cryptography Archives - Page 52 of 56

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Oracle's Password Hashing

Here’s a paper on Oracle’s password hashing algorithm. It isn’t very good.

In this paper the authors examine the mechanism used in Oracle databases for protecting users’ passwords. We review the algorithm used for generating password hashes, and show that the current mechanism presents a number of weaknesses, making it straightforward for an attacker with limited resources to recover a user’s plaintext password from the hashed value. We also describe how to implement a password recovery tool using off-the-shelf software. We conclude by discussing some possible attack vectors and recommendations to mitigate this risk.

Posted on November 3, 2005 at 1:20 PM • View Comments

NIST Hash Workshop Liveblogging (5)

The afternoon started with three brand new hash functions: FORK-256, DHA-256, and VSH. VSH (Very Smooth Hash) was the interesting one; it’s based on factoring and the discrete logarithm problem, like public-key encryption, and not on bit-twiddling like symmetric encryption. I have no idea if it’s any good, but it’s cool to see something so different.

I think we need different. So many of our hash functions look pretty much the same: MD4, MD5, SHA-0, SHA-1, RIPE-MD, HAVAL, SHA-256, SHA-512. And everything is basically a block cipher in Davies-Meyer mode. I want some completely different designs. I want hash functions based on a stream ciphers. I want more functions based on number theory.

The final session was an open discussion about what to do next. There was much debate about how soon we need a new hash function, how long we should rely on SHA-1 or SHA-256, etc.

Hashing is hard. At the ultra-high-level hand-waving level, it takes a lot more clock cycles per message byte to hash than it does to encrypt. No one has any theory to account for this, but it seems like the lack of any secrets in a hash function makes it a harder problem. This may be an artifact of our lack of knowledge, but I think there’s a grain of fundamental truth buried here.

And hash functions are used everywhere. Hash functions are the workhorse of cryptography; they’re sprinkled all over security protocols. They’re used all the time, in all sorts of weird ways, for all sorts of weird purposes. We cryptographers think of them as good hygiene, kind of like condoms.

So we need a fast answer for immediate applications.

We also need “SHA2,” whatever that will look like. And a design competition is the best way to get a SHA2. (Niels Ferguson pointed out that the AES process was the best cryptographic invention of the past decade.)

Unfortunately, we’re in no position to have an AES-like competition to replace SHA right now. We simply don’t know enough about designing hash functions. What we need is research, random research all over the map. Designs beget analyses beget designs beget analyses…. Right now we need a bunch of mediocre hash function designs. We need a posse of hotshot graduate students breaking them and making names for themselves. We need new tricks and new tools. Hash functions are a hot area of research right now, but anything we can do to stoke that will pay off in the future.

NIST is thinking of hosting another hash workshop right after Crypto next year. That would be a good thing.

I need to get to work on a hash function based on Phelix.

Posted on November 1, 2005 at 3:43 PM • View Comments

NIST Hash Workshop Liveblogging (4)

This morning we heard a variety of talks about hash function design. All are esoteric and interesting, and too subtle to summarize here. Hopefully the papers will be online soon; keep checking the conference website.

Lots of interesting ideas, but no real discussion about trade-offs. But it’s the trade-offs that are important. It’s easy to design a good hash function, given no performance constraints. But we need to trade off performance with security. When confronted with a clever idea, like Ron Rivest’s dithering trick, we need to decide if this a good use of time. The question is not whether we should use dithering. The question is whether dithering is the best thing we can do with (I’m making these numbers up) a 20% performance degradation. Is dithering better than adding 20% more rounds? This is the kind of analysis we did when designing Twofish, and it’s the correct analysis here as well.

Bart Preneel pointed out the obvious: if SHA-1 had double the number of rounds, this workshop wouldn’t be happening. If MD5 had double the number of rounds, that hash function would still be secure. Maybe we’ve just been too optimistic about how strong hash functions are.

The other thing we need to be doing is providing answers to developers. It’s not enough to express concern about SHA-256, or wonder how much better the attacks on SHA-1 will become. Developers need to know what hash function to use in their designs. They need an answer today. (SHA-256 is what I tell people.) They’ll need an answer in a year. They’ll need an answer in four years. Maybe the answers will be the same, and maybe they’ll be different. But if we don’t give them answers, they’ll make something up. They won’t wait for us.

And while it’s true that we don’t have any real theory of hash functions, and it’s true that anything we choose will be based partly on faith, we have no choice but to choose.

And finally, I think we need to stimulate research more. Whether it’s a competition or a series of conferences, we need new ideas for design and analysis. Designs beget analyses beget designs beget analyses…. We need a whole bunch of new hash functions to beat up; that’s how we’ll learn to design better ones.

Posted on November 1, 2005 at 11:19 AM • View Comments

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 •