After a spate of SHA-cracking targeting earlier versions of the standard, NIST was under the gun to keep the algorithm strong. "When we started this process [in 2006], we did think the whole SHA family's days were numbered," Schneier says. "But then the SHA hacks stopped."
The most recent version of the algorithm for "fingerprinting" messages and files, SHA-512, so far has held up. That, and the fact that none of the finalist versions are exponentially better solutions means it makes more sense to stick with SHA-512 for now, Schneier says.
"They're all OK, but there's no compelling reason to switch," he says. That's in contrast to the Advanced Encryption Standard (AES), which, when it was announced, was widely adopted to replace the slower and outdated Data Encryption Standard (DES).
NIST was scheduled to announce the winning specification for SHA-3 in the second quarter of this year, but hasn't done so yet. The submission and selection process began in late 2007, and some 64 entries were part of the first round of the competition. The algorithm converts messages into shorter message digests that can be used in digital signatures and message authentication, for example.
[Researchers with IBM highlighted the deteriorating state of password security in the IBM X-Force 2012 Mid-year Trend and Risk Report. See Bashing The Hash: IBM X-Force On Password Follies.]
Schneier, who blogged about SHA-3 today, says his submission, Skein, is among the finalists. But even so, he still believes SHA-512 is sufficient and doesn't require a substitution right now.
That doesn't mean SHA-512 won't ultimately be broken. "I don't know if we have tried hard enough to break SHA-512," he says. And just because it hasn't happened yet doesn't mean there hasn't been multiple attempts, he says.
Robert Graham, CEO of Errata Security, concurs that SHA-512 is doing the job today. "SHA-512 is doing well. There are some threats to it, but that's just because it's really well-understood," Graham says. "SHA-3 won't be well-understood -- there is a good chance that a couple years after adoption, there will be just as many threats as with SHA-512."
Even so, says Graham, SHA-512 is not widely adopted today. "I don't see it in hardware, and software has become incredibly modular, making it easy to plug in SHA-3. After a couple of years, SHA-3 will be just as widely spread as SHA-512," Graham says.
He says the benefits of faster hashing and other features with SHA-3 will ultimately make it worth the transition.
Schneier, meanwhile, says he'll recommend sticking with SHA-512 for now. "...None of the SHA-3 candidates is significantly better. Some are faster, but not orders of magnitude faster. Some are smaller in hardware, but not orders of magnitude smaller. When SHA-3 is announced, I'm going to recommend that, unless the improvements are critical to their application, people stick with the tried and true SHA-512. At least for a while," he wrote in his post.
So what about Skein? "Well, maybe there's one reason NIST should choose Skein. Skein isn't just a hash function, it's the large-block cipher Threefish and a mechanism to turn it into a hash function. I think the world actually needs a large-block cipher, and if NIST chooses Skein, we'll get one," he wrote.
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