GPT-6 Astra breaks the 1941 MVUEH Enigma message, unsolved since 2005; Claude Opus 5 breaks a second one (FMNGI) days later
In September 2026 Carter Leffen, using GPT-6 Astra, broke MVUEH, an 82-letter German Army Enigma message of July 10, 1941 listed among the unbroken messages on Frode Weierud's CryptoCellar site, where "since 2005, the message has resisted all attempts to break it". Astra chose the target, built its own Enigma simulator and Bombe in Python and C++, and found the key with a ROSENOW ROSENOW crib; Weierud confirmed the solution. On Sept 20–21 Jack Willis used Claude Opus 5 to break a second listed message, FMNGI (July 31, 1941).
Key facts
- Message: MVUEH, German Army Enigma, July 10, 1941, from a radio station with callsign 2ny; 82 letters
- Weierud: 'Since 2005, the message has resisted all attempts to break it.' 'After Carter Leffen sent the MVUEH break details, it was immediately clear he had found the correct key and plaintext.'
- Leffen (a product development coach at Bloomberg LP, per The Decoder) gave the directive; Astra picked MVUEH as the most promising target, wrote the simulator/Bombe code and used the crib ROSENOW ROSENOW
- Effort: about 10 hours of direct Astra work over ~2 days (Leffen via The Decoder; Weierud: 'what it has achieved in two days would take a human researcher weeks or even months')
- Plaintext (translated): a request to specify the route of march, 'I am in Rosenow, Rosenow', immediate reply by radio
- The plaintext matched message Nr. 173 (SIPVX) but under a different key (wheel order 253 vs 512)
- Second break: Nr. 285 FMNGI (July 31, 1941, to the quartermaster of the SS-Totenkopf Division) broken with Claude Opus 5 by Jack Willis; key found Sept 20, 2026 in a 13 min 28 s search on an Apple M2, crib XHARTJENSTEINX; CryptoCellar dates the break Sept 21
- Bruce Schneier (Sept 22): 'This is pretty amazing'
What happened
Weierud's CryptoCellar lists a handful of German Wehrmacht Enigma messages that have never been broken. Leffen pointed GPT-6 Astra (with several parallel agents) at the list. The model studied the archival scans, picked MVUEH, wrote an Enigma simulator and a Bombe-style search, and broke it with a place-name crib. Weierud checked the key and plaintext and published the break on his site. A few days later a second listed message, FMNGI, fell to Claude Opus 5 working with a Go cryptanalysis workbench supplied by Jack Willis. Claude also transcribed the scanned message form itself.
Why it matters
A small, verifiable case of frontier agents doing end-to-end expert research (target selection, archival reading, tool building, search) on a problem that human hobbyists had worked on for two decades. The human did little more than set the goal.
Changelog
- 2026-09-30: created (sweep 2026-09-29, HN 737 points)
Related events
- OpenAI releases GPT-6 Astra, its first GPT-6 model ★★★★★
- Anthropic releases Claude Opus 5 — near-Fable-5 intelligence at half the price ★★★★
Sources (6)
- officialCryptoCellar (Frode Weierud): The MVUEH Break
- officialCryptoCellar (Frode Weierud): The FMNGI Break (Claude Opus 5)
- pressThe Decoder: GPT-6 Astra decrypts a Nazi radio message in ten hours
- pressSchneier on Security: GPT-6 Astra breaks an old Enigma message
- pressThe Decoder / mixed-news: GPT-6 Astra cracks a 1941 Enigma message unsolved since 2005
- discussionHacker News discussion (737 points)
id: 2026-09-17-gpt-6-astra-breaks-mvueh-enigma-message · updated 2026-09-30 · open in the interactive timeline