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I am familiar with the differential cryptanalysis of small SPN-based ciphers like here: Tutorial of Amazing King with SPN (or mentioned in the book "The Block Cipher Companion" or the Tutorial of Howard Heys). So far so good.

Currently I want to extend my knowledge an try to attack FEAL-4. My implementation of the FEAL-4 cipher is oriented on the standard with FEAL-8. So the cipher looks like the following: FEAL-4

I am familiar with the publication of Biham and Shamir and the Tutorial of Amazing King about the dca of FEAL-4 here FEAL-4 DCA. The Implementation of Amazing King does not apply the subkeys k8 to kb in the last round.

I am stuck on recovering the last subkeys and got no idea how to do that. May be someone can give me hint?

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  • $\begingroup$ if i understand your question , you have DCA on four rounds of FEAL but not 8. you use the same concept ( i assumed you are familiar how DCA work) but on 8 rounds. number of plain texts required is more than attacking 4 rounds because the differential probability get lower over rounds. $\endgroup$ – hardyrama Jan 30 at 3:33

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