AI Model Cracks a WWI German Radio Message Unsolved for 108 Years

A developer says an OpenAI model, GPT-6 Astra, has decoded an ADFGVX-encrypted German naval radio message transmitted in late November 1918. The plaintext warns that a British cruiser has reached Sevastopol and that an Allied squadron is following — dates that line up with British warship records. Cryptography watchers want independent proof before calling the cipher truly broken.

Key Takeaways

A developer says an OpenAI model, GPT-6 Astra, has decoded an ADFGVX-encrypted German naval radio message transmitted in late November 1918.
The plaintext warns that a British cruiser has reached Sevastopol and that an Allied squadron is following — dates that line up with British warship records.
Cryptography watchers want independent proof before calling the cipher truly broken.

AI synthesis4 sources1

An encrypted German radio message that defied codebreakers for more than a century has apparently been read for the first time. The message, transmitted in late November 1918, was protected with ADFGVX — the hand cipher the Imperial German Army introduced that year, which combines a 6x6 substitution square with a keyed columnar transposition.

The puzzle came from a well-known list of roughly 50 unsolved ciphers maintained by the German science blogging portal Scienceblogs.de, and was known to have been encrypted with ADFGVX. The developer who published the solution, who goes by Prinz, says the model — OpenAI's GPT-6 Astra — identified "TRUPPENVERSCHIEBUNG" (troop movement) as the keyword used to scramble the message, and posted the result on X.

The decrypted German text reads "EIN ENGLISCHER KREUZER EINLIEG X SEWASTOPOL X S4STEN X EIN GESCHWADER DER X ALLIIERTEN FOLGT 26STEN X" — in English, roughly: an English cruiser arrived at Sevastopol on the [2]4th, and an Allied squadron follows on the 26th. The letter X served as a separator in German naval traffic.

The reconstruction was checked against naval records. The British cruiser HMS Canterbury did arrive at Sevastopol, in Crimea, on 24 November 1918, which matches the cruiser date apart from a garbled digit that looks like a transmission typo. The Allied squadron date of 26 November also lines up with the historical record the developer consulted.

The model's explanation for why the message resisted earlier attempts is that codebreakers believed "TRUPPENVERSCHIEBUNG" only came into use as a key from 9 December 1918, and therefore never tried it on this earlier message. Commenters on Hacker News and Tom's Hardware read that differently: the anecdote suggests a known word was never tested rather than that the cipher itself was unbreakable, and the solve has not been independently verified.

It is not an isolated case. Days earlier, a developer at Bloomberg said GPT-6 Astra decrypted an 83-year-old Wehrmacht Enigma message in about ten hours. Whether or not this particular reconstruction survives scrutiny, the episode shows general-purpose models being pointed at work — historical cryptanalysis — that once required specialised, laborious human effort.