Editing Hill cipher (section)

==Mechanical implementation==
When operating on 2 symbols at once, a Hill cipher offers no particular advantage over [[Playfair cipher|Playfair]] or the [[bifid cipher]], and in fact is weaker than either, and slightly more laborious to operate by pencil-and-paper. As the dimension increases, the cipher rapidly becomes infeasible for a human to operate by hand.

A Hill cipher of dimension 6 was implemented mechanically. Hill and a partner were awarded a [[patent]] ({{US patent |1,845,947}}) for this device, which performed a 6 &times; 6 matrix multiplication modulo 26 using a system of gears and chains.

Unfortunately the gearing arrangements (and thus the key) were fixed for any given machine, so triple encryption was recommended for security: a secret nonlinear step, followed by the wide diffusive step from the machine, followed by a third secret nonlinear step. (The much later [[Even–Mansour cipher]] also uses an unkeyed diffusive middle step). Such a combination was actually very powerful for 1929, and indicates that Hill apparently understood the concepts of a [[meet-in-the-middle attack]] as well as confusion and diffusion. Unfortunately, his machine did not sell.{{cn|date=September 2020}}