Feeds

Microscope-wielding boffins crack cordless phone crypto

DECT vivisection

Internet Security Threat Report 2014

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. ®

Remote control for virtualized desktops

More from The Register

next story
UK smart meters arrive in 2020. Hackers have ALREADY found a flaw
Energy summit bods warned of free energy bonanza
DRUPAL-OPCALYPSE! Devs say best assume your CMS is owned
SQLi hole was hit hard, fast, and before most admins knew it needed patching
Knock Knock tool makes a joke of Mac AV
Yes, we know Macs 'don't get viruses', but when they do this code'll spot 'em
Feds seek potential 'second Snowden' gov doc leaker – report
Hang on, Ed wasn't here when we compiled THIS document
Mozilla releases geolocating WiFi sniffer for Android
As if the civilians who never change access point passwords will ever opt out of this one
Why weasel words might not work for Whisper
CEO suspends editor but privacy questions remain
prev story

Whitepapers

Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
Getting started with customer-focused identity management
Learn why identity is a fundamental requirement to digital growth, and how without it there is no way to identify and engage customers in a meaningful way.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Storage capacity and performance optimization at Mizuno USA
Mizuno USA turn to Tegile storage technology to solve both their SAN and backup issues.
Internet Security Threat Report 2014
An overview and analysis of the year in global threat activity: identify, analyze, and provide commentary on emerging trends in the dynamic threat landscape.