Italian Enigma: OMI encryption machines

    From the allies of Germany during the Second World War - Bulgaria, Hungary, Romania, Finland, Italy - only Italy had a sufficient level of cryptographic knowledge and technology to create their own versions of rotor crypto machines. Italian cryptographers have
    even developed an adapted version of the Enigma for their fleet. The encryption machine was produced by the Italian company Ottico Meccanica Italiana (OMI)

    Ottico Meccanica Italiana (OMI) is an Italian manufacturer of photogrammetric equipment. The company was founded in Rome in 1926 by Humbert Nistri (1895-1962). After Umberto’s death in 1962, his son Raffaello (1920–1981) headed the company for almost 20 years. After the death of Raffaello in 1981, OMI merged with the manufacturer of helicopters Agusta.

    At the beginning of World War II (1939–1940), OMI developed an electromechanical encryption machine in “secret mode”, which was eventually used by the Italian army (Regio Ersetico), the Air Force (Regia Aeronautica), and the Navy (Regia Marina). The machine was named Cryptograph Alpha, it was built on the principle that the German Enigma. She had 5 rotors, the extreme left served as a reflector (reflector). However, unlike Enigma, the machine was equipped with a built-in printer, information was displayed directly on paper punched tape. Cryptograph Alpha was with irregular stepping of rotors, as in Enigma G. Recall that Enigma G had four metal rotors: the extreme right three rotors are coding rotors, on the left one reflector. The reflector moved during encryption,

    In the early 1950s, OMI developed a successor to the Cryptograph Alpha, known as the Criptograph. Its dimensions were larger than its predecessor, the machine already contained an improved 7 rotary drum: 5 coding rotors with two cores each, 1 adjustable coding rotor and 1 adjustable reflector. Like the Cryptograph Alpha, this machine was distinguished by the irregular movement of the rotors.

    How it all began or a little from the history of the company OMI

    OMI was founded by Umberto Nistri, who was born on September 16, 1895 in Rome, the eldest son of Raphael and Letitia Nistri. His parents were cousins ​​to each other and bore the same last name, were from Quinto, a town near Sesto Fiorentino (Italy). Shortly before the birth of Umberto, the family moved to Rome, today it is the Prati district. Here Umberto was born and made his first steps.

    Umberto's father, Raphael, came from a family of farmers, but in order to ensure a better life for his children, he went to serve in the Italian army. After the birth of five more children, the family moved to Fort Trionfale, not far from Monte Mario, the father was provided with housing at a military base. It was here that Umberto developed his passion for aerial photography.

    Despite his desire to become an engineer, due to lack of funds, Umberto had to learn to be a surveyor (1913) and work in this specialty. In 1915, when Italy entered the First World War, Umberto became interested in military aviation, he was attracted by the sky. He left his job and took his place in the ranks of the army (artillery). Later was sent to the front (east of Italy).

    In 1916, he briefly returned home, his mother was ill and her condition worsened significantly. After her death, He died, forgot about his promise to his mother not to fly, and in 1917 enrolled in a training course to become an observer pilot. After training, he joined the 35th Squadron in Santa Justin, he monitored enemy territory and took photographs. He was awarded two silver medals - as distinguished for his bravery during the war.

    Father Raphael died after the end of the First World War in 1918, Umberto and his brother Amedeo took care of their younger children. It was necessary to support the family, because he decided to stay in the Air Force. A year later (1919), Umberto married an elementary school teacher Lola, their acquaintance took place before the war in Rome. Two sons were born in marriage: Paolo Emilio and Raphael.

    Thanks to his military experience of flying, photographing and mapping, Umberto Nistri was able to develop a tool for obtaining topographic maps using stereoscopic aerial photographs.

    The first patent for the rudimentary version, “fotocartografo”, was obtained in 1919, and by 1922 the final version of its photogrammetric converter was ready. The rest of the patents were obtained in 1925 (Model II) and 1929 (Model III). At the same time, in order to finance his current research in the field of photogrammetry, Nistri developed his first instrument for air navigation.

    In 1921, together with his brother Amedeo, he founded the first company engaged in the commercial production of topographic maps made using aerial photography and photogrammetry - known as Società Anonima Rilevamenti Aerofotogrammetric or SARA-Nistri. In 1930, Ottico Meccanica Italiana, also known as OMI or OMI-Nistri, began its work.

    Alas, such events as the death of Brother Amedeo in 1936 and the beginning of the Second World War became fatal: in 1939 SARA-Nistri ceased to exist, and production at OMI-Nistri was suspended. Fortunately, Nistri received orders for the secret development and production of a cipher machine for the Italian armed forces.

    After the end of the war, the company gradually regained consciousness, the opportunity to sell their products and cryptomachines around the world. In 1961, with the advent of the computer, the company was the first to offer digital photogrammetry to the market. In 1954, another encryption machine was developed, the Criptograph, then the Cryptograph-CR.

    Umberto Nistri died on April 24 in 1962. His son Raffaello led the company for another 20 years, after his death she was acquired by the Italian helicopter manufacturer Agusta (1981). During his long and impressive career, Umberto Nistri won numerous awards, received honorary degrees from universities around the world and was an honorary member of the most prestigious societies and academic institutions. His street in the hometown of Rome is named after him, located near the historic headquarters of the OMI.

    Directly about OMI cryptomachines

    OMI Alpha

    Cryptograph-Alpha, or Alpha, was a rotary-based electromechanical cryptographic device, secretly developed and manufactured by OMI in Rome (Italy) around 1939, at the beginning of World War II. It was intended for use by the Italian army (Regio Ersetico), the Air Force (Regia Aeronautica) and the Navy (Regia Marina). As mentioned earlier was similar to the German Enigma, had 5 encryption rotors, including a moving reflector.

    A machine with irregular stepping of rotors, with grooves around the circumference of each rotor, which is similar to the Zählwerk device in Enigma G. The difference with Enigma was that Alpha had another encryption wheel and was driven by a motor, which added to the speed of the crypto device. Information was displayed directly on a paper punched tape, which allowed "transfer" control of the machine into the hands of only one operator. The keyboard consisted of 26 keys, 26 letters of the Latin alphabet, the letter “W” was used as a space.

    The image above is a typical Alpha naval cipher. It is very similar to Enigma Zählwerk, but more refined. Perhaps the statement is not quite true, since so far there is little information about these machines in open access. Only a small number of cars survived to this day. After the end of World War II, OMI gradually began to resume its usual activities, several successors of OMI Alpha were developed, again for the Italian armed forces, the 1954 OMI Criptograph - the first of them.


    The diagram below shows the various controls and OMI Alpha functionality. The mechanism is a body with a keyboard in front. The keys are arranged in the order of QZERTY, instead of a space, the letter “W” is used. Below to the right is a device for feeding paper tape.

    In front of the left is a printer that outputs the output to a paper tape. Five cipher rotors are located on the right, immediately above the paper tape feeder, they can be installed without opening the machine.


    Five encryption rotors are located on the right side of the machine and protrude above the top cover of the case, they are protected by a transparent hinged cover, the user can easily install a message key without even opening the machine. True to change the order of the rotors, you must first remove the top cover, which is closed by a physical lock, it is located at the top center in the front panel. Only the officers who had the proper security clearance were allowed to install the daily key.

    The image above shows the rotors when the top cover is removed. Each rotor has 26 spring-loaded contacts on the right side and 26 flat contacts on the left. Spring-loaded contacts of the rightmost rotor are paired with 26 flat contacts on the contact plate (or the input disc), on the right.

    The rotors are mounted on the spindle, it is inserted into the machine on the right, protected by a hinged lid and another physical lock.

    The leftmost rotor is a reflector, which is driven during operation. In fact, the Alpha design is similar to the Enigma design. The reflector has only 26 pins on the right and returns current to the encryption rotors.

    The simplified diagram above shows the flow of current through the encryption rotors when a key is pressed. In the example, the letter “A” is pressed, the current is applied to the contact “A” of the input disk (ED). From there, the current passes through the encryption rotors and puts them into action (in this order IV, III, II, I). Reflector ®, which contains 13 wires, returns the current to the encryption rotors (in order I, II, III, and IV) until it leaves the drum again through the input disk. In this example, the letter “A” is converted to the letter “D”.

    Four encryption rotors (I, II, III and IV) are interchangeable and can be installed on the spindle in 24 different orders (4 x 3 x 2). The reflector is different from other rotors, as it has contacts only on one side. It is fixed in place and has a gear wheel attached to the body (left). This wheel moves one step forward each time you press a key.

    Although the rotor's step-by-step movement mechanism in OMI Alpha is almost identical to the Zählwerk mechanism in Enigma, it should be noted that, compared with Enigma, the step-by-step movement of the wheels works from left to right and not from right to left. In other words: the reflector is a fast rotor.

    Each time you press a key, the outermost rotor on the left (i.e., the reflector) takes one step, during which the upper part of the rotor moves towards the rear of the machine. This means that if the letter “A” was visible before pressing, then after “B” would be visible.

    Each rotor has 26 pins on the left and a limited number of pins on the right. A limited number of pins on the right side of the reflector is adjacent to the 26 pins of the encryption rotor. They are connected by a small gear for the rotors. Whenever there is a contact on the right side of the rotor, it drives the gear - as a result, it drives the adjacent wheel and voila a step is taken. Thus the reflector, which is also a reflector, contributes to the fact that the first encryption rotor takes a step, etc. The far right rotor wheel itself is slow.

    What is inside OMI Alpha

    It is easy to get access to the “inner world” of OMI Alpha, for this you only need to remove the top cover using a physical key, the lock is located in the center from the top on the front panel. Under the cover is quite simple machine design. The rotors are located at the front right.

    The mechanism is started using an electric motor, which is located behind the rotors. He sets in motion a small gearbox on the left, which, in turn, drives the printer. Printer time is controlled by an electrical switch that is installed between the front panel and the chassis.

    The mechanism of the printer is quite simple and consists of several gears, dogs and levers. Its time is controlled by an electrical switch.

    OMI Criptograph

    The Criptograph is an electromechanical cryptographic rotary machine, developed and produced by OMI in Rome (Italy) immediately after World War II, around 1954. It was originally intended for use by the Italian armed forces, but later was also offered to foreign customers. The machine is the successor to the OMI Alpha of wartime and contains 5 rotors, a customizable stator and a customizable reflector.

    As far as is known, there are no surviving copies of this car. The photo above was taken from the recently declassified NSA document, which describes the functionality of the device. The document was created in 1954, probably after the NSA received a car for evaluation.

    The criptograph is also very similar to the German Enigma, with its encrypted “drum” consisting of an input disk, 5 encryption rotors, a stator and a reflector. It differs from the German brother in a simple step-by-step rotation of the rotors. Each rotor has only one notch, which causes the pitch of the adjacent rotor, following the example of an odometer in a car. However, unlike Enigma, the Criptograph is driven by an electric motor and outputs data directly to paper tape. The design is clearly based on OMI Alpha, which had a simpler design, but similar characteristics. In the late 1950s, a slightly improved Cryptograph-CR followed Criptograph.

    Office Criptograph

    The above image shows the location of the various Criptograph OMI controls. The front panel is a keyboard with 26 letters of the Latin alphabet, in order QZERTY. The letter “W” is also used as a space. Immediately behind the keyboard is the printer, which consists of a double print head, it is driven by the switch. Everything is printed directly on the paper tape in the drawer on the right.

    Encryption rotors are located to the left of the center of the machine. The whole mechanism is driven by an electric motor (rear right).


    The encryption rotors are located inside the machine, to the left of the center, and the longitudinal axis is from the front of the machine to the rear. Each rotor has 26 contacts on each side and, therefore, has 26 possible positions, each of which is identified by one of the letters of the Latin alphabet (AZ). There are 7 rotors in the car, 5 of which are mounted on a removable axle. The complete set of wheels is called the “drum”.

    The drum consists of five moving encryption rotors, a stator and a reflector. Encryption rotors move as you type a message on the keyboard. The stator does not move, but it can be installed in any of the 26 positions. The reflector is also fixed, but, like the stator, can be installed in any of the 26 positions. All 5 encryption wheels are removable and mounted on a spindle. Keyboard wiring is connected to the input drive on the right, which consists of 26 flat contacts. From there, the current flows to one of the spring-loaded contacts of the rightmost rotor. The wiring inside the rotor supplies current to one of the flat contacts on the left side. Thus, the current passes through all 5 rotors and the stator (S) until it reaches the reflector ® on the left. Then the current returns.

    Above, a simplified diagram demonstrates how current flows from the input disc, through the rotors, the stator, the reflector, and vice versa. The entry path is shown in red, and the return path is in blue. In this example, the letter “A” is encoded in “D”. Due to the fact that a reflector is used, the path is reversible. This means that with the same settings and rotor positions, the letter “D” will be encoded in “A” as in Enigma. It turns out that the letter can never be encoded in itself. In other words: if “A” is pressed, it can become any letter, but not “A.”


    Five encryption rotors are mounted on an axis, which can be removed by releasing the drum lock levers at either of its ends. However, before this you must first disable the gear coupling for the rotors.

    Before removing the rotors from the spindle, it is necessary to remove the blocker at one of its ends using a special tool (if any). If this tool is not available, you can use a large screwdriver as an alternative.

    Each rotor consists of three main parts: a metal frame, a red wire core and a black wire core, as shown in the image above. Each frame has a unique number (from I to V), all rotors are equipped with two unique cores: black and red. Black is always mounted on the right with spring-loaded contacts facing out. Similarly, the red core is always on the left with flat contacts facing outwards.

    The frame is nothing but a cast holder for two cores, each of which can be inserted in 26 different positions. The red core is always inserted on the left in such a way that the 26 spring-loaded contacts coincide with the 26 holes in the central part of the frame. Then the core is screwed to the frame with a folding clip in the center. Accordingly, the black core can be inserted to the right in 26 ways and secured with a clamp.

    7 rotors protrude from above, their position can be viewed and changed. Each of the rotors has 26 letters of the alphabet, printed on a circle, so that the operator can read them freely while working with the keyboard. The rotor's stepping mechanism is very similar to the Zählwerk Enigma, driven by gear wheels. This makes it possible to make corrections by simply turning the "forward / back" knob just behind the keyboard.

    When typing on the keyboard, the rightmost rotor moves counterclockwise to the next position. This means that after “A”, “B” should be visible. The stator (S) and reflector ® do not move. To illustrate the step of the five encryption rotors, three consecutive steps of the fast rotor are shown below from the operator’s position:

    Electrical circuit

    Although the original Criptograph scheme is not available and was not presented in the NSA report, it is reasonable to assume that it is almost identical to Cryptograph-CR, which appeared after a few years.


    The Cryptograph-CR is an electromechanical crypto rotor device developed and manufactured by OMI (Italy) in the late 1950s as the successor to the Criptograph OMI. Cryptograph-CR was intended for use by the Italian armed forces (in particular, MMI 2) and, probably, by foreign customers. The body of the car, as a rule, was green, and it was stored in a wooden green case.

    In front was a 27-button keypad, on which the letter “W” was missing (W is not used in Italian). It has been replaced by a space. The arrow key in the lower right corner was used to move the paper continuously. A counter that is visible through the top cover shows the number of characters entered.

    Cryptograph-CR worked similarly to the German Enigma: the same set of electromechanical rotors with 26 contacts on each side, an input disk and a reflector. However, unlike Enigma, the OMI Cryptograph-CR had a built-in printer, the output data was printed on two paper tapes (in front of the machine, right behind the keyboard). One tape showed the plaintext, the second - encrypted.

    Paper ribbons were fed from the right side of the machine, passed through the printer in the front center. Empty paper reels were stored in a box on the right side of the machine. In the early 1960s, some Cryptograph-CRs were upgraded, the mechanical keyboard was replaced with a fully electric one. The color of the car was replaced by gray.

    Control Cryptograph-CR

    The image below shows the various controls and Cryptograph-CR functionality, the top cover is removed. The rotors are on the left, the axis moves from front to back, and the input disk is closer to the operator. The stator and the reflector are located at the back. Encryption rotors are driven by a series of gear rotors, which are located in the center of the machine. The electrical connection (solenoid) ensures that the entire mechanism makes one complete revolution with each key press.

    Cryptograph-CR Mark II, or CR-2

    The Cryptograph-CR Mark II, or CR-2, is an electromechanical cryptographic device manufactured by OMI in the early 1960s; it was an updated version of the OMI Cryptograph-CR. It was intended for use by the Italian armed forces, in particular, the Italian Navy (MMI).

    The original mechanical keyboard was removed and replaced with a fully electric keyboard, the keys of which are located closer to each other. The space has been removed, the letter “W” has been added, so now the machine supported the full alphabet AZ. At the same time, the car body was repainted gray.

    Two switches, providing printing in the form of open and encrypted text, were “thrown away”, and their openings were closed. As a result, CR-2 always printed both open and encrypted text. Inside the car, parts of the power supply unit (PSU) were upgraded and 26 electric relays were added, each of which is connected to one of the switches on the keyboard.

    Control Cryptograph-CR Mark II

    The diagram below shows the various OMI Cryptograph-CR Mark II controls. The upper part of the interior is largely identical to the Cryptograph-CR, but the keyboard is completely different. Now it contains all 26 letters of the Latin alphabet (AZ) plus a key for feeding paper. To simplify the management of the keys are located closer to each other. The engine compartment is located behind the right. A paper ribbon printer is located just above / behind the keyboard. The rotors are located on the left, and the mechanical (gear) clutch is on the right.

    Access to the inside of the machine is possible on both sides: top and bottom. At the top are mechanical parts, such as rotors, printer, main drive axle, motor, and switch. Below are electrical parts such as power supply and relays.

    The printer has two alphabets: one for the encrypted text and one for the open. Paper tape runs from right to left. Two printheads are connected, so they always rotate synchronously under the control of a dual switch.

    As history shows, Ottico Meccanica Italiana, or OMI, originally an Italian manufacturer of photogrammetric equipment, has also become a manufacturer of a number of electromechanical rotor cryptographic machines, similar to the German Enigma. It would at least be wrong to underestimate the role of such equipment for the Italian armed forces. And the enormous work of the guys Cryptomuseum .

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