I've heard that Constantijn Huygens Sr. (1596-1687; the father of the famous physicist, Christiaan Huygens) did codebreaking, but it was only recently that I learned that he regularly served in that capacity in Chapter 2 of Nadine Akkerman and Pete Langman (2024), Spycraft (p.153-156). According to this book, he studied cryptanalysis at the University of Leiden in 1616 and even got a pay raise while serving as a secretary to Prince of Orange Frederick Henry since 1624. The authors translate his proud words about his achievements in his autobiography: "At every siege, I proved my skills, anticipating the tricks of the enemy by means of my own knowledge of deceit ...." Particular reference was made to his contribution to the siege of Breda (1637) when requesting a pay raise.
His first achievement in the field appears to have been during Frederick Henry's siege of 's-Hertogenboschin 1629, when he was asked to decipher intercepted Spanish letters in cipher by using his knowledge of Spanish (Christopher Joby (2014), The Multilingualism of Constantijn Huygens (1596-1687), p.78).
He was not always successful. At one time in 1634, he said ciphers of the king of Spain were "more difficult to conquer than" the king himself. (Akkerman and Langman, p.154)
While his library contained many books on cryptography, ciphers he designed for royalists during the English Civil War were simple homophonic substitution ciphers albeit with an extensive nomenclator (ibid. p.156). (I'm inclined to think such ciphers were the most practical after all. John Wallis also proposed a simple Caesar cipher when asked for an "easy cipher", as noted in "John Wallis and Cryptanalysis".)
(By the way, Joby (2014) discusses "code switching", which has nothing to do with cryptography and may be broadly understood as switching to different languages when quoting etc.)
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