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.