A simple cryptosystem that keeps the same letters and shuffles the order is an example of what?

A permutation cipher, also known as a transposition cipher, preserves all original plaintext characters and rearranges their order according to a key or algorithm. This exactly matches the described behavior of shuffling character order while keeping the same letters.

A rotation cipher shifts each letter a fixed number of positions in the alphabet, changing the letter values themselves rather than rearranging their positions.

Monolithic is not a recognized standard classification for cipher types in cryptography.

A substitution cipher replaces each plaintext character with a different character or symbol, changing the actual letters rather than their arrangement.