RE: CCM data structure

Håkon Alseth — Mon, 11 Sep 2023 12:56:14 GMT

Hi,

There is not much information about this, as it is aimed for bluetooth. However, there is some discussion on this topic here:

Encrypting/decrypting packets on-the-fly

As well as an example on github: https://github.com/NordicPlayground/nrf52-esb-ccm-example

[quote user=""]Does the packet counter (PKTCTR) automatically increments, when packet is encrypted or does it need to be incremented by software?[/quote]

You need to increment it.

[quote user=""]How often initialization vector (IV) need to be re-generated? I plan to use RNG for updating the IV field, which would take ~1ms. If the IV field has to be re-generated each time, the packet is encrypted/decrypted, it will create ~1ms spacing between each transmitted packet, which is a lot.[/quote]

on boot up, unless stored and used at a later point, and on "reconnect" / "re-pair" / "re-sync". Be sure to always change the counter, and never re-use a counter value unless the IV is also re-generated.

Kind regards,

Håkon