Developer uses OpenAI GPT-6 Astra to crack 83-year-old German military cipher

A technology developer has successfully cracked an 83-year-old German military radio message, encrypted by an Enigma machine, utilizing OpenAI's GPT-6 Astra. The 82-character encrypted message, sent in 1941, requested march route instructions from Rosenow, Germany, and had remained uncracked for over eight decades.

Carter Leffen, a product development coach at Bloomberg LP, employed the "Extra High" version of GPT-6 Astra, dedicating approximately 10 hours to solve the message. The process involved retrieving historical archives, comparing potentially erroneous characters, constructing an Enigma simulator, writing cryptanalysis code, conducting parallel experiments, and testing keys alongside verifying results.

The breakthrough came from another message sent the same day and already decrypted, which mentioned "Rosenow" twice. Leffen and his AI hypothesized that this location might also appear in the unsolved cipher. A known weakness of the Enigma machine—that a letter never encrypts to itself—helped rapidly eliminate a vast number of possible key combinations.

Ultimately, the correct settings were identified, and the remaining 68 characters were decoded into coherent German text, including phrases like "Sofort Funkantwort" (immediate radio response) and "Angabe des Marschweges" (statement of march route). The presence of spelling errors in the original message further supports the authenticity of the decryption.

Leffen emphasized that the AI functionalities served as tools, with him setting the objectives. A significant portion of his effort was dedicated to creating and explaining the project's website rather than the decryption itself. The published code and data allow for verification of the findings and reproduction of the process.