I used GPT-6 Astra to break an unsolved cipher to one of Napoleon's generals that had gone unread for 217 years.
What makes this impressive isn't actually the codebreaking, but that Astra completed the entire multi-modal workflow in ~6 hours from a single image and goal.
1/6🧵
Carter Church
@CarterWChurch
The letter to Marshal Marmont opens with one line of plain French, then 24 rows of numbers, letters and invented symbols.
It sat on Cryptiana's Unsolved Historical Ciphers list for decades. Last week, Satoshi Tomokiyo officially confirmed this solution and marked it solved.
2/6
It sat on Cryptiana's Unsolved Historical Ciphers list for decades. Last week, Satoshi Tomokiyo officially confirmed this solution and marked it solved.
2/6
5:27 AM UTC · Sep 30, 2026 · 225K Views
223760133
Carter Church
@CarterWChurch
From one prompt and one image, Astra:
- Transcribed 1,300 hand-drawn signs.
- Found a partial key previously unconnected to this letter
- Cracked the rest with its own simulated-annealing solver.
- Cross-referenced other surrounding letters to correct the published date.
3/6
- Transcribed 1,300 hand-drawn signs.
- Found a partial key previously unconnected to this letter
- Cracked the rest with its own simulated-annealing solver.
- Cross-referenced other surrounding letters to correct the published date.
3/6
5:27 AM UTC · Sep 30, 2026 · 216.7K Views
22166762
Carter Church
@CarterWChurch
It's a war briefing sent two weeks before Austria invaded. It also fills a gap:
Napoleon's actual order in his 1865 memoir breaks off mid-sentence: Marmont mustn't be held back by "a handful of ..."
This letter contains the remainder, intact: "a gathering of rabble."
4/6
Napoleon's actual order in his 1865 memoir breaks off mid-sentence: Marmont mustn't be held back by "a handful of ..."
This letter contains the remainder, intact: "a gathering of rabble."
4/6
5:27 AM UTC · Sep 30, 2026 · 190K Views
61649342
Carter Church
@CarterWChurch
Astra's multi-modal execution is what's actually impressive in this.
The cipher itself isn't difficult, and cryptographers could have cracked this easily given the time/energy. But, the work to transcribe, catalog, translate, then crack is involved and multi-disciplinary.
5/6
The cipher itself isn't difficult, and cryptographers could have cracked this easily given the time/energy. But, the work to transcribe, catalog, translate, then crack is involved and multi-disciplinary.
5/6
5:27 AM UTC · Sep 30, 2026 · 148.6K Views
21453032
Carter Church
@CarterWChurch
Every field has an unsolved backlog of niche problems that specialists don't have the bandwidth to tackle. The takeaway here is that the people shortening those lists will increasingly be outsiders who were simply curious.
Full Writeup: carter.church/writeups/the-l…
6/6
Full Writeup: carter.church/writeups/the-l…
6/6
carter.church
Breaking the Marmont Cipher, 1809
A letter to General Marmont, listed as unsolved and known only from a mis-dated 1969 reproduction, read in full: redated to March 1809, placed two weeks before Austria invaded Bavaria, and checked against the war that followed.
5:27 AM UTC · Sep 30, 2026 · 145.1K Views
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