First of the Islamic philosophers — and the first man to break ciphers with mathematics.
Al-Kindi (c. 801–c. 873) was an Arab polymath of Baghdad's House of Wisdom, hailed as the father of Arab philosophy, whose Manuscript on Deciphering Cryptographic Messages invented cryptanalysis — including frequency analysis, the earliest known use of statistical inference, eleven centuries before the computer age.
Born in Kufa and educated in Baghdad, he oversaw the translation of Greek science into Arabic for Abbasid caliphs and then wrote hundreds of original treatises of his own, from metaphysics and optics to medicine, music theory and perfumes.
Abu Yusuf Ya'qub ibn Ishaq al-Kindi was born around 801 in Kufa to a family of the Kinda tribe, and rose in Baghdad under the caliphs al-Ma'mun and al-Mu'tasim. In the House of Wisdom he directed the translation of Aristotle, Euclid and Ptolemy into Arabic.
That encounter with Greek thought made him the first Islamic peripatetic philosopher: he argued that philosophy — 'the philosophy of the ancients' — was compatible with faith, and wrote on ethics, logic, cosmology and the nature of the soul. Some 260 treatises are attributed to him, though most are lost.
His most startlingly modern work is the 'Risala fi Istikhraj al-Mu'amma' — Manuscript on Deciphering Cryptographic Messages. In it he shows how to break a cipher by counting how often each symbol appears and matching the frequencies to the known frequencies of letters in the language.
It is the earliest known description of frequency analysis and the earliest known use of statistical inference — the foundation of all codebreaking, from the deciphering of enemy messages to modern cryptanalysis, eleven centuries before computers.
With Al-Khwarizmi, al-Kindi helped introduce the Indian decimal numerals to the Islamic world — the digits Europe would later call Arabic. He wrote on optics, including the geometry of mirrors and shadows, and devised a scale for quantifying the strength of drugs, an early step toward measured dosage.
He also wrote the earliest known treatise relating musical harmony to mathematics in the Arabic tradition. Late in life he fell from court favor; he died around 873 in Baghdad, leaving a reputation his successors called 'the philosopher of the Arabs'.
