One of the most famous wartime ciphers was the German ADFGVX cipher, introduced on 5 March 1918, just before the major German offensive that began on 21 March. Like any attack, the German thrust would benefit from the element of surprise, and a committee of cryptographers had selected the ADFGVX cipher from a variety of candidates, believing that it offered the best security. In fact, they were confident that it was unbreakable. The cipher's strength lay in its convoluted nature, a mixture of a substitution and transposition.
By the beginning of June 1918, the German artillery was only 100 km from Paris, and was preparing for one final push. The only hope for the Allies was to break the ADFGVX cipher to find just where the Germans were planning to punch through their defences. Fortunately, they had a secret weapon, a cryptanalyst by the name of Georges Painvin. This dark, slender Frenchman with a penetrating mind had recognised his talent for the Bureau du Chiffre soon after the outbreak of war. Thereafter, his priceless skill was devoted to pinpointing the weaknesses in German ciphers. He grappled day and night with ADFGVX cipher, in the process losing 15 kg in weight.
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