diff --git a/tools/ndncert-ca-server.cpp b/tools/ndncert-ca-server.cpp
index 8260502..a8af693 100644
--- a/tools/ndncert-ca-server.cpp
+++ b/tools/ndncert-ca-server.cpp
@@ -25,15 +25,15 @@
 #include <boost/program_options/options_description.hpp>
 #include <boost/program_options/parsers.hpp>
 #include <boost/program_options/variables_map.hpp>
-#include <iostream>
+
 #include <chrono>
 #include <deque>
+#include <iostream>
 
 #include <ndn-cxx/face.hpp>
 #include <ndn-cxx/security/key-chain.hpp>
 
-namespace ndncert {
-namespace ca {
+namespace ndncert::ca {
 
 static ndn::Face face;
 static ndn::KeyChain keyChain;
@@ -42,7 +42,8 @@
 const size_t MAX_CACHED_CERT_NUM = 100;
 
 static bool
-writeDataToRepo(const Data& data) {
+writeDataToRepo(const Data& data)
+{
   boost::asio::ip::tcp::iostream requestStream;
 #if BOOST_VERSION >= 106600
     requestStream.expires_after(std::chrono::seconds(3));
@@ -162,8 +163,7 @@
   return 0;
 }
 
-} // namespace ca
-} // namespace ndncert
+} // namespace ndncert::ca
 
 int
 main(int argc, char* argv[])
diff --git a/tools/ndncert-ca-status.cpp b/tools/ndncert-ca-status.cpp
index 2d0c0f9..c4f14c1 100644
--- a/tools/ndncert-ca-status.cpp
+++ b/tools/ndncert-ca-status.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2017-2021, Regents of the University of California.
+ * Copyright (c) 2017-2022, Regents of the University of California.
  *
  * This file is part of ndncert, a certificate management system based on NDN.
  *
@@ -27,8 +27,7 @@
 
 #include <iostream>
 
-namespace ndncert {
-namespace ca {
+namespace ndncert::ca {
 
 static int
 main(int argc, char* argv[])
@@ -74,8 +73,7 @@
   return 0;
 }
 
-} // namespace ca
-} // namespace ndncert
+} // namespace ndncert::ca
 
 int
 main(int argc, char* argv[])
diff --git a/tools/ndncert-client.cpp b/tools/ndncert-client.cpp
index c99104a..b2e3593 100644
--- a/tools/ndncert-client.cpp
+++ b/tools/ndncert-client.cpp
@@ -31,11 +31,10 @@
 
 #include <iostream>
 
-namespace ndncert {
-namespace requester {
+namespace ndncert::requester {
 
 static void
-selectCaProfile(std::string configFilePath);
+selectCaProfile(const std::string& configFilePath);
 
 static void
 runProbe(CaProfile profile);
@@ -92,7 +91,7 @@
             << " The CA may reject your application if your expected period is too long."
             << " The maximum validity period allowed by this CA is " << maxValidityPeriod << "."<< std::endl;
   size_t count = 0;
-  while (true && count < 3) {
+  while (count < 3) {
     std::string periodStr = "";
     getline(std::cin, periodStr);
     try {
@@ -161,7 +160,7 @@
   }
 }
 
-static void
+[[noreturn]] static void
 onNackCb()
 {
   std::cerr << "Got NACK\n";
@@ -171,7 +170,7 @@
 static void
 timeoutCb()
 {
-  std::cerr << "Interest sent time out\n";
+  std::cerr << "Interest timeout\n";
 }
 
 static void
@@ -223,62 +222,61 @@
   }
 
   size_t challengeIndex = 0;
-  if (challengeList.size() < 1) {
+  if (challengeList.empty()) {
     std::cerr << "There is no available challenge provided by the CA. Exit" << std::endl;
     exit(1);
   }
-  else if (challengeList.size() >= 1) {
-    auto item = std::find(challengeList.begin(), challengeList.end(), defaultChallenge);
-    if (item != challengeList.end()) {
-      runChallenge(defaultChallenge);
-    }
-    else {
-      // default challenge not available
-      std::cerr << "\n***************************************\n"
-                << "Step " << nStep++
-                << ": CHALLENGE SELECTION" << std::endl;
-      size_t count = 0;
-      std::string choice = "";
-      for (auto item : challengeList) {
-        std::cerr << "> Index: " << count++ << std::endl
-                  << ">> Challenge: " << item << std::endl;
-      }
-      std::cerr << "Please type in the index of the challenge that you want to perform:" << std::endl;
-      size_t inputCount = 0;
-      while (inputCount < 3) {
-        getline(std::cin, choice);
-        try {
-          challengeIndex = std::stoul(choice);
-        }
-        catch (const std::exception&) {
-          std::cerr << "Your input is not valid. Try again:" << std::endl;
-          inputCount++;
-          continue;
-        }
-        if (challengeIndex >= count) {
-          std::cerr << "Your input index is out of range. Try again:" << std::endl;
-          inputCount++;
-          continue;
-        }
-        break;
-      }
-      if (inputCount == 3) {
-        std::cerr << "Invalid input for too many times, exit. " << std::endl;
-        exit(1);
-      }
 
-      auto it = challengeList.begin();
-      std::advance(it, challengeIndex);
-      std::cerr << "The challenge has been selected: " << *it << std::endl;
-      runChallenge(*it);
+  auto item = std::find(challengeList.begin(), challengeList.end(), defaultChallenge);
+  if (item != challengeList.end()) {
+    runChallenge(defaultChallenge);
+  }
+  else {
+    // default challenge not available
+    std::cerr << "\n***************************************\n"
+              << "Step " << nStep++
+              << ": CHALLENGE SELECTION" << std::endl;
+    size_t count = 0;
+    std::string choice = "";
+    for (const auto& item : challengeList) {
+      std::cerr << "> Index: " << count++ << std::endl
+                << ">> Challenge: " << item << std::endl;
     }
+    std::cerr << "Please type in the index of the challenge that you want to perform:" << std::endl;
+    size_t inputCount = 0;
+    while (inputCount < 3) {
+      getline(std::cin, choice);
+      try {
+        challengeIndex = std::stoul(choice);
+      }
+      catch (const std::exception&) {
+        std::cerr << "Your input is not valid. Try again:" << std::endl;
+        inputCount++;
+        continue;
+      }
+      if (challengeIndex >= count) {
+        std::cerr << "Your input index is out of range. Try again:" << std::endl;
+        inputCount++;
+        continue;
+      }
+      break;
+    }
+    if (inputCount == 3) {
+      std::cerr << "Invalid input for too many times, exit. " << std::endl;
+      exit(1);
+    }
+
+    auto it = challengeList.begin();
+    std::advance(it, challengeIndex);
+    std::cerr << "The challenge has been selected: " << *it << std::endl;
+    runChallenge(*it);
   }
 }
 
 static void
 infoCb(const Data& reply, const Name& certFullName)
 {
-  optional<CaProfile> profile;
+  std::optional<CaProfile> profile;
   try {
     if (certFullName.empty()) {
       profile = Request::onCaProfileResponse(reply);
@@ -329,7 +327,7 @@
   Name selectedName;
   Name redirectedCaFullName;
   // always prefer redirection over direct assignment
-  if (redirects.size() > 0) {
+  if (!redirects.empty()) {
     if (redirects.size() < 2) {
       redirectedCaFullName = redirects.front();
     }
@@ -373,7 +371,7 @@
         [] (auto&&...) { onNackCb(); },
         [] (auto&&...) { timeoutCb(); });
   }
-  else if (names.size() > 0) {
+  else if (!names.empty()) {
     if (names.size() < 2) {
       selectedName = names.front().first;
     }
@@ -413,7 +411,7 @@
 }
 
 static void
-selectCaProfile(std::string configFilePath)
+selectCaProfile(const std::string& configFilePath)
 {
   ProfileStorage profileStorage;
   try {
@@ -426,7 +424,7 @@
   size_t count = 0;
   std::cerr << "***************************************\n"
             << "Step " << nStep++ << ": CA SELECTION" << std::endl;
-  for (auto item : profileStorage.getKnownProfiles()) {
+  for (const auto& item : profileStorage.getKnownProfiles()) {
     std::cerr << "> Index: " << count++ << std::endl
               << ">> CA prefix:" << item.caPrefix << std::endl
               << ">> Introduction: " << item.caInfo << std::endl;
@@ -547,7 +545,7 @@
               << "\nExit." << std::endl;
     exit(1);
   }
-  if (requirement.size() > 0) {
+  if (!requirement.empty()) {
     if (requesterState->m_status == Status::BEFORE_CHALLENGE && challengeType == defaultChallenge) {
       requirement.find(challengeType)->second = capturedProbeParams->find(defaultChallenge)->second;
     }
@@ -630,8 +628,7 @@
   return 0;
 }
 
-} // namespace requester
-} // namespace ndncert
+} // namespace ndncert::requester
 
 int
 main(int argc, char* argv[])