Configure ECDH mode for key destination

Author: jezcrypt

examples/ECCX08ECDH/ECCX08ECDH.ino

@@ -43,13 +43,22 @@ void setup() {
   }
 
   byte sharedSecret[32];
-  if (!ECCX08.ecdh(privateKeySlot, counterPartyPubKey, sharedSecret)) {
+  if (!ECCX08.ecdh(privateKeySlot, ECDH_MODE_OUTPUT, counterPartyPubKey, sharedSecret)) {
     Serial.println("The ecdh function failed!");
     while (1);
   }
 
   Serial.print("Shared secret = ");
   printHex(sharedSecret, 32);
+
+  byte output[1];
+  if (!ECCX08.ecdh(privateKeySlot, ECDH_MODE_TEMPKEY, counterPartyPubKey, output)) {
+    Serial.println("The ecdh function failed!");
+    while (1);
+  }
+
+  Serial.print("Return code = ");
+  printHex(output, 1);
 }
 
 void loop() {

src/ECCX08.cpp

@@ -326,20 +326,26 @@ int ECCX08Class::endSHA256(const byte data[], int length, byte result[])
   return 1;
 }
 
-int ECCX08Class::ecdh(int slot, const byte pubKeyXandY[], byte sharedSecret[])
+int ECCX08Class::ecdh(int slot, byte mode, const byte pubKeyXandY[], byte output[])
 {
   if (!wakeup()) {
     return 0;
   }
 
-  if (!sendCommand(0x43, 0x0c, slot, pubKeyXandY, 64)) {
+  if (!sendCommand(0x43, mode, slot, pubKeyXandY, 64)) {
     return 0;
   }
 
   delay(55);
 
-  if (!receiveResponse(sharedSecret, 32)) {
-    return 0;
+  if (mode == ECDH_MODE_OUTPUT) {
+    if (!receiveResponse(output, 32)) {
+      return 0;
+    }
+  } else if (mode == ECDH_MODE_TEMPKEY) {
+    if (!receiveResponse(output, 1)) {
+      return 0;
+    }
   }
 
   delay(1);

src/ECCX08.h

@@ -50,7 +50,9 @@ class ECCX08Class
   int endSHA256(byte result[]);
   int endSHA256(const byte data[], int length, byte result[]);
 
-  int ecdh(int slot, const byte pubKeyXandY[], byte sharedSecret[]);
+  int ecdh(int slot, byte mode, const byte pubKeyXandY[], byte sharedSecret[]);
+  #define ECDH_MODE_TEMPKEY               ((uint8_t)0x08)         //!< ECDH mode: write to TempKey
+  #define ECDH_MODE_OUTPUT                ((uint8_t)0x0c)         //!< ECDH mode: write to buffer
 
   int readSlot(int slot, byte data[], int length);
   int writeSlot(int slot, const byte data[], int length);