OMI cryptograph

The OMI cryptograph was a rotor cipher machine produced and sold by Italian firm Ottico Meccanica Italiana (OMI) in Rome.

The rotors stepped regularly.

Each rotor could be assembled from two sections with different wiring: one section consisted of a "frame" containing ratchet notches, as well as some wiring, while the other section consisted of a "slug" with a separate wiring.

The slug section fitted into the frame section, and different slugs and frames could be interchanged with each other.

As a consequence, there were many permutations for the rotor selection.