CW305_ECC Threshold

[AlanLee]

Dear all,
The first picture to come is the correlation vs bit plot, even though the tutorial suggests us to use Y’s curve(in my case, the attack result failed in many bits with different thresholds), I chose X’s and find a one-bit failed attack result, which is more satisfying.

Then, I chose thresholds as follows,

The attack is just a bit far from a success,

I changed different thresholds for many times; however, it always failed in the bit 255, and this confused me a lot. Why can it always fail in the same bit?

Alan.

[jpthibault]

Hi Alan,

Try plotting the correlation scores to see how far bit 255 is from being correctly guessed. Perhaps more traces would help?
Also keep in mind that if you have an attack which fails at correctly guessing a single fixed bit, that is still very much a successful attack: you just need to brute-force that one bit.
Already in the demo, bit zero needs to be guessed, so you can just add bit 255 to the guesses; you’ll have 4 candidate guesses instead of 2.

Jean-Pierre