# Correlation attack on Lagged Fibonacci Generator

Say that one uses a known LFG (2 known lags $a$ & $b$, known inner state length $N$, known modulo $m$) to hide some text with a basic à la Vigenère cipher: $C_i=(P_i + {PRNG}_i) \bmod 26$.

Say that the adversary intercepts some ciphered text (not the LFG output), could they use it to perform a correlation attack to get the initial inner state of the LFG? And if so, how much ciphertext would be needed?

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