Entries Tagged "cryptography"

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NIST Hash Workshop Liveblogging (3)

I continue to be impressed by the turnout at this workshop. There are lots of people here whom I haven’t seen in a long time. It’s like a cryptographers’ family reunion.

The afternoon was devoted to cryptanalysis papers. Nothing earth-shattering; a lot of stuff that’s real interesting to me and not very exciting to summarize.

The list of papers is here. NIST promises to put the actual papers online, but they make no promises as to when.

Right now there is a panel discussing how secure SHA-256 is. “How likely is SHA-256 to resist attack for the next ten years?” Some think it will be secure for that long, others think it will fall in five years or so. One person pointed out that if SHA-256 lasts ten years, it will be a world record for a hash function. The consensus is that any new hash function needs to last twenty years, though. It really seems unlikely that any hash function will last that long.

But the real issue is whether there will be any practical attacks. No one knows. Certainly there will be new cryptanalytic techniques developed, especially now that hash functions are a newly hot area for research. But will SHA-256 ever have an attack that’s faster than 280?

Everyone thinks that SHA-1 with 160 rounds is a safer choice than SHA-256 truncated to 160 bits. The devil you know, I guess.

Niels Ferguson, in a comment from the floor, strongly suggested that NIST publish whatever analysis on SHA-256 it has. Since this is most likely by the NSA and classified, it would be a big deal. But I agree that it’s essential for us to fully evaluate the hash function.

Tom Berson, in another comment, suggested that NIST not migrate to a single hash function, but certify multiple alternatives. This has the interesting side effect of forcing the algorithm agility issue. (We had this same debate regarding AES. Negatives are: 1) you’re likely to have a system that is as strong as the weakest choice, and 2) industry will hate it.)

If there’s a moral out of the first day of this workshop, it’s that algorithm agility is an essential feature in any Internet protocol.

Posted on October 31, 2005 at 4:00 PM • View Comments

NIST Hash Workshop Liveblogging (2)

In the morning we had a series of interesting papers: “Strengthening Digital Signatures via Randomized Hashing,” by Halevi and Krawczyk; “Herding Hash Functions and the Nostradamus Attack,” by Kelsey and Kohno; and “Collision-Resistant usage of MD5 and SHA-1 via Message Preprocessing,” by Szydlo and Yin. The first and third papers are suggestions for modifying SHA-1 to make it more secure. The second paper discusses some fascinating and cool, but still theoretical, attacks on hash functions.

The last session before lunch was a panel discussion: “SHA-1: Practical Security Implications of Continued Use.” The panel stressed that these are collision attacks and not pre-image attacks, and that many protocols simply don’t care. Collision attacks are important for digital signatures, but less so for other uses of hash functions. On the other hand, this difference is only understood by cryptographers; there are issues if the public believes that SHA-1 is “broken.”

Niels Ferguson pointed out that the big problem is MD5, which is still used everywhere. (Hell, DES is still everywhere.) It takes much longer to upgrade algorithms on the Internet than most people believe; Steve Bellovin says it takes about one year to get the change through the IETF, and another five to seven years to get it depoloyed. And that’s after we all figure out which algorithm they should use.

Georg Illies gave a perspective from Germany, where there is a digital-signature law in effect. In addition to the technology, there are legal considerations that make it harder to switch.

The panel seemed to agree that it’s still safe to use SHA-1 today, but that we need to start migrating to something better. It’s way easier to change algorithms when you’re not in the middle of a panic.

There was more talk about algorithm agility. This problem is larger than SHA. Our Internet protocols simply don’t have a secure methodology for migrating from one cryptographic algorithm to another.

Bottom line: Don’t use SHA-1 for anything new, and start moving away from it as soon as possible. To SHA-256, probably.

And now it’s lunchtime.

Posted on October 31, 2005 at 11:50 AM • View Comments

NIST Hash Workshop Liveblogging (1)

I’m in Gaithersburg, MD, at the Cryptographic Hash Workshop hosted by NIST. I’m impressed by the turnout; a lot of the right people are here.

Xiaoyun Wang, the cryptographer who broke SHA-1, spoke about her latest results. They are the same results Adi Shamir presented in her name at Crypto this year: a time complexity of 263.

(I first wrote about Wang’s results here, and discussed their implications here. I wrote about results from Crypto here. Here are her two papers from Crypto: “Efficient Collision Search Attacks on SHA-0” and “Finding Collisions in the Full SHA-1 Collision Search Attacks on SHA1.”)

Steve Bellovin is now talking about the problems associated with upgrading hash functions. He and his coauthor Eric Rescorla looked at S/MIME, TLS, IPSec (and IKE), and DNSSEC. Basically, these protocols can’t change algorithms overnight; it has to happen gradually, over the course of years. So the protocols need some secure way to “switch hit”: to use both the new and old hash functions during the transition period. This requires some sort of signaling, which the protocols don’t do very well. (Bellovin’s and Rescorla’s paper is here.)

Posted on October 31, 2005 at 9:02 AM • View Comments

RFID Car Keys

RFID car keys (subscription required) are becoming more popular. Since these devices broadcast a unique serial number, it’s only a matter of time before a significant percentage of the population can be tracked with them.

Lexus has made what it calls the “SmartAccess” keyless-entry system standard on its new IS sedans, designed to compete with German cars like the BMW 3 series or the Audi A4, as well as rivals such as the Infiniti G35 or the U.S.-made Cadillac CTS. BMW offers what it calls “keyless go” as an option on the new 3 series, and on its higher-priced 5, 6 and 7 series sedans.

Volkswagen AG’s Audi brand offers keyless-start systems on its A6 and A8 sedans, but not yet on U.S.-bound A4s. Cadillac’s new STS sedan, big brother to the CTS, also offers a pushbutton start.

Starter buttons have a racy flair—European sports cars and race cars used them in the past. The proliferation of starter buttons in luxury sedans has its roots in theft protection. An increasing number of cars now come with theft-deterrent systems that rely on a chip in the key fob that broadcasts a code to a receiver in the car. If the codes don’t match, the car won’t start.

Cryptography can be used to make these devices anonymous, but there’s no business reason for automobile manufacturers to field such a system. Once again, the economic barriers to security are far greater than the technical ones.

Posted on October 5, 2005 at 8:13 AM • View Comments

The Doghouse: Lexar LockTight

Do you think we should tell these people that SHA-1 is not an encryption algorithm?

Developed by Lexar, the new security solution is based on a 160-bit encryption technology and uses SHA-1 (Secure Hash Algorithm), a standard approved by the National Institute of Standards and Technology (NIST). The 160-bit encryption technology is among the most effective and widely accepted security solutions available.

This seems not to be a typo. They explain themselves in more detail here:

Lexar has provided us with the following explanation as to how data is protected on the LockTight cards: (we understand that the encryption is carried out on the communications layer between the card and camera/computer rather than the data itself).

“Lexar employs a unique strategy to protect data on LockTight cards. LockTight cards are always ‘locked.’ In other words no computer or camera can read or write data from/to a LockTight card until a critical authorization process takes place between the LockTight card and the host computer or host camera. This authorization process is where the 160-bit HMAC SHAH-1 encryption algorithm is employed.”

Posted on October 3, 2005 at 8:22 AM • View Comments

NSA Watch

Three things.

U.S. Patent #6,947,978:

Method for geolocating logical network addresses

Abstract: Method for geolocating logical network addresses on electronically switched dynamic communications networks, such as the Internet, using the time latency of communications to and from the logical network address to determine its location. Minimum round-trip communications latency is measured between numerous stations on the network and known network addressed equipment to form a network latency topology map. Minimum round-trip communications latency is also measured between the stations and the logical network address to be geolocated. The resulting set of minimum round-trip communications latencies is then correlated with the network latency topology map to determine the location of the network address to be geolocated.

“Fact Sheet NSA Suite B Cryptography“:

The entire suite of cryptographic algorithms is intended to protect both classified and unclassified national security systems and information. Because Suite B is a also subset of the cryptographic algorithms approved by the National Institute of Standards, Suite B is also suitable for use throughout government. NSA’s goal in presenting Suite B is to provide industry with a common set of cryptographic algorithms that they can use to create products that meet the needs of the widest range of US Government (USG) needs.

“The Case for Elliptic Curve Cryptography“:

Elliptic Curve Cryptography provides greater security and more efficient performance than the first generation public key techniques (RSA and Diffie-Hellman) now in use. As vendors look to upgrade their systems they should seriously consider the elliptic curve alternative for the computational and bandwidth advantages they offer at comparable security.

Posted on September 30, 2005 at 7:31 AM • View Comments

The Doghouse: CryptIt

It’s been far too long since I’ve had one of these.

CryptIt looks like just another one-time pad snake-oil product:

Most file encryptions use methods that mathematically hash a password to a much larger number and rely on the time taken to reverse this process to prevent unauthorised decryption. Providing the key length is 128 bits or greater this method works well for most purposes, but since these methods do have predictable patterns they can be cracked. CPUs are increasing in speed at a fast rate and these encryption methods can be beaten given luck and/or enough computers. XorIt uses the XOR encryption method (also known as Vernam encryption) that can have keys the same size as the file to be encrypted. Thus, if you are encrypting a 5MB file, then you can have what is in effect a 40 Million bit key! This is virtually unbreakable by any computer, especially when you consider that the file must also be checked with each combination to see if it is decrypted. To put is another way, since XorIt gives no pass/fail results brute force methods are difficult to implement. In fact, if you use a good key file that is the same size or larger than the source and do not reuse the key file then it it impossible to decrypt the file, no matter how fast the computer is. Furthermore, the key file can be anything – a program, a swap file, an image of your cat or even a music file.

Amazingly enough, some people still believe in this sort of nonsense. Before defending them, please read my essay on snake oil.

Posted on September 28, 2005 at 1:25 PM •

New Cryptanalytic Results Against SHA-1

Xiaoyun Wang, one of the team of Chinese cryptographers that successfully broke SHA-0 and SHA-1, along with Andrew Yao and Frances Yao, announced new results against SHA-1 yesterday at Crypto’s rump session. (Actually, Adi Shamir announced the results in their name, since she and her student did not receive U.S. visas in time to attend the conference.)

Shamir presented few details—and there’s no paper—but the time complexity of the new attack is 263. (Their previous result was 269; brute force is 280.) He did say that he expected Wang and her students to improve this result over the next few months. The modifications to their published attack are still new, and more improvements are likely over the next several months. There is no reason to believe that 263 is anything like a lower limit.

But an attack that’s faster than 264 is a significant milestone. We’ve already done massive computations with complexity 264. Now that the SHA-1 collision search is squarely in the realm of feasibility, some research group will try to implement it. Writing working software will both uncover hidden problems with the attack, and illuminate hidden improvements. And while a paper describing an attack against SHA-1 is damaging, software that produces actual collisions is even more so.

The story of SHA-1 is not over. Again, I repeat the saying I’ve heard comes from inside the NSA: “Attacks always get better; they never get worse.”

Meanwhile, NIST is holding a workshop in late October to discuss what the security community should do now. The NIST Hash Function Workshop should be interesting, indeed. (Here is one paper that examines the effect of these attacks on S/MIME, TLS, and IPsec.)

EDITED TO ADD: Here are Xiaoyun Wang’s two papers from Crypto this week: “Efficient Collision Search Attacks on SHA-0” and “Finding Collisions in the Full SHA-1Collision Search Attacks on SHA1.” And here are the rest of her papers.

Posted on August 17, 2005 at 2:06 PM • View Comments

Chinese Cryptographers Denied U.S. Visas

Chinese cryptographer Xiaoyun Wang, the woman who broke SHA-1 last year, was unable to attend the Crypto conference to present her paper on Monday. The U.S. government didn’t give her a visa in time:

On Monday, she was scheduled to explain her discovery in a keynote address to an international group of researchers meeting in California.

But a stand-in had to take her place, because she was not able to enter the country. Indeed, only one of nine Chinese researchers who sought to enter the country for the conference received a visa in time to attend.

Sadly, this is now common:

Although none of the scientists were officially denied visas by the United States Consulate, officials at the State Department and National Academy of Sciences said this week that the situation was not uncommon.

Lengthy delays in issuing visas are now routine, they said, particularly for those involved in sensitive scientific and technical fields.

These delays can make it impossible for some foreign researchers to attend U.S. conferences. There are researchers who need to have their paper accepted before they can apply for a visa. But the paper review and selection process, done by the program committee in the months before the conference, doesn’t finish early enough. Conferences can move the submission and selection deadlines earlier, but that just makes the conference less current.

In Wang’s case, she applied for her visa in early July. So did her student. Dingyi Pei, another Chinese researcher who is organizing Asiacrypt this year, applied for his in early June. (I don’t know about the others.) Wang has not received her visa, and Pei got his just yesterday.

This kind of thing hurts cryptography, and hurts national security. The visa restrictions were designed to protect American advanced technologies from foreigners, but in this case they’re having the opposite effect. We are all more secure because there is a vibrant cryptography research community in the U.S. and the world. By prohibiting Chinese cryptographers from attending U.S. conferences, we’re only hurting ourselves.

NIST is sponsoring a workshop on hash functions (sadly, it’s being referred to as a “hash bash”) in October. I hope Wang gets a visa for that.

Posted on August 17, 2005 at 11:53 AM • View Comments

Cryptographically-Secured Murder Confession

From the Associated Press:

Joseph Duncan III is a computer expert who bragged online, days before authorities believe he killed three people in Idaho, about a tell-all journal that would not be accessed for decades, authorities say.

Duncan, 42, a convicted sex offender, figured technology would catch up in 30 years, “and then the world will know who I really was, and what I really did, and what I really thought,” he wrote May 13.

Police seized Duncan’s computer equipment from his Fargo apartment last August, when they were looking for evidence in a Detroit Lakes, Minn., child molestation case.

At least one compact disc and a part of his hard drive were encrypted well enough that one of the region’s top computer forensic specialists could not access it, The Forum reported Monday.

This is the kind of story that the government likes to use to illustrate the dangers of encryption. How can we allow people to use strong encryption, they ask, if it means not being able to convict monsters like Duncan?

But how is this different than Duncan speaking the confession when no one was able to hear? Or writing it down and hiding it where no one could ever find it? Or not saying anything at all? If the police can’t convict him without this confession—which we only have his word for as existing—then maybe he’s innocent?

Technologies have good and bad uses. Encryption, telephones, cars: they’re all used by both honest citizens and by criminals. For almost all technologies, the good far outweighs the bad. Banning a technology because the bad guys use it, denying everyone else the beneficial uses of that technology, is almost always a bad security trade-off.

EDITED TO ADD: Looking at the details of the encryption, it’s certainly possible that the authorities will break the diary. It probably depends on how random a key Duncan chose, although possibly on whether or not there’s an implementation error in the cryptographic software. If I had more details, I could speculate further.

Posted on August 15, 2005 at 2:17 PM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.