Entries Tagged "encryption"

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Substitution Cipher Based on The Voynich Manuscript

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.

Posted on December 8, 2025 at 7:04 AM • View Comments

IACR Nullifies Election Because of Lost Decryption Key

The International Association of Cryptologic Research—the academic cryptography association that’s been putting conferences like Crypto (back when “crypto” meant “cryptography”) and Eurocrypt since the 1980s—had to nullify an online election when trustee Moti Yung lost his decryption key.

For this election and in accordance with the bylaws of the IACR, the three members of the IACR 2025 Election Committee acted as independent trustees, each holding a portion of the cryptographic key material required to jointly decrypt the results. This aspect of Helios’ design ensures that no two trustees could collude to determine the outcome of an election or the contents of individual votes on their own: all trustees must provide their decryption shares.

Unfortunately, one of the three trustees has irretrievably lost their private key, an honest but unfortunate human mistake, and therefore cannot compute their decryption share. As a result, Helios is unable to complete the decryption process, and it is technically impossible for us to obtain or verify the final outcome of this election.

The group will redo the election, but this time setting a 2-of-3 threshold scheme for decrypting the results, instead of requiring all three

News articles.

Posted on November 24, 2025 at 7:03 AM • View Comments

Book Review: The Business of Secrets

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.

Posted on November 13, 2025 at 7:09 AM • View Comments

Signal’s Post-Quantum Cryptographic Implementation

Signal has just rolled out its quantum-safe cryptographic implementation.

Ars Technica has a really good article with details:

Ultimately, the architects settled on a creative solution. Rather than bolt KEM onto the existing double ratchet, they allowed it to remain more or less the same as it had been. Then they used the new quantum-safe ratchet to implement a parallel secure messaging system.

Now, when the protocol encrypts a message, it sources encryption keys from both the classic Double Ratchet and the new ratchet. It then mixes the two keys together (using a cryptographic key derivation function) to get a new encryption key that has all of the security of the classical Double Ratchet but now has quantum security, too.

The Signal engineers have given this third ratchet the formal name: Sparse Post Quantum Ratchet, or SPQR for short. The third ratchet was designed in collaboration with PQShield, AIST, and New York University. The developers presented the erasure-code-based chunking and the high-level Triple Ratchet design at the Eurocrypt 2025 conference. At the Usenix 25 conference, they discussed the six options they considered for adding quantum-safe forward secrecy and post-compromise security and why SPQR and one other stood out. Presentations at the NIST PQC Standardization Conference and the Cryptographic Applications Workshop explain the details of chunking, the design challenges, and how the protocol had to be adapted to use the standardized ML-KEM.

Jacomme further observed:

The final thing interesting for the triple ratchet is that it nicely combines the best of both worlds. Between two users, you have a classical DH-based ratchet going on one side, and fully independently, a KEM-based ratchet is going on. Then, whenever you need to encrypt something, you get a key from both, and mix it up to get the actual encryption key. So, even if one ratchet is fully broken, be it because there is now a quantum computer, or because somebody manages to break either elliptic curves or ML-KEM, or because the implementation of one is flawed, or…, the Signal message will still be protected by the second ratchet. In a sense, this update can be seen, of course simplifying, as doubling the security of the ratchet part of Signal, and is a cool thing even for people that don’t care about quantum computers.

Also read this post on X.

Posted on October 29, 2025 at 7:09 AM • View Comments

A Surprising Amount of Satellite Traffic Is Unencrypted

Here’s the summary:

We pointed a commercial-off-the-shelf satellite dish at the sky and carried out the most comprehensive public study to date of geostationary satellite communication. A shockingly large amount of sensitive traffic is being broadcast unencrypted, including critical infrastructure, internal corporate and government communications, private citizens’ voice calls and SMS, and consumer Internet traffic from in-flight wifi and mobile networks. This data can be passively observed by anyone with a few hundred dollars of consumer-grade hardware. There are thousands of geostationary satellite transponders globally, and data from a single transponder may be visible from an area as large as 40% of the surface of the earth.

Full paper. News article.

Posted on October 17, 2025 at 7:03 AM • View Comments

Digital Threat Modeling Under Authoritarianism

Today’s world requires us to make complex and nuanced decisions about our digital security. Evaluating when to use a secure messaging app like Signal or WhatsApp, which passwords to store on your smartphone, or what to share on social media requires us to assess risks and make judgments accordingly. Arriving at any conclusion is an exercise in threat modeling.

In security, threat modeling is the process of determining what security measures make sense in your particular situation. It’s a way to think about potential risks, possible defenses, and the costs of both. It’s how experts avoid being distracted by irrelevant risks or overburdened by undue costs.

We threat model all the time. We might decide to walk down one street instead of another, or use an internet VPN when browsing dubious sites. Perhaps we understand the risks in detail, but more likely we are relying on intuition or some trusted authority. But in the U.S. and elsewhere, the average person’s threat model is changing—specifically involving how we protect our personal information. Previously, most concern centered on corporate surveillance; companies like Google and Facebook engaging in digital surveillance to maximize their profit. Increasingly, however, many people are worried about government surveillance and how the government could weaponize personal data.

Since the beginning of this year, the Trump administration’s actions in this area have raised alarm bells: The Department of Government Efficiency (DOGE) took data from federal agencies, Palantir combined disparate streams of government data into a single system, and Immigration and Customs Enforcement (ICE) used social media posts as a reason to deny someone entry into the U.S.

These threats, and others posed by a techno-authoritarian regime, are vastly different from those presented by a corporate monopolistic regime—and different yet again in a society where both are working together. Contending with these new threats requires a different approach to personal digital devices, cloud services, social media, and data in general.

What Data Does the Government Already Have?

For years, most public attention has centered on the risks of tech companies gathering behavioral data. This is an enormous amount of data, generally used to predict and influence consumers’ future behavior—rather than as a means of uncovering our past. Although commercial data is highly intimate—such as knowledge of your precise location over the course of a year, or the contents of every Facebook post you have ever created—it’s not the same thing as tax returns, police records, unemployment insurance applications, or medical history.

The U.S. government holds extensive data about everyone living inside its borders, some of it very sensitive—and there’s not much that can be done about it. This information consists largely of facts that people are legally obligated to tell the government. The IRS has a lot of very sensitive data about personal finances. The Treasury Department has data about any money received from the government. The Office of Personnel Management has an enormous amount of detailed information about government employees—including the very personal form required to get a security clearance. The Census Bureau possesses vast data about everyone living in the U.S., including, for example, a database of real estate ownership in the country. The Department of Defense and the Bureau of Veterans Affairs have data about present and former members of the military, the Department of Homeland Security has travel information, and various agencies possess health records. And so on.

It is safe to assume that the government has—or will soon have—access to all of this government data. This sounds like a tautology, but in the past, the U.S. government largely followed the many laws limiting how those databases were used, especially regarding how they were shared, combined, and correlated. Under the second Trump administration, this no longer seems to be the case.

Augmenting Government Data with Corporate Data

The mechanisms of corporate surveillance haven’t gone away. Compute technology is constantly spying on its users—and that data is being used to influence us. Companies like Google and Meta are vast surveillance machines, and they use that data to fuel advertising. A smartphone is a portable surveillance device, constantly recording things like location and communication. Cars, and many other Internet of Things devices, do the same. Credit card companies, health insurers, internet retailers, and social media sites all have detailed data about you—and there is a vast industry that buys and sells this intimate data.

This isn’t news. What’s different in a techno-authoritarian regime is that this data is also shared with the government, either as a paid service or as demanded by local law. Amazon shares Ring doorbell data with the police. Flock, a company that collects license plate data from cars around the country, shares data with the police as well. And just as Chinese corporations share user data with the government and companies like Verizon shared calling records with the National Security Agency (NSA) after the Sept. 11 terrorist attacks, an authoritarian government will use this data as well.

Personal Targeting Using Data

The government has vast capabilities for targeted surveillance, both technically and legally. If a high-level figure is targeted by name, it is almost certain that the government can access their data. The government will use its investigatory powers to the fullest: It will go through government data, remotely hack phones and computers, spy on communications, and raid a home. It will compel third parties, like banks, cell providers, email providers, cloud storage services, and social media companies, to turn over data. To the extent those companies keep backups, the government will even be able to obtain deleted data.

This data can be used for prosecution—possibly selectively. This has been made evident in recent weeks, as the Trump administration personally targeted perceived enemies for “mortgage fraud.” This was a clear example of weaponization of data. Given all the data the government requires people to divulge, there will be something there to prosecute.

Although alarming, this sort of targeted attack doesn’t scale. As vast as the government’s information is and as powerful as its capabilities are, they are not infinite. They can be deployed against only a limited number of people. And most people will never be that high on the priorities list.

The Risks of Mass Surveillance

Mass surveillance is surveillance without specific targets. For most people, this is where the primary risks lie. Even if we’re not targeted by name, personal data could raise red flags, drawing unwanted scrutiny.

The risks here are twofold. First, mass surveillance could be used to single out people to harass or arrest: when they cross the border, show up at immigration hearings, attend a protest, are stopped by the police for speeding, or just as they’re living their normal lives. Second, mass surveillance could be used to threaten or blackmail. In the first case, the government is using that database to find a plausible excuse for its actions. In the second, it is looking for an actual infraction that it could selectively prosecute—or not.

Mitigating these risks is difficult, because it would require not interacting with either the government or corporations in everyday life—and living in the woods without any electronics isn’t realistic for most of us. Additionally, this strategy protects only future information; it does nothing to protect the information generated in the past. That said, going back and scrubbing social media accounts and cloud storage does have some value. Whether it’s right for you depends on your personal situation.

Opportunistic Use of Data

Beyond data given to third parties—either corporations or the government—there is also data users keep in their possession.This data may be stored on personal devices such as computers and phones or, more likely today, in some cloud service and accessible from those devices. Here, the risks are different: Some authority could confiscate your device and look through it.

This is not just speculative. There are many stories of ICE agents examining people’s phones and computers when they attempt to enter the U.S.: their emails, contact lists, documents, photos, browser history, and social media posts.

There are several different defenses you can deploy, presented from least to most extreme. First, you can scrub devices of potentially incriminating information, either as a matter of course or before entering a higher-risk situation. Second, you could consider deleting—even temporarily—social media and other apps so that someone with access to a device doesn’t get access to those accounts—this includes your contacts list. If a phone is swept up in a government raid, your contacts become their next targets.

Third, you could choose not to carry your device with you at all, opting instead for a burner phone without contacts, email access, and accounts, or go electronics-free entirely. This may sound extreme—and getting it right is hard—but I know many people today who have stripped-down computers and sanitized phones for international travel. At the same time, there are also stories of people being denied entry to the U.S. because they are carrying what is obviously a burner phone—or no phone at all.

Encryption Isn’t a Magic Bullet—But Use It Anyway

Encryption protects your data while it’s not being used, and your devices when they’re turned off. This doesn’t help if a border agent forces you to turn on your phone and computer. And it doesn’t protect metadata, which needs to be unencrypted for the system to function. This metadata can be extremely valuable. For example, Signal, WhatsApp, and iMessage all encrypt the contents of your text messages—the data—but information about who you are texting and when must remain unencrypted.

Also, if the NSA wants access to someone’s phone, it can get it. Encryption is no help against that sort of sophisticated targeted attack. But, again, most of us aren’t that important and even the NSA can target only so many people. What encryption safeguards against is mass surveillance.

I recommend Signal for text messages above all other apps. But if you are in a country where having Signal on a device is in itself incriminating, then use WhatsApp. Signal is better, but everyone has WhatsApp installed on their phones, so it doesn’t raise the same suspicion. Also, it’s a no-brainer to turn on your computer’s built-in encryption: BitLocker for Windows and FileVault for Macs.

On the subject of data and metadata, it’s worth noting that data poisoning doesn’t help nearly as much as you might think. That is, it doesn’t do much good to add hundreds of random strangers to an address book or bogus internet searches to a browser history to hide the real ones. Modern analysis tools can see through all of that.

Shifting Risks of Decentralization

This notion of individual targeting, and the inability of the government to do that at scale, starts to fail as the authoritarian system becomes more decentralized. After all, if repression comes from the top, it affects only senior government officials and people who people in power personally dislike. If it comes from the bottom, it affects everybody. But decentralization looks much like the events playing out with ICE harassing, detaining, and disappearing people—everyone has to fear it.

This can go much further. Imagine there is a government official assigned to your neighborhood, or your block, or your apartment building. It’s worth that person’s time to scrutinize everybody’s social media posts, email, and chat logs. For anyone in that situation, limiting what you do online is the only defense.

Being Innocent Won’t Protect You

This is vital to understand. Surveillance systems and sorting algorithms make mistakes. This is apparent in the fact that we are routinely served advertisements for products that don’t interest us at all. Those mistakes are relatively harmless—who cares about a poorly targeted ad?—but a similar mistake at an immigration hearing can get someone deported.

An authoritarian government doesn’t care. Mistakes are a feature and not a bug of authoritarian surveillance. If ICE targets only people it can go after legally, then everyone knows whether or not they need to fear ICE. If ICE occasionally makes mistakes by arresting Americans and deporting innocents, then everyone has to fear it. This is by design.

Effective Opposition Requires Being Online

For most people, phones are an essential part of daily life. If you leave yours at home when you attend a protest, you won’t be able to film police violence. Or coordinate with your friends and figure out where to meet. Or use a navigation app to get to the protest in the first place.

Threat modeling is all about trade-offs. Understanding yours depends not only on the technology and its capabilities but also on your personal goals. Are you trying to keep your head down and survive—or get out? Are you wanting to protest legally? Are you doing more, maybe throwing sand into the gears of an authoritarian government, or even engaging in active resistance? The more you are doing, the more technology you need—and the more technology will be used against you. There are no simple answers, only choices.

This essay was originally published in Lawfare.

Posted on September 26, 2025 at 7:04 AM • View Comments

Encryption Backdoor in Military/Police Radios

I wrote about this in 2023. Here’s the story:

Three Dutch security analysts discovered the vulnerabilities­—five in total—­in a European radio standard called TETRA (Terrestrial Trunked Radio), which is used in radios made by Motorola, Damm, Hytera, and others. The standard has been used in radios since the ’90s, but the flaws remained unknown because encryption algorithms used in TETRA were kept secret until now.

There’s new news:

In 2023, Carlo Meijer, Wouter Bokslag, and Jos Wetzels of security firm Midnight Blue, based in the Netherlands, discovered vulnerabilities in encryption algorithms that are part of a European radio standard created by ETSI called TETRA (Terrestrial Trunked Radio), which has been baked into radio systems made by Motorola, Damm, Sepura, and others since the ’90s. The flaws remained unknown publicly until their disclosure, because ETSI refused for decades to let anyone examine the proprietary algorithms.

[…]

But now the same researchers have found that at least one implementation of the end-to-end encryption solution endorsed by ETSI has a similar issue that makes it equally vulnerable to eavesdropping. The encryption algorithm used for the device they examined starts with a 128-bit key, but this gets compressed to 56 bits before it encrypts traffic, making it easier to crack. It’s not clear who is using this implementation of the end-to-end encryption algorithm, nor if anyone using devices with the end-to-end encryption is aware of the security vulnerability in them.

[…]

The end-to-end encryption the researchers examined recently is designed to run on top of TETRA encryption algorithms.

The researchers found the issue with the end-to-end encryption (E2EE) only after extracting and reverse-engineering the E2EE algorithm used in a radio made by Sepura.

These seem to be deliberately implemented backdoors.

Posted on August 26, 2025 at 7:06 AM • View Comments

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

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.

Posted on August 21, 2025 at 7:02 AM • View Comments

“Encryption Backdoors and the Fourth Amendment”

Law journal article that looks at the Dual_EC_PRNG backdoor from a US constitutional perspective:

Abstract: The National Security Agency (NSA) reportedly paid and pressured technology companies to trick their customers into using vulnerable encryption products. This Article examines whether any of three theories removed the Fourth Amendment’s requirement that this be reasonable. The first is that a challenge to the encryption backdoor might fail for want of a search or seizure. The Article rejects this both because the Amendment reaches some vulnerabilities apart from the searches and seizures they enable and because the creation of this vulnerability was itself a search or seizure. The second is that the role of the technology companies might have brought this backdoor within the private-search doctrine. The Article criticizes the doctrine­ particularly its origins in Burdeau v. McDowell­and argues that if it ever should apply, it should not here. The last is that the customers might have waived their Fourth Amendment rights under the third-party doctrine. The Article rejects this both because the customers were not on notice of the backdoor and because historical understandings of the Amendment would not have tolerated it. The Article concludes that none of these theories removed the Amendment’s reasonableness requirement.

Posted on July 22, 2025 at 7:05 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.