Entries Tagged "Applied Cryptography"

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Declassified NSA Newsletters

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

Posted on April 2, 2024 at 1:05 PM • View Comments

NIST Draft Document on Post-Quantum Cryptography Guidance

NIST has released a draft of Special Publication1800-38A: “Migration to Post-Quantum Cryptography: Preparation for Considering the Implementation and Adoption of Quantum Safe Cryptography.” It’s only four pages long, and it doesn’t have a lot of detail—more “volumes” are coming, with more information—but it’s well worth reading.

We are going to need to migrate to quantum-resistant public-key algorithms, and the sooner we implement key agility the easier it will be to do so.

News article.

Posted on May 2, 2023 at 10:10 AM • View Comments

"The Cult of Schneier"

If there’s actually a cult out there, I want to hear about it. In an essay by that name, John Viega writes about the dangers of relying on Applied Cryptography to design cryptosystems:

But, after many years of evaluating the security of software systems, I’m incredibly down on using the book that made Bruce famous when designing the cryptographic aspects of a system. In fact, I can safely say I have never seen a secure system come out the other end, when that is the primary source for the crypto design. And I don’t mean that people forget about the buffer overflows. I mean, the crypto is crappy.

My rule for software development teams is simple: Don’t use Applied Cryptography in your system design. It’s fine and fun to read it, just don’t build from it.

[…]

The book talks about the fundamental building blocks of cryptography, but there is no guidance on things like, putting together all the pieces to create a secure, authenticated connection between two parties.

Plus, in the nearly 13 years since the book was last revised, our understanding of cryptography has changed greatly. There are things in it that were thought to be true at the time that turned out to be very false….

I agree. And, to his credit, Viega points out that I agree:

But in the introduction to Bruce Schneier’s book, Practical Cryptography, he himself says that the world is filled with broken systems built from his earlier book. In fact, he wrote Practical Cryptography in hopes of rectifying the problem.

This is all true.

Designing a cryptosystem is hard. Just as you wouldn’t give a person—even a doctor—a brain-surgery instruction manual and then expect him to operate on live patients, you shouldn’t give an engineer a cryptography book and then expect him to design and implement a cryptosystem. The patient is unlikely to survive, and the cryptosystem is unlikely to be secure.

Even worse, security doesn’t provide immediate feedback. A dead patient on the operating table tells the doctor that maybe he doesn’t understand brain surgery just because he read a book, but an insecure cryptosystem works just fine. It’s not until someone takes the time to break it that the engineer might realize that he didn’t do as good a job as he thought. Remember: Anyone can design a security system that he himself cannot break. Even the experts regularly get it wrong. The odds that an amateur will get it right are extremely low.

For those who are interested, a second edition of Practical Cryptography will be published in early 2010, renamed Cryptography Engineering and featuring a third author: Tadayoshi Kohno.

EDITED TO ADD (9/16): Commentary.

Posted on September 3, 2009 at 1:56 PM • View Comments

The Doghouse: Net1

They have technology:

The FTS Patent has been acclaimed by leading cryptographic authorities around the world as the most innovative and secure protocol ever invented to manage offline and online smart card related transactions. Please see the independent report by Bruce Schneider [sic] in his book entitled Applied Cryptography, 2nd Edition published in the late 1990s.

I have no idea what this is referring to.

EDITED TO ADD (5/20): Someone, probably from the company, said in comments that this is referring to the UEPS protocol, discussed on page 589. I still don’t like the hyperbole and the implied endorsement in the quote.

Posted on May 22, 2009 at 11:29 AM • View Comments

Quantum Cryptography

Quantum cryptography is back in the news, and the basic idea is still unbelievably cool, in theory, and nearly useless in real life.

The idea behind quantum crypto is that two people communicating using a quantum channel can be absolutely sure no one is eavesdropping. Heisenberg’s uncertainty principle requires anyone measuring a quantum system to disturb it, and that disturbance alerts legitimate users as to the eavesdropper’s presence. No disturbance, no eavesdropper—period.

This month we’ve seen reports on a new working quantum-key distribution network in Vienna, and a new quantum-key distribution technique out of Britain. Great stuff, but headlines like the BBC’s “‘Unbreakable’ encryption unveiled” are a bit much.

The basic science behind quantum crypto was developed, and prototypes built, in the early 1980s by Charles Bennett and Giles Brassard, and there have been steady advances in engineering since then. I describe basically how it all works in Applied Cryptography, 2nd Edition (pages 554-557). At least one company already sells quantum-key distribution products.

Note that this is totally separate from quantum computing, which also has implications for cryptography. Several groups are working on designing and building a quantum computer, which is fundamentally different from a classical computer. If one were built—and we’re talking science fiction here—then it could factor numbers and solve discrete-logarithm problems very quickly. In other words, it could break all of our commonly used public-key algorithms. For symmetric cryptography it’s not that dire: A quantum computer would effectively halve the key length, so that a 256-bit key would be only as secure as a 128-bit key today. Pretty serious stuff, but years away from being practical. I think the best quantum computer today can factor the number 15.

While I like the science of quantum cryptography—my undergraduate degree was in physics—I don’t see any commercial value in it. I don’t believe it solves any security problem that needs solving. I don’t believe that it’s worth paying for, and I can’t imagine anyone but a few technophiles buying and deploying it. Systems that use it don’t magically become unbreakable, because the quantum part doesn’t address the weak points of the system.

Security is a chain; it’s as strong as the weakest link. Mathematical cryptography, as bad as it sometimes is, is the strongest link in most security chains. Our symmetric and public-key algorithms are pretty good, even though they’re not based on much rigorous mathematical theory. The real problems are elsewhere: computer security, network security, user interface and so on.

Cryptography is the one area of security that we can get right. We already have good encryption algorithms, good authentication algorithms and good key-agreement protocols. Maybe quantum cryptography can make that link stronger, but why would anyone bother? There are far more serious security problems to worry about, and it makes much more sense to spend effort securing those.

As I’ve often said, it’s like defending yourself against an approaching attacker by putting a huge stake in the ground. It’s useless to argue about whether the stake should be 50 feet tall or 100 feet tall, because either way, the attacker is going to go around it. Even quantum cryptography doesn’t “solve” all of cryptography: The keys are exchanged with photons, but a conventional mathematical algorithm takes over for the actual encryption.

I’m always in favor of security research, and I have enjoyed following the developments in quantum cryptography. But as a product, it has no future. It’s not that quantum cryptography might be insecure; it’s that cryptography is already sufficiently secure.

This essay previously appeared on Wired.com.

EDITED TO ADD (10/21): It’s amazing; even reporters responding to my essay get it completely wrong:

Keith Harrison, a cryptographer with HP Laboratories, is quoted by the Telegraph as saying that, as quantum computing becomes commonplace, hackers will use the technology to crack conventional encryption.

“We have to be thinking about solutions to the problems that quantum computing will pose,” he told the Telegraph. “The average consumer is going to want to know their own transactions and daily business is secure.

“One way of doing this is to use a one time pad essentially lists of random numbers where one copy of the numbers is held by the person sending the information and an identical copy is held by the person receiving the information. These are completely unbreakable when used properly,” he explained.

The critical feature of quantum computing is the unique fact that, if someone tampers with an information feed between two parties, then the nature of the quantum feed changes.

This makes eavesdropping impossible.

No, it wouldn’t make eavesdropping impossible. It would make eavesdropping on the communications channel impossible unless someone made an implementation error. (In the 80s, the NSA broke Soviet one-time-pad systems because the Soviets reused the pad.) Eavesdropping via spyware or Trojan or TEMPEST would still be possible.

EDITED TO ADD (10/26): Here’s another commenter who gets it wrong:

Now let me get this straight: I have no doubt that there are many greater worries in security than “mathematical crypography.” But does this justify totally ignoring the possibility that a cryptographic system might possibly be breakable? I mean maybe I’m influenced by this in the fact that I’ve been sitting in on a cryptanalysis course and I just met a graduate student who broke a cryptographic pseudorandom number generator, but really what kind of an argument is this? “Um, well, sometimes our cryptographic systems have been broken, but that’s nothing to worry about, because, you know, everything is kosher with the systems we are using.”

The point isn’t to ignore the possibility that a cryptographic system might possibly be broken; the point is to pay attention to the other parts of the system that are much much more likely to be already broken. Security is a chain; it’s only as secure as the weakest link. The cryptographic systems, as potentially flawed as they are, are the strongest link in the chain. We’d get a lot more security devoting our resources to making all those weaker links more secure.

Again, this is not to say that quantum cryptography isn’t incredibly cool research. It is, and I hope it continues to receive all sorts of funding. But for an operational network that is worried about security: you’ve got much bigger worries than whether Diffie-Hellman will be broken someday.

Posted on October 21, 2008 at 6:48 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.