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.

8 thoughts on “New paper on fifteenth century cryptography

  1. Mark Knowles on July 9, 2017 at 11:02 am said:

    Nick: Thanks for writing this; it’s really appreciated.

    Now I have what might seem a rather hard and possibly silly question to ask.

    How likely do you think that more evidence of cipher development will come forward for this period?

    Obviously the more we have to work with the better. I suppose I wonder how thoroughly the historical archives in search of other examples or related information from this period have been explored and exhausted.

    You mention the Urbino cipher which had been to some extent ignored by the academic community. Could there be others like it?

    I guess I am asking you a close to impossible question to answer. Nevertheless I would be curious as to your opinion. More understanding of the cipher used and written from the period I think could be invaluable in understanding the Voynich.

  2. Mark: while I would be surprised if a new primary fifteenth century source on codebreaking (such as Simonetta or Alberti) were to appear, few of the cipher ledgers have been studied in depth, and there are lots of unknown cipher documents yet to be even seen, let alone studied.

  3. Congratulations. This is precisely the argument my brother James Comegys makes. This is precisely why my documentation that both the EVA k and EVA t are tl as documented in the historic record, and not different as Tucker would have it, is important. I have requested to join the conversation on academia.edu If you have trouble with my website my 2013 article is posted on academia.edu

  4. Thanks Nick for your summary. May I add background to the number side pre-15th century cryptolgrapghers by


    Our modern base 10 decimal system formally ended 3,600 years of unit fraction based 10 encoded number systems, facts known by many that created the interesting word based cryptology methods.

    Welcome to Academia.edu.

    Milo Gardner
    Reading ancient math and word texts as originally written

  5. Mark Knowles on July 9, 2017 at 3:32 pm said:

    Nick: Given your comments, how do you see these other examples of ciphers coming to light?

    Given the dearth of examples of cipher from the early 15th century, which is my particular interest, any more data could make so much difference.

    I don’t know if any programs are being implemented to digitise these documents and I would assume also other non-cipher containing documents. Obviously these actions would greatly assist Voynich and other researchers worldwide. I would guess that improvements in handwriting recognition would make it easier for researchers to find what they are looking for amongst the plethora of documents. I would also imagine that advances in technology could make the digitisation process faster, cheaper and easier. (I suppose automated transcription of the Voynich would be nice and could be much more reliable than human transcription.)

    I mentioned before the place of technology in assisting Voynich researchers obviously such as the role of the internet, carbon dating and future developments, I have speculated, such as specifically uniquely author DNA extraction and chemically isolating the geographical origins of many the materials used in the makeup of the manuscript.

    I have made some preliminary enquiries with the Vatican Archives, but if the contents of their library was digitised it would make things so much easier.

    What do you think we can expect going forward in terms of the putting of relevant documents online?

  6. Mark Knowles on July 9, 2017 at 9:36 pm said:

    *programme NOT program(in the computing context)
    Rather programme as an organised plan
    I thought this was unclear.

  7. Mark Knowles on July 10, 2017 at 8:46 pm said:

    Nick: Reread the article. Great stuff! Just the kind of subject I need to know more about.

    How are we going to hunt out the as yet unstùdied studied cipher texts? We need a Wilfred Voynich type to go and find these and record them and make them available online. When you carried out your research in Italy how much of the relevant historical documents were you able to access?

    It is cheering to think that the solution to the Voynich is in a manuscript somewhere waiting to be discovered.

  8. Mark Knowles on July 10, 2017 at 8:49 pm said:

    Nick: Being a newby, I have no idea which are the key archives in Italy and where such documents might be.

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