Lost Nazi cipher manuals regarding a code believed to be more advanced than the famous Enigma cipher have been discovered in Prague after greater than 80 years.
The unique wartime manuals for the key German cipher machine were discovered in archives.
Researchers say the documents relate to the Schlüsselgerät 41 (SG-41), a highly classified encryption device utilized by the German Wehrmacht in the ultimate years of the war.
The papers were uncovered during an educational investigation by cryptography researchers Eugen Antal, Carola Dahlke and Robert Jahn. They were present in two Czech institutions; the Military History Institute in Prague and the country’s Security Services Archive.
The files include operating instructions, encryption rules and original key tables used through the closing weeks of the war in 1945.
As with Enigma, British cryptographers did reach breaking some SG-41 as a consequence of errors by the German operators of the machines in October 1944, but didn’t fully understand what they were coping with until the ultimate months of the war when machines were captured and analysed.
Nevertheless, historians say there are still remaining questions on how the SG-41 operated as a consequence of the shortage of surviving documentation – ones that these latest documents can answer.
‘The recently found documents provide insightful information on several levels,’ the researchers, led by Eugen Antal of the Slovak University of Technology in Bratislava, wrote.
‘Firstly, the extent of cryptanalysis in Central Europe and its influence becomes clearer in a broad historical context, because the elaborate Czechoslovak investigations weren’t known to this extent.
‘Secondly, for the primary time it is feasible to view complete instructions on use the machine in the sphere. Especially, the very precise instructions on use and maintain the machine and solve mechanical problems are very interesting on this respect.
‘The documents on key design are particularly exciting, confirming the previously assumed cipher operation and answering other previously unanswered questions.’
Through the Second World War, the German military relied heavily on encrypted communications.
The Enigma machine became one of the best known of those systems after Allied codebreakers succeeded in deciphering its supposedly unbreakable code.
The SG-41, designed in 1941 by German engineer Fritz Menzer, was widely thought to be a more sophisticated device.
Unlike Enigma, which used electrically powered rotors, the SG-41 relied on a totally mechanical system based on a ‘pin-and-lug’ principle first developed by Swedish cryptography pioneer Boris Hagelin.
The machine used six rotating wheels fitted with movable pins. These pins might be set to lively or inactive positions in line with every day encryption settings.
When an operator typed a letter on the keyboard, the interior mechanism analysed the pin positions and generated a pseudo-random number. That number was added to the unique letter to supply the encrypted text. To decrypt the message, the receiving machine needed to be configured identically so the identical value might be subtracted.
The research suggests the SG-41 incorporated several innovations that made it difficult to analyse.
One was an irregular stepping mechanism. In lots of cipher machines, internal wheels rotate in predictable sequences.
Within the SG-41, nonetheless, the wheels influenced one another’s movement, creating irregular patterns that complicated attempts to discover repeating sequences in encrypted messages.
A second feature was a ‘negation’ function built into the sixth wheel. When activated, it reversed the state of pins on the opposite wheels, immediately changing the machine’s behaviour and increasing its unpredictability.
Together, these features made the SG-41 one of the crucial advanced mechanical cipher systems developed through the war.
On the Military History Institute, researchers situated a folder titled Wehrmacht Encryption Guidelines containing several original German documents in good condition. Amongst them was the official operating manual for the SG-41 and its variant, the SG-41Z, dated 2 September, 1944
The archive also contained a field manual for operators, a regulation often known as Vorschrift Nr. 90 explaining how encryption keys were generated, and monthly key tables used between 16 and 31 March, 1945.
These tables are considered particularly worthwhile as they reveal how the machine was configured through the final weeks of the conflict.
Researchers also found a 41-page document written in Czech describing the machine’s technical design together with a post-war cryptanalysis carried out by Czechoslovak intelligence. The manuals also make clear the machine’s physical design.
Although intended for field use, the SG-41 was removed from lightweight. The device itself weighed around 10kg and about 17kg when fully assembled with its protective lid and base plate.
To make it usable in the sphere, German engineers developed a padded wood support often known as a Knieplatte, or “knee plate”. This allowed operators to rest the machine on their knees while typing messages, in a fashion just like using a notebook computer.
The board is also converted right into a backpack frame so soldiers could carry the heavy device during transport.
The newly found documents also make clear how the machine’s complicated key system worked.
Operators used a monthly table containing 26 possible pin configurations, corresponding to the letters of the alphabet.
Every day they received a six-letter every day key that determined which configuration from the table can be used for every of the machine’s six wheels.
Additional settings included a ‘camouflage key’, designed to disguise the starting position of messages, and a two-digit identification number assigned to every communication station.
Before sending a message, operators needed to set all of those values appropriately.
Despite the invention, several questions remain unanswered – as few working machines exist today, with a few of one of the best examples considered possibly languishing in Russian state archives. In consequence, manuals like these might be key to carrying out simulations to get a feel for a way th SG-41 actually worked.
‘Unfortunately, there are only a number of intact machines on the planet,’ the authors write. ‘Most of them are unlikely to be in perfect working order, as regular maintenance of the mechanics is completely essential.
‘Cryptanalytic studies comparable to these can subsequently only be carried out with the assistance of simulations today.’
For now, the Prague discovery represents one of the crucial significant breakthroughs in understanding the SG-41.
After a long time of mystery, researchers say the forgotten documents are finally helping to disclose how one in every of the Second World War’s most complex cipher machines actually worked.
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