GPT-6 Astra cracks 1941 Enigma, but Bitcoin's crypto remains secure

A German Army Enigma message from July 1941 has finally been deciphered. Carter Leffen used OpenAI's GPT-6 Astra this week to break it, and the archive that had listed the intercept as unsolved now records a solution.

The plaintext is almost mundane. Obtaining it took about 10 hours of model runtime, one borrowed phrase, and 14.8 million key checks.

How GPT-6 Astra Cracked the Enigma

The message carries the indicator MVUEH and is dated July 10, 1941. It originated from German Army traffic during the invasion of the Soviet Union. The decryption recovered the full machine setup, including rotor order II-V-III and 10 plugboard pairs.

A crib made the attack practical. Leffen used the repeated place name Rosenow from a related solved message, which reduced the search space to a workable size. GPT-6 Astra then searched archives, built an Enigma simulator, wrote cryptanalysis code, and tested competing keys in parallel.

“Please specify the route of march. I am in Rosenow, Rosenow. Immediate reply by radio,” Carter Leffen, site

Two independent implementations reproduced the plaintext. Frode Weierud's CryptoCellar archive has since logged the GPT-6 Astra Enigma break and credited Leffen by name.

Two days ago, GPT-6 Astra broke a yet unsolved German Army Enigma message from 1941. Amazingly Astra was able to autonomously:

– Search historical archives
– Compare uncertain letters
– Find contextual clues
– Build an Enigma simulator
– Write cryptanalysis code
– Run parallel… pic.twitter.com/m5usF56bsH

— Carter Leffen (@carterleffen) September 17, 2026

Where Human Guidance Still Mattered

The cipher itself is not the story. Allied codebreakers solved Enigma in the 1940s, and any modern machine can handle a three-rotor key space once a crib narrows it.

Nor was the break autonomous. Leffen set the goal, supplied the crib, and pushed the investigation forward, while the agents handled evidence, search, and review. The model executed tasks rather than making judgments.

This division of labor keeps appearing. In July, Anthropic said its model found weaknesses in encryption systems that researchers had not documented.

None of this, however, touches modern cryptography. Enigma is a 1930s rotor machine, and the mathematics protecting Bitcoin wallets is in a far harder category. The quantum threat to Bitcoin remains a live question.

Leffen offered his own measure of the effort. He said the website explaining the GPT-6 Astra Enigma solution required 99 times more work than the codebreaking itself.