Enigma

by Jim Stebinger

The fall of Poland did not mean the end of a remarkable Polish undertaking. 1939 was merely the end of act one in a bid to crack and replicate a strategic German secret weapon that could turn the war around—Engima.

By 1930 the German military was using Enigma cipher machines. In theory, Enigma offered ciphering possibilities reaching a staggering 10 to the 114th power. Fortunately, Germany never fully utilized Enigma’s potential and badly underestimated the brilliance, perseverance and luck of her enemies. The designers of Enigma, and those who unraveled its secrets, are paragons of human ingenuity.

The machine that sealed their reputations was a technological marvel. Its interface consisted of a 26-character keyboard, onto which messages were typed. Inside were a number of rotor wheels and a plug board, much like a switchboard, and a maze of internal wiring that connected each of the 26 inputs to a different output. Each rotor’s wiring was different.

The rotors themselves had a notched moveable placement ring connected to an outside ring. The notch forced a rotor to the left to move one place forward. The ring could be rotated manually, which the Germans did daily. The plug board, connecting letters, was also changed daily. Operators could also rotate rotors in or change their order.

The keystrokes used to compose messages sent electrical current through the plug board, resulting in a permutation. The charge then followed a path through each of the rotors, changing direction at each rotor. A reflecting plate then changed the letter and sent the charge back through the rotors, complicating the variable equation. The pulse then passed through the plug board a final time before traveling to a light panel where it ended its journey.

The Germans were sure messages could not be read unless the recipient had the same machine with the same rotors, wiring, plug board , notch board and settings, all of which were constantly changed. A matched Enigma sent the electrical impulse along the same pathway in reverse and gave a plain message.

Even with so many safeguards, however, Enigma eventually was breached. Espionage, accident, Allied brainwork, laziness and luck worked against Germany from an early date. Poland and France had been attacking Enigma since its introduction, with Polish mathematicians working to deduce the sequence of rotor wiring essential to deconstructing it.

In 1931, their work was advanced by a cash-strapped German traitor whose appetite for mistresses and a flashy lifestyle led him to sell critical information to Polish agents. Combined with strides they had already made, the state secrets enabled the Poles to finally unravel Enigma. It was a stunning achievement.

Although the Poles could now read Enigma messages, doing so was a slow process: There were still too many possibilities to sift through. What the Poles needed was an Enigma of their own to expedite matters. Toward this end they developed a “Bomba,” a machine that rapidly separated improbable combinations. Resembling three pairs of Enigmas linked together, by 1938 the Bomba was able to quickly identify exact German messages, sometimes within two hours. Not to be denied, the Germans added more rotors to their machines to overwhelm the upstart. Using Bomba would now require linking 60 Engima replicates.

Taking on the challenge were British crytographers at Bletchley Park, Britain’s intelligence-gathering headquarters. The top secret group designed its own Bomba with two major changes. One was that instead of looking for the correct setting, the new version would make assumptions about what the text was and find all the combinations that could allow that text. The second was the addition of a diagonal board to illustrate possible plug board connections. By August 1940 their machine, called a “Bombe”—weighing in at one ton and measuring 6.5' by 7' by 2'—was up and running. The machine was so successful that Britain built 210 of the devices.

Because the German army and air force trusted Enigma they were lax in security and complacent about delivery. As a result, their messages were vulnerable and soon read by the Allies: The Bombe could decode messages in hours. The Kriegsmarine was warier. The German navy branch enforced message security and used eight rotors. Although only four were used on any given day, analysts had to figure out which were in use.

Meanwhile, German submarines were wreaking havoc in the Atlantic. Because the British declined to use an equation pioneered by the Poles, the wiring of the new rotors remained a mystery until May 1941, when British sailors hauled Enigma material off a sinking U-boat. The hijacking allowed the British to read messages for a brief time. Although the British were careful to create a cover story when they used Enigma decrypts, the German navy redesigned Engima anyway in early 1942 and changed the code. Ultra,the code name for the Enigma-breaking program, was in the dark again.

Britain needed to redesign the Bombe, under heavy pressure from the U.S. Navy after Pearl Harbor. Responding, the British promised to have an improved Bombe by the summer of 1942. That appeared unlikely to the navy, which in any event thought it could come up with a better model. In conjunction with the National Cash Register Company it did in September 1942. The British were critical of the design at first, and privately wished the navy would butt out. But the American unit proved superior and the British had no choice but to grudgingly accept it.

Thus, a total of 200 sailors and 600 WAVES, women serving in the navy, went to work producing the latest Enigma incarnation. Eventually, the United States built 96 of its own Bombes, which were taller, longer and twice as heavy as its British counterpart. Nevertheless, by mid-1943 the U.S. Bombe paid off fully—decrypts could be obtained in 12 hours—and the U-boat menace was tamed. As the threat diminished, surplus American Bombes were used to decrypt the flood of German army and air force messages, extending their value.

Ultra was so significant that its secret was kept under wraps for more than 30 years with an astonishing degree of fidelity. Some historians estimate Ultra shortened the war by as much as two years. If so, Ultra saved several million lives in dozens of countries and probably prevented the complete destruction of European Jewry.

Sources:

Solving the Enigma: History of the Cryptanalytic Bombe (A National Security Agency publication) Jennifer E. Wilcox

Enigma, the Battle for the Code, Hugh Sebag-Montefiore, 2000, John Wiley and Sons, Inc New York

Enigma: How the Poles Broke the Nazi Code, Wladyslaw Kozaczuk and Jerzy Straszak, 2004 Hippocrene Books, 171 Madison Ave New York Ny 10016.