Leading up to World War II, Poles found their country increasingly insecure. Between Germany and Russia, its potential foes, Poland’s intelligence service focused on breaking Germany’s radio broadcasts to assess possible threats. However, Poland needed to figure out how to decipher the encrypted radio transmission.
While familiar with industrial Enigma machines, Poles were not familiar with Germany’s unique military design. The race to decode Germany’s encrypted radio transmission began. They took their existing Enigma machine knowledge and started their work.
Message encoding worked with the machine’s rotors. Rotors had 26 pins, one for every alphabet letter were connected to complimentary rotors. Individual rotors (or wheels) moved as one at different “set points.” Encoding machines with only two rotors and one “set point” could create nearly 17,000 daily combinations. Letters were rearranged through random electrical signals controlled by the rotors. For seamless encryption and decryption, cipher readers had to know the same settings. German military codebooks ensured a unique framework to decrease chances of the interception and decryption.
Germans created high-level encryption through its exponential plugboard wiring and letter swapping technology. Plugboards featured 10 connections, permitting letter swapping when coupled with cables. Plugboards scrambled letter pairs prior to and after the primary mixing unit. Ciphers transposed letters according to the wiring setup. Messages were expressed with a printer that was hooked up to the lamp panel. Encryption was enhanced because the signal officer did not see the decoded message.
Codebooks instructed ciphers to set unique ring settings on rotors daily. Along with a random message key, the combination encrypted the message. Both ends had to ensure rotors were in their identical order and starting points, along with plugboard connections. They also dictated the rotors’ starting position (uniquely determined by the cipher), plug connections, reflector’s wiring design, ring settings and their wheel order.
Ring settings exclusively dictated the starting rotor setting, determining the German recipient’s decoding methods. The session key complemented the ring settings and the starting rotor position by ensuring the text was, in fact, encrypted.
The indicator encrypted messages based upon the rotor starting position. Rotors were set at a random beginning point, serving as the day’s encryption code. The starting point was entered in twice, giving the Poles a clue of the German’s starting point. This unique word would start the message and the military code would follow. Rotors were then moved to the transmission’s settings and entered the un-encoded text. To decrypt, the process was reversed.
Poland put its sharpest mathematicians to work to break Germany’s code. Jerzy Rozycki, Marian Rejewski, and Henrky Zygalski became Poland’s decryption experts. Poland’s first decryption attempt was with Zygalski Sheets. This method relied on looking at encrypted correspondence and observing character positioning.
Zygalski observed encrypted patterns in Germany’s radio transmissions in predictable positions. He found correlations between the 1st and 4th, 2nd and 5th and 3rd and 6th sets. Based on Germany’s triple letter key encryption methods, wheel order and machine starting points, Zygalski created his namesake decryption sheets.
Containing 4 squares, each with 26 letters of the alphabet, vertically and horizontally, his sheets would decode enigma machines with 6 unique wheel configurations. Between 75 and 156 tries would be needed to decrypt each encrypted text. While not time-efficient, it led to a breakthrough while collaborating with Rejewski.
Rejewski hypothesized if each wheel was set one starting position ahead of the previous one and all wheels moved simultaneously, the team would find a pattern of redundant encryption letters. His “Bomba” project required six machines to test his theory of running wheels at different starting points.
Ultimately, the machine with six wheels and a staggered starting position worked. Showing a pattern, it led the Poles to break Germany’s encrypted radio transmissions. The Poles were able to wire their own Enigma machines based on the necessary code.
The next problem was documenting and organizing the German code on every wheel and every start position to have Enigma machines automatically decode messages. There were more than 105,000 characters in the German’s Enigma code. The Poles merged two Enigma machines, side-by-side, with right-hand wheels offset by three places, creating the Cyclometer. Germany outsmarted the Poles decryption ability when they re-arranged their machine’s wheel combinations every day.
The Poles countered this with part espionage and part deduction. Hans-Thilo Schmidt or “Asche,” a French spy, gave the Polish copies of codebooks recently used by German ciphers.
The last piece of the Enigma puzzle was figuring out the correct wiring patterns. The Polish team deduced that industrial Enigma machine wiring was different from the German’s wiring setup. Using part logic and part-educated guess, the Poles wired it according to the ABCDEFG pattern, compared to the standard QWERTZUIO.
Cat-and-mouse spying prompted Germany to increase the code’s complexity with two additional encoding wheels. Forecasting a German attack, coupled with the increasing effort necessary to decode radio transmissions, the Poles approached the Allies to work together to continue decrypting radio transmissions more efficiently at Chateau Vignolless, in Paris, France.
With the Allies increased decoding resources, Germany’s manual errors, inconsistent encryption systems, and ciphering apathy created unsecure radio transmissions.