Tokyo (AFP) – Napoleon Bonaparte ordered the wartime missive written in code, creating a puzzle that went unsolved for more than 200 years – until AI cracked it in a matter of hours.

Artificial intelligence is helping non-specialists unlock the secrets of historical sources, a trend described as a “turning point” in a field previously the preserve of scholars and dedicated hobbyists.

One new sleuth is Carter Church, a 27-year-old AI engineer who decrypted a 19th-century letter to one of Napoleon’s generals.

Without digital tools, the task could have taken weeks, but the latest model from ChatGPT-maker OpenAI broke the cipher in just six hours.

“What AI mostly brings is persistence,” Church told AFP, saying he felt “an unbelievable sense of satisfaction and excitement when I saw the result”.

The message from 1809 – detailing French and allied troops’ positions in two dozen lines of symbols, numbers and letters – had lain ignored in an online academic archive.

Because traditional, low-tech methods to crack ciphers are effective but time- and labour-intensive, historians “have more important problems to solve, so many ciphers like this often sit unattended”, said Church.

To find the solution, Church, who works at US cybersecurity firm SentinelOne, needed to learn “very little” about code-breaking techniques or the historical period.

He spent some evenings going over it, then consulted Japanese patent engineer Satoshi Tomokiyo, who maintains an online list of unsolved ciphers, to verify it.

“2026 will be remembered as a turning point for codebreaking of historical ciphers,” Tomokiyo wrote on his website Cryptiana, a go-to resource for the small but enthusiastic global community of amateur cryptographers.

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