Mind-Benders of Islamic History
The oldest known guide to code-breaking is 1,200 years old
Around 850 CE the Baghdad scholar al-Kindi wrote a manuscript on deciphering coded messages, describing frequency analysis — counting how often each letter turns up in a text to crack the cipher. It is the oldest surviving work of systematic codebreaking known, and it predates the next by roughly three centuries.
How we know
al-Kindi, c.801–873 CE, wrote 'A Manuscript on Deciphering Cryptographic Messages' c.850 CE — the first known description of frequency analysis and the oldest surviving systematic cryptanalysis, predating the next by about three centuries.
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