Hildegard of Bingen used her own alphabet to write letters.Giovanni Fontana (engineer), wrote two encrypted books.Giovan Battista Bellaso, Italian cryptologist.Best known for developing the ' Bazeries Cylinder' and his influential 1901 text Les Chiffres secrets dévoilés ('Secret ciphers unveiled'). Étienne Bazeries, French, military, considered one of the greatest natural cryptanalysts.Giovanni Battista della Porta, author of a seminal work on cryptanalysis.Leone Battista Alberti, polymath/universal genius, inventor of polyalphabetic substitution (more specifically, the Alberti cipher), and what may have been the first mechanical encryption aid.Charles Babbage, UK, 19th century mathematician who, about the time of the Crimean War, secretly developed an effective attack against polyalphabetic substitution ciphers.The list of ciphers in this work included both substitution and transposition, and for the first time, a cipher with multiple substitutions for each plaintext letter. Ahmad al-Qalqashandi: Author of Subh al-a 'sha, a fourteen volume encyclopedia in Arabic, which included a section on cryptology.

Ibn al-Durayhim: gave detailed descriptions of eight cipher systems that discussed substitution ciphers, leading to the earliest suggestion of a 'tableau' of the kind that two centuries later became known as the 'Vigenère table'.Duke of Mantua Francesco I Gonzaga is the one who used the earliest example of homophonic Substitution cipher in early 1400s.Ibn 'Adlan: 13th-century cryptographer who made important contributions on the sample size of the frequency analysis.John Dee, wrote an occult book, which in fact was a cover for crypted text.Ibn Wahshiyya: published several cipher alphabets that were used to encrypt magic formulas.Augustus the Younger, Duke of Brunswick-Lüneburg, wrote a standard book on cryptography.Athanasius Kircher, attempts to decipher crypted messages.Al-Kindi, 9th century Arabic polymath and originator of frequency analysis.Al-Khalil ibn Ahmad al-Farahidi: wrote a (now lost) book on cryptography titled the ' Book of Cryptographic Messages'.Cryptography is the practice and study of techniques for secure communication in the presence of third parties called adversaries.

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