December 15, 1999

by Bruce Schneier
Founder and CTO
Counterpane Internet Security, Inc.

A free monthly newsletter providing summaries, analyses, insights, and commentaries on computer security and cryptography.

Back issues are available at To subscribe or unsubscribe, see below.

Copyright (c) 1999 by Bruce Schneier

In this issue:

“Security Is Not a Product; It’s a Process”

In April 1999, someone discovered a vulnerability in Microsoft Data Access Components (MDAC) that could let an attacker take control of a remote Windows NT system. This vulnerability was initially reported on a public mailing list. Although the list moderator withheld the details of that risk from the public for more than a week, some clever hacker reverse-engineered the available details to create an exploit.

Then, an exploit script (written in PERL) was publicly posted on the Internet. At about the same time, Microsoft created a patch and work-around to prevent attackers from exploiting the vulnerability on users’ systems. Microsoft also issued a security bulletin on the topic, as did several other security news outlets.

But patches don’t magically fix security vulnerabilities. Over Halloween weekend, hackers attacked and defaced more than 25 NT-based Web sites. Seems like a bunch of security administrators didn’t bother updating their configurations.

This sort of thing goes on all the time. Another example: Microsoft issued a bulletin and a patch for a data access vulnerability in Internet Information Server (IIS) last year. Recently, experts demonstrated that Compaq, Dell, CompuServe, PSINet, and NASDAQ-AMEX never bothered installing the patch and were still vulnerable.

A vulnerability is reported and a patch is issued. If you believe the news reports, that’s the end of the story. But in most cases patches never get installed. This is why most systems on the Internet are vulnerable to known attacks for which fixes exist.

Security is not a product; it’s a process. It’s the process of paying attention to vendor updates for your products. Not only network and network security products—browsers, firewalls, network operating systems, Web server software—but every piece of software you run. Vulnerabilities in your word processor can compromise the security of your network.

It’s the process of watching your systems, carefully, for signs of attack. Your firewall produces audit logs. So do your UNIX and NT servers. So do your routers and network servers. Learn to read them, daily. Learn what an attack looks like and how to recognize it.

No security product acts as magical security dust; they all require time and expertise to make work properly. You have to baby-sit them, every day.

The Microsoft bug mentioned above:……

News report:…

Why vulnerabilities don’t get fixed:… [link dead; try…]

Sarah Flannery’s Public-Key Algorithm

In January 1999, a 16-year old Irish woman named Sarah Flannery made international news by announcing a new public-key algorithm, called Cayley-Purser, that was supposedly faster and better than RSA and ElGamal.

The only problem is that no one knew what the algorithm was.

Well, it’s finally public.

Flannery’s paper, describing the Cayley-Purser algorithm, has been published on the Internet by an unknown source. It’s interesting work, but it’s not secure. Flannery herself publishes a break of the algorithm in an appendix.

To me, this makes Flannery even more impressive as a young cryptographer. As I have said many times before, anyone can invent a new cryptosystem. Very few people are smart enough to be able to break them. By breaking her own system, Flannery has shown even more promise as a cryptographer. I look forward to more work from her.

Flannery’s paper:

News stories from January:……

ECHELON Technology

The NSA has been patenting, and publishing, technology that is relevant to ECHELON.

ECHELON is a code word for an automated global interception system operated by the intelligence agencies of the U.S., the UK, Canada, Australia and New Zealand. (The NSA takes the lead.) According to reports, it is capable of intercepting and processing many types of transmissions, throughout the globe.

Over the past few months, the U.S. House of Representatives has been investigating ECHELON. As part of these investigations, the House Select Committee on Intelligence requested documents from the NSA regarding its operating standards for intelligence systems like ECHELON that may intercept communications of Americans. To everyone’s surprise, NSA officials invoked attorney-client privilege and refused to disclose the documents. EPIC has taken the NSA to court.

I’ve seen estimates that ECHELON intercepts as many as 3 billion communications everyday, including phone calls, e-mail messages, Internet downloads, satellite transmissions, and so on. The system gathers all of these transmissions indiscriminately, then sorts and distills the information through artificial intelligence programs. Some sources have claimed that ECHELON sifts through 90% of the Internet’s traffic.

How does it do it? Read U.S. Patent 5,937,422, “Automatically generating a topic description for text and searching and sorting text by topic using the same,” assigned to the NSA. Read two papers titled “Text Retrieval via Semantic Forests,” written by NSA employees.

Semantic Forests, patented by the NSA (the patent does not use the name), were developed to retrieve information “on the output of automatic speech-to-text (speech recognition) systems” and topic labeling. It is described as a functional software program.

The researchers tested this program on numerous pools of data, and improved the test results from one year to the next. All this occurred in the window between when the NSA applied for the patent, more than two years ago, and when the patent was granted this year.

One of the major technological barriers to implementing ECHELON is automatic searching tools for voice communications. Computers need to “think” like humans when analyzing the often imperfect computer transcriptions of voice conversations.

The patent claims that the NSA has solved this problem. First, a computer automatically assigns a label, or topic description, to raw data. This system is far more sophisticated than previous systems because it labels data based on meaning not on keywords.

Second, the patent includes an optional pre-processing step which cleans up text, much of which the agency appears to expect will come from human conversations. This pre-processing will remove what the patent calls “stutter phrases.” These phrases “frequently occurs [sic] in text based on speech.” The pre-processing step will also remove “obvious stop words” such as the article “the.”

The invention is designed to sift through foreign language documents, either in text, or “where the text may be derived from speech and where the text may be in any language,” in the words of the patent.

The papers go into more detail on the implementation of this technology. The NSA team ran the software over several pools of documents, some of which were text from spoken words (called SDR), and some regular documents. They ran the tests over each pool separately. Some of the text documents analyzed appear to include data from “Internet discussion groups,” though I can’t quite determine if these were used to train the software program, or illustrate results.

The “30-document average precision” (whatever that is) on one test pool rose significantly in one year, from 19% in 1997 to 27% in 1998. This shows that they’re getting better.

It appears that the tests on the pool of speech- to text-based documents came in at between 20% to 23% accuracy (see Tables 5 and 6 of the “Semantic Forests TREC7” paper) at the 30-document average. (A “document” in this definition can mean a topic query. In other words, 30 documents can actually mean 30 questions to the database).

It’s pretty clear to me that this technology can be used to support an ECHELON-like system. I’m surprised the NSA hasn’t classified this work.

The Semantic Forest papers:

The patent: [link moved to]

News reports on this:……

General information on ECHELON:,1294,32586,00.html

Excellent article on ECHELON:

EPIC files lawsuit against NSA to get ECHELON document released:
EPIC’s complaint:
NY Times article:…

Counterpane—Featured Research

“Ten Risks of PKI: What You’re Not Being Told About Public-Key Infrastructure”

C. Ellison and B. Schneier, Computer Security Journal, vol. 16, n. 1, 2000, pp. 1-7.

Public-key infrastructure has been oversold as the answer to many network security problems. We discuss the problems that PKI doesn’t solve, and that PKI vendors don’t like to mention.


There’s a product, PawSense, that claims to detect when cats are stepping on your keyboard and a) require a password, just in case it’s a human doing it, and b) make a noise that annoys the cat. It’s a bizarre form of biometrics, I suppose.

And on the more mundane biometrics front, a security system is being developed that can identify people by their gait.

Jon Carroll’s essay on the FBI’s new anti-terrorist strategy is pretty funny. “Bob, show Mr. Carroll the attractive pen and pencil set we’re offering just for a chance to talk to you about terrorism for a few minutes.”…

The German government is going to help fund the GPG effort. GPG is an open-source program that is compatible with (some versions of) PGP.…

Risks of “anonymous” e-mail accounts: Someone sent a bomb threat from an account from an account named The police contacted Hotmail, and found that the Hotmail account had been accessed at a particular date and time, using an IP address owned by America Online. Using the AOL information, police identified exactly who was using that IP address at that time and were able to trace the sender to his apartment in Brooklyn.
I posted this to comp.risks, and people pointed out that the police didn’t need to contact Hotmail. The information is in the e-mail header.

This essay describes a copy-protection scheme from several years back that was actually successful (in part because the game it protected was never all that popular). There’s a discussion of how software cracking works, and some interesting attempts to psych out what crackers don’t like to do and force them to do a lot of it in order to crack the game. It’s security through obfuscation, of course, but the author is very clear that copy-protection is ultimately impossible and all you can do is discourage attackers that aren’t determined enough.…

I know nothing about the Windows 2000 Encryption Pack, except what I read at this URL:…

An interesting article on simulating Web attacks:

And someone’s listing of the top ten computer hacks of all time:…

EPIC (Electronic Privacy Information Center), EFF (Electronic Frontier Foundation), and the ACLU have asked a federal appeals court to block rules that give the FBI power to determine appropriate wiretapping capabilities for new communications systems. The groups claim that the levels of surveillance the FBI wants exceed what it is entitled to under the law.………

E-mail eavesdropping: Online bookseller Alibris will plead guilty to charges that they intercepted the e-mail sent by to business partners. This may be the first conviction of industrial e-mail espionage.…

Seymour Hirsch writes about the NSA’s failures in the Internet age:
An NPR report on the same topic (audio):

Opinions on UNIX and Windows NT security, and the differing philosophies of the two operating systems:…

Is buggy software inevitable? It is, as long as market forces reward it. There is no liability for buggy software, so there is no economic incentive to create quality software. In fact, there is an economic incentive to create the lowest quality the market will bear. This _Business Week_ article discusses the problem:

The DVD crypto break affects the release of new products:

The Smart Card Security Users Group (SCSUG), which is composed of Visa, AmEx, Europay, MasterCard, Mondex, JCB, and the National Information Assurance Partnership (NIAP = NIST + NSA). They’ve written a Protection Profile, and have posted it for comment:

PGP got a world-wide export license:… [link dead; try…]…

And two smart card breaks to finish things off:

Number 1. A French engineer succeeded in factoring the 640-bit RSA key stored in the chip on the card (all French “CB” credit cards have had a chip since 1990). He contacted the conglomerate (GIE) that makes these cards; now he’s being sued by GIE for fraud and intrusion and risks seven years in prison, as well as a 5M-franc ($800K) fine. GIE has also censored TV programs where he should have been interviewed, and claim he is blackmailing them. Meanwhile, they are not fixing the problem. The weakness? The payment terminal: another good illustration of “weakest link in the chain” attack.

Number 2. German hackers have succeeded in cracking the Siemens digital signature chip, used in electronic payment and access control systems throughout Germany. It seems that there was an undocumented test mode of the chip that allows someone to dump the card’s memory. Already the code has been disassembled, and some private keys have been compromised.

New U.S. Crypto Export Regulations—Draft

On November 22, the White House released a draft of its new crypto export regulations. These new regulations are part of the changes promised in September. These regulations were due to be released on December 15, but have been delayed until January 15.

The regulations do some of what’s promised—allow for export of 56-bit and 64-bit encryption products—but fall far short of the promises made in September.

I have three main objections:

One: These regulations affect end-user products only. The primary uses of cryptography are not for end-user products. They do not affect Internet routers, firewalls, VPNs, CAs, etc. They do not affect software toolkits. These regulations do not affect technical assistance.

Two: While these regulations permit the export of open-source cryptography code, there are some nasty complications. Near as I can tell, I can post crypto source on my Web page, but if a foreign company wants to use it I am obligated to make them get U.S. approval for the end product. Not only is this ridiculous, it is completely unenforceable. (Although you can see the NSA salivating at the chance to get their hands on all of those foreign products.)

Three: These regulations are much too complicated. Instead of simply lifting export restrictions, this proposal just adds to the confusion. Heavy reporting and review requirements have always served the interests of those trying to stop the spread of strong cryptography. There are so many ifs, ands, and buts in these regulations that many will simply not bother. There are enough ambiguities to keep the lawyers busy for years. This is not the simplified and streamlined export process that we have been promised.

Rumor has it that the Administration is addressing these (and other) concerns in the final regulations, and that the month delay was to make sure they were addressed. They are redoing the definition of “non-commercial” source code, trying to spell out the screening requirements (which they claim will be easy to comply with), and streamlining any reporting requirements. If this is true, the final version of this could be quite good. People I trust, who are closer to the process than I am, are “guardedly optimistic.” We’ll see.

Draft regulations:…

News reports:………,1283,32732,00.html

Counterpane Internet Security News

You may have some noticed some changes around Counterpane. Here’s the news:

Last summer I teamed up with seasoned start-up CEO Tom Rowley to start a new company: Counterpane Internet Security, Inc. This company will address the critical need for higher level security services on the Internet. My motto is: “The fundamental problems in computer security are no longer about technology; they’re about applying the technology.”

We have raised funding, and are now putting the technical and business management teams in place. We’re keeping a low profile for now, but we’re actively hiring. See for details.

My consulting company, Counterpane Systems, has become the research division and working laboratory of Counterpane Internet Security, Inc. Renamed Counterpane Labs, it will provide ongoing research and critical resources to the newly formed company. Counterpane Labs will continue to engage in cryptography research, and to support the Twofish AES submission.

Bruce Schneier’s article on attack trees has been published in Dr. Dobb’s Journal:
See also the presentation on the topic at:
And the discussion on Slashdot:

The Doghouse: Egg

Egg, a UK banking and investment firm, sent customer credit card details out in unencrypted e-mails. “We didn’t think [sending credit card details in unsafe e-mails] was a security problem,” a spokeswoman for Egg conceded today. “We’ve now accepted that this was not best business practice.”

Fast Software Encryption 2000

Fast Software Encryption is an annual workshop on cryptography. The first Fast Software Encryption workshop was held in Cambridge in 1993, followed by Leuven in 1994, Cambridge in 1996, Haifa in 1997, Paris in 1998, and Rome in 1999. The workshop concentrates on all aspects of traditional cryptographic algorithms, including the design and analysis of block ciphers, stream ciphers, and hash functions.

The seventh Fast Software Encryption workshop, FSE 2000, will be held from 10-12 April 2000, in New York, at the Hilton New York and Towers. It will be in conjunction with the 3rd AES Candidate Conference (same location, 13-14 April 2000). We expect that most people will attend both FSE and AES.

Come, experience the wonders of symmetric cryptography. Watch the AES finalists battle it out in a war of cryptanalyses, comparisons, and vague innuendoes. If you’re a corporation, please help by sponsoring the event. Register by the end of the year and save some money.

Fast Software Encryption Workshop:

Third AES Candidate Conference:…

European Cellular Encryption Algorithms

There’s been a lot of bad information about what kinds of encryption are out there, what’s been broken, and how bad the situation really is. Here’s a summary of what’s really going on.

GSM is the world’s most widely used mobile telephony system (51% market share of all cellular phones, both analog and digital), with over 215 million subscribers in America, Europe, Asia, Africa, and Australia. In the US, GSM is employed in the “Digital PCS” networks of such telecommunications giants as Pacific Bell, Bell South, and Omnipoint.

There are four cryptographic algorithms in the GSM standard, although not all the algorithms are necessarily implemented in very GSM system. They are:

A3, the authentication algorithm to prevent phone cloning
A5/1, the stronger of the two voice-encryption algorithms A5/2, the weaker of the two voice-encryption algorithms
A8, the voice-privacy key-generation algorithm

(Remember, these voice-encryption algorithms only encrypt voice between the cellphone and the base station. It does not encrypt voice within the phone network. It does not encrypt end to end. It only encrypts the over-the-air portion of the transmission.)

These algorithms were developed in secret, and were never published. “Marc Briceno” (with the Smartcard Developer Association) reverse-engineered the algorithms, and then Ian Goldberg and David Wagner at U.C. Berkeley cryptanalyzed them.

Most GSM providers use an algorithm called COMP128 for both A3 and A8. This algorithm is cryptographically weak, and it is not difficult to break the algorithm and clone GSM digital phones.

The attack takes just 2^19 queries to the GSM smart-card chip, which takes roughly 8 hours over the air. This attack can be performed on as many simultaneous phones in radio range as your rogue base station has channels.

The Berkeley group published their COMP128 analysis in April 1998. They also demonstrated that all A8 implementations they looked at, including the few that did not use COMP128, were deliberately weakened. The algorithm takes a 64-bit key, but ten key bits were set to zero. This means that the keys that secure the voice-privacy algorithms are weaker than the documentation indicates.

They published and analyzed A5/2 in August 1999. As the weaker of the two voice-encryption algorithms, it proved to be very weak. It can be broken in real-time without any trouble; the work factor is around 2^16. Supposedly this algorithm was developed with “help” from the NSA, so these weaknesses are not surprising.

The Berkeley group published A5/1 in May 1999. The first attack was by Jovan Golic, which gives the algorithm a work factor of 2^40. This means that it can be broken in nearly real-time using specialized hardware. Currently the best attack is by Biryukov and Shamir. Earlier this month they showed that they can find the A5/1 key in less than a second on a single PC with 128 MB RAM and two 73 GB hard disks, by analyzing the output of the A5/1 algorithm in the first two minutes of the conversation.

All GSM providers and equipment vendors are part of the GSM Association. The algorithms were designed and analyzed by the secretive “SAGE” group (which is really part of ETSI). We don’t know who the people are or what their resumes look like. What we do know is that the SAGE security analyses of the ciphers are online at ETSI’s homepage in PDF format. Read it; it’s entertaining. A5/1 is purported to be a modified French naval cipher. This is mentioned in the leaked Racal document.

What’s most interesting about these algorithms is how robustly lousy they are. Both voice-encryption algorithms are flawed, but not obviously. The attacks on both A5/1 and A5/2 make use of subtle structures of the algorithm, and result in the ability to decrypt voice traffic in real time on average computer equipment. At the same time, the output of the A8 algorithm that provides key material for A5/1 and A5/2 has been artificially weakened by setting ten key bits to zero. And also, the COMP128 algorithm that provides the keying material that is eventually weakened and fed into the weakened algorithms is, itself, weak.

And remember, this encryption only encrypts the over-the-air portion of the transmission. Any legal access required by law enforcement is unaffected; they can always get a warrant and listen at the base station. The only reason to weaken this system is for *illegal* access. Only wiretaps lacking a court authorization need over-the-air intercepts.

The industry reaction to this has been predictably clueless. One GSM spokesman claimed that it is impossible to intercept GSM signals off the air, so the encryption breaks are irrelevant. Notwithstanding the fact that GSM interception equipment was once sold openly—now it’s illegal—certainly the *phone* can receive signals off the air. Estimated cost for a high-quality interception station is well under $10K.

GSM analysis:

GSM Association Web site:

News reports:……

Comments from Readers

From: bill carpenter.ORG (WJCarpenter)
Subject: Electronic voting, replying to Greg Weiss

> Are e-votes more prone to voter coercion?
> I used to agree with you on this. But when talking with someone
> about absentee balloting this last week, it seems to me this
> problem is equally present in today’s non-virtual scenario. How?
> Well, absentee ballots enable voter coercion in the privacy of
> non-public polling places. E-votes are not particularly more
> subvertible than absentee ballot votes at least from the voter
> coercion threat.

> Now with absentee ballots, there is one further protection. One
> can apparently still vote in person at the polling place, and their
> polling-place vote takes precedence over their absentee ballot.

Hmmm. I had the opportunity to describe the coercion problem to a non-technical person recently, and the absentee ballot parallel was immediately obvious. Equally obvious were the critical differences.

First, it is probably true that only a small percentage of voters use absentee ballots (beats me, an ambitious person could easily find out; my guess is that 15-20% is a big number). So, even if the absentee ballot system is completely corrupted by coercion, its effects are limited. Sure, absentee ballots decide some elections, but those are close elections to begin with.

There is a dis-incentive to use absentee ballots because you must commit your vote several days in advance of the election. My intuition tells me that for most common cases people make up their minds at the last minute, perhaps even in the voting booth, and they are subconsciously aware of this. It seems likely to me that more people who truly need an absentee ballot (because they will be out of town or whatever) will forgo voting altogether.

Electronic voting would presumably be made more convenient, even more convenient than traditional voting booth voting (no standing in line, no finding a parking place, no finding someone to watch your toddler for you). It is this convenience that should make it much more popular than absentee ballots have ever been. One could probably look at the case of electronic filing of tax returns (where you have to actually pay a fee) for how fast something like this could catch on. Electronic voting should be even more popular.

Second, the forced delay in the absentee ballot process should be missing from electronic voting. Electronic voting doesn’t carry the logistical burden of paper absentee ballots, and so it could be done exactly on election day. The success rate of a coercion scheme is probably related to how long you would have to control someone to keep them from going to the voting booth. (This doesn’t mean that electronic voting wouldn’t come with an artificial delay if one or more dominating political parties saw an advantage in that.)

From: Dave Sill <de5>
Subject: “Why Computers are Insecure”

Regarding your “Why Computers are Insecure” piece, I think you’re almost completely wrong.

Yes, designing and implementing secure software is very hard, but it’s not as hard as you make it sound.

Proving security is, of course, impractical for any reasonably complex system, but, then, so is proving correctness. Does the inability to prove that software does the right thing mean we can never build software that works? Of course not.

We’re in the midst of a software quality crisis, and security problems are just one symptom.

The problem is simply that users don’t put a premium on reliability or security. Users want features above all else, and they’re willing to accept a wide range of bugs as long as a product has the desired features. Until reliability and security are features that users demand, vendors won’t go to the expense of providing them.

We’ve got to get up, go to our windows, and shout “I’m as mad as hell, and I’m not going to take it anymore!” We’ve simply got to stop using poorly designed and implemented software.

Yes, “virtually all software is developed using a ‘try-and-fix’ methodology”—but that’s not the only software development methodology available. Software can be engineered for reliability and security just like it can be engineered to implement certain capabilities.

And, yes, Windows 2000 will have many more bugs than any software system in history. But that’s due more to Microsoft’s poor design and engineering than it is to the mind boggling complexity of the system.

From: bartels
Subject: “Why Computers are Insecure”

> Almost every week the computer press covers another security flaw:
> When will it get better? … I don’t believe it ever will….
> Security engineering is different from any other type of engineering. …
> In many ways this is similar to safety engineering. …
> The only reasonable way to “test” security is to perform security reviews. …
> Satan’s computer is hard to test.

I believe you’re missing the real problem here.

I was a verification engineer for two years, testing the software in the Boeing 777 fly by wire computer. I’ve worked on “Satan’s computer” as you put it. We played “devil’s advocate” continuously looking for flaws in the design or flaws in the code that might lead to a bug. A benchmark to thoroughness, one module consisted of 30 pages of B size “schematics” which showed the arithmetic flow and design for the module. I cant remember the exact number of lines of code, but I seem to recall it was roughly 20 pages of solid code. I spent three months reviewing that one module.

Here’s the part I think you’re missing though. Our group was self driven to do their job. Boeing paid us to do our job, sure. And Boeing could be liable if the plane crashed, absolutely. The FAA gave us the requirements for testing software, yes. But at the heart of it all, I think we were clearly driven by a simple concept: We could all see the consequences if we failed our task.

People were putting their lives in our hands. Our software literally keeps the plane in the air. If we didn’t do our job, people could die. It was a universally clear cut mission. It was something everyone on the team could identify with.

There is not a universally clear consequence to bad encryption systems. Companies who produce systems have no clear cut consequence that the engineers “in the trenches” can identify with. They get paid, either way. They have never been held liable for poorly implemented encryptions systems.

From: Greg Guerin <glguerin>
Subject: Security engineering comparison

I really liked the feature article in Nov 99 Crypto-Gram. The analogy to safety engineering was excellent. It left me with a nagging feeling I’d recently read something about safety engineering, but I couldn’t pin it down. The answer recently clicked into place while filing magazine back-issues.

There is an article entitled “Safety Critical Embedded Systems” in the Oct 1999 issue of “Embedded Systems Programming”: <>

Unfortunately, this particular article isn’t on-line, but reprints or back-issues can be ordered.

Anyway, the article was a clear concise overview of safety engineering, with an emphasis on embedded systems. I won’t try to summarize it, because I’d just end up repeating the whole article. But I will list the safety guidelines at the end of the article:

* All safety-related systems have hard real-time deadlines.
* Safety always requires some level of redundancy.
* Whenever possible, separate and isolate the safety-critical aspects of the system.
* Safety is a system issue, not a software issue.
* The key to a safe design is predictability.
* Err on the side of simplicity.
* Good design practices are required.
* Good design practices are not enough.
* Plan for all your assumptions to be violated.

It’s kind of eerie to realize that every one of these applies in full measure to security engineering, even the “hard real-time deadline.” In safety systems, it means that a fault must be detected quickly enough for it to be acted on in order to avoid an accident. A fault-detector that triggers only after an accident has happened is worthless. In security systems, not detecting a breach in a timely manner diminishes the usefulness of detection. Security systems have the added difficulty of not always being able to detect a breach—encryption algorithms usually can’t tell if they’ve been cracked or not.

From: “Nicholas C. Weaver” <nweaver CS.Berkeley.EDU>
Subject: DVD encryption, reason for multiple keys…

The reason for the multiple key structure (session key for the DVD, encrypted separately by the 400 odd player keys) was so that if, say, a single key was made public, they could remove that key from future DVDs produced, essentially acting as a limited key rescission measure. A good idea if their encryption algorithm itself wasn’t incredibly dinky and highly vulnerable to a known plaintext attack.

Also, they probably did deliberately choose a 40-bit scheme, simply to avoid any potential export complications. It would be bad to have a DVD player classed as a “munition,” even if it is perfectly useless to actually encrypt real data.

One other observation: The encryption never prevented organized, digital, DVD piracy, since that only requires the manufacturing of a bitwise copy of the DVD. It only prevented the organized pirates from removing region encoding information.

Similarly, the many keys is probably for region encoding. Since software players were often set up (and I know my computer hardware player is) to specify a region with limited abilities to change it, the different keys probably represented the player acting as a different “region.”

Finally, the only reason why people bothered to crack the encryption at this time is because there were no players which worked under Linux. If there was a Linux software DVD player, the encryption probably wouldn’t have been publicly cracked for months or years, because there wouldn’t have been an incentive for it.

From: NBII <afn41391>
Subject: DVD encryption cracked

A good article.

In addition to your recommended links, I would suggest you include the following VERY well written treatise on Digital IP and Copyrights by J.P. Barlow:…

I have yet to read a better overview of the problems inherent in the current presumptions about IP and how it “will work” in the coming economy.

You’ll note that, in 1994, he “predicted” what is essentially exactly the problem and the situation you describe.

From: Roger Schlafly
Subject: Elliptic Curve Public Key Cryptography

I’d go with elliptic curves if you need security for decades. The elliptic curve DL problem seems to be much more intrinsically difficult than the RSA problem. Elliptic curve systems also give better protection against Moore’s Law. If you accept the Lenstra-Verheul analysis, then you need to use 3000-bit keys with RSA, and almost no one is doing that.

CRYPTO-GRAM is a free monthly newsletter providing summaries, analyses, insights, and commentaries on computer security and cryptography.

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CRYPTO-GRAM is written by Bruce Schneier. Schneier is founder and CTO of Counterpane Internet Security Inc., the author of “Applied Cryptography,” and an inventor of the Blowfish, Twofish, and Yarrow algorithms. He served on the board of the International Association for Cryptologic Research, EPIC, and VTW. He is a frequent writer and lecturer on computer security and cryptography.

Counterpane Internet Security, Inc. is a venture-funded company bringing innovative managed security solutions to the enterprise.

Sidebar photo of Bruce Schneier by Joe MacInnis.