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Authors: David Kahn
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rights to the Gewerkschaft Securitas. Though a
Gewerkschaft
was, in the German law of the time, a corporation for mining (and this one was indeed headed by a mining director), this one’s name, Securitas, and the fact that it had also been granted the rights to the Dutch rotor patent suggests that it may have been established to funnel risk capital into cipher machines. On July 9, 1923, Securitas founded the Chiffriermaschinen Aktien-Gesellschaft (Cipher Machines Stock Corporation), which began operating in August 1923 at Steglitzerstrasse 2, in central Berlin. Scherbius and Ritter sat on its board of directors.
The firm publicized its cipher machine—by now named the Enigma—as much as it could. It printed flyers and exhibited the Enigma at the 1923 congress of the International Postal Union. A number of articles about the machine appeared in German and foreign electrical and business publications. Many were illustrated with diagrams of rotors and photographs of the firm’s ponderous printing version of the Enigma—a 15-inch-high monster with knobs and handles on its right side that weighed more than 100 pounds. This was being tested by the
Deutsche Reichspost
. Another version worked directly from and to punched teletypewriter tape.
Gradually the simpler version that indicated its output by illuminating letters, the “Glow Lamp” Enigma, became the most widely known and, eventually, the only one produced by the firm. It was much more compact than the printing version, standing only 4½ inches high, 10 inches wide, and 10¾ inches deep, and it weighed only 15 pounds. At the front stood three rows of typewriter keys. Behind them lay the three rows of circular windows for the output letters. In back of these and to the right was a switch allowing the operator to choose battery or house current. On the left, the tops offour rotors and four toothed thumbwheels for setting them poked up through the closed lid of the machine. The lid also had little windows through which showed the letters on the rims of the rotors.
The mechanism incorporated three significant improvements by other people over the straightforward system described by Scherbius in his letter of 1918. Two came from Willi Korn, an engineer in Scherbius’s employ, and one from Paul Bernstein, a Berliner.
Korn designed rotors that were removable. Previously their order left to right was fixed, but now the operator could put them into the machine in any order. This made possible Bernstein’s improvement: a movable ring with indicator letters on it on each rotor. The ring rode the circumference of the rotor like a tire on a wheel; the ring could be turned to any position and locked in place with a pin. Previously, a particular indicator letter meant that the rotor was in a particular position; now the indicator letters bore no relation to the position of the rotor. The position of the alphabet ring on the rotor had to be known to the decipherer, so it became part of the key. In addition, Bernstein shifted from the rotor to the ring the notch or notches that caused the rotor to the left to move one space at a certain point or points in the rotor’s revolution. This disjoined the rotor moves from the rotor encipherment, throwing up a further obstacle to solution.
Finally, Korn converted the leftmost of the four rotors into a reflector. Although it was called a rotor, it did not turn. It had contacts only on one face, and it sent the current that had come from the three normal rotors back through them along a different path before it illuminated an output letter. The reflector was sometimes called a half rotor because its wiring went from one contact on the side facing the three main rotors to another contact on the same side; it consequently had only thirteen connections instead of the twenty-six of the main rotors. The current’s double traversing of the rotors meant that encipherment was like decipherment: if plaintext
a
became ciphertext X,
Gewerkschaft
was, in the German law of the time, a corporation for mining (and this one was indeed headed by a mining director), this one’s name, Securitas, and the fact that it had also been granted the rights to the Dutch rotor patent suggests that it may have been established to funnel risk capital into cipher machines. On July 9, 1923, Securitas founded the Chiffriermaschinen Aktien-Gesellschaft (Cipher Machines Stock Corporation), which began operating in August 1923 at Steglitzerstrasse 2, in central Berlin. Scherbius and Ritter sat on its board of directors.
The firm publicized its cipher machine—by now named the Enigma—as much as it could. It printed flyers and exhibited the Enigma at the 1923 congress of the International Postal Union. A number of articles about the machine appeared in German and foreign electrical and business publications. Many were illustrated with diagrams of rotors and photographs of the firm’s ponderous printing version of the Enigma—a 15-inch-high monster with knobs and handles on its right side that weighed more than 100 pounds. This was being tested by the
Deutsche Reichspost
. Another version worked directly from and to punched teletypewriter tape.
Gradually the simpler version that indicated its output by illuminating letters, the “Glow Lamp” Enigma, became the most widely known and, eventually, the only one produced by the firm. It was much more compact than the printing version, standing only 4½ inches high, 10 inches wide, and 10¾ inches deep, and it weighed only 15 pounds. At the front stood three rows of typewriter keys. Behind them lay the three rows of circular windows for the output letters. In back of these and to the right was a switch allowing the operator to choose battery or house current. On the left, the tops offour rotors and four toothed thumbwheels for setting them poked up through the closed lid of the machine. The lid also had little windows through which showed the letters on the rims of the rotors.
The mechanism incorporated three significant improvements by other people over the straightforward system described by Scherbius in his letter of 1918. Two came from Willi Korn, an engineer in Scherbius’s employ, and one from Paul Bernstein, a Berliner.
Korn designed rotors that were removable. Previously their order left to right was fixed, but now the operator could put them into the machine in any order. This made possible Bernstein’s improvement: a movable ring with indicator letters on it on each rotor. The ring rode the circumference of the rotor like a tire on a wheel; the ring could be turned to any position and locked in place with a pin. Previously, a particular indicator letter meant that the rotor was in a particular position; now the indicator letters bore no relation to the position of the rotor. The position of the alphabet ring on the rotor had to be known to the decipherer, so it became part of the key. In addition, Bernstein shifted from the rotor to the ring the notch or notches that caused the rotor to the left to move one space at a certain point or points in the rotor’s revolution. This disjoined the rotor moves from the rotor encipherment, throwing up a further obstacle to solution.
Finally, Korn converted the leftmost of the four rotors into a reflector. Although it was called a rotor, it did not turn. It had contacts only on one face, and it sent the current that had come from the three normal rotors back through them along a different path before it illuminated an output letter. The reflector was sometimes called a half rotor because its wiring went from one contact on the side facing the three main rotors to another contact on the same side; it consequently had only thirteen connections instead of the twenty-six of the main rotors. The current’s double traversing of the rotors meant that encipherment was like decipherment: if plaintext
a
became ciphertext X,
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