Attacking AES first round on CW305

[AAA]

Hello,

Is there a way to attack the AES first round on CW305. I found an old discussion on the forum explaining a HD attack on the Sakura. The attack compares the ‘previous ciphertext’ with the value of ‘textin XOR kguess’. Will this model work for the CWs AES implementation?

From the simulation it looks like the previous ciphertext gets overwritten by the new textin value.

Regards,
Ali

[Alex_Dewar]

Hi Ali,

Not sure which thread you’re referring to, but I don’t think that would work on the CW305 or the Sakura G, as from my understanding both load the plaintext then run it through a full round.

The best attack I’m aware of is a chosen plaintext attack detailed here: chipwhisperer-jupyter/courses/sca201/Lab 2_3 - Attacking Across MixColumns.ipynb at main · newaetech/chipwhisperer-jupyter · GitHub.

Alex

[AAA]

Thanks for your reply Alex.

I was referring to this post:

Side Channel Analysis/Power Analysis Attack in SAKURA X

Hello, You’ll have to concentrate based on your desired model - for example if your hypothetical value is based on the leakage of the first S-Box operation that would be the one to concentrate on. But using a Hamming Distance (HD) model would be more suitable. I haven’t used the SAKURA X myself so don’t know details of how many traces it would take. What speed is the AES core running at? Regards, -Colin

Regards,
Ali

[Alex_Dewar]

Oh, that thread is just talking about the normal last round state diff leakage model by the end. I believe the original poster was talking about the attack in general and trying it with the normal sbox output model, which doesn’t work well for hardware AES. Colin’s post referring to HD on the first round is that because of the presence of MixColumns, you need to guess 4 bytes at a time, which ChipWhisperer’s software doesn’t support.