MICSTATUS is not set to 1 when decrypting packet

RE: MICSTATUS is not set to 1 when decrypting packet

Harald_F — Tue, 17 Apr 2018 11:31:50 GMT

Hello,

i had the same problem.

A failed MIC Check after decryption of radio packets

I tried to encrypt packets on the fly at the transmitter.

So NRF_CCM->INPTR and NRF_CCM->OUTPTR both pointed to the same array-address as RADIO->PACKETPTR.

At the receiver side i had the problem, that the decrypted data was ok, but the MICSTATUS was still zero.

Following step solved the issue:

I removed the inplace operation, by letting NRF_CCM->INPTR and NRF_CCM->OUTPTR point to different arrays.

The calculated MIC was different... and the MIC check at the receiver passed.

RE: MICSTATUS is not set to 1 when decrypting packet

Kevin — Mon, 20 Feb 2017 18:18:11 GMT

Nordic Team informed me that the space reserved for area pointed by scratchpointer must be the size of the maximum packet size the length field can permit + 16 bytes. For example if you work with a 8 bit length field, the space reserved for scratch pointer area must be 255 + 16 bytes. you can heve more details here : devzone.nordicsemi.com/.../

RE: MICSTATUS is not set to 1 when decrypting packet

Kevin — Thu, 16 Feb 2017 10:16:39 GMT

OK i found the problem: the buffer pointed by scratch pointer was placed in memory just before the buffer pointed by cnfpointer. So the data pointed by cnfpointer was overwritten by ccm peripheral! In my case data is written on 267 bytes after the scratchpointer start address (value stored in SCRATCHPTR register of CCM peripheral) . So if you use ccm peripheral and have the same problem you should try to reserve a big memory area for scratchpointer (>300 bytes). Ps : thanks you for your answer Roger!

RE: MICSTATUS is not set to 1 when decrypting packet

Kevin — Thu, 16 Feb 2017 08:48:46 GMT

Yes i try to do the same thing on the same device (encryption+decryption without transmitting packet) and the buffer content at the output of the encryption is the same than the buffer at decryption input. The decryption gives the good result but the mic check fails every time.

RE: MICSTATUS is not set to 1 when decrypting packet

Roger Clark — Thu, 16 Feb 2017 02:18:21 GMT

Did you try writing a test application which just encrypts to a buffer and the decrypts the same buffer (no transmission etc) ?