Attempting a machine that would make codes impossible to break, the German military, as seen above, made a number of modifications to their Enigma machines. The plug board for example enabled the machine to increase its number of possible cipher starting points to something between two and three billion. The Enigma's rotors were also interchangeable while being wired differently, adding even more protection and encryption. In order to decipher codes created in this way, the code breaker would need to know not only the positions of each rotor, but also each starting position. Incredibly, according to Cooper, 100 machines working 24 hours per day would take 5.8 years to exhaust all the possibilities created in this way. It was therefore impossible to decipher the codes without the actual machine, the cipher key, and the correct rotor placements.
Nevertheless, there were those who attempted the impossible, and eventually succeeded, because the Enigma machine was not as flawless as the German officials believed it at first. The first attempts at deciphering the codes emerged from Poland's Cipher Bureau during 1932. According to Rijmenants, Marian Rejewski, Henryk Zyglaski and Jerzy Rozicki used two major security flaws - the "Achilles heel" of the Enigma - to eventually attain success. These are the global ground setting and the twice encoded message key - the latter was implemented to exclude possible errors from encrypted messages. The initial success was however short lived, and elements such as increased sophistication, new procedures, and lack of funds defeated the Polish effort by 1939. Poland succumbed to German invasion, but their initial efforts survived to reach French an British shores.
The Government Code and Cipher School from the United Kingdom built upon the Polish work to break the Enigma code initially by hand and later by increasingly complicated deciphering machines (Rijmenants). These were developed by Alan Turing and Gordon Welchman, who many credit with winning the war as a result of their deciphering efforts. In short, the Turing machine searched for given pieces of plain and cipher text, which were then used to identify the key settings that served as the basis for deciphering the rest of each message.
Extraordinary measures were taken to keep the German forces from suspecting that their ciphers might be compromised.
It is interesting that these measures were so well camoflaged that, even when heavy U-boat and crew losses occurred as a result of the deciphering efforts, the German forces attributed these to technologies such as sonar systems, boat detection planes, and destroyers. Meanwhile, the British were intercepting more or less the entire German communication system via "Y-stations," and deciphered with the help of more than 7, 000 workers at Bletchley Park. With the deciphered messages helping the Allies to intercept U-boats and steal encryption documents and machinery, all improvements the Germans attempted to make to the Enigma were successfully thwarted.
Because they were unaware of the extent of the British code breaking system, German officials made another fatal error in judgment that could have resulted in a much different outcome at the end of World War II. This is the use of the D. reflector, of which the key was changed every ten days. This could have created a problem for code breakers, as the time factor would have made deciphered keys useless. Fortunately for the Allies, and unfortunately for the Germans, the D. reflector proved too cumbersome to implement for all messages. Instead the B. reflector was used by default, making the code breaker's task much easier.
According to Kozaczuk, the Enigma story remained a secret with governments for many decades after the World Wars, and only gradually came to light recently. The new discoveries shed light upon the extraordinary human minds that created and broke secret messages.
Carlson, Andy. About Enigma and its Decryption. 2000. http://homepages.tesco.net/~andycarlson/enigma/about_enigma.html
Cooper, Charles. The Enigma Machine. Probs and Stats, 16 April 2002. http://web.usna.navy.mil/~wdj/sm230_cooper_enigma.html
Kozaczuk, Wladyslaw. The Origins of the Enigma/Ultra Operation. 2001. http://www.enigmahistory.org/text.html
Lycett, Andrew. Breaking Germany's Enigma Code. BBC History, 4 Feb 2008. http://www.bbc.co.uk/history/worldwars/wwtwo/enigma_01.shtml
Rijmenants, Dirk. The German Enigma Cipher Machine. 2004-2008. http://users.telenet.be/d.rijmenants/en/enigma.htm