########################################################################## # Anatomy of Enigma # # Anuradha Weeraman, 23 November 2004 # # $Id: enigma.txt,v 1.6 2004/11/22 22:02:02 anuradha Exp $ # ########################################################################## Enigma was a device employed by Nazi Germany during World War II to ensure secure communications between the various military entities. The cracking of the Enigma was pivotal for the Allied cause and helped tip the balance of power during the War. Enigma uses a very complex scrambling mechanism, which if properly employed, would have rendered the cipher uncrackable. The cracking of the Enigma was abetted by the German belief that the cipher was impossible to crack which led to the insecure use of the machine that eventually led to its downfall. Much of the cryptanalytic headway into breaking the Enigma was conducted by the Polish. Having gotten the blueprints of the machine by way of the French, the Polish made very significant advancement where the French failed to deliver. This was partly due to the constant threat of invasion, being bounded by the German's on one side and the Russians on the other. The cracking effort was spearheaded by the brilliant Marian Rejewski for which he designed and implemented brute-forcing machines known as "bombes", named because of the ticking sound it used to make. The Enigma was built by Arthur Scherbius, who initially had trouble convincing the military and businesses to adopt encryption devices. He didn't live to see the success of his amazing machines as he was killed in a riding accident. In appearance, the Enigma is a like a typewriter, with keys and set of bulbs on top that illuminates the ciphertext as the operator types in the plaintext. A rule of the Enigma was that the encrypted character could NEVER be the same character that was typed in. Thus if the character 'A' was encrypted, no matter how many times it was typed in, the ciphertext could NEVER be 'A'. This is a weakness that was later exploited to break into the cipher. The scrambling ability of enigma is performed by : a) A plugboard b) Three scrambling units c) A reflector A plugboard is similar to a primitive switchboard which can be used to switch characters before being fed into the scrambling rotors. This is basically a form of simple monoalphabetic substitution which in itself is weak, but when combined with the rest of the scrambling mechanism makes it a formidable cipher. Another restriction placed by the Enigma was that no two consecutive characters of the alphabet may appear in the plugboard. Yet another weakness in the Enigma cipher. The three scrambling units are basically three rotors that can be placed in any order. The operator selects the three scrambling units out of a possible five depending on the code settings for the day. The day code also contains the plugboard settings to use for the duration of 24 hours. The initial settings of the plugboard and scrambler orientation determines the how the plaintext will be encrypted. The reflector simply reroutes the encrypted text that had reached upto that point back through a different route. Given these settings, on any given day, the Enigma can assume any of 10,000,000,000,000,000 possible keys making raw brute forcing practically impossible. The work of Rejewski et al, was to discover weaknesses in the use of the cipher to cut down the possible keys by orders of magnitude making brute forcing possible. This made the task of the bombes very much easier and the cipher could be broken in a matter of hours, making the enemy transmissions transparent to the Allies. Success is very shortlived because the Germans changed the key on a daily basis based on a code book. The code book was printed on blotting paper with soluble ink which made disposal very easy. The Germans picked the scrambler orientations and plugboard settings randomly making it very secure, but the transmissions contained common elements, known by the cryptanalysts as "cribs". These cribs were used to perform known-plaintext attacks on the cipher. All this time the Germans were blissfully unaware that their communication was being intercepted. When the War erupted, most of the Polish mathematicians ended up in Britain where the codebreaking nerve center for the Allies was set up at Bletchley Park. Some of the best minds of Britain, from mathematicians to Chess Grand Masters found themselves working as cryptanalysts. Amongst this motleyd bunch was Alan Turing, mathematician extraodinaire. This gathering of intellectuals was so effective that Churchill dubbed them "The geese that laid the golden eggs and never cackled". The naval Enigma was an even more difficult beast to tame. There was a choice of eight scramblers and the reflector can be configured in 26 different orientations as opposed to fixed version in the standard Enigma. The navy also made sure to prevent easily guessable messages that drastically reduced cribs. This had devastating effects on Allied forces as they struggled in the battle of the Atlantic. This plotline is captured in the fictional work of Robert Harris in his "Enigma", although much of the setting is based on fact in the form of Bletchley park. Despite the great breakthroughs in cryptanalysis that saved millions of lives, much of the work of these great minds went unnoticed for decades, hidden behind the veil of Government secrecy. They could only watch as their discoveries were being rediscovered and taken credit for. The genius of Turing was rewarded with public humiliation and in 1954, the lone genius outcast committed suicide. The Enigma remains to this day, a fascinating machine of a very rare elegance that took the collective genius of hundreds of mathematicians to tame.