OpenAI's GPT-6 Astra decrypts a Nazi radio message in ten hours that went unsolved for 83 years

A Bloomberg developer claims to have cracked an Enigma-encrypted Wehrmacht message that went unsolved for more than 80 years, using OpenAI's GPT-6 Astra. The 82-character radio message from 1941 is from a soldier asking for marching orders.

On July 10, 1941, a German soldier used an Enigma machine to encrypt a short radio message. He reported being in the town of Rosenow, needed instructions for his march route, and requested an immediate radio reply. For 83 years, nobody managed to decrypt the 82-character message.

According to a detailed case study, Carter Leffen, a product development coach at Bloomberg LP in New York, has now done it using OpenAI's GPT-6 Astra. The "GPT-6 Astra Extra High" variant worked about ten hours on the problem, Leffen says, handling everything from searching historical archives and comparing uncertain letters to building an Enigma simulator, writing cryptanalysis code, running parallel experiments, testing competing keys, and cross-checking the results.

The message, tagged MVUEH, had been listed as unsolved in an archive of intercepted German army messages. The Enigma machine was one of the most important encryption devices of its era and was first broken in 1932 by Polish mathematician Marian Rejewski.

A known town name cracked the puzzle open

The Enigma machine offered roughly 159 quintillion possible daily settings. Brute-forcing all of them was never an option. Several approaches failed early on. Known keys from the same day didn't fit, and automated searches returned nothing useful.

The breakthrough came from an already-decrypted message sent the same day, which contained the town name "Rosenow" twice in a row. Leffen and his AI agents guessed that name might also appear in the unsolved message and used it as a search term.

A well-known Enigma weakness helped, too. The machine never encrypts a letter as itself, so if the plaintext contains an R, the ciphertext at that position can be anything except R. That alone let them rule out many positions right away.

At one position, everything lined up. The team calculated the matching machine settings, and the remaining 68 characters produced coherent German text, including "Sofort Funkantwort" ("immediate radio reply") and "Angabe des Marschweges" ("specify the march route"). A message header preserved separately in the archive confirmed the settings.

The decrypted text even contains typos that likely came from the radio operator himself, like "BTTE" instead of "BITTE" and "WASCHBBSCH" instead of what was probably "Waschbusch," the sender's name. Leffen sees these mistakes as evidence the decryption is authentic, because a fabricated result would more likely be error-free.

AI didn't do it alone, but Leffen says it wasn't much work

GPT-6 Astra and several specialized AI agents served as Leffen's tools throughout the process. Some analyzed historical sources, others wrote search programs, and others compared results against already-solved messages. Leffen set the goals and made the calls on how to proceed. By his own account, the codebreaking wasn't even the hard part. He says he put "99 times more effort into building the website that describes the problem and the solution than into actually cracking the code."

All code, search data, and a working 3D Enigma simulator are available for download on the project page. The provided packages verify the calculations and replicate the key search sequence, but they don't prove the message's historical identity or that the solution is the only possible one. The work builds on cryptanalytic contributions by Frode Weierud, Geoff Sullivan, and Olaf Ostwald. Whether the decryption holds up to independent review will depend on experts evaluating the published materials.