Feeds

AES encryption not as tough as you think

Cipher attack shaves safety margin

SANS - Survey on application security programs

Cryptographers have found a new chink in the widely used AES encryption standard that suggests the safety margin of its most powerful cipher is not as high as previously thought.

In a soon-to-be-published paper, researchers Alex Biryukov, Orr Dunkelman, Nathan Keller, Dmitry Khovratovich, and Adi Shamir show that the 256-bit version of AES is susceptible to several so-called related-key attacks that significantly diminish the amount of time it takes to guess a key. One technique against the 11-round version of the cipher can be completed in 270 operations, an improvement that cryptographer Bruce Schneier says was strong enough to be "almost practical."

Another attack uses only two related keys to crack the complete key of a nine-round version in 239 time, a vast improvement over the 2120 time of the best previous attack. A third attack breaks a 10-round version in 245 time.

Like previous attacks on AES, the latest techniques are still wildly impractical, cryptographers say. But because most of the world depends on the encryption standard to keep sensitive records and communications secure from outsiders, the findings are nonetheless significant. AES is also the foundation of several candidates for a new cryptographic hashing algorithm called SHA-3 that will be adopted by the US National Institute of Standards and Technology.

"When you're trying to build a system with a long life span, you want to have ciphers that are very conservative, so if there is a new attack that comes along, you have a long safety margin," says Paul Kocher, president and chief scientist at Cryptography Research, a San Francisco-based consultancy. "If you're trying to design a system that will be in the field for 30 years, you start worrying about stuff like this."

Kocher says that banks and other organizations have already spent billions of dollars moving away from DES, or the Data Encryption Standard, which enjoyed widespread use until cryptographers uncovered significant weaknesses that allowed it to be cracked using practical attacks.

Related-key attacks require a message to be encrypted with one key that is later changed to one or more different keys. It's usually hard for an outsider to control what keys get used, so the technique is considered hard to carry out under real-world settings.

Still, the findings have the surprising effect of making 256-bit AES less hardened than the 192-bit version. The related-key attack doesn't work on either AES-192 or AES-128.

The attack builds off of previous research that described a way to infer clues about keys used in AES by employing what's known as boomerang switching techniques to infer clues about the keys used in the algorithm.

That attack is also extremely hard to carry out in practical environments, but the latest findings suggest that new data continues to chip away at the viability of the AES ciphers. ®

Combat fraud and increase customer satisfaction

More from The Register

next story
Parent gabfest Mumsnet hit by SSL bug: My heart bleeds, grins hacker
Natter-board tells middle-class Britain to purée its passwords
Obama allows NSA to exploit 0-days: report
If the spooks say they need it, they get it
Web data BLEEDOUT: Users to feel the pain as Heartbleed bug revealed
Vendors and ISPs have work to do updating firmware - if it's possible to fix this
Samsung Galaxy S5 fingerprint scanner hacked in just 4 DAYS
Sammy's newbie cooked slower than iPhone, also costs more to build
Mounties always get their man: Heartbleed 'hacker', 19, CUFFED
Canadian teen accused of raiding tax computers using OpenSSL bug
Snowden-inspired crypto-email service Lavaboom launches
German service pays tribute to Lavabit
One year on: diplomatic fail as Chinese APT gangs get back to work
Mandiant says past 12 months shows Beijing won't call off its hackers
prev story

Whitepapers

Designing a defence for mobile apps
In this whitepaper learn the various considerations for defending mobile applications; from the mobile application architecture itself to the myriad testing technologies needed to properly assess mobile applications risk.
3 Big data security analytics techniques
Applying these Big Data security analytics techniques can help you make your business safer by detecting attacks early, before significant damage is done.
Five 3D headsets to be won!
We were so impressed by the Durovis Dive headset we’ve asked the company to give some away to Reg readers.
The benefits of software based PBX
Why you should break free from your proprietary PBX and how to leverage your existing server hardware.
Securing web applications made simple and scalable
In this whitepaper learn how automated security testing can provide a simple and scalable way to protect your web applications.