 Hello, everyone. I'm Sam Lemley, curator of special collections at Carnegie Mellon University Libraries. Welcome to the second episode of Coffee with the Curator, a video series in which I share some of the many fascinating artifacts and books that are held in Carnegie Mellon's special collections. In this episode, we'll be looking at an early cryptographic technology or instrument called cipher disc. These are relatively common in printed books of the 16th and 17th centuries, but they're not very widely known about. Ticking together right in their thousands, though, I think they illustrate a really rich and fascinating history of cryptography, particularly as it was practiced in the Renaissance. To narrow our focus, I will be looking at a set of cipher discs that appears in one of my favorite books at CMU, and that's this book here. It's titled De Fertivis Literarum, which basically translates as On Secret Writing. It was written by Giambattista della Porta, who was an occult scientist in the Renaissance in Italian. It was originally published in 1563, but as you can see, this is a copy of the second edition published in London in 1591. So I'll return to that book in a moment, but I want to point out first that there's actually an interactive component to this video that requires downloading a PDF, and I'll link that here. So this PDF is a reproduction of one of the cipher discs that appears in della Porta's book. And to work with it, you'll need to print it out, of course. You'll need scissors, a needle and thread, or a brass fastener, and some patience to put it together. So we'll return to that in a moment. So the topic of ciphers in cryptography is especially important at CMU, which, you know, because special collections hold a growing number of books and artifacts from the history of cryptology, which is basically the science and study of ciphers, cipher systems, and cryptographic machines. So by way of one well-known example, we have two enigma machines, one three-rotor model and another four-rotor model, both of which were donated by Pamela McCordick in memory of her husband Joseph Traub in 2018. The story of how the enigma machine was deciphered, first by Marian Rajewski of Polish Intelligence in the 1930s, and then later by a British team of crypt analysts that included Alan Turing at Bletchley Park, is sort of well-known, right? We've all read books or seen films about that story. But the enigma machine sits at a long and fascinating history that's sort of riddled with inventions, prototypes, and devices that were designed to shroud or disguise sensitive information. We tend to think of encryption as a fairly modern strategy, but there is a history behind it. And, you know, things like block ciphers and pseudo-random number generators, which are very much sort of of the moment, actually sort of owe a lot to some of the early technologies like we'll be seeing today. So in this episode we'll be revisiting one of these early ancestors of enigma, and it's actually not a machine at all, but this book, right? And I hope to convince you by the end of this episode that a book can function like a machine, right? It can be a kind of instrument. So we'll start just by looking at the book itself. You can see that CMU's copy of Della Porta's book on secret writing is bound in vellum, which is a kind of treated calf or cowskin that can be distinguished by the texture and color. And if you look closely, you can actually see where the hair follicles, the animal's fur was right before it was scraped away when the vellum was prepared. The book is a quarto in size, which means that the individual sheets of paper that make it up were folded twice before being bound together, making four leaves, which is where the term quarto comes from. And this is actually a fairly recent acquisition to CMU. It was purchased last year in the antiquarian book trade, and it joins our other books on the history of cryptography, which are many. So John Batista Della Porta, who wrote this book, sort of worked at a sort of transitional moment in the history of science. And what I mean by that is that while what Porta understood by the term science in his 16th and 17th century context, at least it resembled our own kind of modern ideas about what qualifies as scientific investigation, the strategies and precepts of experimental science were still in the process of being invented in the 16th and 17th century when Porta was working and writing. And this is one reason why I find Porta so fascinating. He sort of sits between worlds and works and writes at the cusp of what is typically seen as the beginning of modern scientific inquiry. He was born in 1535 and died in 1615. So he's almost exactly a generation older than Galileo and Kepler, for instance. And I think this is quite sad in some ways. Porta knew by the end of his life that the winds were changing. He knew Galileo personally and recognized him for the sort of brilliant upstart that he was. And you can't help assuming when you read about Porta that he knew which way things were headed. His brand of science was sort of on the way out. Porta practiced a kind of scientific investigation that was known at the time as natural magic. And he wasn't just a kind of dabbler in the field and there were many dabblers in this field. He was almost its high priest. His first and most successful book was kind of the sort of reference work, the Encyclopedia on Natural Magic. In fact, it was titled Natural Magic and it was published in 1558 and again kind of in a vastly expanded form in 1589. And as I said, it was almost certainly Porta's most popular book. It was sold incredibly well. The idea, the guiding idea behind Porta's sort of natural magic was that scientific learning in its most advanced state amounted to a form of magic that required a kind of occult knowledge and spiritual insight that only someone like Porta could offer. It had studied for decades. That's what it required. Of course, Galileo and Galileo's successors rightly scoffed at this kind of mystical science. But it's also what makes Porta so fascinating. In many ways, Porta represents the last generation of scientists that could claim an almost universal knowledge of the natural world, even if that universal knowledge was somewhat flawed or incomplete. But nevertheless, Porta believed that intense and prolonged scientific investigation could reveal or disclose a kind of theory of everything, unifying all the various branches of learning into a single crystallized truth. And in search of this singular truth, Porta wrote broadly across disciplines, including works on optics, psychology, horticulture, chemistry, and of course cryptography. For Porta, scientific knowledge was as much a source of wonder as it was of certainty, which I think is a sentiment that was very much of his moment. So Porta even established an institute that was dedicated to drawing out the mysteries of nature and science. And he actually called this group that met at his home in Naples the Academia dei Segretti, the Academy of Secrets, which is widely considered to be the earliest scientific institute in the Western world. So like I said, this academy would meet at Porta's house in Naples through the 1570s, but it was actually eventually closed by the Inquisition. So in retrospect, of course, we know that science took a different path away from Porta's ideas of universal secrets and natural magic and toward Galileo's mathematical certainty, mathematical science. And after Galileo, science became increasingly specialized and compartmentalized, which was kind of the opposite of the science that Porta wanted to build and sought during his life. But the posthumous decline of Porta's reputation shouldn't suggest that he was peripheral or somehow insignificant in early modern scientific circles, far from it. In fact, his reputation was almost at its height in the early 17th century. So after Porta's academy was forcibly closed by the Catholic Church, a second academy founded by the Roman nobleman Federico Cezi took its name from one of Porta's books. And this is a fairly well-known academy. But Cezi's academy was called the Academia dei Lincei, or the Academy of the Link's Eye, which was named for the mythological figure of Linceius, who was sort of known for his exceptional eyesight and exceptionally acute vision. So the Academy of the Link's Eye took its emblem, actually from an image of a link that was found on the title page of the first edition of Porta's Natural Magic. And this was in part because the links, like Linceius, the mythological figure, was believed to be a particularly observant animal. And of course, careful observation was the sort of foundation of the scientific method. So I think that's kind of interesting to realize that people like Galileo and Cezi were consciously borrowing from Porta's sort of older vision of science and crafting this new sort of observational method that we've sort of inherited in modern science today. So returning to the book, though, when we page through it, you can see that it's laid out in a fairly conventional way for books of the period. So after the title page, you get this sort of prefatory letter, which dedicates the work to Henry Percy, who was an English nobleman, and it's signed by the works editor, who was Giacomo Castelvertro here in Latin. And he was editing this printing of Porta's book. There were other printings, as I mentioned, but he likely edited this and had it printed without Porta's permission, right, about which I might have more to say later. But I want to pause on this letter because it reveals the kind of person that would have bought and read this book in particular. And you know, this is the kind of thing that we can learn from the material that's printed before and around the text of an early printed book, right, namely who was buying it and what did the author or the editor, the printer, what did they hope to accomplish by distributing it to readers. So the editor of this book, or at least this edition, Giacomo Castelvertro, was an Italian convert to Protestantism who had fled to England to escape anti-Protestant persecution in Italy. And after he arrived, he quickly sort of gained favor at the English court and was eventually appointed as the Italian tutor for James VI of Scotland. In fact, just a year after this book was published. And this was fairly good timing. It was a significant position to gain because, of course, James VI of Scotland would become James the First of England after Queen Elizabeth's death and the end of the Tudor monarchy in 1603. So he was a fairly well connected guy. Interestingly, in his letter to Henry Percy at the beginning of the book, Castelvertro explains that he funded and sponsored the printing of Porta's book on cryptography because copies of the first edition, which was printed in 1563, had become so scarce. So plainly, there was a demand for the cryptographic techniques that Porta's work describes. There was kind of a simmering curiosity about methods of secret communication. And Porta's book was unusual in its kind of detailed treatment of the subject. If you wanted to learn about how to communicate secretly to use ciphers, to use cryptography, this was the book to buy. So the first point that we learn from the letter prefacing Porta's book is that Castelvertro's motive for getting this published is partly commercial. He recognized a demand for a increasingly difficult to find book. And he sought to meet this demand by funding a new edition. So the second interesting thing about this letter is its intended recipient, right, Henry Percy, who was the ninth Earl of Northumberland. He was sort of a wealthy and influential figure in Elizabethan England, and also a kind of strange character who much like Porta kind of towed the line that separated magic and science in the period. He was even known as the wizard Earl for his well-known experiments with magnetism, electricity, and alchemy. So, you know, I think Henry Percy's association with Porta's book not only underscores Porta's reputation for arcane and occult learning in the period, it also tells us that Henry Percy and his associates, right, his circle, were the were the intended audience of this new edition. You know, that was ushered through the press by Castelvertro. And certainly Castelvertro addressed to Henry Percy in the hopes of sort of garnering his favor and sort of joining the circle. So thereafter, right after the introductory letter, we have an introduction to the reader's electorates. But after that, you know, you get an index, which is helpful. Just page through this. It's alphabetized, which is nice. But then the book begins. And it sort of treats its subject in sort of useful categories and runs through the definitions meant to kind of demystify what Porta calls the art of secret letters or the art of secret writing. So you can see that chapter one here of book one is titled, you know, What Are Secret Letters? What Is Secret Writing? I'm going to see skip ahead a bit to get to the interesting bits of this book, which will be spending the rest of this sort of episode exploring, which I'll try to explain. So most of these appear in the middle of the book. I have them marked. So there are three of them. Here's one. Right. There's another. There's the third. So we're actually going to spend our time looking at the this one here, the third one. So you can see that it's made up of kind of two concentric dials or these circles, right, which are made up of cells. The inner circle has a modified Latin alphabet. That's obviously scrambled. It's in no apparent order. And then the outermost circle has cells containing Roman numerals from one to 20. So, you know, the observant among you will notice that there's this sort of void at the middle at the center of the dial, a kind of blank circle. And it seems like something is missing, right? So what is this thing? How is it used? What was it meant to impart to the reader? So it turns out that Porta's book is not only a book about cryptography. It's also a cryptographic instrument. And this is what's known as a cipher disk, right, which is a kind of paper in ciphering tool that revolves to encode a message. And one thing I'll just talk about, you know, what's going on in the page here briefly. One thing I love about this particular cipher disk is the figures that surround it, right? You can see that there's these sort of two sort of animal female figures with, you know, lion legs, lion heads at least, you know, and these, of course, these strange hybrids or sphinxes, which I think, you know, they're so appropriate in a book on cryptography, given that the sphinx was the riddler of classical mythology. And so I think it's kind of fitting that they're guarding Porta's cipher disk, cipher instrument on its side, you know, they're kind of guarding its secrets. So to return to the question of how this thing works, right? So it turns out that there's some assembly required paper instruments like this that appear in books are known as volvels, which is a term that comes from the Latin verb volvere or rolere to turn. And I hope for an obvious reason, right? They actually revolve, you spin them. So some volvels are incredibly complex. They involve, you know, several overlapping slips of paper that are usually all tacked together with a bit of metal, you know, metal pin or piece of thread. And I think it's no stretch to describe these as one of the first mechanical calculators, right? They commonly appear in works on astronomy and the Renaissance and can be used to predict or calculate the position of a planet, for example, at a given point in the year, you know, and other things like that, that sort of are a seed to calculation, right? So what Porta has done is adopted that technology to make an encrypting device for his readers to use. Of course, we've already noticed that this cipher disk, this volvel is incomplete, right? And if you turn to the end of the book, you'll see, you'll see why, right? So the centerpieces were actually printed on a separate page at the back. And I call these indexes or indices because they indicate the position or the setting of the cipher disk. So yeah, they were printed separately. And they were actually intended to be removed to be cut out very carefully by the book's buyer, by the book's reader and actually mounted at the appropriate points in the book, right? So you cut these out and you sort of pin them or stitch them into place so they'd spin at the center of the cipher disks. And I love that these have been labeled, right? One, two, and three, I think by the printer. And that those numbers tell you which volvel, which cipher disk they belong to. So keep that in mind. We'll have our own example of a functioning cipher disk to work with later. But I'll turn back to the one we were looking at earlier that's missing that centerpiece. Now, of course, in some ways, it's kind of disappointing that CMU's copy wasn't assembled in 1591 when it was printed and purchased. Because that tells us that this book, you know, wasn't exactly used as intended, right? It's early reader or early readers never engage in the kind of ciphering that Porta's book invites and demands, right? And we'll have to sit with that disappointment because we can't unfortunately cut up this copy and put it together ourselves. What we can do, though, is make copies and assemble our own facsimiles of Porta's cipher disk to learn how it worked. So to do that, as I mentioned at the beginning of this video, I've scanned this page that I just showed you and created a printable kit that you can download here and I'll link that again. So once that's assembled, this is sort of what you have. This is what it looks like. So you can see that the centerpiece rotates. I've used a brass pin here and the kit that is in the PDF also includes a blank index of these symbols, these strange sigla that are around the circumference of the index, the centerpiece. Those cells are blank, so you can actually make up your own alphabet of hieroglyphics or symbols to work with. But we'll use Porta's cipher disk, his alphabet of hieroglyphs, to demonstrate how it works. So to begin, you cut out the index, you tack it to the center of the cipher disk, and then once that's done, the center disk should rotate freely. So make sure that's loose, sometimes they get kind of sticky. So let's give it a try. So looking at the book itself, Delaporta actually gives a number of examples. So there's his hieroglyphic alphabet and you're meant to use the cipher disk to decipher what's written sort of in this ornamental frame. So this one is quite long. It's also in Latin. I think few of us read Latin, so we're going to make up our own shorter secret message. So the way this works is that for every letter in the message, either the original plain text that you want to encode or the encoded message you want to decipher, decode, you advance the wheel one step clockwise for clockwise for each character or letter, starting at position number one, which is there. So starting with the index at one, notice how there's a little hand at the center that shows you where it's pointing, which is quite helpful. So we'll decode the first symbol and I'm going to put up an enciphered message here. So let's begin. So we're at one. That's where we start. The first symbol is this sort of open circle, which leads to a number of possibilities, right? We have F, H, and I. So let's just let's just jot all of those down for the time being. This will kind of have to work through the variant readings of the cipher text. So what did I say? So we have F, H, and I. So it's going to be one of those. And notice that in repeating that hieroglyphic, that's sort of adding security to Delaporta's cipher system. When you repeat symbols like that, generally the cipher system is more secure if you're encoding your plain text under sort of repetitive symbolic alphabet. Okay, so that's the first. It's going to be one of those. That's the first character. And we advance the wheel one step. And the next symbol is again, an open circle. Okay, so it's either it's the S, R, or E. Okay, it's going to be one of those. All right, so we'll rotate it again until we're in position three, right? Let me make sure I'm lined up here. Yeah, so we're in position three. The next symbol is, oh gosh, an open circle. Okay, so we're sticking with that repeated figure. So it's either G, position four, I'll put that down here. L, V, right? And notice that in Delaporta's modified Latin alphabet, at least on this disc, there is no U. And, you know, this is probably too much information, but the V also functions as a U in the Latin alphabet because there was no U originally in the Latin alphabet. So if you want to encrypt a U, you would use the V in its place. Okay, so that's the third letter advancing once more to the fourth position, which is the fourth letter. Okay, let's go ahead and find it. It's this little shape there. And luckily here, there are only one of those. So that can only be L. All right. Last letter, advance once more to position five. It's a five-letter word. We're looking for an open circle in a square. So there it is. Oh, right? Okay, so now we have to sort of figure out which reading of these three letter blocks makes the most sense. So I see something here, right? So the encrypted message is just greeting us. It says hello, right? So the cool thing about ciphers or Porta's cipher and cipher disc is that they work in either direction, right? So say, for example, you wanted to encrypt the plain text, which is hello, hello. You again start one, and you do the same thing just in reverse, right? So with the wheel of one, you look for H. There's that open circle. So you would encode that as an open circle. You advance it one step. You look for E. There it is. Sure enough, another open circle. Advance again. You're going to look for L. Another open circle. Advance again. You look for O, right? Or another L, sorry. You have that strange symbol there, which I'll attempt to draw. Okay, and then finally, one more position. You're looking for the letter O, and you get a box enclosing a circle, right? So that's our original string of sort of hieroglyphic letters. So that's kind of how it works. It's nice in a way that the same instrument is used to encrypt and decrypt, right? Now one disadvantage of this system is that after you encode a message, you or someone else who receives that message has to reverse the process using the exact same cipher wheel, like the only way to read in ciphered messages using the cipher system quickly is to actually have a cipher disk on hand. So that's kind of an inherent flaw in the system, right? If the cipher disk fell into your enemy's hands, right, she could potentially decipher it just as easily as the recipient. So that's Porto's cipher disk, and I invite you to visit the online exhibition that accompanies this video. I'll link that here. There you'll find more information and instructional exercises on how to use Porto's cipher disk, and of course, you can print out your own facsimile and use it however you'd like. Thanks, and I look forward to the next episode.