NRF_CCM->MICSTATUS bit not set, even though it's computed correctly

RE: NRF_CCM->MICSTATUS bit not set, even though it's computed correctly

Hung Bui — Wed, 24 Jan 2018 15:05:23 GMT

Hi Elias,

I think there is a misunderstanding here. Both MIC and data payload are encrypted after the CCM block. This is why you don't receive MIC check passed when you put b1d8a011 at the end of the payload. It has to be the encrypted MIC you need to put there.

You can find at section 2.3 Vol 6 Part 5 Bluetooth 5:

The CCM algorithm uses the Ai blocks to generate keystream that is used to
encrypt the MIC and the Data Channel PDU payload. Block A0 is always used
to encrypt and decrypt the MIC.

Same, inside nRF52832 spec, you can find at Table 59 Data structure for encrypted packet, it's the 4 byte encrypted MIC at the end.

You can find the encrypted MIC using ccm_crypt_packet_encrypt() function.

RE: NRF_CCM->MICSTATUS bit not set, even though it's computed correctly

Hung Bui — Tue, 23 Jan 2018 13:16:59 GMT

@Elias: Thanks, we will try to test here and get back to you. It's been pretty busy here.

RE: NRF_CCM->MICSTATUS bit not set, even though it's computed correctly

Elias — Fri, 19 Jan 2018 20:33:02 GMT

I've uploaded a minimal example here: gist.github.com/.../b203de23b2ee1b869bb950c388003ece

RE: NRF_CCM->MICSTATUS bit not set, even though it's computed correctly

Hung Bui — Mon, 08 Jan 2018 12:43:30 GMT

Hi Elias,

Could you send us a simplified example of your code that can reproduce the issue, so we can test here ?