Shihāb al-Dīn Abū 'l-Abbās Aḥmad ibn ‘Alī ibn Aḥmad ‘Abd Allāh al-Qalqashandī al-Fazari or al-Qalqashandī (1355 or 1356 – 1418), was a medieval Egyptian encyclopedist, polymath and mathematician. A native of the Nile Delta, he became a Scribe of the Scroll (Katib al-Darj), or clerk of the Mamluk chancery in Cairo, Egypt. His magnum opus is the voluminous administrative encyclopedia Ṣubḥ al-Aʿshá.
Ṣubḥ al-Aʿshá fī Ṣināʿat al-Inshāʾ ('The Dawn of the Blind' or 'Daybreak for the Night-Blind regarding the Composition of Chancery Documents'); a fourteen-volume encyclopedia completed in 1412, is an administrative manual on geography, political history, natural history, zoology, mineralogy, cosmography, and time measurement. It has been called "one of the final expressions of the genre of Arabic administrative literature". Selections on "Seats of Government " and "Regulations of the Kingdom ", from Early Islam to the Mamluks' have been published separately. Ibn al-Durayhim (1312 - 1361), whose book on cryptology (now lost), described a section on cryptology from Al-Ṣubḥ al-aʿshā. Durayhim is also the source for an exposition on, and worked example of, cryptanalysis, including the use of tables of letter frequencies and sets of letters which cannot occur together in one word. The Ṣubḥ al-aʿshā was the first published discussion of the substitution and transposition of ciphers, and the first description of a polyalphabetic cipher, in which each plaintext letter is assigned more than one substitution.