Free Seizing the Enigma by David Kahn Page B

Major Rudolf Schmidt, a World War I signals officer who had written the chapter on communications for a major study of the war. He and his cryptologists saw the merits of the Enigma. They made some changes to suit it better for army practice: twenty-six-contact rotors, only three rotors (perhaps to have less to carry in mobile warfare), a standard QWERTY keyboard, and a system of message keys that required no booklet,only a set of keys that enabled the cipher operator to make up a different key for each message. On July 15, 1928, the Enigma went into the army’s service.
    That year a single Enigma cost 600 reichsmarks, or $144 ($900 in 1991 dollars); volume purchases may have reduced this price. But the firm’s sales remained low. A few machines were sold to businesses, but the commercial market never materialized (nor did it for other cipher-machine makers). By the end of the decade the navy had bought no more than a couple of hundred machines, and the army about as many. Still, it was a start.
    Then, one spring day in 1929, the team of a horse-drawn wagon that Scherbius was driving at his factory shied and smashed the wagon against a wall. Scherbius suffered severe internal injuries. On May 13, he died, only fifty years old. But his business survived.
    By the mid-1930s the firm was manufacturing a variety of cryptographic machines. The army experimented with an eight-rotor printing version for a while. The most important change had come in 1930 with the army’s addition of a plugboard on the front of its machine. This consisted of a plate with twenty-six sockets, each representing a letter, that could be connected with one another by short cables with jacks on the end. The sockets were connected by wires to the keyboard and to the lamps, so that the enciphering and deciphering current passed through the plugboard. It added an extra substitution that overlay the rotor substitution. If on the plugboard the C socket and the R socket were joined by a cable and if without the plugboard the cipher letter for a plaintext
e
was C, the plugboard would convert the C to R. If the plugboardless cipher letter was R, the plugboard would replace this with C. The army connected only six pairs of letters, meaning that twelve letters were enciphered through the plugboard, the others being enciphered only with the rotors. But even twelve encipherments increased the number of keys—and so, theoretically, the number of trials a cryptanalyst would have to make—by billions. The plugboard was an excellent improvement.
    In 1935, Hitler denounced the Versailles treaty and began his enormous expansion of Germany’s armed forces. They needed cipher machines, and they continued to buy Enigmas. Other agencies also purchased them: the railroad administration, the
Abwehr
(the military espionage service), and the
Sicherheitsdienst
, or SD (the Nazi party intelligence service).
    During those rearmament years, both the army and the navy continually improved the Enigma and developed their systems of secret communication.
    The navy alertly scanned the cryptologic horizons for
new
ideas. In the summer of 1930, for example, its cryptographers reported on a cipher machine devised by one Dr. Ruckhaber. “In its mechanical construction the method resembles in many points the not very successful Kryha system,” they wrote. Its mechanism slipped or jumped and caused many enciphering errors. Its output letters were harder to read than those of an illuminating system. Changing its setting took longer than changing the Enigma’s. It appeared easy to solve. The navy turned it down.
    The
Reichsmarine
(its name was changed in 1935 to
Kriegsmarine
) developed its own cryptosystems, mostly for specialized uses. Some naval attachés held
Schlüssel A
(Code A), a code with a numerical superencipherment. The
Werftschlüssel
(Dockyard Cipher), a pencil-and-paper system, served shipyards and small ships. Early in 1939 the navy reworked and reissued the
Funkschlüssel