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.

30 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

    https://www.academia.edu/27481937/Arabic_numerals_Update_

    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.

  9. @Mark,

    I can tell you at a University near where I live, a 1 year project (pending additional funding) was just started to digitize manuscripts in their archives. It is one of the top 20 libraries in the US for holdings, and have documents dating back to at least 900 A.D.

    I personally think the documents could be anywhere- the wealthy bought these items, passed them down in their family, and many went on to donate their collections to universities or even public libraries.

    I do know one of the questions they are facing is annotation and search ability. And of course, funding. I also don’t know if they will be made publicly available, though most projects that use government money now need to have their data public so I assume it will be but I have hit paywalls on some European sites.

    I have to assume most libraries with precious material in their collections would be moving toward digitization. Heck, card catalogs are a thing of the past- I can’t imagine even digitizing that 20 years ago when you have millions of articles in your collection!

    -Marie

  10. Mark Knowles on June 9, 2018 at 5:16 pm said:

    Are we saying that if the Nazi military used the Voynich cipher instead of the Enigma machine then they might have won World War II?

    I think not, because one thing which I believed greatly helped in solving the Enigma machine ciphers was being able to guess how a message might have started or ended e.g. “Heil Hitler” and then being able to use that like a crib. With the Voynich we are in a much poorer state on the crib/block paradigm front despite the quantity of text we have to work with.

    Still it is not inconceivable I think that once the Voynich cipher is known it could even have some effect on contemporary cryptography, given how hard it is to crack.

  11. You’re taking an awful lot for granted there Nobby; besides Lily was in our camp; Voynich that is; not Lily of the lamp light Marlaine, who some say worked in the nazi lines of an evening.

  12. M R Knowles on August 7, 2020 at 6:26 pm said:

    Someone referred me to the following:

    Le Croniche di Giovanni Sercambi lucchese. A cura di Salvatore Bongi 1892

    I don’t recall having seen this before, but it is possible.

    Downloadable at:

    https://warburg.sas.ac.uk/pdf/hnh5100b2477167v1.pdf

    Pages 408 to 410 appear to contain late 14th century Milanese diplomatic ciphers.

    “CCCCLXI Chome lo duga di Milano mandava E RICEVEA LÈCTORE CONTRAEACTE.”

    So I take that to mean that we can date the ciphers to around 1461 missing the M for 1000. Tell me if I have got that wrong.

    If so what strikes me is how little development in ciphers there has been in roughly the next 40 years in comparison to roughly the following 40 years.

    With the 1461 cipher key we have 3 homophones on the vowels and a single substitution on the other letters.

    In the Francesco Barbavara cipher key in Mantua cipher ledger, which must be dated to between 1395 and 1403, we see exactly the same 3 homophones on the vowels and a single substitution on the other letters.

    So in 40 years there appears to be little or no developments.

    If we look at the 1435 Modena “In Milano” cipher key we see a big jump in the complexity of the Milanese cipher keys.

    Then if we look at the Filippo Maria Visconti 1447 cipher key we see another big jump in the complexity of the Milanese cipher keys.

    The complexity of diplomatic cipher keys does then not appear to increase until near the end of the 15th century.

    So in a period of at most 45 years it looks like we have a transformation in the complexity of cipher keys. It is clear that in some of the more minor city states we barely see any advances in cipher design over this period. Which city states were leading the charge in these advances is as yet unclear from the cipher data I have at the moment, but Milan was certainly one of the leaders.

  13. M R Knowles on August 7, 2020 at 8:35 pm said:

    According to wikipedia:

    Giovanni Sercambi (1348–1424) was an Italian author from Lucca who wrote a history of his city, Le croniche di Luccha, as well as Il novelliere (or Novelle), a collection of 155 tales.

    This dates the cipher to at least 40 years earlier than I suggested. Which suggests even less change in ciphers over a long period of time.

  14. M R Knowles on August 7, 2020 at 9:19 pm said:

    After all my to-ing and fro-ing on dating the ciphers in the Giovanni Sercambi book have been suggested online by someone to be dated to 1397, which makes sense. Still this is a useful reference point for where Milanese ciphers were at that time.

  15. M R Knowles on August 11, 2020 at 3:44 pm said:

    I find the following quote from:

    “The First Resident Embassies: Mediaeval Italian Origins of Modern Diplomacy” by Garrett Mattingly” in “Speculum: A Journal of Mediaeval Studies Volume 12 October, 1937 No. 4 pages 423 to 439”

    of particular interest. Though much of this article is of interest.

    “Permanent diplomacy made important advances in the reign of Filippo Maria. The last of the Visconti trusted in guile rather than force, and found diplomacy a congenial arm. He knew the advantages of organization, of regular channels of information, of established methods of procedure. Perhaps, too, his indecisive temperament found in long and tortuous negotiation a refuge and a substitute for action. His secretary, Francesco Barbavara(Not to be confused with his uncle who was Gian Galeazzo’s chancellor), built up the Milanese chancery along lines which were to make it, under Cicco Simonetta, perhaps the most efficient in Europe. His secret political agents reported from all quarters of Italy. He welcomed ambassadors from the Italian states, and did his best to establish diplomatic liaisons among the remaining Ghibelline powers. But, until the last year or so of his life, it is his diplomacy outside the peninsula which is most significant. He sent embassies to the kings of Aragon and Burgundy, and twice to the Turks, probably with the idea of stirring up the enemies of Christendom against the Venetians. And, for more than seven years, he was continuously represented at the court of the King of the Romans, during most of which time Sigismund was also represented at Milan.”

    I need to read more in Osio on the subject to understand more on the diplomatic activities under Filippo Maria Visconti.

  16. M R Knowles on September 8, 2020 at 8:08 pm said:

    Cardinal Francesco Capaccini(1784-1845) apparently studied the historical ciphers in the Vatican Archives. However I don’t know where in the archive the ciphers that he studied were, they may be in a place in the archives that I already know contains ciphers or somewhere new.

    I need to look further into the Vatican archives. Other writers like Meister seemed to have missed some, which makes me wonder if there is much more to be seen.

    For completeness I should look further into the ciphers listed in Bischoff’s writing.

  17. M R Knowles on September 8, 2020 at 8:33 pm said:

    Quoting from Intrighi in Vaticano: Misteri e segreti all’ombra di San Pietro, dai Borgia al Corvo by Nina Fabrizio (2013)->

    ‘One of these consisted of a type of encryption that a century later was known as “homophonic”. Capaccini discovered the original of this system in a manuscript written in 1401, in the Duchy of Mantua, and preserved in the Vatican Library.’

    I wonder if this is a mistake and she is referring to Martino Ghisolfi Cipher Ledger in the Mantova Archive or if, fingers crossed, there is another manuscript, unknown to me. She says he discovered the origin of the system though the origin of homophonic ciphers pre-dates 1401. In short the accuracy of this information may be limited.

  18. M R Knowles on September 8, 2020 at 8:44 pm said:

    Francesco Capaccini was the 1st head of the Cryptographic Department of the Vatican and it appears made a systematic study of the historical ciphers in the Vatican Archive. One could hope that one might find a reference to where all the ciphers are, in any writings regarding him.

  19. M R Knowles on September 9, 2020 at 8:46 pm said:

    Pre-Vatican Archives

    The Pre-Vatican period ranged from about 1370 to 1446. The library was scattered during this time, with parts in Rome, Avignon and elsewhere.

    This is the period that we are interested in.

    I believe the Avignon archive was reincorporated later.

    It is not clear to me how the documents from this pre-Vatican period are distributed through the archive.

    My particular interest is the reigns of Pope Martin V and Pope Eugene IV

  20. M R Knowles on September 25, 2020 at 7:51 pm said:

    I have been thinking about looking at non-diplomatic ciphers from pre-1450, having already studied diplomatic ciphers a great deal. Perusing Philip Neal’s list taken from Bischoff, I believe, it appears that many of the ciphers could be described within the framework of diplomatic ciphers even if they were not used for diplomatic ciphers. So the atbash or caesar cipher could be defined with a simple diplomatic cipher key. I am interested in cipher ideas contemporaneous with the Voynich that cannot be described with the framework of diplomatic ciphers of the time.

    So my interest has to be in ciphers that are distinct and different from early 15th century diplomatic ciphers. For example, these could be ciphers that used anagrams as that does not tend to be a feature of diplomatic ciphers.

    So from my point of view simple substitution ciphers that use all sorts of different invented alphabets could be covered under the heading of diplomatic style ciphers, they merely differ in symbol choice, and as such are of little interest to me; there appear to be many listed by Neal/Bischoff that fall into that category.

    There are some ciphers which, whilst they are not described within the framework of diplomatic ciphers, are relatively trivial, though there is no harm including them. Reversal of words or sentences and omission of letters are such. Remember the Voynich could draw on multiple distinct cipher sources conceivably.

    An overview makes it clear that the most sophisticated of the non-diplomatic ciphers cannot nearly compare with the complexity of the kind of diplomatic ciphers that we see by the 1440s.

  21. M R Knowles on September 25, 2020 at 8:28 pm said:

    I have been thinking a little about Alberti and his influences in developing the cipher disk. I get the impression that the idea for it occurred to him a significant period of time before he wrote on the subject.

  22. Mark: Alberti explicitly claimed the opposite, i.e. that he only looked at ciphers because he was asked to.

  23. M R Knowles on September 25, 2020 at 8:49 pm said:

    Nick: Interesting. Thanks for that. I will have to read further. Out of interest, who asked him to and when?

  24. M R Knowles on September 25, 2020 at 8:54 pm said:

    According to the internet “Alberti’s treatise was written for his friend Leonardo Dati”. In wikipedia it links to a Leonardo Dati who died in 1425, which I assume can’t be the correct one, maybe the father.

  25. M R Knowles on September 25, 2020 at 10:25 pm said:

    Nick: It is clearly a complicated subject. I think when reading about Fontana’s disk which was somewhat similar to Alberti’s disk I confused the two. I was looking into the question as to whether the origins of the cipher disk could be found in the period from which the Voynich is carbon dated and therefore whether it should be considered as amongst the contemporary ciphers. I think it is a stretch to try to date some kind of cipher disk as having been invented before 1438, which I suppose means it can be excluded as a direct influence, though I think there is scope for arguing that the author of the Voynich could have been influenced by the same influences as Alberti or Fontana such as Ramon Llull.

  26. M R Knowles on September 25, 2020 at 10:35 pm said:

    If Ramon Llull should be considered a possible influence then are there other potential non-cipher influences on the Voynich cipher that need to be considered.

    In general terms I am inclined to the view that everything has its antecedents. So if Voynichese is a cipher then it did not emerge out of the clear blue sky, but finds its origins in something that precedes it. Diplomatic ciphers are by far and away the strongest contenders I think, but there could be others. So combinatorial mechanisms could be something to consider.

  27. M R Knowles on September 26, 2020 at 12:10 pm said:

    Nick: What you say about Alberti only looking at ciphers, because he was asked to, does seem consistent with what I have read and I can’t see any reason to doubt him in that respect.

  28. M R Knowles on September 26, 2020 at 4:40 pm said:

    The simplicity of the non-diplomatic ciphers we find in Bischoff would make me inclined to believe that if they had any influence at all on Voynichese it was a very small one.

    However learning about Ramon Llull actually appears to open the door to Voynichese being a polyalphabetic cipher or exhibiting features related to polyalphabetic ciphers. Whilst Fontana did not invent a cipher disk it seems that he invented something similar and I believe that Alberti possessed many books by Ramon Llull, also I think Kahn suggests a link between the two. If the author of the Voynich also had books by Ramon llull then perhaps he/she also developed some kind of cipher disk or even conceivably if the author knew directly or indirectly Fontana’s work then that could have influenced the development of a cipher disk of some kind given Fontana’s development of something very similar to a cipher disk.

    Anyway, the Voynich script is much more consistent with diplomatic ciphers. Though it is possible that Voynichese is a hybrid of a complex diplomatic cipher of the 1400s and Lullian influenced polyalphabetic cipher, producing something very complicated indeed.

    All in all, my inclination is still towards Voynichese being a verbose cipher influenced by diplomatic ciphers and using a significant filler text in the form of “null” words and so probably with no polyalphabetic influences. But I must confess the idea of some combinatorial mechanism being used as part of the cipher working is enticing. Are there other mechanisms outside those of Llull which could have been an influence?

  29. M R Knowles on September 26, 2020 at 9:40 pm said:

    Regarding Llull and the origins of the cipher disk and Voynichese in general I think it is to be expected that most technological developments have precursors. So if Voynichese is a cipher there must have been influences on it. It seems inconceivable that someone would invent as sophisticated a cipher as Voynichese with no acquaintance with ciphers or technologies which could be modified for encipering. People make intellectual jumps from one idea to another, so they do invent new things, but normally those new things have a source that is pre-existing. Probably the greater the imagination and ability of the inventor the greater the intellectual jump they may have made from one idea to the next.

    I was curious and to some extent still am curious about the history of the invention of the steal engine. The conventional presentation is that James Watt invented the steam engine and George Stephenson the steam train. This greatly simplifies reality. Here is a less simplified, though of course still simplified idea of how it was developed:

    1) Robert Boyle developed his Boyle’s law, which deals with how the pressure and volume of a gas are connected. (This was enhanced to include temperature.)
    2) Denis Papin developed the pressure cooker.
    3) Thomas Savery developed a model of a steam pump that he demonstrated to the Royal Society.
    4) Thomas Newcomen constructed a full size steam pump and installed it at various mines for pumping out the water.
    5) James Watt improved the design of the steam pump to greatly increase its efficiency and extend its possible uses.

    Steam Train

    1) Richard Trevithick created the first high-pressure steam engine and the first steam train.
    2) George Stephenson improved on Trevithick’s design making for a much more efficient and faster steam train.

    We tend to remember the people who made these inventions a widely used commercial success.

    So what is the point of all this? Well, I fundamentally oppose the idea that Voynichese if it is a cipher it was developed without significant influences on it. It may have been influenced by diplomatic ciphers of the time, it may have been influenced by the precursors of the cipher disk, it may have been influenced by some ideas from non-diplomatic ciphers and it may have been influenced by 2 of these or all 3. (There may be another potential influence(s) that I am as yet unaware of.)

    Voynichese has visually most in common with diplomatic ciphers given the nature of the symbols in the script, it also, I would argue, gives some indications that nulls of some kind may be present in the text. Diplomatic ciphers are, as if often pointed out, in and of themselves insufficient to predict the properties that we see in the Voynich. Non-diplomatic ciphers are too simple to be the sole influence and it seems they are few and far between, making it unlikely that the author would come into contact with them. I think it is hard to say whether some kind of disk or other pre-existing mechanism could be the basis for the encoding, but if so why the need for the special script?

  30. M R Knowles on October 3, 2020 at 10:49 pm said:

    Nick: Thanks for the comment on Ninja. There is obviously no urgency to look at what I think must be a cipher key for King Rupert of Germany, but I was curious about the shorthand, not being familiar with such things. In general there are a few cipher keys that I have found interesting, because of their distinctive features and some others because of their links to Milan/B. As an example the Venetian cipher in the Guinigi cipher ledger includes some number shorthand/symbols that I don’t think I have seen elsewhere. I haven’t yet made a list of the cipher keys that interest me.

    I mentioned the Tironian notes not, because I necessarily think they have anything to do with the Voynich, but just because I don’t really understand them and how I should use them and which ones appear in cipher keys and which don’t.

    Regarding your point about nulls you are right that I haven’t studied their usage. I haven’t studied the usage of homophones, in the sense that I don’t know if people tend to loop through them in sequence when substituting or do they select each homophone in a randomish way. How do people tend to select which null symbol to use and when? I suppose one cannot glean this from looking just at cipher keys and one would need to study a significant number of letters to see how different people implemented the cipher key in practice.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Post navigation