https://devzone.nordicsemi.com/f/nordic-q-a/13371/encrypted-advertiseI want to use NRF51822 to advertise is door close/open. No need bidirectional data sending. Only one way from NRF sensor to mobile phone app. Actually I have only two different packets: door open, door close. I have to encrypt that packets. It&#39;s easyen-USTelligent Community 13Thu, 21 Apr 2016 05:30:28 GMThttps://devzone.nordicsemi.com/thread/50993?ContentTypeID=1Thu, 21 Apr 2016 05:30:28 GMT137ad170-7792-4731-bb38-c0d22fbe4515:fe333e04-d5d8-4306-85e5-f4cf866bea8furiy<p>Thank you! It looks very good solution for me!</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/50992?ContentTypeID=1Thu, 21 Apr 2016 03:30:07 GMT137ad170-7792-4731-bb38-c0d22fbe4515:92371c70-014e-4824-b348-f1e3af266412RK<p>No need for CBC mode. When you agree the AES key reset a counter (something long) to zero on each side. When you encrypt a packet, increment the counter and encrypt the packet + counter, decrypt on the other side. As long as the counter is larger than any you have seen, it&#39;s a new packet not a replay so accept it and then bump your own expected counter.</p> <p>If you change the key, reset the counter to zero. Doesn&#39;t matter if you lose packets, as long as the counter keeps increasing you can be sure you&#39;re not getting a replay attack.</p><div style="clear:both;"></div>