Keys with nomenclatures in the early modern Europe

Abstract

We give an overview of the development of European historical cipher keys originating from early Modern times. We describe the nature and the structure of the keys with a special focus on the nomenclatures. We analyze what was encoded and how and take into account chronological and regional differences. The study is based on the analysis of over 1,600 cipher keys, collected from archives and libraries in 10 European countries. We show that historical cipher keys evolved over time and became more secure, shown by the symbol set used for encoding, the code length and the code types presented in the key, the size of the nomenclature, as well as the diversity and complexity of linguistic entities that are chosen to be encoded.

Historical Language Models in Cryptanalysis: Case Studies on English and German

“…The reason behind varying the number of homophones for each plaintext letter is to create more authentic ciphers which are similar to original ciphers, as retrieved from European archives and libraries. Previous studies showed that in homophonic substitu-tion ciphers we can find variable number of code elements for different plaintext letters depending on their frequency in the particular language; frequently occurring plaintext letters usually receive two or three code elements, while less frequent letters are assigned one code element (Kahn, 1996) and (Megyesi et al, 2022).…”