Feeds

RSA crypto defiled again, with factoring of 768-bit keys

More where that came from

Seven Steps to Software Security

Yet another domino in the RSA encryption scheme has fallen with the announcement Thursday that cryptographers have broken 768-bit keys using the widely used public-key algorithm.

An international team of mathematicians, computer scientists and cryptographers broke the key though NFS, or number field sieve, which allowed them to deduce two prime numbers that when multiplied together generated a number with 768 bits. The discovery, which took about two-and-a-half years and hundreds of general-purpose computers, means 768-bit RSA keys can no longer be counted on to encrypt or authenticate sensitive communications.

More importantly, it means it's only a matter of another decade or so - sooner assuming there's some sort of breakthrough in NFS or some other form of mathematical factoring - until the next largest RSA key size, at 1024 bits, is similarly cracked. The accomplishment was reached on December 12.

"It's an important milestone," said Benjamin Jun, vice president of technology at security consultancy Cryptography Research. "There's indisputable evidence here that 768-bit key are not enough. It's a pretty interesting way to close out a decade."

The team managed to factor the 232-digit number that RSA held out as a representative 768-bit modulus from a now-obsolete challenge. They spent half a year using 80 processors on polynomial selection. Sieving took almost two years and was done on "many hundreds of machines". Using a single-core 2.2GHz AMD Opteron with 2GB RAM, sieving would have taken about 1,500 years, they estimated.

Factoring the 768-bit key was "several thousand times harder" than factoring a 512-bit one, a feat that was first performed in 1999. By contrast, factoring a 1024-bit RSA modulus, will be about 1,000 times harder than this most recent milestone. That's more than five times easier than a 768-bit RSA modulus looked just a decade ago.

"If we are optimistic, it may be possible to factor a 1024-bit RSA modulus within the next decade by means of an academic effort on the same limited scale as the effort presented here," authors of the research wrote. "From a practical security point of view this is not a big deal, given that standards recommend phasing out such moduli by the end of the year 2010."

But Nate Lawson, a cryptographer who is principal of security consultancy Root Labs, said smaller keys continue to be used for a variety of purposes, often by smaller embedded devices that don't have the processing power to handle larger keys.

The research team includes Thorsten Kleinjung, Arjen K. Lenstra, Joppe W. Bos and Dag Arne Osvik of EPFL IC LACAL, in Lausanne, Switzerland; Kazumaro Aoki of NTT, in Tokyo; Jens Franke of the University of Bonn's Department of Mathematics; Emmanuel Thomé, Pierrick Gaudry, Alexander Kruppa and and Paul Zimmermann of France; and Peter L Montgomery, Herman te Riele and Andrey Timofeev of Microsoft. A copy of their paper is here (pdf). ®

Mobile application security vulnerability report

More from The Register

next story
Yorkshire cops fail to grasp principle behind BT Fon Wi-Fi network
'Prevent people that are passing by to hook up to your network', pleads plod
HIDDEN packet sniffer spy tech in MILLIONS of iPhones, iPads – expert
Don't panic though – Apple's backdoor is not wide open to all, guru tells us
NEW, SINISTER web tracking tech fingerprints your computer by making it draw
Have you been on YouPorn lately, perhaps? White House website?
LibreSSL RNG bug fix: What's all the forking fuss about, ask devs
Blow to bit-spitter 'tis but a flesh wound, claim team
Attackers raid SWISS BANKS with DNS and malware bombs
'Retefe' trojan uses clever spin on old attacks to grant total control of bank accounts
Manic malware Mayhem spreads through Linux, FreeBSD web servers
And how Google could cripple infection rate in a second
Mozilla fixes CRITICAL security holes in Firefox, urges v31 upgrade
Misc memory hazards 'could be exploited' - and guess what, one's a Javascript vuln
Don't look, Snowden: Security biz chases Tails with zero-day flaws alert
Exodus vows not to sell secrets of whistleblower's favorite OS
prev story

Whitepapers

Designing a Defense for Mobile Applications
Learn about the various considerations for defending mobile applications - from the application architecture itself to the myriad testing technologies.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Reducing security risks from open source software
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Consolidation: the foundation for IT and business transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.