More slide attacks

In the previous section, we discussed attacking a cipher with a repeated round key. What if we're repeating two round keys, as below?

a, b = random_roundkey(BITS), random_roundkey(BITS)
cipher = Present(rounds=32, custom_roundkeys=[a, b] * 16)

The idea is actually quite similar. Instead of treating our function $f$ to be just one round, we say it's two rounds, and execute the slide attack as normal. Having covered MITM, we already know how to attack two-rounds of PRESENT if the keys are sufficiently weak.

TODO: Provide an example/walkthrough/challenges