Entries Tagged "Applied Cryptography"

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Microsoft Is Finally Killing RC4

After twenty-six years, Microsoft is finally upgrading the last remaining instance of the encryption algorithm RC4 in Windows.

One of the most visible holdouts in supporting RC4 has been Microsoft. Eventually, Microsoft upgraded Active Directory to support the much more secure AES encryption standard. But by default, Windows servers have continued to respond to RC4-based authentication requests and return an RC4-based response. The RC4 fallback has been a favorite weakness hackers have exploited to compromise enterprise networks. Use of RC4 played a key role in last year’s breach of health giant Ascension. The breach caused life-threatening disruptions at 140 hospitals and put the medical records of 5.6 million patients into the hands of the attackers. US Senator Ron Wyden (D-Ore.) in September called on the Federal Trade Commission to investigate Microsoft for “gross cybersecurity negligence,” citing the continued default support for RC4.

Last week, Microsoft said it was finally deprecating RC4 and cited its susceptibility to Kerberoasting, the form of attack, known since 2014, that was the root cause of the initial intrusion into Ascension’s network.

Fun fact: RC4 was a trade secret until I published the algorithm in the second edition of Applied Cryptography in 1995.

Posted on December 22, 2025 at 12:05 PM • View Comments

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

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Sidebar photo of Bruce Schneier by Joe MacInnis.