Feeds

'Sandwich attack' busts new cellphone crypto

Kasumi cipher cracked (in theory)

Protecting users from Firesheep and other Sidejacking attacks with SSL

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. ®

The next step in data security

More from The Register

next story
Israeli spies rebel over mass-snooping on innocent Palestinians
'Disciplinary treatment will be sharp and clear' vow spy-chiefs
Infosec geniuses hack a Canon PRINTER and install DOOM
Internet of Stuff securo-cockups strike yet again
THREE QUARTERS of Android mobes open to web page spy bug
Metasploit module gobbles KitKat SOP slop
'Speargun' program is fantasy, says cable operator
We just might notice if you cut our cables
Apple Pay is a tidy payday for Apple with 0.15% cut, sources say
Cupertino slurps 15 cents from every $100 purchase
YouTube, Amazon and Yahoo! caught in malvertising mess
Cisco says 'Kyle and Stan' attack is spreading through compromised ad networks
Hackers pop Brazil newspaper to root home routers
Step One: try default passwords. Step Two: Repeat Step One until success
Greater dev access to iOS 8 will put us AT RISK from HACKERS
Knocking holes in Apple's walled garden could backfire, says securo-chap
prev story

Whitepapers

Providing a secure and efficient Helpdesk
A single remote control platform for user support is be key to providing an efficient helpdesk. Retain full control over the way in which screen and keystroke data is transmitted.
Saudi Petroleum chooses Tegile storage solution
A storage solution that addresses company growth and performance for business-critical applications of caseware archive and search along with other key operational systems.
Security and trust: The backbone of doing business over the internet
Explores the current state of website security and the contributions Symantec is making to help organizations protect critical data and build trust with customers.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.