diff --git a/src/challenge-module/challenge-credential.cpp b/src/challenge-module/challenge-credential.cpp
index bdc8b37..15d8721 100644
--- a/src/challenge-module/challenge-credential.cpp
+++ b/src/challenge-module/challenge-credential.cpp
@@ -18,10 +18,13 @@
  */
 
 #include "challenge-credential.hpp"
-#include "../logging.hpp"
+
+#include <iostream>
 #include <ndn-cxx/security/verification-helpers.hpp>
 #include <ndn-cxx/util/io.hpp>
 
+#include "../logging.hpp"
+
 namespace ndn {
 namespace ndncert {
 
@@ -36,7 +39,7 @@
 const std::string ChallengeCredential::JSON_CREDENTIAL_SELF = "self-signed";
 
 ChallengeCredential::ChallengeCredential(const std::string& configPath)
-  : ChallengeModule("Credential")
+    : ChallengeModule("Credential")
 {
   if (configPath.empty()) {
     m_configFile = std::string(SYSCONFDIR) + "/ndncert/challenge-credential.conf";
@@ -84,39 +87,45 @@
   if (m_trustAnchors.empty()) {
     parseConfigFile();
   }
-  // load credential parameter
-  // TODO: instead of string, should pass certificate byte value directly
-  std::istringstream ss1(readString(params.elements().at(1)));
-  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);
-    return;
+  shared_ptr<security::v2::Certificate> selfSigned, credential;
+  auto& elements = params.elements();
+  for (size_t i = 0; i < elements.size(); i++) {
+    if (elements[i].type() == tlv_parameter_key) {
+      if (readString(elements[i]) == JSON_CREDENTIAL_CERT) {
+        std::istringstream ss(readString(params.elements()[i + 1]));
+        credential = io::load<security::v2::Certificate>(ss);
+        if (credential == nullptr) {
+          _LOG_ERROR("Cannot load credential parameter: cert");
+          request.m_status = STATUS_FAILURE;
+          request.m_challengeStatus = FAILURE_INVALID_FORMAT_CREDENTIAL;
+          updateRequestOnChallengeEnd(request);
+          return;
+        }
+      }
+      else if (readString(elements[i]) == JSON_CREDENTIAL_SELF) {
+        std::istringstream ss(readString(params.elements()[i + 1]));
+        selfSigned = io::load<security::v2::Certificate>(ss);
+        if (selfSigned == nullptr) {
+          _LOG_ERROR("Cannot load credential parameter: cert");
+          request.m_status = STATUS_FAILURE;
+          request.m_challengeStatus = FAILURE_INVALID_FORMAT_SELF_SIGNED;
+          updateRequestOnChallengeEnd(request);
+          return;
+        }
+      }
+      else {
+        continue;
+      }
+    }
   }
-  ss1.str("");
-  ss1.clear();
-
-  // load self-signed data
-  std::istringstream ss2(readString(params.elements().at(3)));
-  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);
-    return;
-  }
-  ss2.str("");
-  ss2.clear();
 
   // verify the credential and the self-signed cert
-  Name signingKeyName = cert->getSignature().getKeyLocator().getName();
+  Name signingKeyName = credential->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(*selfSigned, anchor) &&
+          security::verifySignature(*selfSigned, *credential) &&
+          readString(selfSigned->getContent()) == request.m_requestId) {
         request.m_status = STATUS_PENDING;
         request.m_challengeStatus = CHALLENGE_STATUS_SUCCESS;
         updateRequestOnChallengeEnd(request);
@@ -168,9 +177,9 @@
   if (status == STATUS_BEFORE_CHALLENGE && challengeStatus == "") {
     request.push_back(makeStringBlock(tlv_selected_challenge, CHALLENGE_TYPE));
     request.push_back(makeStringBlock(tlv_parameter_key, JSON_CREDENTIAL_CERT));
-    request.push_back(makeStringBlock(tlv_parameter_value, params.get(JSON_CREDENTIAL_CERT,"")));
+    request.push_back(makeStringBlock(tlv_parameter_value, params.get(JSON_CREDENTIAL_CERT, "")));
     request.push_back(makeStringBlock(tlv_parameter_key, JSON_CREDENTIAL_SELF));
-    request.push_back(makeStringBlock(tlv_parameter_value, params.get(JSON_CREDENTIAL_SELF,"")));
+    request.push_back(makeStringBlock(tlv_parameter_value, params.get(JSON_CREDENTIAL_SELF, "")));
   }
   else {
     _LOG_ERROR("Client's status and challenge status are wrong");
@@ -178,5 +187,5 @@
   request.encode();
   return request;
 }
-} // namespace ndncert
-} // namespace ndn
+}  // namespace ndncert
+}  // namespace ndn
diff --git a/tests/database-fixture.hpp b/tests/database-fixture.hpp
index 4223c98..06c63f5 100644
--- a/tests/database-fixture.hpp
+++ b/tests/database-fixture.hpp
@@ -40,10 +40,7 @@
 public:
   DatabaseFixture()
   {
-    auto parentDir = boost::filesystem::path(getenv("TEST_HOME"));
-    if (!boost::filesystem::exists(parentDir)) {
-      boost::filesystem::create_directory(parentDir);
-    }
+    auto parentDir = boost::filesystem::path(getenv("HOME"));
     dbDir = parentDir / ".ndncert";
     if (!boost::filesystem::exists(dbDir)) {
       boost::filesystem::create_directory(dbDir);
diff --git a/tests/unit-tests/bench.t.cpp b/tests/unit-tests/bench.t.cpp
index 46b56ef..f21b06d 100644
--- a/tests/unit-tests/bench.t.cpp
+++ b/tests/unit-tests/bench.t.cpp
@@ -36,7 +36,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   ca.setProbeHandler([&](const Block& probeInfo) {
     return "example";
@@ -87,7 +87,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   advanceClocks(time::milliseconds(20), 60);
 
diff --git a/tests/unit-tests/ca-module.t.cpp b/tests/unit-tests/ca-module.t.cpp
index 40cb3d6..cb3cfcd 100644
--- a/tests/unit-tests/ca-module.t.cpp
+++ b/tests/unit-tests/ca-module.t.cpp
@@ -34,7 +34,7 @@
 
 BOOST_AUTO_TEST_CASE(Initialization)
 {
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   BOOST_CHECK_EQUAL(ca.getCaConf().m_caPrefix, "/ndn");
 
@@ -55,7 +55,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   ca.setProbeHandler([&](const Block& probeInfo) {
     return "example";
@@ -96,7 +96,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   ca.setProbeHandler([&](const Block& probeInfo) {
     return "example";
@@ -130,7 +130,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   advanceClocks(time::milliseconds(20), 60);
 
@@ -168,7 +168,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   advanceClocks(time::milliseconds(20), 60);
 
@@ -218,7 +218,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test");
   advanceClocks(time::milliseconds(20), 60);
 
@@ -251,7 +251,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   ca.m_config.m_probe = "email";
   advanceClocks(time::milliseconds(20), 60);
@@ -286,7 +286,7 @@
   auto key = identity.getDefaultKey();
   auto cert = key.getDefaultCertificate();
 
-  util::DummyClientFace face(io, {true, true});
+  util::DummyClientFace face(io, m_keyChain, {true, true});
   CaModule ca(face, m_keyChain, "tests/unit-tests/ca.conf.test", "ca-storage-memory");
   advanceClocks(time::milliseconds(20), 60);
 
diff --git a/tests/unit-tests/challenge-credential.t.cpp b/tests/unit-tests/challenge-credential.t.cpp
index 566ffd8..2b8e9b2 100644
--- a/tests/unit-tests/challenge-credential.t.cpp
+++ b/tests/unit-tests/challenge-credential.t.cpp
@@ -70,7 +70,6 @@
   selfSigned.setContent(makeStringBlock(tlv::Content, "123"));
   m_keyChain.sign(selfSigned, signingByCertificate(trustAnchor));
 
-  // generate SELECT interest
   std::stringstream ss;
   io::save<security::v2::Certificate>(selfSigned, ss);
   auto checkCert = *(io::load<security::v2::Certificate>(ss));
@@ -89,10 +88,12 @@
   ss.clear();
 
   Block params = makeEmptyBlock(tlv_encrypted_payload);
-  params.push_back(makeStringBlock(tlv_parameter_key, ChallengeCredential::JSON_CREDENTIAL_SELF));
-  params.push_back(makeStringBlock(tlv_parameter_value, selfSignedStr));
+  params.push_back(makeStringBlock(tlv_selected_challenge, "Credential"));
   params.push_back(makeStringBlock(tlv_parameter_key, ChallengeCredential::JSON_CREDENTIAL_CERT));
   params.push_back(makeStringBlock(tlv_parameter_value, credentialStr));
+  params.push_back(makeStringBlock(tlv_parameter_key, ChallengeCredential::JSON_CREDENTIAL_SELF));
+  params.push_back(makeStringBlock(tlv_parameter_value, selfSignedStr));
+  params.encode();
 
   challenge.handleChallengeRequest(params, request);
   BOOST_CHECK_EQUAL(request.m_status, STATUS_PENDING);