Can a byte/word inserted as an entry in a Feistel S-box be breakable?

pf flag

Let's suppose I insert these two 4-byte words (32-bits) in a feistel S-box with 1024-bytes of size (256*32-bits), (like Blowfish does):

blah bleh

What kind of attacks could possible be made to discover the words faster than brute-forcing the entire S-box (if they exist)?

Does inserting words/bytes in feistel S-boxes have a formula or a reverse operation for recovering the words/bytes without discovering the entire S-box?

fgrieu avatar
ng flag
Can adversaries experiment with known key/plaintext? The context in which the S-box is used matters. Things like how the S-box is used to build the Feistel round, width of the block cipher, number of rounds...
Daniel S avatar
ru flag
May I ask how the question arises? This feels like it might be a CTF.

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