Feeds

Microscope-wielding boffins crack cordless phone crypto

DECT vivisection

High performance access to file storage

Cryptographers have broken the proprietary encryption used to prevent eavesdropping on more than 800 million cordless phones worldwide, demonstrating once again the risks of relying on obscure technologies to remain secure.

The attack is the first to crack the cipher at the heart of the DECT, or Digital Enhanced Cordless Telecommunications, standard, which encrypts radio signals as they travel between cordless phones in homes and businesses and corresponding base stations. A previous hack, by contrast, merely exploited weaknesses in the way the algorithm was implemented.

The fatal flaw in the DECT Standard Cipher is its insufficient amount of "pre-ciphering," which is the encryption equivalent of shaking a cup of dice to make sure they generate unpredictable results. Because the algorithm discards only the first 40 or 80 bits during the encryption process, it's possible to deduce the secret key after collecting and analyzing enough of the protected conversation.

"This standard, as with everything else we have broken, has been designed some 20 years ago, and it is proprietary encryption," said Karsten Nohl, one of the cryptographers who helped devise the attack. "It relied on the fact that the encryption was unknown and hence could not be broken. This is a case where something that has some potential for being strong is broken by just this one design decision that in any public review would have been spotted immediately."

Nohl, 28, is the same University of Virginia microscope-wielding reverse engineer to crack the encryption in the world's most widely used smartcard. In December, he struck again after devising a practical attack for eavesdropping on cellphone calls.

He and fellow researchers Erik Tews of the Darmstadt University of Technology and Ralf-Philipp Weinmann of the University of Luxembourg, plan to present their findings Monday at the 2010 Fast Software Encryption workshop in Korea.

Like several of Nohl's previous hacks, it began with nitric acid and an electron optical microscope. After dissolving away the epoxy on the silicon chip and then shaving down and magnifying the section dedicated to the DECT encryption, he was able to glean key insights into the underlying algorithm. He then compared the findings against details selectively laid out in a patent and exposed during a debug process.

The results of all three probe methods revealed the fatally insufficient amount of pre-ciphering in the DECT Standard Cipher.

In practical terms, the attack works by collecting bits of the encrypted data stream with known unencrypted contents. In cordless phones, this often comes from a device's control channel, which broadcasts a variety of predictable data, including call duration and button responses. Sniffing an encrypted conversation with a USRP antenna and the average PC, an attacker would need to collect about four hours of data to break the key in typical scenarios.

In others - such as where DECT is used in restaurants and bars to wirelessly zap payment card details - the time needed to crack the key could be dramatically shorter, Nohl said. The time can also be sped up in a variety of other ways, including by adding certain types of graphics cards to beef up the power of the attacking PC. In some cases, the attack can retrieve the secret key in 10 minutes.

"We expect that some smarter cryptographers than ourselves will find better attacks, of course," Nohl told El Reg. "We found the algorithm and then implemented the first attack. It's almost guaranteed that this is not the best attack."

The DECT Forum, the international body that oversees the standard, said it takes the attack scenarios laid out in the paper seriously and "continues to investigate their applicability."

The crack of DECT is only the latest time Nohl has defeated the proprietary encryption of a device with critical mass. His 2008 attack on the Mifare Classic smartcard used similar techniques of filing down a silicon chip and then tracing the connections between transistors. His proposed attack of GSM encryption affects cellphones used by more than 800 carriers in 219 countries. ®

High performance access to file storage

More from The Register

next story
Obama allows NSA to exploit 0-days: report
If the spooks say they need it, they get it
Parent gabfest Mumsnet hit by SSL bug: My heart bleeds, grins hacker
Natter-board tells middle-class Britain to purée its passwords
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
OpenSSL Heartbleed: Bloody nose for open-source bleeding hearts
Bloke behind the cockup says not enough people are helping crucial crypto project
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
Call of Duty 'fragged using OpenSSL's Heartbleed exploit'
So it begins ... or maybe not, says one analyst
German space centre endures cyber attack
Chinese code retrieved but NSA hack not ruled out
Experian subsidiary faces MEGA-PROBE for 'selling consumer data to fraudster'
US attorneys general roll up sleeves, snap on gloves
prev story

Whitepapers

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.
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.
HP ArcSight ESM solution helps Finansbank
Based on their experience using HP ArcSight Enterprise Security Manager for IT security operations, Finansbank moved to HP ArcSight ESM for fraud management.
The benefits of software based PBX
Why you should break free from your proprietary PBX and how to leverage your existing server hardware.
Mobile application security study
Download this report to see the alarming realities regarding the sheer number of applications vulnerable to attack, as well as the most common and easily addressable vulnerability errors.