NotesThe Enigma machine was originally designed by German engineer Arthur Scherbius. He developed Enigma in 1915, about the same time others were developing similar rotor-based code machines around the world. For example, two Dutch naval officers, Theo A van Hengel and PRC Sprengler, had devised a rotor-based machine that was similar to Enigma. Scherbius applied for his patent on 23 February 1918.
Scherbius, after initially failing to convince the German military of Enigma's ciphering potential, established the Chiffriermaschinen Aktiengesellschaft (Cipher Machine Stock Company) in 1923. The company produced commercial versions of the machine that were sold to businesses. During this time Enigma, originally over 100 pounds (about 45kg), was streamlined into a device that was no bigger than a portable typewriter.
Enigma cannot transmit or receive messages on its own. It may only be used to encipher and decipher messages, or convert plain text to and from code. The most basic type of code substitutes a word, letter or symbol for another word. Enigma was different in that the code it produced was much more complex, as each letter was substituted for another letter. Depressing the key for a given letter causes a signal for that letter to pass through the three rotors and the plug board. This operation causes a cascade of substitutions for the original letter. In this manner, a message can be encoded so that it can only be decoded by playing back through the same sequence of substitutions. The operator doing the decryption would have to know the specific key settings to decipher any incoming messages.
A team of two was used to code and decode messages. The operator would type the message, limited to 250 words, into the machine. The machine would substitute letters and relay the code, one letter at a time, on its lamp board. The operator's assistant would record the code for the radio operator to transmit. The keys, which dictated the configuration and placement settings of the rotors and the plug board, could be changed daily. The key for a given day was relayed in the code book; there were up to 159 million million million (159,000,000,000,000,000,000) possible keys.
The device was intended to prevent the repetition of a sequence of letters, even if the same letter is struck multiple times. Each rotor is covered with 26 electrical contact points that connect randomly to similar contacts on the other side of the rotor. Each contact point represented a letter. The rotor turned 1/26th rotation with each keystroke to the keyboard, so that each subsequent letter would always be different. Once the first rotor had gone through an entire cycle, the second rotor would be engaged; it would turn 1/26th with each complete rotation of the first rotor. The third rotor would likewise only move when the second had completed a rotation.
The German Navy (Kriegsmarine) adopted the Enigma machine to encrypt their communications in 1925 and implemented a number of modifications. In 1928, the German Army (Wehrmacht) followed in the Navy's footsteps and adopted the Enigma machine. The Wehrmacht also modified its machines, adding a plug board (Steckerbrett) to the base of the device. The plug board consisted of 26 sockets, representing letters, which were connected to both the keyboard and the lamp board. This plug board swapped letters before they entered the rotors and again after they exited them, effectively increasing the size of the mathematical variables for the encoded letter.
These modifications lulled the German authorities into thinking that the Enigma was unbreakable, and they used it until the end of the war. Various versions of Enigma were also adopted by the German Air Force (Luftwaffe), the railway service, the Abwehr and the SS. It was continually modified and updated throughout the war, usually with the addition of more rotors to increase encryption.
MadeChiffriermaschinen AG 1919-1945
DesignedScherbius, Arthur 1915