Security critical messages are to be sent from master SLR to slave SLR in an encrypted form. For any message to be sent to SSLRn , master PLM increments current IV of SSLRn by two and sends the message by encrypting with current key-IV pair of that SSLRn. SSLRn decrypts the message using the current key and (current IV+1). Slave SLR processes and prepares response, increments IV by two, and sends response by encrypting with current key and IV. Master SLR decrypts the response received with current key and IV+1 of SSLRn.