MontImageMedia - In Memoriam
The Lorenz SZ42 machine with its covers removed.
The Lorenz SZ40, SZ42A and SZ42B were German rotor stream cipher machines used by the German Army during World War II. They were developed by C. Lorenz AG in Berlin and the model name SZ was derived from Schlüsselzusatz, meaning cipher attachment. The instruments implemented a Vernam stream cipher.
British cryptographers, who referred to encrypted German teleprinter traffic as Fish, dubbed the machine and its traffic Tunny.
The SZ machines were in-line attachments to standard Lorenz teleprinters. An experimental link using SZ40 machines was started in June 1941. The enhanced SZ42 machines were brought into substantial use from mid-1942 onwards for high-level communications between the German High Command in Berlin, and Army Commands throughout occupied Europe. The more advanced SZ42A came into routine use in February 1943 and the SZ42B in June 1944.
Wireless telegraphy (WT) rather than land-line circuits was used for this traffic. These non-Morse (NoMo) messages were picked up by Britain's Y-stations at Knockholt and Denmark Hill and sent to Government Code and Cypher School at Bletchley Park (BP). Some were deciphered using hand methods before the process was partially automated, first with Robinson machines and then with the Colossus computers. The deciphered messages made an important contribution to Ultra military intelligence.
On 30 August 1941, a message of some 4,000 characters was transmitted from Athens to Vienna. However, the message was not received correctly at the other end, so (after the recipient sent an unencoded request for retransmission, which let the codebreakers know what was happening) the message was retransmitted with the same key settings (HQIBPEXEZMUG); a forbidden practice. Moreover, the second time the operator made a number of small alterations to the message, such as using abbreviations, making the second message somewhat shorter. From these two related ciphertexts, known to cryptanalysts as a depth, the veteran cryptanalyst Brigadier John Tiltman in the Research Section teased out the two plaintexts and hence the keystream. Then, after three months of the Research Section failing to diagnose the machine from the almost 4,000 characters of key, the task was handed to mathematician Bill Tutte. He applied a technique that he had been taught in his cryptographic training, of writing out the key by hand and looking for repetitions. Tutte did this with the original teleprinter 5-bit Baudot codes, which led him to his initial breakthrough of recognising a 41 character repetition. Over the following two months up to January 1942, Tutte and colleagues worked out the complete logical structure of the cipher machine. This remarkable piece of reverse engineering was later described as "one of the greatest intellectual feats of World War II".
After this cracking of Tunny, a special team of code breakers was set up under Ralph Tester, most initially transferred from Alan Turing's Hut 8. The team became known as the Testery. It performed the bulk of the subsequent work in breaking Tunny messages, but was aided by machines in the complementary section under Max Newman known as the Newmanry.
Several complex machines were built by the British to aid the attack on Tunny. The first was the British Tunny. This machine was designed by Bletchley Park, based on the reverse engineering work done by Tiltman's team in the Testery, to emulate the Lorenz Cipher Machine. When the pin wheel settings were found by the Testery, the Tunny machine was set up and run so that the messages could be printed.
A family of machines known as "Robinsons" were built for the Newmanry. These used two paper tapes, along with logic circuitry, to find the settings of the chi pin wheels of the Lorenz machine. The Robinsons had major problems keeping the two paper tapes synchronized and were relatively slow, reading only 2000 characters per second.
The most important machine was the Colossus of which ten were in use by the war's end. They were the world's first large-scale programmable electronic digital computers, the first becoming operational in December 1943. These were developed by senior engineer Tommy Flowers at the Post Office Research Station at Dollis Hill in London. Like the later ENIAC of 1946, Colossus did not have a stored program, and was programmed through plugboards and jumper cables. It was faster, more reliable and more capable than the Robinsons, so speeding up the process of finding the Lorenz chi pin wheel settings. Since Colossus generated the putative keys electronically, it only had to read one tape. It did so with an optical reader which, at 5000 characters per second, was driven much faster than the Robinsons' and meant that the tape travelled at almost 30 miles per hour (48 km/h). This, and the clocking of the electronics from the optically read paper tape sprocket holes, completely eliminated the Robinsons' synchronisation problems.
The Lorenz SZ42 machine with its covers removed.
The Lorenz SZ40, SZ42A and SZ42B were German rotor stream cipher machines used by the German Army during World War II. They were developed by C. Lorenz AG in Berlin and the model name SZ was derived from Schlüsselzusatz, meaning cipher attachment. The instruments implemented a Vernam stream cipher.
British cryptographers, who referred to encrypted German teleprinter traffic as Fish, dubbed the machine and its traffic Tunny.
The SZ machines were in-line attachments to standard Lorenz teleprinters. An experimental link using SZ40 machines was started in June 1941. The enhanced SZ42 machines were brought into substantial use from mid-1942 onwards for high-level communications between the German High Command in Berlin, and Army Commands throughout occupied Europe. The more advanced SZ42A came into routine use in February 1943 and the SZ42B in June 1944.
Wireless telegraphy (WT) rather than land-line circuits was used for this traffic. These non-Morse (NoMo) messages were picked up by Britain's Y-stations at Knockholt and Denmark Hill and sent to Government Code and Cypher School at Bletchley Park (BP). Some were deciphered using hand methods before the process was partially automated, first with Robinson machines and then with the Colossus computers. The deciphered messages made an important contribution to Ultra military intelligence.
On 30 August 1941, a message of some 4,000 characters was transmitted from Athens to Vienna. However, the message was not received correctly at the other end, so (after the recipient sent an unencoded request for retransmission, which let the codebreakers know what was happening) the message was retransmitted with the same key settings (HQIBPEXEZMUG); a forbidden practice. Moreover, the second time the operator made a number of small alterations to the message, such as using abbreviations, making the second message somewhat shorter. From these two related ciphertexts, known to cryptanalysts as a depth, the veteran cryptanalyst Brigadier John Tiltman in the Research Section teased out the two plaintexts and hence the keystream. Then, after three months of the Research Section failing to diagnose the machine from the almost 4,000 characters of key, the task was handed to mathematician Bill Tutte. He applied a technique that he had been taught in his cryptographic training, of writing out the key by hand and looking for repetitions. Tutte did this with the original teleprinter 5-bit Baudot codes, which led him to his initial breakthrough of recognising a 41 character repetition. Over the following two months up to January 1942, Tutte and colleagues worked out the complete logical structure of the cipher machine. This remarkable piece of reverse engineering was later described as "one of the greatest intellectual feats of World War II".
After this cracking of Tunny, a special team of code breakers was set up under Ralph Tester, most initially transferred from Alan Turing's Hut 8. The team became known as the Testery. It performed the bulk of the subsequent work in breaking Tunny messages, but was aided by machines in the complementary section under Max Newman known as the Newmanry.
Several complex machines were built by the British to aid the attack on Tunny. The first was the British Tunny. This machine was designed by Bletchley Park, based on the reverse engineering work done by Tiltman's team in the Testery, to emulate the Lorenz Cipher Machine. When the pin wheel settings were found by the Testery, the Tunny machine was set up and run so that the messages could be printed.
A family of machines known as "Robinsons" were built for the Newmanry. These used two paper tapes, along with logic circuitry, to find the settings of the chi pin wheels of the Lorenz machine. The Robinsons had major problems keeping the two paper tapes synchronized and were relatively slow, reading only 2000 characters per second.
The most important machine was the Colossus of which ten were in use by the war's end. They were the world's first large-scale programmable electronic digital computers, the first becoming operational in December 1943. These were developed by senior engineer Tommy Flowers at the Post Office Research Station at Dollis Hill in London. Like the later ENIAC of 1946, Colossus did not have a stored program, and was programmed through plugboards and jumper cables. It was faster, more reliable and more capable than the Robinsons, so speeding up the process of finding the Lorenz chi pin wheel settings. Since Colossus generated the putative keys electronically, it only had to read one tape. It did so with an optical reader which, at 5000 characters per second, was driven much faster than the Robinsons' and meant that the tape travelled at almost 30 miles per hour (48 km/h). This, and the clocking of the electronics from the optically read paper tape sprocket holes, completely eliminated the Robinsons' synchronisation problems.