Feeds

'Sandwich attack' busts new cellphone crypto

Kasumi cipher cracked (in theory)

Top 5 reasons to deploy VMware with Tegile

A new encryption scheme for protecting 3G phone networks hasn't even gone into commercial use and already cryptographers have cracked it - at least theoretically.

In a paper published Tuesday, the cryptographers showed that the Kasumi cipher, which is also referred to as A5/3, can be broken using what's known as a related-key attack, in which a message encrypted with one key is later changed to one or more different keys. The team dubbed the technique a sandwich attack because it was broken into three parts: two thick slices at the top and bottom and a thin slice in the middle.

"By using this distinguisher and analyzing the single remaining round, we can derive the complete 128 bit key of the full Kasumi by using only 4 related keys, 226 data, 230 bytes of memory, and 232 time," they wrote. "These complexities are so small that we have actually simulated the attack in less than two hours on a single PC, and experimentally verified its correctness and complexity."

The results come two weeks after a separate team released a practical method for cracking A5/1, the cipher currently used to prevent snooping on GSM networks. The technique relies on about $4,000 worth of equipment and requires the capture of only a few minutes worth of an encrypted conversation in order to break it. The attack exploits weaknesses in the decades-old cipher.

The GSM Association, which represents about 800 cellular carriers in 219 countries, has vowed to switch to the much more modern A5/3 cipher, but so far, it has provided no time line for doing so.

By contrast, the exploit against A5/3 is much less practical, because it requires an attacker to collect "several million known plaintexts" in order to deduce the key that encrypts a conversation, said Karsten Nohl, a cryptography expert and researcher at the University of Virginia. During a typical call, such plaintexts are transmitted every second or so. Still, he said the research is important because it shows the realistic limitations of the cipher.

"The attack should stand as a reminder that A5/3 and any other cipher will need to be replaced eventually," he told The Register. "Hopefully this fact is considered when upgrading GSM."

Nohl's comments are particularly poignant since the attack, limited as it may be, exploits weaknesses in the algorithm itself, rather than ways the algorithm is implemented.

The paper was published by Orr Dunkelman, Nathan Keller, and Adi Shamir, the last researcher being the S in the widely used RSA public-key encryption algorithm. They are faculty members with the Mathematics and Computer Science at the Weizmann Institute of Science in Israel. A PDF of the paper is here. ®

Internet Security Threat Report 2014

More from The Register

next story
'Kim Kardashian snaps naked selfies with a BLACKBERRY'. *Twitterati gasps*
More alleged private, nude celeb pics appear online
Home Depot ignored staff warnings of security fail laundry list
'Just use cash', former security staffer warns friends
Hackers pop Brazil newspaper to root home routers
Step One: try default passwords. Step Two: Repeat Step One until success
UK.gov lobs another fistful of change at SME infosec nightmares
Senior Lib Dem in 'trying to be relevant' shocker. It's only taxpayers' money, after all
Who.is does the Harlem Shake
Blame it on LOLing XSS terroristas
Snowden, Dotcom, throw bombs into NZ election campaign
Claim of tapped undersea cable refuted by Kiwi PM as Kim claims extradition plot
Freenode IRC users told to change passwords after securo-breach
Miscreants probably got in, you guys know the drill by now
THREE QUARTERS of Android mobes open to web page spy bug
Metasploit module gobbles KitKat SOP slop
BitTorrent's peer-to-peer chat app Bleep goes live as public alpha
A good day for privacy as invisble.im also reveals its approach to untraceable chats
prev story

Whitepapers

Secure remote control for conventional and virtual desktops
Balancing user privacy and privileged access, in accordance with compliance frameworks and legislation. Evaluating any potential remote control choice.
Intelligent flash storage arrays
Tegile Intelligent Storage Arrays with IntelliFlash helps IT boost storage utilization and effciency while delivering unmatched storage savings and performance.
WIN a very cool portable ZX Spectrum
Win a one-off portable Spectrum built by legendary hardware hacker Ben Heck
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?
Beginner's guide to SSL certificates
De-mystify the technology involved and give you the information you need to make the best decision when considering your online security options.