE("Challenge Interest arrives. Init the challenge");
     // for the first time, init the challenge
@@ -54,7 +55,7 @@
     JsonSection secretJson;
     secretJson.add(JSON_PIN_CODE, secretCode);
     request.m_challengeSecrets = secretJson;
-    request.m_challengeTp = time::toIsoString(time::system_clock::now());
+    request.m_challengeTp = time::toIsoString(currentTime);
     request.m_remainingTime = m_secretLifetime.count();
     request.m_remainingTries = m_maxAttemptTimes;
     _LOG_TRACE("Secret for request " << request.m_requestId << " : " << secretCode);
@@ -63,9 +64,9 @@
   else if (request.m_challengeStatus == NEED_CODE || request.m_challengeStatus == WRONG_CODE) {
     _LOG_TRACE("Challenge Interest arrives. Challenge Status: " << request.m_challengeStatus);
     // the incoming interest should bring the pin code
-    std::string givenCode = params.get<std::string>(JSON_PIN_CODE);
+    std::string givenCode = params.get(JSON_PIN_CODE, "");
     const auto realCode = request.m_challengeSecrets.get<std::string>(JSON_PIN_CODE);
-    if (time::system_clock::now() - time::fromIsoString(request.m_challengeTp) >= m_secretLifetime) {
+    if (currentTime - time::fromIsoString(request.m_challengeTp) >= m_secretLifetime) {
       // secret expires
       request.m_status = STATUS_FAILURE;
       request.m_challengeStatus = CHALLENGE_STATUS_FAILURE_TIMEOUT;
@@ -86,7 +87,7 @@
       if (request.m_remainingTries > 1) {
         request.m_challengeStatus = WRONG_CODE;
         request.m_remainingTries = request.m_remainingTries - 1;
-        auto remainTime = m_secretLifetime - (time::system_clock::now() - time::fromIsoString(request.m_challengeTp));
+        auto remainTime = m_secretLifetime - (currentTime - time::fromIsoString(request.m_challengeTp));
         request.m_remainingTime = remainTime.count();
         _LOG_TRACE("PIN code didn't match. Remaining Tries - 1.");
         return;
@@ -138,11 +139,11 @@
   }
   else if (status == STATUS_CHALLENGE && challengeStatus == NEED_CODE) {
     result.put(JSON_CLIENT_SELECTED_CHALLENGE, CHALLENGE_TYPE);
-    result.put(JSON_PIN_CODE, params.get<std::string>(JSON_PIN_CODE, ""));
+    result.put(JSON_PIN_CODE, params.get(JSON_PIN_CODE, ""));
   }
   else if (status == STATUS_CHALLENGE && challengeStatus == WRONG_CODE) {
     result.put(JSON_CLIENT_SELECTED_CHALLENGE, CHALLENGE_TYPE);
-    result.put(JSON_PIN_CODE, params.get<std::string>(JSON_PIN_CODE, ""));
+    result.put(JSON_PIN_CODE, params.get(JSON_PIN_CODE, ""));
   }
   else {
     _LOG_ERROR("Client's status and challenge status are wrong");