# Final Permutation in Feistel function

As the final permutation of the Feistel function is the inverse of the initial permutation, it undoes the initial permutation.So how is this helpful?

• You need to mention the cipher and i guess you mean DES – hardyrama Feb 24 '19 at 14:04
• Wikipedia IP and FP have no cryptographic significance, but were included in order to facilitate loading blocks in and out of mid-1970s 8-bit based hardware. – kelalaka Feb 24 '19 at 14:07
• @Lucifer: unfortunately, the question being part of an assignment is not an assurance that it is consistent and self-contained enough. Somme assignments are poorly worded, or make the assumption that the audience knows conventions set in the course, or some particular text, when in fact that convention is far from universal. That even happens for national exams. Here: according to many texts, there is no IP or FP in a generic Feistel cipher. Texts that present IP and FP typically are DES-centric. – fgrieu Feb 24 '19 at 15:36