New answers tagged substitution-cipher
Kasiski's test only considers repeated sequences of characters, under assumption that the text contains repeated words with distance between them being a multiple of key length. Autocorrelation analysis simply counts matching characters between shifted ciphertexts. Then you have to identify "maxima", which are shift distances with higher match counts than ...
In the substitution step of a typical Substitution-Permutation Network (e.g. in AES SubBytes), the whole state is broken in parts and each part substituted. That's not the case in (the core of) a Feistel cipher, where at each step/round some sizable part of the state is bound to remain unchanged (in order that each step be reversible).
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