What are the steps in the Feistel function?(a) expansion, mixing, substitution, permutation(b) extract, transform, load(c) extract, load, transform(d) expansion, divide, mixing, permutationI got this question in unit test.This intriguing question originated from Cryptography in division Number Theory and Cryptography of Discrete Mathematics

What are the steps in the Feistel function?(a) expansion, mixing, subs

1.	What are the steps in the Feistel function?(a) expansion, mixing, substitution, permutation(b) extract, transform, load(c) extract, load, transform(d) expansion, divide, mixing, permutationI got this question in unit test.This intriguing question originated from Cryptography in division Number Theory and Cryptography of Discrete Mathematics
Answer» Right choice is (a) expansion, mixing, substitution, permutation Easy explanation: The Feistel function which occurs in EVERY block has 3 steps i) Expansion:- The incoming 32-bit block has half of its bits duplicated, making it a 48-bit block. ii) Mixing:- The new, 48-bit input block is PUT through an XOR gate with this round’s unique subkey. iii) Substitution:- The MIXED, 48-bit block is divided into 8 6-bit pieces. Each of these 8 pieces is put through an S-block which will output only 4-bits using non-linear-transformation. Permutation: The 32 output bits are then arranged in a SPECIFIC permutation that ensures that they will be distributed among different S-blocks in the NEXT round. This is the most important part of security in DES and it helps to avoid simple, algebra-based attacks.

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