Hebern rotor machine

It is claimed that, with time on his hands, he started thinking about the problem of encryption, and eventually devised a means of mechanizing the process with a typewriter.

[4][2] Agnes Driscoll, the chief civilian employee of the US Navy's cryptography operation (later to become OP-20-G) between WWI and WWII, spent some time working with Hebern before returning to Washington and OP-20-G in the mid-'20s.

Over the next few years he repeatedly tried to sell the machines both to the US Navy and Army, as well as to commercial interests such as banks.

Perhaps the best indication of a general distaste for such matters was the statement by Henry Stimson in his memoirs that "Gentlemen do not read each other's mail.

The key to the Hebern design was a disk with electrical contacts on either side, known today as a rotor.

The power then operated the mechanicals of an electric typewriter to type the encrypted letter, or alternately simply lit a bulb or paper tape punch from a teletype machine.

This turns the basic substitution into a polyalphabetic one similar to the well known Vigenère cipher, with the exception that it required no manual lookup of the keys or cyphertext.

In these cases the resulting ciphertext consisted of a series of single-substitution cyphers, each one 26 letters long.