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Hard-working chips may reveal encryption keys
* 15:35 20 November 2006
* NewScientist.com news service
* Will Knight
Details of a possible weakness in the way modern microchips process
cryptographic information have been published by an international team of
researchers.
The flaw could let a hacker steal the cryptographic keys used to protect
sensitive communications and financial transactions, simply by monitoring
the amount of effort the microchip is expending, the researchers claim.
Jean-Pierre Seifert, who is affiliated with the university of Haifa,
Israel, and the university of Innsbruck, Austria, and colleagues posted
their findings online on Saturday.
The team say the problem is the result of a trick employed by modern
microchips to speed up information processing, called "branch prediction".
This involves second-guessing whether the logical flow of a computer
program will follow one branch or another, prior to its actual execution.
Spy software
Branch prediction lets a modern microprocessor perform the same type of
function again and again very rapidly. However, if a chip suddenly needs to
perform another type of operation, or makes a mistaken branch prediction,
the amount of work it has to perform, and the time required, will suddenly
increase.
Understanding this effect and monitoring these fluctuations over time can
reveal crucial details about encryption keys being processed, the
researchers say. Although similar techniques have been proposed in the
past, they have involved monitoring a chip for much longer periods.
The researcher claim to have used the attack method, dubbed "Simple Branch
Prediction Analysis", to work out a highly-security 512-bit encryption key
in just a few thousandths of a second. The key is of a type widely used to
secure both online financial transactions and email messages against
eavesdropping.
'Horrendously complicated'
The researchers suggest that a small piece of software, hidden on a target
computer, could pick up cryptographic keys covertly. "Security has been
sacrificed for the benefit of performance," Seifert told French newspaper
Le Monde.
Markus Kuhn, a cryptography researcher at the university of Cambridge, UK,
says programmers typically try to guard against so-called "timing attacks"
but notes that it can be difficult to foresee every potential problem.
"Modern processors are horrendously complicated and do a lot behind the
scenes," he told New Scientist.
Although Simple Branch Prediction Analysis requires spy software to be
installed on a target computer, Kuhn says this would be relatively simple
if the computer system is open to more than one user. "If it's a multi-user
machine, then it's quite a feasible threat," he says.
Seifert will present details of the attack at the RSA Security conference,
in February 2007.
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