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Crypto guru thinks outside the box with Cube attack

Stream ciphers easily split (maybe)

Senior cryptologist Adi Shamir is developing a new attack for rooting out potential weaknesses in encryption ciphers, dubbed the Cube Attack.

Shamir, the S in RSA, explained at a talk at the Crypto2008 conference earlier this month that the attack methodology would succeed against cypher schemes providing that they can be represented by "low-degree polynomial equations"*. If that sounds as complex as working out the meaning of the numbers used to signify the location of rooms and whether they are booby-trapped in the cult film Cube, then you are on the right page.

Block ciphers - anything ranging from AES to DES - are too complex for the approach to work, but functions such as linear feedback shift register (LFSR) schemes might be attacked using the approach, cryptography guru Bruce Schneier writes. That means functions such as pseudo-random number generators used in stream ciphers might be unpicked, creating a new and possibly more powerful technique for decrypting the forms of encryption used by GSM mobile phone and Bluetooth devices, for example.

Attack techniques that target the weaknesses of cryptographic systems on systems constrained to using less robust encryption because of either size or power limitations already exist but the Cube technique is potentially faster and more elegant.

Shamir gave only a tantalizing glimpse of his work at Crypto2008 during a talk entitled How to solve it: New Techniques in Algebraic Cryptanalysis.

Shamir and co-author plan to present a full treatment of the work at the Eurocrypt 2009 conference in Germany next April. ®

* A very simple low-order polynomial equation would be something like ƒ(x) = x2 - 2x.

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