How many distinct stages are there in DES algorithm, which is parameterized by…

Answer: 16 distinct stages (rounds).

Explanation:

• DES is implemented as a 16-round Feistel network; each round is a separate stage where the data is transformed using a round subkey.

• The 56-bit key (commonly represented as 64 bits with parity) is processed by key schedule operations (permutation choice, rotations, and permutation choice) to produce sixteen 48-bit subkeys, one per round.

• Initial and final permutations are fixed bit reorderings. They are not counted as Feistel rounds; if someone counted those as stages in addition to the 16 rounds they would get 18 operations, but the conventional count of distinct DES rounds is 16.

• Within each round the main steps are expansion of the right half, XOR with the round subkey, substitution via S-boxes, and permutation; these are the transformations applied in each of the 16 stages.