Lorenz key machine

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SZ 42 without hood, approx. 1943, on the right Lorenz telex T32 , approx. 1936, (Bletchley Park, 2007)

The Lorenz key machine (own name: key addition ; in short: SZ with the models SZ 40 and SZ 42 as well as SZ 42a , SZ 42b and SZ 42c ; German code name of the radio teleprinter systems operated with it: " Sägefisch "), from the British code breakers in Bletchley Park with the code name Tunny (German: " Tunfisch "), later also called Lorenz Machine , is a rotor key machine from the Second World War . It was developed by C. Lorenz AG in Berlin on behalf of the German military command and was used by the Wehrmacht for secret communication using encrypted telex connections .

history

Sound sample of a radio teletype transmission.
Sound sample of a standard Morse transmission.
The twelve “cam wheels” of the key extension are located as the cryptographic heart of the machine for security reasons in a separate, lockable housing that is closed on all sides.

The purpose was to simplify and automate the machine encryption compared to the laboriously operated Enigma machine and to achieve significantly higher message volumes and transmission speeds than was possible using hand-keyed Morse code . For this purpose as an accessory to a been Telegraph of Lorenz of Key Accessories (SZ) developed. As usual with teleprinters, the Baudot-Murray code (CCITT-2) with 5  bits was used for the transmission of 32 characters. The binary representation is particularly suitable for the binary addition of a pseudo-random key , which cryptographically implements the function of a mixer :

Secret text = plain text XOR key

The device was after the year 1940, in which it was developed, S chlüssel- Z usatz 40 , shortly SZ 40 called. Cryptographically improved (but almost identical looking) successor models were designated as SZ 42, SZ 42a, SZ 42b and SZ 42c.

The Germans gave the encrypted telex traffic and the shortwave frequency range between 4  MHz and 7.5 MHz the code name "sawfish". (This applies not only to the traffic running through the SZ, but also to traffic that was handled by the "secret writers" from Siemens & Halske , i.e. T52 or later also T43 .) From deciphered Enigma radio messages in which " Sawfish ”was the topic, the British learned about the German innovation. They followed this requirement and from then on referred to German telex traffic with the English code name Fish . Special teleprinter routes, such as from the Wehrmacht's telecommunications hub in Strausberg (near Berlin) to Commander-in-Chief West (OB West) in Paris or from Königsberg to Riga to the High Command of Army Group North , they gave special "fish names" such as Jellyfish ( jellyfish ) or Whiting ( Whiting ), see also map under web links .

An important advantage of the key teletypewriter (SFM) was that plain text was entered on the sender end , which was then output as plain text on the recipient end. The user himself did not come into contact with the key text , which was seen as a great advantage. However, the machine was too heavy and too big to replace the easily portable Enigma. The Lorenz key addition was used for the secret radio communication of high and highest, mostly fixed command posts, such as the High Command of the Army (OKH) and Army High Command (AOK).

Exhibits

It is believed that around 200 Lorenz machines were in use across Europe during the war. As far as is known, only four of them survived.

construction

The differently set switching cams, i.e. the adjustable pins, here the Spring-Caesar wheels No. 3 and 4

For the encryption , the key used additional twelve "cam-bearing wheels" (abbreviated to "cam wheels"), which are numbered from 1 to 12, thus rotating rollers with irregularly settable pins. These form three functional groups. The first group consists of five wheels, each with a different number of cams (indicated in brackets): wheel 1 (43), wheel 2 (47), wheel 3 (51), wheel 4 (53) and wheel 5 (59). Depending on the next two wheels, wheel 6 (37) and wheel 7 (61), the first five wheels turn or are temporarily stopped ("irregular progression"), while the last five wheels, wheel 8 (41), wheel 9 (31), wheel 10 (29), wheel 11 (26) and wheel 12 (23) can be turned forward by one step for each individual character to be encrypted ("regular progression").

According to the German terminology of the time , a substitution , i.e. the replacement of characters by others, was called "Caesar". At that time, the term was given a wider definition than is common today when speaking of Caesar encryption . Unlike today, any monoalphabetic substitution and even a polyalphabetic substitution were called "Caesar" for short. With this nomenclature, the first five wheels (called “Spri Wheels”), as described in the original manual, cause a “Spring Caesar” and the last five (called “Spa Wheels”) cause a “Column Caesar”.

Wheel number 1 2 3 4th 5 6th 7th 8th 9 10 11 12
Number of cams 43 47 51 53 59 37 61 41 31 29 26th 23

The first group (wheels 1 to 5) and the third group (wheels 8 to 12) together generate the “pseudo-random” key for the subsequent Vernam substitution of the 5-bit code of each individual character. Wheel 7 moves the second group “regularly” and controls wheel 6, which in turn moves the first group of rollers “irregularly”. All rollers can be "programmed" as required using the cams. In addition, the adjustable starting position of all rollers allows an individual twelve-digit key . The machine has a period greater than 10 19 . According to Tony Sale (1931–2011), who led the reconstruction and rebuilding of the legendary Colossus computer , the world's first programmable mainframe computer to work with electron tubes , at the National Computer Museum of Great Britain (TNMOC) , the machine-generated pseudo-random key generation of the Lorenz Machine, however, “ more pseudo than random” .

Procedure

Perforated tape for 5  bits with
"ZCZC WIKIPEDIA 1234567890 NNNN"
Reading board 40 for the telex message key sheet (message board)

For encryption, the plain text is entered via the keyboard of the key suffix (SZ). Each of the five bits of each plaintext character is exclusively-or-combined (mixed) with a “pseudo-random” key bit generated by the machine . The result, i.e. the ciphertext character generated in this way, is sent and decrypted again on the recipient side using the key addition there . Since the contravalence function (XOR operation) used for mixing is involutorial ( self-inverse ), it is sufficient to relink the received ciphertext character with the key character in order to recover the decrypted original plaintext character as the result.

To do this, it is imperative that the sending and receiving SZ are set identically, that is, all cams of the twelve key wheels ("basic key") and their starting positions ("saying key") are exactly the same. The cams of the wheels were changed only relatively rarely. Before the summer of 1944, the cams of the Spri wheels were only changed monthly or quarterly, those of the Spa wheels were changed monthly and only the cams of the two command wheels were set differently every day. This usually happened in the morning around 9 o'clock, since experience has shown that there was little telex traffic at this time ("quiet time"). If necessary, the sender and recipient exchanged briefly and then simultaneously switched to the new daily key known to them with the help of secret basic key sheets .

The starting position of the twelve wheels, i.e. the key to the phrase, had to be chosen individually for each telex. In order for the sender to be able to secretly inform the recipient of his freely chosen key, he used a special reading board, of which - as far as known - only two copies survived the war. One of them (see picture) is in the National Computer Museum (TNMOC) in Bletchley Park . With the help of the reading table, each position of one of the twelve wheels, for example position 01 for wheel 1, is assigned a secret letter, in the example the letter H. Overall, the starting position is 01-13-34-06-51-01-56-21-23 -07-15-11 as HQIBPEXEZMUG encrypted . These twelve letters are placed in front of the ciphertext and serve as important information for the recipient to know which starting position he has to set the twelve wheels of his handset to in order to read the telex correctly.

Decipherment

During the test on August 30, 1941, a four-thousand-character message was sent twice with the same key, i.e. the identical starting position of all twelve key wheels, i.e. encrypted with the same key on the Wehrmacht's radio telex line Vienna-Athens. The recipient had asked the sender to resend the message after not receiving it correctly the first time. The German intelligence soldier now made two serious mistakes. First, he used the same key HQIBPEXEZMUG as the first time, which was forbidden. And secondly, he now slightly shortened the text. So he replaced the word "SPRUCHNUMMER" at the very beginning with "SPRUCHNR.", Which led to a different ciphertext for the rest of the text, while the plaintext was otherwise the same. The British noticed this "plaintext-plaintext compromise" and used it to decipher it.

The British cryptanalyst John Tiltman was able to determine the slightly “phase-shifted” and almost identical two plaintexts in weeks of manual labor . To do this, he calculated the difference between the two intercepted radio messages and tried to use probable words . This enabled him to reconstruct not only the plaintext, but above all a section of the "pseudo-random" key with a length of four thousand characters. This ultimately led to the exposure of the logical structure of the key addition.

With the knowledge of the structure and mode of operation of the similarly working "secret writer" described in open patents , the T52 cipher telex from Siemens (British code name: Sturgeon ; German  " Stör " ), the young mathematician William Thomas Tutte succeeded in determining the number and periods of each Find Out Key Accessory Key Wheels. In January 1942, the entire structure was cleared up, including the location of the cams (switch pins) on the wheels. Now "only" had to find the correct starting position of the key wheels. The cracking by hand under Ralph Tester in the Testery took about four days. Until then, the reports may have been out of date. Therefore the aim was to automate the process. This was done under the direction of Max Newman in Newmanry neighboring the Testery , also on the premises of Bletchley Park. It was here that the then top-secret and now world-famous Colossus was developed, which was successfully used against the SZ 42 from February 1944.

literature

Web links

Commons : Lorenz machine  - album with pictures, videos and audio files

Individual evidence

  1. Lorenz SZ-40/42 in the Crypto Museum (English). Retrieved January 23, 2017.
  2. Tunny gallery in the TNMOC (English). Retrieved January 23, 2017.
  3. The key addition 42 . P. 10.
  4. ^ James A. Reeds, Whitfield Diffie, J.V. Field: Breaking Teleprinter Ciphers at Bletchley Park: An edition of I.J. Good, D. Michie and G. Timms: General Report on Tunny with Emphasis on Statistical Methods (1945). Wiley-IEEE Press, 2015, p. 14. ISBN 978-0-470-46589-9 .
  5. ^ The Lorenz Cipher (English). Retrieved February 1, 2017.
  6. ^ Friedrich L. Bauer: Decrypted Secrets, Methods and Maxims of Cryptology . Springer, Berlin 2007 (4th edition), p. 168, ISBN 3-540-24502-2 .
  7. James A. Reeds, Whitfield Diffie , JV Field: Breaking Teleprinter Ciphers at Bletchley Park: An edition of I. J. Good , D. Michie and G. Timms: General Report on Tunny with Emphasis on Statistical Methods (1945). Wiley - IEEE Press, 2015, p. 19 (English). ISBN 978-0-470-46589-9 .
  8. Friedrich L. Bauer: Deciphered secrets. Methods and maxims of cryptology. 3rd, revised and expanded edition. Springer, Berlin a. a. 2000, p. 388.