On September 15, 2026, cryptanalyst Carter Leffer reported that OpenAI’s GPT-6 Astra had successfully broken the German Army Enigma message MVUEH, sent on July 10, 1941, which had resisted decryption attempts for over two decades.
According to the Crypto Cellar Research website, the message was transmitted by a radio station with tactical callsign 2ny and received by the SS-Totenkopf Quartiermeister’s Ib radio station at 17:30, where it was logged as message Nr. 172. Despite years of effort by human cryptanalysts, the message remained unbroken.
What distinguishes this break is that GPT-6 Astra accomplished it largely autonomously. Leffer directed the AI to examine unbroken Enigma messages on the Crypto Cellar Research website, and the system independently selected MVUEH as the most promising target. GPT-6 Astra then developed its own Python and C++ software to simulate the Enigma machine and build a Bombe (the electromechanical device used to break Enigma).
The AI discovered that the plaintext of message Nr. 173, SIPVX—broken by cryptanalyst Alex Shovkoplyas in 2017—was nearly identical to MVUEH’s plaintext. Using the repeated place name “ROSENOW ROSENOW” as a crib (a known plaintext fragment), GPT-6 Astra conducted an exhaustive cryptanalytic attack that ultimately recovered the correct key and plaintext.
The break revealed complications that likely hindered earlier solution attempts. The MVUEH ciphertext contained transcription errors from the original message form, and the decryption showed that the Enigma’s left-hand wheel makes a turnover at the 72nd letter—a rare occurrence that substantially increases cryptanalytic difficulty.
Perhaps most remarkably, GPT-6 Astra accessed archival information beyond the Crypto Cellar website. According to the research logs, it referenced specific file numbers (RS 3–3/20a and RS 3–3/63b) from the German Bundesarchiv that contain related radio messages from the SS-Totenkopf Division’s logistics command. The source notes it remains unclear whether the AI successfully accessed digitized Bundesarchiv collections or obtained these files through other means.
Frode Weierud, the cryptanalyst documenting the break, observed that the work GPT-6 Astra completed in two days would typically require weeks or months of human research.
Key facts
- GPT-6 Astra broke the MVUEH Enigma message from July 10, 1941, which had resisted solution since 2005
- The AI independently developed Enigma simulator and Bombe software to conduct the break
- GPT-6 Astra identified a connection between MVUEH and the previously-broken message SIPVX and used the repeated place name ‘ROSENOW ROSENOW’ as a crib
- The MVUEH message contained transcription errors and involved a rare Enigma left-hand wheel turnover at the 72nd letter, both factors that likely prevented earlier breaks
- The task took GPT-6 Astra approximately two days and reportedly would require weeks or months of human cryptanalytic work