World War I is over, and only a few years have passed since the American president attempted to usher in a new era of trust in international affairs, and his Secretary of State even went so far as to dismantle the Black Chambers office (composed of about twenty cryptanalysts), solemnly declaring that “gentlemen should not reach each other’s mail.” But there is one nation that cannot relax. It is Poland, caught between two uncomfortable neighbors: the Soviet Union and Germany. On November 8, 1931, Hans-Thilo Schmidt arrives at the Grand Hotel in Versiers, Belgium. Hans-Thilo is a German who hates Germany, where he has failed to establish himself, unlike his brother Rudolph, who has made a career in the army. And Hans-Thilo seeks redemption. He is in Belgium to contact a French secret agent, codenamed Rex, in exchange for 10,000 German marks. Schmidt has Rex photograph some documents detailing how to use an Enigma machine, which allows the Allies to build a replica of the Enigma machine (which obviously doesn’t mean they’re able to decipher the messages, since the key is unknown and changed daily, but it’s a first step nonetheless). In Poland, Biuro Szyfrow is tasked with trying to decrypt Enigma. He recruits the country’s best mathematicians, including Marian Rejewski, who begins to attack the problem, starting with some weaknesses: repetition is the enemy of security, for example. Repetition leads to patterns, which are a boon to cryptanalysts. For example, the Enigma key is encoded twice at the beginning of each message. By also analyzing the mechanical structure of the Enigma machine, he manages to make the problem 10 billion times easier than it was initially. Then, using other “tricks,” such as partially decoded phrases that can be guessed, such as “alliveinbelrin” (arrive in Berlin), he adds the finishing touches. The Poles are thus able, not without enormous decoding effort, to decode the current version of Enigma (which, however, would later be made much more complex). When Hermann Göring visits Warsaw in 1934, he is completely unaware that his communications are in clear to the Poles.
