char* MFRC522::DumpUid(Uid *uid){
        MIFARE_Key key;
        int size = (uid->size);
        char UID[size];

        for (byte i = 0; i < uid->size; i++) {
                UID[i] = (uid->uidByte[i] < 0x10 ? ' 0' : ' ');
                Serial.print(uid->uidByte[i] < 0x10 ? " 0" : " ");
                UID[i] = (uid->uidByte[i], HEX);
                Serial.print(uid->uidByte[i], HEX);
        }
        Serial.println();
        Serial.println(UID);
        return &(UID[0]);
 }