diff --git a/src/detail/ca-memory.cpp b/src/detail/ca-memory.cpp
index b647dba..b054cc0 100644
--- a/src/detail/ca-memory.cpp
+++ b/src/detail/ca-memory.cpp
@@ -35,11 +35,11 @@
 }
 
 CaState
-CaMemory::getRequest(const std::string& requestId)
+CaMemory::getRequest(const RequestID& requestId)
 {
   auto search = m_requests.find(requestId);
   if (search == m_requests.end()) {
-    NDN_THROW(std::runtime_error("Request " + requestId + " doest not exists"));
+    NDN_THROW(std::runtime_error("Request " + toHex(requestId.data(), requestId.size()) + " doest not exists"));
   }
   return search->second;
 }
@@ -52,7 +52,7 @@
     m_requests[request.m_requestId] = request;
   }
   else {
-    NDN_THROW(std::runtime_error("Request " + request.m_requestId + " already exists"));
+    NDN_THROW(std::runtime_error("Request " + toHex(request.m_requestId.data(), request.m_requestId.size()) + " already exists"));
   }
 }
 
@@ -64,7 +64,7 @@
 }
 
 void
-CaMemory::deleteRequest(const std::string& requestId)
+CaMemory::deleteRequest(const RequestID& requestId)
 {
   auto search = m_requests.find(requestId);
   auto keyName = search->second.m_cert.getKeyName();
diff --git a/src/detail/ca-memory.hpp b/src/detail/ca-memory.hpp
index 842121b..0c2fa34 100644
--- a/src/detail/ca-memory.hpp
+++ b/src/detail/ca-memory.hpp
@@ -37,7 +37,7 @@
    * @throw if request cannot be fetched from underlying data storage
    */
   CaState
-  getRequest(const std::string& requestId) override;
+  getRequest(const RequestID& requestId) override;
 
   /**
    * @throw if there is an existing request with the same request ID
@@ -49,7 +49,7 @@
   updateRequest(const CaState& request) override;
 
   void
-  deleteRequest(const std::string& requestId) override;
+  deleteRequest(const RequestID& requestId) override;
 
   std::list<CaState>
   listAllRequests() override;
@@ -58,7 +58,7 @@
   listAllRequests(const Name& caName) override;
 
 private:
-  std::map<Name, CaState> m_requests;
+  std::map<RequestID, CaState> m_requests;
 };
 
 } // namespace ndncert
diff --git a/src/detail/ca-sqlite.cpp b/src/detail/ca-sqlite.cpp
index 468fd2c..8371cf4 100644
--- a/src/detail/ca-sqlite.cpp
+++ b/src/detail/ca-sqlite.cpp
@@ -55,7 +55,7 @@
 CREATE TABLE IF NOT EXISTS
   CaStates(
     id INTEGER PRIMARY KEY,
-    request_id TEXT NOT NULL,
+    request_id BLOB NOT NULL,
     ca_name BLOB NOT NULL,
     request_type INTEGER NOT NULL,
     status INTEGER NOT NULL,
@@ -123,7 +123,7 @@
 }
 
 CaState
-CaSqlite::getRequest(const std::string& requestId)
+CaSqlite::getRequest(const RequestID& requestId)
 {
   Sqlite3Statement statement(m_database,
                              R"_SQLTEXT_(SELECT id, ca_name, status,
@@ -132,7 +132,7 @@
                              challenge_tp, remaining_tries, remaining_time,
                              request_type, encryption_key, aes_block_counter
                              FROM CaStates where request_id = ?)_SQLTEXT_");
-  statement.bind(1, requestId, SQLITE_TRANSIENT);
+  statement.bind(1, requestId.data(), requestId.size(), SQLITE_TRANSIENT);
 
   if (statement.step() == SQLITE_ROW) {
     Name caName(statement.getBlock(1));
@@ -158,7 +158,7 @@
     }
   }
   else {
-    NDN_THROW(std::runtime_error("Request " + requestId + " cannot be fetched from database"));
+    NDN_THROW(std::runtime_error("Request " + toHex(requestId.data(), requestId.size()) + " cannot be fetched from database"));
   }
 }
 
@@ -171,7 +171,7 @@
                   cert_request, challenge_type, challenge_status, challenge_secrets,
                   challenge_tp, remaining_tries, remaining_time, encryption_key, aes_block_counter)
                   values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?))_SQLTEXT_");
-  statement.bind(1, request.m_requestId, SQLITE_TRANSIENT);
+  statement.bind(1, request.m_requestId.data(), request.m_requestId.size(), SQLITE_TRANSIENT);
   statement.bind(2, request.m_caPrefix.wireEncode(), SQLITE_TRANSIENT);
   statement.bind(3, static_cast<int>(request.m_status));
   statement.bind(4, static_cast<int>(request.m_requestType));
@@ -188,7 +188,7 @@
     statement.bind(11, request.m_challengeState->m_remainingTime.count());
   }
   if (statement.step() != SQLITE_DONE) {
-    NDN_THROW(std::runtime_error("Request " + request.m_requestId + " cannot be added to database"));
+    NDN_THROW(std::runtime_error("Request " + toHex(request.m_requestId.data(), request.m_requestId.size()) + " cannot be added to database"));
   }
 }
 
@@ -217,7 +217,7 @@
     statement.bind(7, 0);
   }
   statement.bind(8, request.m_aesBlockCounter);
-  statement.bind(9, request.m_requestId, SQLITE_TRANSIENT);
+  statement.bind(9, request.m_requestId.data(), request.m_requestId.size(), SQLITE_TRANSIENT);
 
   if (statement.step() != SQLITE_DONE) {
     addRequest(request);
@@ -234,7 +234,8 @@
                              encryption_key, aes_block_counter
                              FROM CaStates)_SQLTEXT_");
   while (statement.step() == SQLITE_ROW) {
-    auto requestId = statement.getString(1);
+    RequestID requestId;
+    std::memcpy(requestId.data(), statement.getBlob(1), statement.getSize(1));
     Name caName(statement.getBlock(2));
     auto status = static_cast<Status>(statement.getInt(3));
     auto challengeStatus = statement.getString(4);
@@ -273,7 +274,8 @@
   statement.bind(1, caName.wireEncode(), SQLITE_TRANSIENT);
 
   while (statement.step() == SQLITE_ROW) {
-    auto requestId = statement.getString(1);
+    RequestID requestId;
+    std::memcpy(requestId.data(), statement.getBlob(1), statement.getSize(1));
     Name caName(statement.getBlock(2));
     auto status = static_cast<Status>(statement.getInt(3));
     auto challengeStatus = statement.getString(4);
@@ -300,11 +302,11 @@
 }
 
 void
-CaSqlite::deleteRequest(const std::string& requestId)
+CaSqlite::deleteRequest(const RequestID& requestId)
 {
   Sqlite3Statement statement(m_database,
                              R"_SQLTEXT_(DELETE FROM CaStates WHERE request_id = ?)_SQLTEXT_");
-  statement.bind(1, requestId, SQLITE_TRANSIENT);
+  statement.bind(1, requestId.data(), requestId.size(), SQLITE_TRANSIENT);
   statement.step();
 }
 
diff --git a/src/detail/ca-sqlite.hpp b/src/detail/ca-sqlite.hpp
index 5d12188..f0ffe1f 100644
--- a/src/detail/ca-sqlite.hpp
+++ b/src/detail/ca-sqlite.hpp
@@ -43,7 +43,7 @@
    * @throw if request cannot be fetched from underlying data storage
    */
   CaState
-  getRequest(const std::string& requestId) override;
+  getRequest(const RequestID& requestId) override;
 
   /**
    * @throw if there is an existing request with the same request ID
@@ -55,7 +55,7 @@
   updateRequest(const CaState& request) override;
 
   void
-  deleteRequest(const std::string& requestId) override;
+  deleteRequest(const RequestID& requestId) override;
 
   std::list<CaState>
   listAllRequests() override;
diff --git a/src/detail/ca-state.cpp b/src/detail/ca-state.cpp
index 334429a..4dad34d 100644
--- a/src/detail/ca-state.cpp
+++ b/src/detail/ca-state.cpp
@@ -64,7 +64,7 @@
 {
 }
 
-CaState::CaState(const Name& caName, const std::string& requestId, RequestType requestType, Status status,
+CaState::CaState(const Name& caName, const RequestID& requestId, RequestType requestType, Status status,
                  const security::Certificate& cert, Block encryptionKey, uint32_t aesBlockCounter)
     : m_caPrefix(caName)
     , m_requestId(requestId)
@@ -76,7 +76,7 @@
 {
 }
 
-CaState::CaState(const Name& caName, const std::string& requestId, RequestType requestType, Status status,
+CaState::CaState(const Name& caName, const RequestID& requestId, RequestType requestType, Status status,
                  const security::Certificate& cert, const std::string& challengeType,
                  const std::string& challengeStatus, const time::system_clock::TimePoint& challengeTp,
                  size_t remainingTries, time::seconds remainingTime, JsonSection&& challengeSecrets,
@@ -97,7 +97,7 @@
 operator<<(std::ostream& os, const CaState& request)
 {
   os << "Request's CA name: " << request.m_caPrefix << "\n";
-  os << "Request's request ID: " << request.m_requestId << "\n";
+  os << "Request's request ID: " << toHex(request.m_requestId.data(), request.m_requestId.size()) << "\n";
   os << "Request's status: " << statusToString(request.m_status) << "\n";
   os << "Request's challenge type: " << request.m_challengeType << "\n";
   if (request.m_challengeState) {
diff --git a/src/detail/ca-state.hpp b/src/detail/ca-state.hpp
index 9f30b6d..897d98d 100644
--- a/src/detail/ca-state.hpp
+++ b/src/detail/ca-state.hpp
@@ -22,10 +22,13 @@
 #define NDNCERT_CA_STATE_HPP
 
 #include "detail/ndncert-common.hpp"
+#include <array>
 
 namespace ndn {
 namespace ndncert {
 
+typedef std::array<uint8_t, 8> RequestID;
+
 // NDNCERT Request status enumeration
 enum class Status : uint16_t {
   BEFORE_CHALLENGE = 0,
@@ -65,9 +68,9 @@
 {
 public:
   CaState();
-  CaState(const Name& caName, const std::string& requestId, RequestType requestType, Status status,
+  CaState(const Name& caName, const RequestID& requestId, RequestType requestType, Status status,
           const security::Certificate& cert, Block m_encryptionKey, uint32_t aesBlockCounter = 0);
-  CaState(const Name& caName, const std::string& requestId, RequestType requestType, Status status,
+  CaState(const Name& caName, const RequestID& requestId, RequestType requestType, Status status,
           const security::Certificate& cert, const std::string& challengeType,
           const std::string& challengeStatus, const time::system_clock::TimePoint& challengeTp,
           size_t remainingTries, time::seconds remainingTime, JsonSection&& challengeSecrets,
@@ -75,7 +78,7 @@
 
 public:
   Name m_caPrefix;
-  std::string m_requestId;
+  RequestID m_requestId;
   RequestType m_requestType;
   Status m_status;
   security::Certificate m_cert;
diff --git a/src/detail/ca-storage.hpp b/src/detail/ca-storage.hpp
index 70a0ac9..b5c2ce7 100644
--- a/src/detail/ca-storage.hpp
+++ b/src/detail/ca-storage.hpp
@@ -33,7 +33,7 @@
    * @throw if request cannot be fetched from underlying data storage
    */
   virtual CaState
-  getRequest(const std::string& requestId) = 0;
+  getRequest(const RequestID& requestId) = 0;
 
   /**
    * @throw if there is an existing request with the same request ID
@@ -45,7 +45,7 @@
   updateRequest(const CaState& request) = 0;
 
   virtual void
-  deleteRequest(const std::string& requestId) = 0;
+  deleteRequest(const RequestID& requestId) = 0;
 
   virtual std::list<CaState>
   listAllRequests() = 0;
diff --git a/src/detail/new-renew-revoke-encoder.cpp b/src/detail/new-renew-revoke-encoder.cpp
index 3afe2ad..ef67146 100644
--- a/src/detail/new-renew-revoke-encoder.cpp
+++ b/src/detail/new-renew-revoke-encoder.cpp
@@ -55,7 +55,8 @@
 
 void
 NewRenewRevokeEncoder::decodeApplicationParameters(const Block& payload, RequestType requestType, std::string& ecdhPub,
-                                              shared_ptr<security::Certificate>& clientCert) {
+                                                   shared_ptr<security::Certificate>& clientCert)
+{
   payload.parse();
 
   ecdhPub = readString(payload.get(tlv::EcdhPub));
@@ -74,13 +75,13 @@
 
 Block
 NewRenewRevokeEncoder::encodeDataContent(const std::string& ecdhKey, const std::string& salt,
-                                    const CaState& request,
-                                    const std::list<std::string>& challenges)
+                                         const CaState& request,
+                                         const std::list<std::string>& challenges)
 {
   Block response = makeEmptyBlock(ndn::tlv::Content);
   response.push_back(makeStringBlock(tlv::EcdhPub, ecdhKey));
   response.push_back(makeStringBlock(tlv::Salt, salt));
-  response.push_back(makeStringBlock(tlv::RequestId, request.m_requestId));
+  response.push_back(makeBinaryBlock(tlv::RequestId, request.m_requestId.data(), request.m_requestId.size()));
   response.push_back(makeNonNegativeIntegerBlock(tlv::Status, static_cast<size_t>(request.m_status)));
   for (const auto& entry: challenges) {
     response.push_back(makeStringBlock(tlv::Challenge, entry));
@@ -97,7 +98,8 @@
   const auto& salt = readString(content.get(tlv::Salt));
   uint64_t saltInt = std::stoull(salt);
   const auto& requestStatus = static_cast<Status>(readNonNegativeInteger(content.get(tlv::Status)));
-  const auto& requestId = readString(content.get(tlv::RequestId));
+  RequestID requestId;
+  std::memcpy(requestId.data(), content.get(tlv::RequestId).value(), content.get(tlv::RequestId).size());
   std::list<std::string> challenges;
   for (auto const& element : content.elements()) {
     if (element.type() == tlv::Challenge) {
diff --git a/src/detail/new-renew-revoke-encoder.hpp b/src/detail/new-renew-revoke-encoder.hpp
index 70e69aa..8b083d6 100644
--- a/src/detail/new-renew-revoke-encoder.hpp
+++ b/src/detail/new-renew-revoke-encoder.hpp
@@ -37,12 +37,13 @@
 
   static Block
   encodeDataContent(const std::string& ecdhKey, const std::string& salt,
-                             const CaState& request,
-                             const std::list<std::string>& challenges);
+                    const CaState& request,
+                    const std::list<std::string>& challenges);
+
   struct DecodedData {
     std::string ecdhKey;
     uint64_t salt;
-    std::string requestId;
+    RequestID requestId;
     Status requestStatus;
     std::list<std::string> challenges;
   };