The Germans introduced the ADFGVX encryption cipher just before the offensive they were about to begin on March 21st. Conceptually, it was nothing new, but “just” very complex, a mix of numerous substitutions and transpositions. The Allies, however, had an ace up their sleeve: the French cryptanalyst Georges Painvin, who managed to break the German code on June 2nd, not in time for the late March offensive, but in time for the next one, whose outcome would be largely determined by the clear reading of German messages. Also in 1918, cryptographers from various countries began experimenting with long, unstructured cryptographic keys (random keys—a long sequence of random numbers spanning hundreds of sheets of paper) and with one-time pad cyphers, i.e., cryptographic keys that were destroyed after use and never used again. In some ways, it’s a holy grail for cryptographers, as it’s an absolutely secure system. Indeed, if it were possible to test all possible keys, the true message would be revealed, along with several false positives. However, the one-time pad cypher was almost never used, due to its impracticality on the battlefield and in general, due to the enormous quantity of documents that had to be delivered somehow, without risking them falling into enemy hands. Curiously, however, in some cases, where communications are rare and cost is irrelevant, the one-time pad cypher is still used: this is the hotline between the American and Russian (formerly Soviet) governments.
