[key-manager] add Kek class (#4674)

This commit adds a class `Kek` to store Key Encryption Key

src/core/mac/mac.cpp

@@ -922,7 +922,7 @@ void Mac::ProcessTransmitSecurity(TxFrame &aFrame, bool aProcessAesCcm)
     switch (keyIdMode)
     {
     case Frame::kKeyIdMode0:
-        aFrame.SetAesKey(keyManager.GetKek());
+        aFrame.SetAesKey(keyManager.GetKek().GetKey());
         extAddress = &GetExtAddress();
 
         if (!aFrame.IsARetransmission())
@@ -1414,7 +1414,7 @@ otError Mac::ProcessReceiveSecurity(RxFrame &aFrame, const Address &aSrcAddr, Ne
     switch (keyIdMode)
     {
     case Frame::kKeyIdMode0:
-        macKey = keyManager.GetKek();
+        macKey = keyManager.GetKek().GetKey();
         VerifyOrExit(macKey != NULL);
         extAddress = &aSrcAddr.GetExtended();
         break;

src/core/meshcop/commissioner.cpp

@@ -1029,8 +1029,8 @@ otError Commissioner::SendRelayTransmit(Message &aMessage, const Ip6::MessageInf
 
     if (aMessage.GetSubType() == Message::kSubTypeJoinerFinalizeResponse)
     {
-        SuccessOrExit(error = Tlv::AppendTlv(*message, Tlv::kJoinerRouterKek, Get<KeyManager>().GetKek(),
-                                             KeyManager::kMaxKeyLength));
+        SuccessOrExit(
+            error = Tlv::AppendTlv(*message, Tlv::kJoinerRouterKek, Get<KeyManager>().GetKek().GetKey(), Kek::kSize));
     }
 
     tlv.SetType(Tlv::kJoinerDtlsEncapsulation);

src/core/meshcop/joiner_router.cpp

@@ -190,7 +190,7 @@ void JoinerRouter::HandleRelayTransmit(Coap::Message &aMessage, const Ip6::Messa
     otError           error;
     uint16_t          joinerPort;
     uint8_t           joinerIid[Ip6::Address::kInterfaceIdentifierSize];
-    uint8_t           kek[KeyManager::kMaxKeyLength];
+    Kek               kek;
     uint16_t          offset;
     uint16_t          length;
     Message *         message  = NULL;
@@ -218,7 +218,7 @@ void JoinerRouter::HandleRelayTransmit(Coap::Message &aMessage, const Ip6::Messa
 
     SuccessOrExit(error = mSocket.SendTo(*message, messageInfo));
 
-    if (Tlv::ReadTlv(aMessage, Tlv::kJoinerRouterKek, kek, sizeof(kek)) == OT_ERROR_NONE)
+    if (Tlv::ReadTlv(aMessage, Tlv::kJoinerRouterKek, &kek, sizeof(kek)) == OT_ERROR_NONE)
     {
         otLogInfoMeshCoP("Received kek");
 
@@ -232,7 +232,7 @@ exit:
     }
 }
 
-otError JoinerRouter::DelaySendingJoinerEntrust(const Ip6::MessageInfo &aMessageInfo, const uint8_t *aKek)
+otError JoinerRouter::DelaySendingJoinerEntrust(const Ip6::MessageInfo &aMessageInfo, const Kek &aKek)
 {
     otError               error   = OT_ERROR_NONE;
     Message *             message = Get<MessagePool>().New(Message::kTypeOther, 0);
@@ -243,7 +243,7 @@ otError JoinerRouter::DelaySendingJoinerEntrust(const Ip6::MessageInfo &aMessage
     metadata.mMessageInfo = aMessageInfo;
     metadata.mMessageInfo.SetPeerPort(kCoapUdpPort);
     metadata.mSendTime = TimerMilli::GetNow() + kJoinerEntrustTxDelay;
-    memcpy(metadata.mKek, aKek, sizeof(metadata.mKek));
+    metadata.mKek      = aKek;
 
     SuccessOrExit(error = metadata.AppendTo(*message));
 
@@ -288,8 +288,7 @@ void JoinerRouter::SendDelayedJoinerEntrust(void)
     // change (i.e., retransmission). Otherweise, we wait for Joiner
     // Entrust Response before handling any other pending delayed
     // Jointer Entrust message.
-    VerifyOrExit(!mExpectJoinEntRsp ||
-                 memcmp(Get<KeyManager>().GetKek(), metadata.mKek, KeyManager::kMaxKeyLength) == 0);
+    VerifyOrExit(!mExpectJoinEntRsp || (Get<KeyManager>().GetKek() == metadata.mKek));
 
     if (TimerMilli::GetNow() < metadata.mSendTime)
     {

src/core/meshcop/joiner_router.hpp

@@ -89,9 +89,9 @@ private:
         otError AppendTo(Message &aMessage) { return aMessage.Append(this, sizeof(*this)); }
         void    ReadFrom(const Message &aMessage);
 
-        Ip6::MessageInfo mMessageInfo;                    // Message info of the message to send.
-        TimeMilli        mSendTime;                       // Time when the message shall be sent.
-        uint8_t          mKek[KeyManager::kMaxKeyLength]; // KEK used by MAC layer to encode this message.
+        Ip6::MessageInfo mMessageInfo; // Message info of the message to send.
+        TimeMilli        mSendTime;    // Time when the message shall be sent.
+        Kek              mKek;         // KEK used by MAC layer to encode this message.
     };
 
     static void HandleStateChanged(Notifier::Callback &aCallback, otChangedFlags aFlags);
@@ -112,7 +112,7 @@ private:
     static void HandleTimer(Timer &aTimer);
     void        HandleTimer(void);
 
-    otError        DelaySendingJoinerEntrust(const Ip6::MessageInfo &aMessageInfo, const uint8_t *aKek);
+    otError        DelaySendingJoinerEntrust(const Ip6::MessageInfo &aMessageInfo, const Kek &aKek);
     void           SendDelayedJoinerEntrust(void);
     otError        SendJoinerEntrust(const Ip6::MessageInfo &aMessageInfo);
     Coap::Message *PrepareJoinerEntrustMessage(void);

src/core/thread/key_manager.cpp

@@ -218,9 +218,15 @@ void KeyManager::IncrementMleFrameCounter(void)
     }
 }
 
+void KeyManager::SetKek(const Kek &aKek)
+{
+    mKek             = aKek;
+    mKekFrameCounter = 0;
+}
+
 void KeyManager::SetKek(const uint8_t *aKek)
 {
-    memcpy(mKek, aKek, sizeof(mKek));
+    memcpy(mKek.m8, aKek, sizeof(mKek));
     mKekFrameCounter = 0;
 }
 

src/core/thread/key_manager.hpp

@@ -137,6 +137,55 @@ public:
 
 } OT_TOOL_PACKED_END;
 
+/**
+ *
+ * This class represents a Key Encryption Key (KEK).
+ *
+ */
+class Kek
+{
+    friend class KeyManager;
+
+public:
+    enum
+    {
+        kSize = 16, // KEK size in bytes.
+    };
+
+    /**
+     * This method returns the KEK.
+     *
+     * @returns A pointer to buffer containing the KEK.
+     *
+     */
+    const uint8_t *GetKey(void) const { return m8; }
+
+    /**
+     * This method evaluates whether or not two KEKs match.
+     *
+     * @param[in]  aOther  The KEK to compare.
+     *
+     * @retval TRUE   If the KEKs match.
+     * @retval FALSE  If the KEKs do not match.
+     *
+     */
+    bool operator==(const Kek &aOther) const { return memcmp(m8, aOther.m8, sizeof(Kek)) == 0; }
+
+    /**
+     * This method evaluates whether or not the KEK match.
+     *
+     * @param[in]  aOther  The KEK to compare.
+     *
+     * @retval TRUE   If the KEK do not match.
+     * @retval FALSE  If the KEK match.
+     *
+     */
+    bool operator!=(const Kek &aOther) const { return !(*this == aOther); }
+
+private:
+    uint8_t m8[kSize]; ///< Buffer containing the KEK.
+};
+
 /**
  * This class defines Thread Key Manager.
  *
@@ -146,8 +195,7 @@ class KeyManager : public InstanceLocator
 public:
     enum
     {
-        kMaxKeyLength = 16,
-        kNonceSize    = 13, ///< Size of IEEE 802.15.4 Nonce (bytes).
+        kNonceSize = 13, ///< Size of IEEE 802.15.4 Nonce (bytes).
     };
 
     /**
@@ -336,7 +384,15 @@ public:
      * @returns A pointer to the KEK.
      *
      */
-    const uint8_t *GetKek(void) const { return mKek; }
+    const Kek &GetKek(void) const { return mKek; }
+
+    /**
+     * This method sets the KEK.
+     *
+     * @param[in]  aKek  A KEK.
+     *
+     */
+    void SetKek(const Kek &aKek);
 
     /**
      * This method sets the KEK.
@@ -479,7 +535,7 @@ private:
 #if OPENTHREAD_MTD || OPENTHREAD_FTD
     Pskc mPskc;
 #endif
-    uint8_t  mKek[kMaxKeyLength];
+    Kek      mKek;
     uint32_t mKekFrameCounter;
 
     uint8_t mSecurityPolicyFlags;