The Lorenz SZ-40 is an electro-mechanical wheel-based cipher machine for teleprinter signals. It was developed by the Germans and was used during World War II for communication at the highest level. Improvised twice although, it was broken by the code breakers at Bletchley Park in the early 1940s. During the WW II, for teleprinter signals, besides Lorenz, the German army also used the Siemens T-52 Geheimschreiber, the Lorenz SZ-40, and later also the Siemens T-43 one-time pad machine.
The Lorenz SZ - 40/42 was used by the German High Commands for communication at the highest level, between Hitler and his generals. The machine was called Schlüsselzusatz (SZ) which means Encryption Add-on. It was connected between a teleprinter and the line and was suitable for both online and offline use.
The Lorenz company built the cipher machine based on an additive method for enciphering teleprinter messages invented in 1918 by Gilbert Verman in America. After world war 2, a group of British and US entered Germany with the front-line troops to capture the documents, technology, and personnel of various German signal intelligence organizations and from the captured, they found SZ40 and SZ42 a/b. The design of the machine they found was feasible with teleprinters.
Gilbert at AT&T Bell Labs in 1917, invented a cipher system that used Boolean “exclusive or” function. Vernam’s cipher is a symmetric-key algorithm which produces the essential reciprocity that allows the same machine with the same settings for encryption as well as decryption. Vernam’s idea was to use conventional telegraphy practice with a paper tape of the plaintext combined with the paper tape of the key but generating them was practically difficult, therefore, he invented rotor cipher machines.
Teleprinters are not based on a 26-alphabet system but are based on 32-symbol Baudot code. The Vernam system enciphered the message by adding to it, character by character, a set of obscuring characters thus producing the enciphered characters which were transmitted to the intended recipient. The simplicity of Vernam's system lay in the fact that the obscuring characters were added in a rather special way (known as modulo-2 addition). Then the same obscuring characters added also by modulo-2 addition to the received enciphered characters, would cancel out the obscuring characters and leave the original message characters which could then be printed. The working of modulo-2 addition is the same as the XOR operation in logic.
For enciphering and deciphering, the transmitter and receiver are set up identically in which there are two components: setting the patterns on cams of the wheel and rotating the wheels for the start of enciphering. The cam settings were changed less frequently initially but it was made more frequent so that the enemies could not intercept them. The wheel settings were sent by 12-letter indicator un-enciphered but in October 1942, it was changed to a book of single-use settings called the QEP book.
As was normal telegraphy practice, messages were typed to teleprinter with a paper tape perforator. The typical method was to type the encrypted message, contact the receiving operator with an EIN/AUS switch on the SZ machine to connect to the circuit, and then run the tape through the reader. At the receiving end, the operator would connect the SZ machine to the circuit and the output would be printed on the sticky tape.
Enigma was considered to be an unsolvable machine and Lorenz was more complicated and sophisticated than that. The Lorenz used 12 wheels and 501 pins and the enciphered message was 5-bit punched paper tape where messages often contained thousands of characters and 1.6 quadrillion starting positions were arguably possible according to the reports and sources.
But the miracle was that Bill Tutte broke the Lorenz system without even seeing the machine ever.
Under the leadership of Major Ralph Tester, “Testery” was formed at Bletchley Park. A lot of information was intercepted but there was no headway for deciphering the messages until the Germans committed a fatal mistake. On 30th August 1941, a German operator sent a 4000-long character message and the receiver wasn’t able to get it, so the message was replied with “didn’t get that - send again”. Both receiver and the sender put their machine with the same starting position which was forbidden and the message sent again was 500 characters lesser than the original probably because the sender was saving his fingers.
The message began with that well known German phrase SPRUCHNUMMER — "message number" in English. The first time the operator keyed in S P R U C H N U M M E R. The second time he keyed in S P R U C H N R and then the rest of the message text. Now NR means the same as NUMMER but it meant that immediately following the N the two texts were different. But the machines were generating the same obscuring sequence, therefore the ciphertexts were different from that point on.
The enemy interpreters acknowledged that the twelve letter indicators were the same both the times. John Tiltman at Bletchley Park applied the same additive technique he figured before and this time he was able to get through more than the previous ones because when he tried SPRUCHNUMMER at the start he immediately spotted that the second message was nearly identical to the first. Thus the combined errors of having the machines back to the same start position and the text being rekeyed with just slight differences enabled Tiltman to recover completely both texts. Now Tiltman could add together, character by character, the corresponding cipher and message texts revealing for the first time a long stretch of the obscuring character sequence being generated by this German cipher machine.
John now passed the obscured characters to Bill Tutte and he recognized the bit patterns at a repetition of 41 had some significance and by Jan 1942, the codebreakers had deduced the working principle of the Lorenz machine, using nothing but the recovered keystream from the August 1941 message.
Several replica machines were built to aid the attack on Tunny (code word for Lorenz). The first was British Tunny built at Bletchley Park based on reverse engineering techniques and after that family of Robinsons were built but the issue was that the two papers synchronized were relatively slow.
The Colossus computers were developed and built by Tommy Flowers, of the Dollis Hill Post Office Research Station, using algorithms developed by W.T. Tutte and his team of mathematicians. Colossus proved to be efficient and quick against the twelve-rotor Lorenz SZ42 on-line teleprinter cipher machine.
It is after the D-Day landings in 1944, the first Lorenz machine was captured and was shown to the codebreakers of Bletchley Park and they were amazed to see the relatively small mechanical machine of which they had created the electronic equivalent. Lorenz was indeed a miraculous machine that would not have been broken if the mistake would not have been committed.
In Germany, examples of Lorenz may be seen at the Heinz Nixdorf MuseumsForum, a computer museum in Paderborn and the Deutsches Museum, a museum of science and technology in Munich. Two further Lorenz machines are also displayed at both Bletchley Park and The National Museum of Computing in the United Kingdom. Another example is also on display at the National Cryptologic Museum in the United States.
With this blog, we come to the end of our mini-series “Decrypting World War 2 communication”. We hope you loved all the blogs and find them interesting and scholarly. Do like, share and comment on our blogs and if you want to read something specific, you can suggest them through our email or you can even comment them down!
Happy Reading!
The Lorenz SZ - 40/42 was used by the German High Commands for communication at the highest level, between Hitler and his generals. The machine was called Schlüsselzusatz (SZ) which means Encryption Add-on. It was connected between a teleprinter and the line and was suitable for both online and offline use.
History
The Lorenz company built the cipher machine based on an additive method for enciphering teleprinter messages invented in 1918 by Gilbert Verman in America. After world war 2, a group of British and US entered Germany with the front-line troops to capture the documents, technology, and personnel of various German signal intelligence organizations and from the captured, they found SZ40 and SZ42 a/b. The design of the machine they found was feasible with teleprinters.
Gilbert at AT&T Bell Labs in 1917, invented a cipher system that used Boolean “exclusive or” function. Vernam’s cipher is a symmetric-key algorithm which produces the essential reciprocity that allows the same machine with the same settings for encryption as well as decryption. Vernam’s idea was to use conventional telegraphy practice with a paper tape of the plaintext combined with the paper tape of the key but generating them was practically difficult, therefore, he invented rotor cipher machines.
Working
Teleprinters are not based on a 26-alphabet system but are based on 32-symbol Baudot code. The Vernam system enciphered the message by adding to it, character by character, a set of obscuring characters thus producing the enciphered characters which were transmitted to the intended recipient. The simplicity of Vernam's system lay in the fact that the obscuring characters were added in a rather special way (known as modulo-2 addition). Then the same obscuring characters added also by modulo-2 addition to the received enciphered characters, would cancel out the obscuring characters and leave the original message characters which could then be printed. The working of modulo-2 addition is the same as the XOR operation in logic.
For enciphering and deciphering, the transmitter and receiver are set up identically in which there are two components: setting the patterns on cams of the wheel and rotating the wheels for the start of enciphering. The cam settings were changed less frequently initially but it was made more frequent so that the enemies could not intercept them. The wheel settings were sent by 12-letter indicator un-enciphered but in October 1942, it was changed to a book of single-use settings called the QEP book.
As was normal telegraphy practice, messages were typed to teleprinter with a paper tape perforator. The typical method was to type the encrypted message, contact the receiving operator with an EIN/AUS switch on the SZ machine to connect to the circuit, and then run the tape through the reader. At the receiving end, the operator would connect the SZ machine to the circuit and the output would be printed on the sticky tape.
Enigma was considered to be an unsolvable machine and Lorenz was more complicated and sophisticated than that. The Lorenz used 12 wheels and 501 pins and the enciphered message was 5-bit punched paper tape where messages often contained thousands of characters and 1.6 quadrillion starting positions were arguably possible according to the reports and sources.
But the miracle was that Bill Tutte broke the Lorenz system without even seeing the machine ever.
Code Breaking
Under the leadership of Major Ralph Tester, “Testery” was formed at Bletchley Park. A lot of information was intercepted but there was no headway for deciphering the messages until the Germans committed a fatal mistake. On 30th August 1941, a German operator sent a 4000-long character message and the receiver wasn’t able to get it, so the message was replied with “didn’t get that - send again”. Both receiver and the sender put their machine with the same starting position which was forbidden and the message sent again was 500 characters lesser than the original probably because the sender was saving his fingers.
The message began with that well known German phrase SPRUCHNUMMER — "message number" in English. The first time the operator keyed in S P R U C H N U M M E R. The second time he keyed in S P R U C H N R and then the rest of the message text. Now NR means the same as NUMMER but it meant that immediately following the N the two texts were different. But the machines were generating the same obscuring sequence, therefore the ciphertexts were different from that point on.
The enemy interpreters acknowledged that the twelve letter indicators were the same both the times. John Tiltman at Bletchley Park applied the same additive technique he figured before and this time he was able to get through more than the previous ones because when he tried SPRUCHNUMMER at the start he immediately spotted that the second message was nearly identical to the first. Thus the combined errors of having the machines back to the same start position and the text being rekeyed with just slight differences enabled Tiltman to recover completely both texts. Now Tiltman could add together, character by character, the corresponding cipher and message texts revealing for the first time a long stretch of the obscuring character sequence being generated by this German cipher machine.
John now passed the obscured characters to Bill Tutte and he recognized the bit patterns at a repetition of 41 had some significance and by Jan 1942, the codebreakers had deduced the working principle of the Lorenz machine, using nothing but the recovered keystream from the August 1941 message.
Decryption Machines
Several replica machines were built to aid the attack on Tunny (code word for Lorenz). The first was British Tunny built at Bletchley Park based on reverse engineering techniques and after that family of Robinsons were built but the issue was that the two papers synchronized were relatively slow.
The Colossus computers were developed and built by Tommy Flowers, of the Dollis Hill Post Office Research Station, using algorithms developed by W.T. Tutte and his team of mathematicians. Colossus proved to be efficient and quick against the twelve-rotor Lorenz SZ42 on-line teleprinter cipher machine.
It is after the D-Day landings in 1944, the first Lorenz machine was captured and was shown to the codebreakers of Bletchley Park and they were amazed to see the relatively small mechanical machine of which they had created the electronic equivalent. Lorenz was indeed a miraculous machine that would not have been broken if the mistake would not have been committed.
In Germany, examples of Lorenz may be seen at the Heinz Nixdorf MuseumsForum, a computer museum in Paderborn and the Deutsches Museum, a museum of science and technology in Munich. Two further Lorenz machines are also displayed at both Bletchley Park and The National Museum of Computing in the United Kingdom. Another example is also on display at the National Cryptologic Museum in the United States.
With this blog, we come to the end of our mini-series “Decrypting World War 2 communication”. We hope you loved all the blogs and find them interesting and scholarly. Do like, share and comment on our blogs and if you want to read something specific, you can suggest them through our email or you can even comment them down!
Happy Reading!
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