I’ve just uploaded a draft paper to academia.edu called Fifteenth Century Cryptography Revisited. This takes a fresh look at the topic (specifically at homophonic ciphers, Simonetta, and Alberti), and takes a view quite different from David Kahn’s (now 50-year-old) interpretation.
Please take a look: I don’t yet know where it will end up (i.e. as a book chapter, a journal article, or whatever), but I thought it would be good to push the current version up, see what people think.
The abstract runs as follows:
Fifteenth Century Cryptography Revisited
In the fifteenth century, the art of secret writing was dramatically transformed. The simple ciphers typical of the preceding century were rapidly replaced by complicated cipher systems built from nulls, nomenclators, homophones and many other tricks.
Homophones – where individual plaintext letters were enciphered by one of a set of different shapes – were, according to David Kahn’s influential interpretation, added specifically to defend against frequency analysis attacks. Kahn interprets this as a sign of the emergence of cryptanalysis, possibly from Arab sources, and also of the growing mathematization and professionalism of cryptology.
However, by closely examining key ciphers and cipher-related texts of this period, this paper instead argues that homophones were instead added as a steganographic defence. That is, the intention was specifically to disguise linguistic weaknesses in Italian and Latin plaintexts that rendered ciphertexts vulnerable to easy decryption.
Building on this analysis, a new account of the history of fifteenth century cryptography is proposed, along with a revised model charting the flow of ideas influencing cryptographic practice during this fascinating period.
Though it runs to eighteen pages, it should be easy to pick up and read. Please let me know if there’s anything that you think needs clarification, or which you think is incorrect etc.