diff --git a/src/security/tpm/tpm.cpp b/src/security/tpm/tpm.cpp
index 0ed1062..d72440b 100644
--- a/src/security/tpm/tpm.cpp
+++ b/src/security/tpm/tpm.cpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
@@ -138,36 +138,27 @@
   return m_backEnd->exportKey(keyName, pw, pwLen);
 }
 
-bool
+void
 Tpm::importPrivateKey(const Name& keyName, const uint8_t* pkcs8, size_t pkcs8Len,
                       const char* pw, size_t pwLen)
 {
-  try {
-    m_backEnd->importKey(keyName, pkcs8, pkcs8Len, pw, pwLen);
-  }
-  catch (const BackEnd::Error&) {
-    return false;
-  }
-  return true;
+  m_backEnd->importKey(keyName, pkcs8, pkcs8Len, pw, pwLen);
 }
 
 const KeyHandle*
 Tpm::findKey(const Name& keyName) const
 {
   auto it = m_keys.find(keyName);
-
   if (it != m_keys.end())
     return it->second.get();
 
-  unique_ptr<KeyHandle> handle = m_backEnd->getKeyHandle(keyName);
+  auto handle = m_backEnd->getKeyHandle(keyName);
+  if (handle == nullptr)
+    return nullptr;
 
-  if (handle != nullptr) {
-    KeyHandle* key = handle.get();
-    m_keys[keyName] = std::move(handle);
-    return key;
-  }
-
-  return nullptr;
+  const KeyHandle* key = handle.get();
+  m_keys[keyName] = std::move(handle);
+  return key;
 }
 
 } // namespace tpm
diff --git a/src/security/tpm/tpm.hpp b/src/security/tpm/tpm.hpp
index dde9d14..4ce57f2 100644
--- a/src/security/tpm/tpm.hpp
+++ b/src/security/tpm/tpm.hpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
@@ -22,10 +22,9 @@
 #ifndef NDN_SECURITY_TPM_TPM_HPP
 #define NDN_SECURITY_TPM_TPM_HPP
 
-#include "../security-common.hpp"
-#include "../../name.hpp"
-#include "../key-params.hpp"
 #include "key-handle.hpp"
+#include "../key-params.hpp"
+#include "../../name.hpp"
 
 #include <unordered_map>
 
@@ -180,7 +179,7 @@
    * @param pw The password to encrypt the private key
    * @param pwLen The length of the password
    * @return The encoded private key wrapper.
-   * @throw BackEnd::Error the key does not exist or it cannot be exported.
+   * @throw BackEnd::Error The key does not exist or it could not be exported.
    */
   ConstBufferPtr
   exportPrivateKey(const Name& keyName, const char* pw, size_t pwLen) const;
@@ -193,16 +192,16 @@
    * @param pkcs8Len The length of the private key wrapper
    * @param pw The password to encrypt the private key
    * @param pwLen The length of the password
-   * @return true if the operation is successful, false otherwise.
+   * @throw BackEnd::Error The key could not be imported.
    */
-  bool
+  void
   importPrivateKey(const Name& keyName, const uint8_t* pkcs8, size_t pkcs8Len,
                    const char* pw, size_t pwLen);
 
   /**
    * @brief Clear the key cache.
    *
-   * An empty cache can force Tpm to do key lookup in back-end.
+   * An empty cache can force Tpm to do key lookup in the back-end.
    */
   void
   clearKeyCache()
diff --git a/src/security/v2/key-chain.cpp b/src/security/v2/key-chain.cpp
index 2d0820d..9f496a1 100644
--- a/src/security/v2/key-chain.cpp
+++ b/src/security/v2/key-chain.cpp
@@ -51,17 +51,11 @@
 // Therefore, the following standard PIB and TPMs need to be registered here.
 // http://stackoverflow.com/q/9459980/2150331
 
-/////////
-// PIB //
-/////////
 namespace pib {
 NDN_CXX_V2_KEYCHAIN_REGISTER_PIB_BACKEND(PibSqlite3);
 NDN_CXX_V2_KEYCHAIN_REGISTER_PIB_BACKEND(PibMemory);
 } // namespace pib
 
-/////////
-// TPM //
-/////////
 namespace tpm {
 #if defined(NDN_CXX_HAVE_OSX_FRAMEWORKS) && defined(NDN_CXX_WITH_OSX_KEYCHAIN)
 NDN_CXX_V2_KEYCHAIN_REGISTER_TPM_BACKEND(BackEndOsx);
@@ -355,8 +349,8 @@
   try {
     encryptedKey = m_tpm->exportPrivateKey(keyName, pw, pwLen);
   }
-  catch (const tpm::BackEnd::Error&) {
-    BOOST_THROW_EXCEPTION(Error("Private `" + keyName.toUri() + "` key does not exist"));
+  catch (const tpm::BackEnd::Error& e) {
+    BOOST_THROW_EXCEPTION(Error("Failed to export private key `" + keyName.toUri() + "`: " + e.what()));
   }
 
   return make_shared<SafeBag>(certificate, *encryptedKey);
@@ -389,8 +383,8 @@
                             safeBag.getEncryptedKeyBag().data(), safeBag.getEncryptedKeyBag().size(),
                             pw, pwLen);
   }
-  catch (const std::runtime_error&) {
-    BOOST_THROW_EXCEPTION(Error("Fail to import private key `" + keyName.toUri() + "`"));
+  catch (const tpm::BackEnd::Error& e) {
+    BOOST_THROW_EXCEPTION(Error("Failed to import private key `" + keyName.toUri() + "`: " + e.what()));
   }
 
   // check the consistency of private key and certificate
@@ -423,7 +417,6 @@
   key.addCertificate(cert);
 }
 
-
 // public: signing
 
 void
@@ -662,7 +655,7 @@
     }
     catch (const Pib::Error&) {
       BOOST_THROW_EXCEPTION(InvalidSigningInfoError("Signing identity `" + identity.getName().toUri() +
-                                                    "` does not have default certificate"));
+                                                    "` does not have a default certificate"));
     }
   }
 
diff --git a/tests/unit-tests/security/tpm/back-end.t.cpp b/tests/unit-tests/security/tpm/back-end.t.cpp
index ad8e39c..f118099 100644
--- a/tests/unit-tests/security/tpm/back-end.t.cpp
+++ b/tests/unit-tests/security/tpm/back-end.t.cpp
@@ -221,6 +221,8 @@
 
   tpm.importKey(keyName, privateKeyBuffer->data(), privateKeyBuffer->size(), password.c_str(), password.size());
   BOOST_CHECK_EQUAL(tpm.hasKey(keyName), true);
+  BOOST_CHECK_THROW(tpm.importKey(keyName, privateKeyBuffer->data(), privateKeyBuffer->size(), password.c_str(), password.size()),
+                    BackEnd::Error);
 
   ConstBufferPtr exportedKey = tpm.exportKey(keyName, password.c_str(), password.size());
   BOOST_CHECK_EQUAL(tpm.hasKey(keyName), true);
@@ -236,6 +238,7 @@
 
   tpm.deleteKey(keyName);
   BOOST_CHECK_EQUAL(tpm.hasKey(keyName), false);
+  BOOST_CHECK_THROW(tpm.exportKey(keyName, password.c_str(), password.size()), BackEnd::Error);
 }
 
 BOOST_AUTO_TEST_CASE(RandomKeyId)
diff --git a/tests/unit-tests/security/v2/key-chain.t.cpp b/tests/unit-tests/security/v2/key-chain.t.cpp
index a874464..9575754 100644
--- a/tests/unit-tests/security/v2/key-chain.t.cpp
+++ b/tests/unit-tests/security/v2/key-chain.t.cpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
@@ -365,6 +365,7 @@
   Block block = exported->wireEncode();
 
   m_keyChain.deleteIdentity(id);
+  BOOST_CHECK_THROW(m_keyChain.exportSafeBag(cert, "1234", 4), KeyChain::Error);
 
   BOOST_CHECK_EQUAL(m_keyChain.getTpm().hasKey(cert.getKeyName()), false);
   BOOST_CHECK_EQUAL(m_keyChain.getPib().getIdentities().size(), 0);
@@ -372,6 +373,7 @@
   SafeBag imported;
   imported.wireDecode(block);
   m_keyChain.importSafeBag(imported, "1234", 4);
+  BOOST_CHECK_THROW(m_keyChain.importSafeBag(imported, "1234", 4), KeyChain::Error);
 
   BOOST_CHECK_EQUAL(m_keyChain.getTpm().hasKey(cert.getKeyName()), true);
   BOOST_CHECK_EQUAL(m_keyChain.getPib().getIdentities().size(), 1);