AES-256 Attacks Get More Sophisticated, But Security is Maintained

Published: August 18, 2009

by Alex Woodie

A group of respected cryptographers recently publicized details of a new attack on the AES-256 encryption algorithm that appears to be quite sophisticated. For years, hackers have used blunt-force attacks to try and crack AES-256--the strongest of the U.S. Government-sanctioned Advanced Encryption Standards--with no major progress. The new approach appears to be easy enough to use that it's making security experts worried, but that doesn't mean you should give up on AES-256 for your enterprise security needs just yet.

Security expert Bruce Schneier, one of the first to alert the industry to the new cryptographic research, dubbed the attack "very impressive" and "completely practical" in his blog entry on the topic last month. "These new results greatly improve" on older attempts to crack AES-256.

However, that doesn't mean that AES-256 is as weak and compromised as your Facebook password just yet.

The security experts over at Pat Townsend Security Solutions say their customers should not worry, and neither should anybody using an AES-256 solution that's been certified by the National Institute of Standards and Technology.

That's because all NIST-certified encryption solutions are required to use at least 14 rounds during the encryption process. The new attack on AES-256 exploits a problem with key management that is evident when 10 or fewer rounds are employed. "There is no known practical attack on 256-bit AES encryption that implements 14 rounds," the Pat Townsend blog says. A list of all NIST-certified encryption solutions can be found at csrc.nist.gov/groups/STM/cavp/documents/aes/aesval.html

While it's not time to pile into the ark just yet, the weakness in AES-256 encryption should serve as a wake-up call for the security-minded. After all, AES-256 was considered the gold standard in encryption. It had a 256-bit key, which supposedly makes it harder to crack than keys with 192-bit or a 128-bit lengths, right? As it turns out, the number of rounds the encryption engine takes could be just as important as key length, and this might encourage the NIST to increase the number of rounds required.

The luster is off AES-256, but other, more important security vulnerabilities will undoubtedly follow. A smart security administrator will use the event as a reminder that is no single silver bullet for achieving good security. "Cryptography is all about safety margins," Schneier writes in his blog. "What we're learning is that the safety margin of AES is much less than previously believed."

Pat Townsend Security Solutions is using the episode to promote the use of trusted partners. If you went the cheap route and hacked together your own encryption routines using AES-256 or installed an open source solution, there's a chance that work may soon be compromised by newly created attacks, the vendor writes on its blog. But if you paid for a validated solution from a vendor like PTSS, then you have less to worry about. There is some truth to that, too.

Good security isn't a black-or-white, on-or-off proposition, but rather an on-going process that requires continual work. Keep that in mind as you're plugging the holes in your enterprise.

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