Entries Tagged "backdoors"

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NSA Backdoors in Crypto AG Ciphering Machines

This story made the rounds in European newspapers about ten years ago—mostly stories in German, if I remember—but it wasn’t covered much here in the U.S.

For half a century, Crypto AG, a Swiss company located in Zug, has sold to more than 100 countries the encryption machines their officials rely upon to exchange their most sensitive economic, diplomatic and military messages. Crypto AG was founded in 1952 by the legendary (Russian born) Swedish cryptographer Boris Hagelin. During World War II, Hagelin sold 140,000 of his machine to the US Army.

“In the meantime, the Crypto AG has built up long standing cooperative relations with customers in 130 countries,” states a prospectus of the company. The home page of the company Web site says, “Crypto AG is the preferred top-security partner for civilian and military authorities worldwide. Security is our business and will always remain our business.”

And for all those years, US eavesdroppers could read these messages without the least difficulty. A decade after the end of WWII, the NSA, also known as No Such Agency, had rigged the Crypto AG machines in various ways according to the targeted countries. It is probably no exaggeration to state that this 20th century version of the “Trojan horse” is quite likely the greatest sting in modern history.

We don’t know the truth here, but the article lays out the evidence pretty well.

See this essay of mine on how the NSA might have been able to read Iranian encrypted traffic.

Posted on January 11, 2008 at 6:51 AM • View Comments

The Strange Story of Dual_EC_DRBG

Random numbers are critical for cryptography: for encryption keys, random authentication challenges, initialization vectors, nonces, key-agreement schemes, generating prime numbers and so on. Break the random-number generator, and most of the time you break the entire security system. Which is why you should worry about a new random-number standard that includes an algorithm that is slow, badly designed and just might contain a backdoor for the National Security Agency.

Generating random numbers isn’t easy, and researchers have discovered lots of problems and attacks over the years. A recent paper found a flaw in the Windows 2000 random-number generator. Another paper found flaws in the Linux random-number generator. Back in 1996, an early version of SSL was broken because of flaws in its random-number generator. With John Kelsey and Niels Ferguson in 1999, I co-authored Yarrow, a random-number generator based on our own cryptanalysis work. I improved this design four years later—and renamed it Fortuna—in the book Practical Cryptography, which I co-authored with Ferguson.

The U.S. government released a new official standard for random-number generators this year, and it will likely be followed by software and hardware developers around the world. Called NIST Special Publication 800-90 (.pdf), the 130-page document contains four different approved techniques, called DRBGs, or “Deterministic Random Bit Generators.” All four are based on existing cryptographic primitives. One is based on hash functions, one on HMAC, one on block ciphers and one on elliptic curves. It’s smart cryptographic design to use only a few well-trusted cryptographic primitives, so building a random-number generator out of existing parts is a good thing.

But one of those generators—the one based on elliptic curves—is not like the others. Called Dual_EC_DRBG, not only is it a mouthful to say, it’s also three orders of magnitude slower than its peers. It’s in the standard only because it’s been championed by the NSA, which first proposed it years ago in a related standardization project at the American National Standards Institute.

The NSA has always been intimately involved in U.S. cryptography standards—it is, after all, expert in making and breaking secret codes. So the agency’s participation in the NIST (the U.S. Commerce Department’s National Institute of Standards and Technology) standard is not sinister in itself. It’s only when you look under the hood at the NSA’s contribution that questions arise.

Problems with Dual_EC_DRBG were first described in early 2006. The math is complicated, but the general point is that the random numbers it produces have a small bias. The problem isn’t large enough to make the algorithm unusable—and Appendix E of the NIST standard describes an optional work-around to avoid the issue—but it’s cause for concern. Cryptographers are a conservative bunch: We don’t like to use algorithms that have even a whiff of a problem.

But today there’s an even bigger stink brewing around Dual_EC_DRBG. In an informal presentation (.pdf) at the CRYPTO 2007 conference in August, Dan Shumow and Niels Ferguson showed that the algorithm contains a weakness that can only be described as a backdoor.

This is how it works: There are a bunch of constants—fixed numbers—in the standard used to define the algorithm’s elliptic curve. These constants are listed in Appendix A of the NIST publication, but nowhere is it explained where they came from.

What Shumow and Ferguson showed is that these numbers have a relationship with a second, secret set of numbers that can act as a kind of skeleton key. If you know the secret numbers, you can predict the output of the random-number generator after collecting just 32 bytes of its output. To put that in real terms, you only need to monitor one TLS internet encryption connection in order to crack the security of that protocol. If you know the secret numbers, you can completely break any instantiation of Dual_EC_DRBG.

The researchers don’t know what the secret numbers are. But because of the way the algorithm works, the person who produced the constants might know; he had the mathematical opportunity to produce the constants and the secret numbers in tandem.

Of course, we have no way of knowing whether the NSA knows the secret numbers that break Dual_EC-DRBG. We have no way of knowing whether an NSA employee working on his own came up with the constants—and has the secret numbers. We don’t know if someone from NIST, or someone in the ANSI working group, has them. Maybe nobody does.

We don’t know where the constants came from in the first place. We only know that whoever came up with them could have the key to this backdoor. And we know there’s no way for NIST—or anyone else—to prove otherwise.

This is scary stuff indeed.

Even if no one knows the secret numbers, the fact that the backdoor is present makes Dual_EC_DRBG very fragile. If someone were to solve just one instance of the algorithm’s elliptic-curve problem, he would effectively have the keys to the kingdom. He could then use it for whatever nefarious purpose he wanted. Or he could publish his result, and render every implementation of the random-number generator completely insecure.

It’s possible to implement Dual_EC_DRBG in such a way as to protect it against this backdoor, by generating new constants with another secure random-number generator and then publishing the seed. This method is even in the NIST document, in Appendix A. But the procedure is optional, and my guess is that most implementations of the Dual_EC_DRBG won’t bother.

If this story leaves you confused, join the club. I don’t understand why the NSA was so insistent about including Dual_EC_DRBG in the standard. It makes no sense as a trap door: It’s public, and rather obvious. It makes no sense from an engineering perspective: It’s too slow for anyone to willingly use it. And it makes no sense from a backwards-compatibility perspective: Swapping one random-number generator for another is easy.

My recommendation, if you’re in need of a random-number generator, is not to use Dual_EC_DRBG under any circumstances. If you have to use something in SP 800-90, use CTR_DRBG or Hash_DRBG.

In the meantime, both NIST and the NSA have some explaining to do.

This essay originally appeared on Wired.com.

Posted on November 15, 2007 at 6:08 AM • View Comments

Is There Strategic Software?

If you define “critical infrastructure” as “things essential for the functioning of a society and economy,” then software is critical infrastructure. For many companies and individuals, if their computers stop working, they stop working.

It’s a situation that snuck up on us. Everyone knew that the software that flies 747s or targets cruise missiles was critical, but who thought of the airlines’ weight and balance computers, or the operating system running the databases and spreadsheets that determine which cruise missiles get shipped where?

And over the years, common, off-the-shelf, personal- and business-grade software has been used for more and more critical applications. Today we find ourselves in a situation where a well-positioned flaw in Windows, Cisco routers or Apache could seriously affect the economy.

It’s perfectly rational to assume that some programmers—a tiny minority I’m sure—are deliberately adding vulnerabilities and back doors into the code they write. I’m actually kind of amazed that back doors secretly added by the CIA/NSA, MI5, the Chinese, Mossad and others don’t conflict with each other. Even if these groups aren’t infiltrating software companies with back doors, you can be sure they’re scouring products for vulnerabilities they can exploit, if necessary. On the other hand, we’re already living in a world where dozens of new flaws are discovered in common software products weekly, and the economy is humming along. But we’re not talking about this month’s worm from Asia or new phishing software from the Russian mafia—we’re talking national intelligence organizations. “Infowar” is an overhyped term, but the next war will have a cyberspace component, and these organizations wouldn’t be doing their jobs if they weren’t preparing for it.

Marcus is 100 percent correct when he says it’s simply too late to do anything about it. The software industry is international, and no country can start demanding domestic-only software and expect to get anywhere. Nor would that actually solve the problem, which is more about the allegiance of millions of individual programmers than which country they happen to inhabit.

So, what to do? The key here is to remember the real problem: current commercial software practices are not secure enough to reliably detect and delete deliberately inserted malicious code. Once you understand this, you’ll drop the red herring arguments that led to CheckPoint not being able to buy Sourcefire and concentrate on the real solution: defense in depth.

In theory, security software are after-the-fact kludges because the underlying OS and apps are riddled with vulnerabilities. If your software were written properly, you wouldn’t need a firewall—right?

If we were to get serious about critical infrastructure, we’d recognize it’s all critical and start building security software to protect it. We’d build our security based on the principles of safe failure; we’d assume security would fail and make sure it’s OK when it does. We’d use defense in depth and compartmentalization to minimize the effects of failure. Basically, we’d do everything we’re supposed to do now to secure our networks.

It’d be expensive, probably prohibitively so. Maybe it would be easier to continue to ignore the problem, or at least manage geopolitics so that no national military wants to take us down.

This is the second half of a point/counterpoint I did with Marcus Ranum (here’s his half) for the September 2006 issue of Information Security Magazine.

Posted on September 12, 2006 at 10:38 AM • View Comments

Man Sues Compaq for False Advertising

Convicted felon Michael Crooker is suing Compaq (now HP) for false advertising. He bought a computer promised to be secure, but the FBI got his data anyway:

He bought it in September 2002, expressly because it had a feature called DriveLock, which freezes up the hard drive if you don’t have the proper password.

The computer’s manual claims that “if one were to lose his Master Password and his User Password, then the hard drive is useless and the data cannot be resurrected even by Compaq’s headquarters staff,” Crooker wrote in the suit.

Crooker has a copy of an ATF search warrant for files on the computer, which includes a handwritten notation: “Computer lock not able to be broken/disabled. Computer forwarded to FBI lab.” Crooker says he refused to give investigators the password, and was told the computer would be broken into “through a backdoor provided by Compaq,” which is now part of HP.

It’s unclear what was done with the laptop, but Crooker says a subsequent search warrant for his e-mail account, issued in January 2005, showed investigators had somehow gained access to his 40 gigabyte hard drive. The FBI had broken through DriveLock and accessed his e-mails (both deleted and not) as well as lists of websites he’d visited and other information. The only files they couldn’t read were ones he’d encrypted using Wexcrypt, a software program freely available on the Internet.

I think this is great. It’s about time that computer companies were held liable for their advertising claims.

But his lawsuit against HP may be a long shot. Crooker appears to face strong counterarguments to his claim that HP is guilty of breach of contract, especially if the FBI made the company provide a backdoor.

“If they had a warrant, then I don’t see how his case has any merit at all,” said Steven Certilman, a Stamford attorney who heads the Technology Law section of the Connecticut Bar Association. “Whatever means they used, if it’s covered by the warrant, it’s legitimate.”

If HP claimed DriveLock was unbreakable when the company knew it was not, that might be a kind of false advertising.

But while documents on HP’s web site do claim that without the correct passwords, a DriveLock’ed hard drive is “permanently unusable,” such warnings may not constitute actual legal guarantees.

According to Certilman and other computer security experts, hardware and software makers are careful not to make themselves liable for the performance of their products.

“I haven’t heard of manufacturers, at least for the consumer market, making a promise of computer security. Usually you buy naked hardware and you’re on your own,” Certilman said. In general, computer warrantees are “limited only to replacement and repair of the component, and not to incidental consequential damages such as the exposure of the underlying data to snooping third parties,” he said. “So I would be quite surprised if there were a gaping hole in their warranty that would allow that kind of claim.”

That point meets with agreement from the noted computer security skeptic Bruce Schneier, the chief technology officer at Counterpane Internet Security in Mountain View, Calif.

“I mean, the computer industry promises nothing,” he said last week. “Did you ever read a shrink-wrapped license agreement? You should read one. It basically says, if this product deliberately kills your children, and we knew it would, and we decided not to tell you because it might harm sales, we’re not liable. I mean, it says stuff like that. They’re absurd documents. You have no rights.”

My final quote in the article:

“Unfortunately, this probably isn’t a great case,” Schneier said. “Here’s a man who’s not going to get much sympathy. You want a defendant who bought the Compaq computer, and then, you know, his competitor, or a rogue employee, or someone who broke into his office, got the data. That’s a much more sympathetic defendant.”

Posted on May 3, 2006 at 9:26 AM • View Comments

Microsoft's BitLocker

BitLocker Drive Encryption is a new security feature in Windows Vista, designed to work with the Trusted Platform Module (TPM). Basically, it encrypts the C drive with a computer-generated key. In its basic mode, an attacker can still access the data on the drive by guessing the user’s password, but would not be able to get at the drive by booting the disk up using another operating system, or removing the drive and attaching it to another computer.

There are several modes for BitLocker. In the simplest mode, the TPM stores the key and the whole thing happens completely invisibly. The user does nothing differently, and notices nothing different.

The BitLocker key can also be stored on a USB drive. Here, the user has to insert the USB drive into the computer during boot. Then there’s a mode that uses a key stored in the TPM and a key stored on a USB drive. And finally, there’s a mode that uses a key stored in the TPM and a four-digit PIN that the user types into the computer. This happens early in the boot process, when there’s still ASCII text on the screen.

Note that if you configure BitLocker with a USB key or a PIN, password guessing doesn’t work. BitLocker doesn’t even let you get to a password screen to try.

For most people, basic mode is the best. People will keep their USB key in their computer bag with their laptop, so it won’t add much security. But if you can force users to attach it to their keychains—remember that you only need the key to boot the computer, not to operate the computer—and convince them to go through the trouble of sticking it in their computer every time they boot, then you’ll get a higher level of security.

There is a recovery key: optional but strongly encouraged. It is automatically generated by BitLocker, and it can be sent to some administrator or printed out and stored in some secure location. There are ways for an administrator to set group policy settings mandating this key.

There aren’t any back doors for the police, though.

You can get BitLocker to work in systems without a TPM, but it’s kludgy. You can only configure it for a USB key. And it only will work on some hardware: because BItLocker starts running before any device drivers are loaded, the BIOS must recognize USB drives in order for BitLocker to work.

Encryption particulars: The default data encryption algorithm is AES-128-CBC with an additional diffuser. The diffuser is designed to protect against ciphertext-manipulation attacks, and is independently keyed from AES-CBC so that it cannot damage the security you get from AES-CBC. Administrators can select the disk encryption algorithm through group policy. Choices are 128-bit AES-CBC plus the diffuser, 256-bit AES-CBC plus the diffuser, 128-bit AES-CBC, and 256-bit AES-CBC. (My advice: stick with the default.) The key management system uses 256-bit keys wherever possible. The only place where a 128-bit key limit is hard-coded is the recovery key, which is 48 digits (including checksums). It’s shorter because it has to be typed in manually; typing in 96 digits will piss off a lot of people—even if it is only for data recovery.

So, does this destroy dual-boot systems? Not really. If you have Vista running, then set up a dual boot system, Bitlocker will consider this sort of change to be an attack and refuse to run. But then you can use the recovery key to boot into Windows, then tell BitLocker to take the current configuration—with the dual boot code—as correct. After that, your dual boot system will work just fine, or so I’ve been told. You still won’t be able to share any files on your C drive between operating systems, but you will be able to share files on any other drive.

The problem is that it’s impossible to distinguish between a legitimate dual boot system and an attacker trying to use another OS—whether Linux or another instance of Vista—to get at the volume.

BitLocker is not a panacea. But it does mitigate a specific but significant risk: the risk of attackers getting at data on drives directly. It allows people to throw away or sell old drives without worry. It allows people to stop worrying about their drives getting lost or stolen. It stops a particular attack against data.

Right now BitLocker is only in the Ultimate and Enterprise editions of Vista. It’s a feature that is turned off by default. It is also Microsoft’s first TPM application. Presumably it will be enhanced in the future: allowing the encryption of other drives would be a good next step, for example.

EDITED TO ADD (5/3): BitLocker is not a DRM system. However, it is straightforward to turn it into a DRM system. Simply give programs the ability to require that files be stored only on BitLocker-enabled drives, and then only be transferrable to other BitLocker-enabled drives. How easy this would be to implement, and how hard it would be to subvert, depends on the details of the system.

Posted on May 2, 2006 at 6:54 AM • View Comments

VOIP Encryption

There are basically four ways to eavesdrop on a telephone call.

One, you can listen in on another phone extension. This is the method preferred by siblings everywhere. If you have the right access, it’s the easiest. While it doesn’t work for cell phones, cordless phones are vulnerable to a variant of this attack: A radio receiver set to the right frequency can act as another extension.

Two, you can attach some eavesdropping equipment to the wire with a pair of alligator clips. It takes some expertise, but you can do it anywhere along the phone line’s path—even outside the home. This used to be the way the police eavesdropped on your phone line. These days it’s probably most often used by criminals. This method doesn’t work for cell phones, either.

Three, you can eavesdrop at the telephone switch. Modern phone equipment includes the ability for someone to listen in this way. Currently, this is the preferred police method. It works for both land lines and cell phones. You need the right access, but if you can get it, this is probably the most comfortable way to eavesdrop on a particular person.

Four, you can tap the main trunk lines, eavesdrop on the microwave or satellite phone links, etc. It’s hard to eavesdrop on one particular person this way, but it’s easy to listen in on a large chunk of telephone calls. This is the sort of big-budget surveillance that organizations like the National Security Agency do best. They’ve even been known to use submarines to tap undersea phone cables.

That’s basically the entire threat model for traditional phone calls. And when most people think about IP telephony—voice over internet protocol, or VOIP—that’s the threat model they probably have in their heads.

Unfortunately, phone calls from your computer are fundamentally different from phone calls from your telephone. Internet telephony’s threat model is much closer to the threat model for IP-networked computers than the threat model for telephony.

And we already know the threat model for IP. Data packets can be eavesdropped on anywhere along the transmission path. Data packets can be intercepted in the corporate network, by the internet service provider and along the backbone. They can be eavesdropped on by the people or organizations that own those computers, and they can be eavesdropped on by anyone who has successfully hacked into those computers. They can be vacuumed up by nosy hackers, criminals, competitors and governments.

It’s comparable to threat No. 3 above, but with the scope vastly expanded.

My greatest worry is the criminal attacks. We already have seen how clever criminals have become over the past several years at stealing account information and personal data. I can imagine them eavesdropping on attorneys, looking for information with which to blackmail people. I can imagine them eavesdropping on bankers, looking for inside information with which to make stock purchases. I can imagine them stealing account information, hijacking telephone calls, committing identity theft. On the business side, I can see them engaging in industrial espionage and stealing trade secrets. In short, I can imagine them doing all the things they could never have done with the traditional telephone network.

This is why encryption for VOIP is so important. VOIP calls are vulnerable to a variety of threats that traditional telephone calls are not. Encryption is one of the essential security technologies for computer data, and it will go a long way toward securing VOIP.

The last time this sort of thing came up, the U.S. government tried to sell us something called “key escrow.” Basically, the government likes the idea of everyone using encryption, as long as it has a copy of the key. This is an amazingly insecure idea for a number of reasons, mostly boiling down to the fact that when you provide a means of access into a security system, you greatly weaken its security.

A recent case in Greece demonstrated that perfectly: Criminals used a cell-phone eavesdropping mechanism already in place, designed for the police to listen in on phone calls. Had the call system been designed to be secure in the first place, there never would have been a backdoor for the criminals to exploit.

Fortunately, there are many VOIP-encryption products available. Skype has built-in encryption. Phil Zimmermann is releasing Zfone, an easy-to-use open-source product. There’s even a VOIP Security Alliance.

Encryption for IP telephony is important, but it’s not a panacea. Basically, it takes care of threats No. 2 through No. 4, but not threat No. 1. Unfortunately, that’s the biggest threat: eavesdropping at the end points. No amount of IP telephony encryption can prevent a Trojan or worm on your computer—or just a hacker who managed to get access to your machine—from eavesdropping on your phone calls, just as no amount of SSL or e-mail encryption can prevent a Trojan on your computer from eavesdropping—or even modifying—your data.

So, as always, it boils down to this: We need secure computers and secure operating systems even more than we need secure transmission.

This essay originally appeared on Wired.com.

Posted on April 6, 2006 at 5:09 AM • View Comments

More on Greek Wiretapping

Earlier this month I blogged about a wiretapping scandal in Greece.

Unknowns tapped the mobile phones of about 100 Greek politicians and offices, including the U.S. embassy in Athens and the Greek prime minister.

Details are sketchy, but it seems that a piece of malicious code was discovered by Ericsson technicians in Vodafone’s mobile phone software. The code tapped into the conference call system. It “conference called” phone calls to 14 prepaid mobile phones where the calls were recorded.

More details are emerging. It turns out that the “malicious code” was actually code designed into the system. It’s eavesdropping code put into the system for the police.

The attackers managed to bypass the authorization mechanisms of the eavesdropping system, and activate the “lawful interception” module in the mobile network. They then redirected about 100 numbers to 14 shadow numbers they controlled. (Here are translations of some of the press conferences with technical details. And here are details of the system used.)

There is an important security lesson here. I have long argued that when you build surveillance mechanisms into communication systems, you invite the bad guys to use those mechanisms for their own purposes. That’s exactly what happened here.

UPDATED TO ADD (3/2): From a reader: “I have an update. There is some news from the ‘Hellenic Authority for the Information and Communication Security and Privacy’ with a few facts and I got a rumor that there is a root backdoor in the telnetd of Ericssons AXE backdoor. (No, I can’t confirm the rumor.)”

Posted on March 1, 2006 at 8:04 AM • View Comments

FBI to Approve All Software?

Sounds implausible, I know. But how else do you explain this FCC ruling (from September—I missed it until now):

The Federal Communications Commission thinks you have the right to use software on your computer only if the FBI approves.

No, really. In an obscure “policy” document released around 9 p.m. ET last Friday, the FCC announced this remarkable decision.

According to the three-page document, to preserve the openness that characterizes today’s Internet, “consumers are entitled to run applications and use services of their choice, subject to the needs of law enforcement.” Read the last seven words again.

The FCC didn’t offer much in the way of clarification. But the clearest reading of the pronouncement is that some unelected bureaucrats at the commission have decreeed that Americans don’t have the right to use software such as Skype or PGPfone if it doesn’t support mandatory backdoors for wiretapping. (That interpretation was confirmed by an FCC spokesman on Monday, who asked not to be identified by name. Also, the announcement came at the same time as the FCC posted its wiretapping rules for Internet telephony.)

Posted on December 2, 2005 at 11:24 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.