The machines of Lorenz SZ 40 and SZ 42 ( Schlüsselzusatz , meaning “quantified enclosure”) were German machines of coding used during the Second world war for the sendings by Téléscripteur. The British cryptographes , which referred in a general way to flow of the coded messages German envoys by teleprinter under name Fish (Poisson), named the machine and its messages Tunny (Tunas). While the fame machine Enigma was used for the infantry, the machine of Lorenz was intended for the high level communications, which could be pressed on this heavy apparatus, its operator and of the dedicated circuits. The machine itself measured 51 Cm × 46 cm × 46 cm and accompanied the teleprinters Lorenz standards. These machines applied a method of Chiffrement of flow.

Operation

The teleprinters of then treated each character, generally quantified with the Code Baudot or an equivalent process, like 5 bits in Parallèle on 5 lines. The machine of Lorenz produced groups of five pseudo-random bits to combine by the operator OR exclusive with the clear text. The pseudo-random bits were generated by ten “wheels cryptographic”, five of them regularly turning, named the wheels $\backslash \; chi$ ( Chi ) and five others with the irregular race, named the wheels $\backslash \; psi$ ( Psi ). The step of rotation of the wheels $\backslash \; psi$ depended on two other wheels, called the “driving wheels”. Except its irregular driving role of five wheels (which, either advanced together, or remained together), the machine of Lorenz constitutes a pseudo-random generator with five parallel flows; no other interaction exists between the five lines. The numbers of “points” on all the wheels were first between them.

These machines were same vein as those proposed in first by the Colonel Parker Hitt of the Armée with the United States of America at the time of the First World War.

Cryptanalyse

The cryptanalystes of Bletchley Park included/understood the operation of the machine as of January 1942 without never to have seen only one specimen of it. That was possible because of an error made by a German operator. The August 30th 1941, a message of 4  000 characters was transmitted; however, the message not having been received correctly with the other end, this one was retransmis with the same key (a practice formally prohibited by the procedure). Moreover, the second time the message was transmitted with some modifications, like the use of certain abbreviations. Starting from these two quantified texts, John Tiltman was able to reconstitute at the same time the plaintext and coding. According to coding, all the structure of the machine was rebuilt by W.T. Tutte.

The transmissions “Tunny” were intercepted with Knockholt in the Kent, before being sent to Bletchley Park.

Several complex machines were worked out by the British to attack this type of messages. The first, of the family known under the name of “Heath Robinson S” , used paper bands circulating quickly along logical electronic circuits, to decipher quantified flow.

The following one was the computer Colossus, the numerical first Ordinateur electronic of the world (however, like ENIAC, it did not comprise any embarked software and was programmed via plug-in charts, of switches and panels of connection). It was at the same time faster and more reliable than the “Heath Robinsons” ; its use made it possible to the British to read a great part of the communications of the type “Tunny” .

Service of Swedish cryptanalyse, the FRA ( Forsvarets Radioanstalt ), had also broken the system of Lorenz; their solution was found in April 1943.

See too

• Sturgeon

• Sigaba ( the United States of America )
• Typex ( the United Kingdom )