Addressing the ACK/NAK keep-alive exchanges from some NXP readers noted by \@lvandenb in emsec#313

Author: maxieds

Firmware/Chameleon-Mini/Application/DESFire/DESFireInstructions.c

@@ -2020,7 +2020,7 @@ uint16_t ISO7816CmdSelect(uint8_t *Buffer, uint16_t ByteCount) {
         return ISO7816CmdSelectDF(Buffer, ByteCount);
     }
     Buffer[0] = ISO7816_ERROR_SW1_INS_UNSUPPORTED;
-    Buffer[1] = ISO7816_ERROR_SW2_INS_UNSUPPORTED;
+    Buffer[1] = ISO7816_ERROR_SW2_FUNC_UNSUPPORTED;
     return ISO7816_STATUS_RESPONSE_SIZE;
 }
 

Firmware/Chameleon-Mini/Application/MifareDESFire.c

@@ -226,6 +226,13 @@ uint16_t MifareDesfireAppProcess(uint8_t *Buffer, uint16_t BitCount) {
     } else if (ByteCount >= 6 && DesfireCLA(Buffer[0]) && Buffer[2] == 0x00 &&
                Buffer[3] == 0x00 && Buffer[4] == ByteCount - 6) {
         return MifareDesfireProcess(Buffer, BitCount);
+    } else if (ByteCount == 4 && Buffer[2] == 0x37 && Buffer[3] == 0xC8) { 
+        // NXP-based PCD sent a "keep alive" response of ACK, 
+	// so we respond with a corresponding NAK (with CRCA bytes appended):
+	Buffer[2] = 0x7E;
+	Buffer[3] = 0x44;
+        ISO14443AAppendCRCA(Buffer, 4);
+	return 6 * BITS_PER_BYTE;
     } else if (IsWrappedISO7816CommandType(Buffer, ByteCount)) {
         uint8_t ISO7816PrologueBytes[2];
         memcpy(&ISO7816PrologueBytes[0], Buffer, 2);