Researchers from Microsoft and the Katholieke Universiteit Leuven have discovered a way to break the widely used Advanced Encryption Standard (AES), the encryption algorithm used to secure most all online transactions and wireless communications.

The attack can recover an AES secret key three to five times faster than previously thought possible, reported the Katholieke Universiteit Leuven, a research university based in Belgium.

The researchers caution that the attack is complex in nature, and so can not be easily carried out using existing technologies. In practice, the methodology used by the researchers would take billions of years of computer time to break the AES algorithm, they noted.

But the work, the result of a long term cryptanalysis project, could be the first chink in the armour of the AES standard, previously considered unbreakable. When an encryption standard is evaluated for vital jobs such as securing financial transactions, security experts judge the algorithm's ability to withstand even the most extreme attacks. Today's seemingly secure encryption method could be more easily broken by tomorrow's faster computers, or by new techniques in number crunching.

The US NIST (National Institute of Standards and Technology) agency commissioned AES in 2001, to replace the DES Digital Encryption Standard (DES), which was then repeatedly being shown to be fragile even as it provided adequate security for most everyday tasks.

With this work, the "safety margin" of AES continues to erode, noted security expert Bruce Schneier. "Attacks always get better; they never get worse," he wrote, quoting an expert from the National Security Agency.

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Though unwieldy to execute, the attack can be applied to all versions of AES.

KU Leuven researcher Andrey Bogdanov, Microsoft Research's Dmitry Khovratovich and Christian Rechberger from the École Normale Supérieure in Paris completed the work. The creators of AES, Joan Daemen and Vincent Rijmen have acknowledged the validity of the attack, according to KU Leuven.