Damnit, this telco is down again. It’s fine, we know exactly how they encrypted the message, maybe you might be able to help us decode it?
Files given:
The challenge here is that we have 4 lfsr, and a very funny way to combine them. As we are given the first 9 characters, we have the first 72 outputs of the combined stream cipher.
Initially I thought of running correlation attacks, but this would be extremely troublesome. Eventually I recalled that there was a similar challenge - zer0lfsr, so I used the lfsr implementation as that worked with z3 and modified a little, and got z3 to work and it immeidately gave the solution (after remembering to remove newline in the plaintext).
The solution script can be found at solve.py
Flag:
CTFSG{C0rRel4t10N_AtT4cK$_0n_LsFR_101}