DES ((Data Encryption Standard) operation splits a 64 bits block to two halves,
ID: 3797838 • Letter: D
Question
DES ((Data Encryption Standard) operation splits a 64 bits block to two halves, which get switched every round. The left-half is mixed with key bits before the switch
Mark the appropriate comment:
a) Nothing like this in DES. Why split to halves?
b) No! The whole idea of DES is that it works symmetrically between encryption and decryption, and this can only happen if no bit mixing takes place, so that by back-switching the ciphertext the plaintext emerges.
c) Yes, this is the procedure in all of DES rounds.
d) True, except that the bits of the left half are mixed between themselves, the key is used upfront in the transposition stage.
Explanation / Answer
Answer is c.
This is the exact procedure done in all the 16 rounds of DES.
Option a: DES relies on splitting the input into 2 halves. So its wrong.
Option b: DES is a symmetric key algorithm but it does involve BIT mixing starting from Initial Permutation stage iteself.
Option d: Bits in the left half are not mixed among themselves. They are mixed with the Key block generated.
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