6 1. HISTORICAL INTRODUCTION Figure 1.2. A forged nomenclator used in the Babington Plot in 1585. (Image from Wikipedia Commons.) constructing a message to a friend by substituting the codeword for each word in the message that is on your list, and for those not in the list, use the alphabet you created. This should sound quite familiar to those who are used to texting. The difference here is that this uses your own codewords and alphabet, rather than commonly used phrases such as “lol” and “ttyl”. It wasn’t until the seventeenth century that the French realized that listing the codewords in alphabetical order as well as the nomenclator al- phabet in alphabetical order made the code more readily breakable. Figure 1.2 shows a portion of a fifteenth century nomenclator. The Renaissance was a period of substantial advances in cryptography by such pioneer cryptographers, mostly mathematicians, as Leon Alberti, Johannes Trithemius, Giovanni Porta, Geirlamo Cardano, and Blaise de Vigen` ere. Cryptography moved from simple substitutions and the use of symbols to the use of keys (see Chapters 2 to 5) and decryption using prob- ability. Secrets were kept and divulged to serve many different purposes. Secret messages were passed in many ways, including being wrapped in leather and

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