psa_cipher_set_iv error -135 and general help with AES-CTR 128-bit

[Glen M]

Hi,

I'm porting an older product that used a Microchip MRF24J40 SPI radio and a PIC processor to an nRF52840 and I'm struggling with how to replicate both the CRC calculations and the  AES-128 encryption/decryption that the MRF24J40 radio did in hardware.

The code I'm porting has a 128-bit array of bytes to use for a key and it uses a received CRC value to fill in its 13-byte NONCE registers (which it seems are the equivalent of the iv Input Vector).

I upgraded to the latest NCS v2.0.0 last night as I understand from this thread that earlier versions have some block size limitations that the new code doesn't have: 

 RE: PSA encryption - AES CTR 128 - message input length 

I've managed to get together some code that I thought should work based on the \v2.0.0\nrf\samples\crypto\aes_ctr example, and the ecdsa example for setting my own pre-existing key with psa_import_key().

I just gave it a try, but I'm getting a -135 error code from psa_cipher_set_iv. It's not happy with the 13 byte iv length (the function succeeds if I change it to 16).

I assume I need to use the same NONCE/IV value that the old product used to get a successful decryption - is that right? How can I make it work with the 13-byte initial value?

Thanks,

Glen

[Glen M]

Just an update - I was able to verify that my Nordic test code generates the same encoded packets that I get from an encryption-checker website I found: https://cryptii.com/pipes/aes-encryption

So it looks like the Nordic stuff is working - but the Microchip radio's packets don't match... so I'm asking them for support. 

Do you know if there is anything that has changed between 802.15.4-2003 (which is what that radio is designed to) and now that would make the encryption not forward compatible?

[Einar Thorsrud]

I am not sure what that could be. 128 bit AES-CTR is the same as it has always been. As long as you can understand the configuration that was used on the old device, you should be able to do the same operations on the nRF. But I cannot say much about the Microchip device, so it is good you are in contact with them regarding that.