Tag Archives: history of cryptography

Substitution Cipher Based on The Voynich Manuscript

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2025/12/substitution-cipher-based-on-the-voynich-manuscript.html

Here’s a fun paper: “The Naibbe cipher: a substitution cipher that encrypts Latin and Italian as Voynich Manuscript-like ciphertext“:

Abstract: In this article, I investigate the hypothesis that the Voynich Manuscript (MS 408, Yale University Beinecke Library) is compatible with being a ciphertext by attempting to develop a historically plausible cipher that can replicate the manuscript’s unusual properties. The resulting cipher­a verbose homophonic substitution cipher I call the Naibbe cipher­can be done entirely by hand with 15th-century materials, and when it encrypts a wide range of Latin and Italian plaintexts, the resulting ciphertexts remain fully decipherable and also reliably reproduce many key statistical properties of the Voynich Manuscript at once. My results suggest that the so-called “ciphertext hypothesis” for the Voynich Manuscript remains viable, while also placing constraints on plausible substitution cipher structures.

Book Review: The Business of Secrets

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2025/11/book-review-the-business-of-secrets.html

The Business of Secrets: Adventures in Selling Encryption Around the World by Fred Kinch (May 24, 2024)

From the vantage point of today, it’s surreal reading about the commercial cryptography business in the 1970s. Nobody knew anything. The manufacturers didn’t know whether the cryptography they sold was any good. The customers didn’t know whether the crypto they bought was any good. Everyone pretended to know, thought they knew, or knew better than to even try to know.

The Business of Secrets is the self-published memoirs of Fred Kinch. He was founder and vice president of—mostly sales—at a US cryptographic hardware company called Datotek, from company’s founding in 1969 until 1982. It’s mostly a disjointed collection of stories about the difficulties of selling to governments worldwide, along with descriptions of the highs and (mostly) lows of foreign airlines, foreign hotels, and foreign travel in general. But it’s also about encryption.

Datotek sold cryptographic equipment in the era after rotor machines and before modern academic cryptography. The company initially marketed computer-file encryption, but pivoted to link encryption—low-speed data, voice, fax—because that’s what the market wanted.

These were the years where the NSA hired anyone promising in the field, and routinely classified—and thereby blocked—publication of academic mathematics papers of those they didn’t hire. They controlled the fielding of strong cryptography by aggressively using the International Traffic in Arms regulation. Kinch talks about the difficulties in getting an expert license for Datotek’s products; he didn’t know that the only reason he ever got that license was because the NSA was able to break his company’s stuff. He had no idea that his largest competitor, the Swiss company Crypto AG, was owned and controlled by the CIA and its West German equivalent. “Wouldn’t that have made our life easier if we had known that back in the 1970s?” Yes, it would. But no one knew.

Glimmers of the clandestine world peek out of the book. Countries like France ask detailed tech questions, borrow or buy a couple of units for “evaluation,” and then disappear again. Did they break the encryption? Did they just want to see what their adversaries were using? No one at Datotek knew.

Kinch “carried the key generator logic diagrams and schematics” with him—even today, it’s good practice not to rely on their secrecy for security—but the details seem laughably insecure: four linear shift registers of 29, 23, 13, and 7 bits, variable stepping, and a small nonlinear final transformation. The NSA probably used this as a challenge to its new hires. But Datotek didn’t know that, at the time.

Kinch writes: “The strength of the cryptography had to be accepted on trust and only on trust.” Yes, but it’s so, so weird to read about it in practice. Kinch demonstrated the security of his telephone encryptors by hooking a pair of them up and having people listen to the encrypted voice. It’s rather like demonstrating the safety of a food additive by showing that someone doesn’t immediately fall over dead after eating it. (In one absolutely bizarre anecdote, an Argentine sergeant with a “hearing defect” could understand the scrambled analog voice. Datotek fixed its security, but only offered the upgrade to the Argentines, because no one else complained. As I said, no one knew anything.)

In his postscript, he writes that even if the NSA could break Datotek’s products, they were “vastly superior to what [his customers] had used previously.” Given that the previous devices were electromechanical rotor machines, and that his primary competition was a CIA-run operation, he’s probably right. But even today, we know nothing about any other country’s cryptanalytic capabilities during those decades.

A lot of this book has a “you had to be there” vibe. And it’s mostly tone-deaf. There is no real acknowledgment of the human-rights-abusing countries on Datotek’s customer list, and how their products might have assisted those governments. But it’s a fascinating artifact of an era before commercial cryptography went mainstream, before academic cryptography became approved for US classified data, before those of us outside the triple fences of the NSA understood the mathematics of cryptography.

This book review originally appeared in AFIO.

1965 Cryptanalysis Training Workbook Released by the NSA

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2025/09/1965-cryptanalysis-training-workbook-released-by-the-nsa.html

In the early 1960s, National Security Agency cryptanalyst and cryptanalysis instructor Lambros D. Callimahos coined the term “Stethoscope” to describe a diagnostic computer program used to unravel the internal structure of pre-computer ciphertexts. The term appears in the newly declassified September 1965 document Cryptanalytic Diagnosis with the Aid of a Computer, which compiled 147 listings from this tool for Callimahos’s course, CA-400: NSA Intensive Study Program in General Cryptanalysis.

The listings in the report are printouts from the Stethoscope program, run on the NSA’s Bogart computer, showing statistical and structural data extracted from encrypted messages, but the encrypted messages themselves are not included. They were used in NSA training programs to teach analysts how to interpret ciphertext behavior without seeing the original message.

The listings include elements such as frequency tables, index of coincidence, periodicity tests, bigram/trigram analysis, and columnar and transposition clues. The idea is to give the analyst some clues as to what language is being encoded, what type of cipher system is used, and potential ways to reconstruct plaintext within it.

Bogart was a special-purpose electronic computer tailored specifically for cryptanalytic tasks, such as statistical analysis of cipher texts, pattern recognition, and diagnostic testing, but not decryption per se.

Listings like these were revolutionary. Before computers, cryptanalysts did this type of work manually, painstakingly counting letters and testing hypotheses. Stethoscope automated the grunt work, allowing analysts to focus on interpretation, and cryptanalytical strategy.

These listings were part of the Intensive Study Program in General Cryptanalysis at NSA. Students were trained to interpret listings without seeing the original ciphertext, a method that sharpened their analytical intuitive skills.

Also mentioned in the report is Rob Roy, another NSA diagnostic tool focused on different cryptanalytic tasks, but also producing frequency counts, coincidence indices, and periodicity tests. NSA had a tradition of giving codebreaking tools colorful names—for example, DUENNA, SUPERSCRITCHER, MADAME X, HARVEST, and COPPERHEAD.

Jim Sanborn Is Auctioning Off the Solution to Part Four of the Kryptos Sculpture

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2025/08/jim-sanborn-is-auctioning-off-the-solution-to-part-four-of-the-kryptos-sculpture.html

Well, this is interesting:

The auction, which will include other items related to cryptology, will be held Nov. 20. RR Auction, the company arranging the sale, estimates a winning bid between $300,000 and $500,000.

Along with the original handwritten plain text of K4 and other papers related to the coding, Mr. Sanborn will also be providing a 12-by-18-inch copper plate that has three lines of alphabetic characters cut through with a jigsaw, which he calls “my proof-of-concept piece” and which he kept on a table for inspiration during the two years he and helpers hand-cut the letters for the project. The process was grueling, exacting and nerve wracking. “You could not make any mistake with 1,800 letters,” he said. “It could not be repaired.”

Mr. Sanborn’s ideal winning bidder is someone who will hold on to that secret. He also hopes that person is willing to take over the system of verifying possible solutions and reviewing those unending emails, possibly through an automated system.

Here’s the auction listing.

SIGINT During World War II

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2025/08/sigint-during-world-war-ii.html

The NSA and GCHQ have jointly published a history of World War II SIGINT: “Secret Messengers: Disseminating SIGINT in the Second World War.” This is the story of the British SLUs (Special Liaison Units) and the American SSOs (Special Security Officers).

List of Old NSA Training Videos

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2024/09/list-of-old-nsa-training-videos.html

The NSA’s “National Cryptographic School Television Catalogue” from 1991 lists about 600 COMSEC and SIGINT training videos.

There are a bunch explaining the operations of various cryptographic equipment, and a few code words I have never heard of before.

On the Voynich Manuscript

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2024/08/on-the-voynich-manuscript.html

Really interesting article on the ancient-manuscript scholars who are applying their techniques to the Voynich Manuscript.

No one has been able to understand the writing yet, but there are some new understandings:

Davis presented her findings at the medieval-studies conference and published them in 2020 in the journal Manuscript Studies. She had hardly solved the Voynich, but she’d opened it to new kinds of investigation. If five scribes had come together to write it, the manuscript was probably the work of a community, rather than of a single deranged mind or con artist. Why the community used its own language, or code, remains a mystery. Whether it was a cloister of alchemists, or mad monks, or a group like the medieval Béguines—a secluded order of Christian women—required more study. But the marks of frequent use signaled that the manuscript served some routine, perhaps daily function.

Davis’s work brought like-minded scholars out of hiding. In just the past few years, a Yale linguist named Claire Bowern had begun performing sophisticated analyses of the text, building on the efforts of earlier scholars and on methods Bowern had used with undocumented Indigenous languages in Australia. At the University of Malta, computer scientists were figuring out how to analyze the Voynich with tools for natural-language processing. Researchers found that the manuscript’s roughly 38,000 words—and 9,000-word vocabulary—had many of the statistical hallmarks of actual language. The Voynich’s most common word, whatever it meant, appeared roughly twice as often as the second-most-common word and three times as often as the third-commonest, and so on—a touchstone of natural language known as Zipf’s law. The mix of word lengths and the ratio of unique words to total words were similarly language-like. Certain words, moreover, seemed to follow one another in predictable order, a possible sign of grammar.

Finally, each of the text’s sections—as defined by the drawings of plants, stars, bathing women, and so on—had different sets of overrepresented words, just as one would expect in a real book whose chapters focused on different subjects.

Spelling was the chief aberration. The Voynich alphabet—if that’s what it was—appeared to have a conventional 20-odd letters. But compared with known languages, too many of those letters repeated in the same order, both within words and across neighboring words, like a children’s rhyme. In some places, the spellings of adjacent words so converged that a single word repeated two or three times in a row. A rough English equivalent might be something akin to “She sells sea shells by the sea shore.” Another possibility, Bowern told me, was something like pig Latin, or the Yiddishism—known as “shm-reduplication”—that begets phrases such as fancy shmancy and rules shmules.

Whale Song Code

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2024/04/whale-song-code.html

During the Cold War, the US Navy tried to make a secret code out of whale song.

The basic plan was to develop coded messages from recordings of whales, dolphins, sea lions, and seals. The submarine would broadcast the noises and a computer—the Combo Signal Recognizer (CSR)—would detect the specific patterns and decode them on the other end. In theory, this idea was relatively simple. As work progressed, the Navy found a number of complicated problems to overcome, the bulk of which centered on the authenticity of the code itself.

The message structure couldn’t just substitute the moaning of a whale or a crying seal for As and Bs or even whole words. In addition, the sounds Navy technicians recorded between 1959 and 1965 all had natural background noise. With the technology available, it would have been hard to scrub that out. Repeated blasts of the same sounds with identical extra noise would stand out to even untrained sonar operators.

In the end, it didn’t work.

Declassified NSA Newsletters

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2024/04/declassified-nsa-newsletters.html

Through a 2010 FOIA request (yes, it took that long), we have copies of the NSA’s KRYPTOS Society Newsletter, “Tales of the Krypt,” from 1994 to 2003.

There are many interesting things in the 800 pages of newsletter. There are many redactions. And a 1994 review of Applied Cryptography by redacted:

Applied Cryptography, for those who don’t read the internet news, is a book written by Bruce Schneier last year. According to the jacket, Schneier is a data security expert with a master’s degree in computer science. According to his followers, he is a hero who has finally brought together the loose threads of cryptography for the general public to understand. Schneier has gathered academic research, internet gossip, and everything he could find on cryptography into one 600-page jumble.

The book is destined for commercial success because it is the only volume in which everything linked to cryptography is mentioned. It has sections on such-diverse topics as number theory, zero knowledge proofs, complexity, protocols, DES, patent law, and the Computer Professionals for Social Responsibility. Cryptography is a hot topic just now, and Schneier stands alone in having written a book on it which can be browsed: it is not too dry.

Schneier gives prominence to applications with large sections.on protocols and source code. Code is given for IDEA, FEAL, triple-DES, and other algorithms. At first glance, the book has the look of an encyclopedia of cryptography. Unlike an encyclopedia, however, it can’t be trusted for accuracy.

Playing loose with the facts is a serious problem with Schneier. For example in discussing a small-exponent attack on RSA, he says “an attack by Michael Wiener will recover e when e is up to one quarter the size of n.” Actually, Wiener’s attack recovers the secret exponent d when e has less than one quarter as many bits as n, which is a quite different statement. Or: “The quadratic sieve is the fastest known algorithm for factoring numbers less than 150 digits…. The number field sieve is the fastest known factoring algorithm, although the quadratric sieve is still faster for smaller numbers (the break even point is between 110 and 135 digits).” Throughout the book, Schneier leaves the impression of sloppiness, of a quick and dirty exposition. The reader is subjected to the grunge of equations, only to be confused or misled. The large number of errors compounds the problem. A recent version of the errata (Schneier publishes updates on the internet) is fifteen pages and growing, including errors in diagrams, errors in the code, and errors in the bibliography.

Many readers won’t notice that the details are askew. The importance of the book is that it is the first stab at.putting the whole subject in one spot. Schneier aimed to provide a “comprehensive reference work for modern cryptography.” Comprehensive it is. A trusted reference it is not.

Ouch. But I will not argue that some of my math was sloppy, especially in the first edition (with the blue cover, not the red cover).

A few other highlights:

  • 1995 Kryptos Kristmas Kwiz, pages 299–306
  • 1996 Kryptos Kristmas Kwiz, pages 414–420
  • 1998 Kryptos Kristmas Kwiz, pages 659–665
  • 1999 Kryptos Kristmas Kwiz, pages 734–738
  • Dundee Society Introductory Placement Test (from questions posed by Lambros Callimahos in his famous class), pages 771–773
  • R. Dale Shipp’s Principles of Cryptanalytic Diagnosis, pages 776–779
  • Obit of Jacqueline Jenkins-Nye (Bill Nye the Science Guy’s mother), pages 755–756
  • A praise of Pi, pages 694–696
  • A rant about Acronyms, pages 614–615
  • A speech on women in cryptology, pages 593–599

Mary Queen of Scots Letters Decrypted

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2023/02/mary-queen-of-scots-letters-decrypted.html

This is a neat piece of historical research.

The team of computer scientist George Lasry, pianist Norbert Biermann and astrophysicist Satoshi Tomokiyo—all keen cryptographers—initially thought the batch of encoded documents related to Italy, because that was how they were filed at the Bibliothèque Nationale de France.

However, they quickly realised the letters were in French. Many verb and adjectival forms being feminine, regular mention of captivity, and recurring names—such as Walsingham—all put them on the trail of Mary. Sir Francis Walsingham was Queen Elizabeth’s spymaster.

The code was a simple replacement system in which symbols stand either for letters, or for common words and names. But it would still have taken centuries to crunch all the possibilities, so the team used an algorithm that homed in on likely solutions.

Academic paper.

EDITED TO ADD (2/13): More news.

Charles V of Spain Secret Code Cracked

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2022/11/charles-v-of-spain-secret-code-cracked.html

Diplomatic code cracked after 500 years:

In painstaking work backed by computers, Pierrot found “distinct families” of about 120 symbols used by Charles V. “Whole words are encrypted with a single symbol” and the emperor replaced vowels coming after consonants with marks, she said, an inspiration probably coming from Arabic.

In another obstacle, he used meaningless symbols to mislead any adversary trying to decipher the message.

The breakthrough came in June when Pierrot managed to make out a phrase in the letter, and the team then cracked the code with the help of Camille Desenclos, a historian. “It was painstaking and long work but there was really a breakthrough that happened in one day, where all of a sudden we had the right hypothesis,” she said.

Gus Simmons’s Memoir

Post Syndicated from Bruce Schneier original https://www.schneier.com/blog/archives/2022/03/gus-simmonss-memoir.html

Gus Simmons is an early pioneer in cryptography and computer security. I know him best for his work on authentication and covert channels, specifically as related to nuclear treaty verification. His work is cited extensively in Applied Cryptography.

He has written a memoir of growing up dirt-poor in 1930s rural West Virginia. I’m in the middle of reading it, and it’s fascinating.

More blog posts.