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6/10/2008 4:47:00 PM

New Supercomputer Record - Does it Matter to Cryptography?

by Andrew Y. Lindell

IBM set a new record with a supercomputer than can carry out one thousand trillion calculation per second (otherwise known as a petaflop); go here for more details. Does this have any influence on the security of cryptosystems? The answer is an unequivocal NO, as long as you are using keys that are long enough. For example, if you are encrypting with plain DES (something that you shouldn't have been doing already 15 years ago), then your secret key could be found by such a machine in just a few minutes. This is because there are about 72,000 trillion possible DES keys. Assuming that 1,000 trillion keys can be tried per second (this probably isn't true, it would take a bit longer than this), this means that 70 seconds or so is enough to try all possible key. OK, but we already know that we shouldn't be using DES. What about 3DES or AES with 128 bit keys? Well, for AES-128, the number of keys is 2128, or about 278 thousand trillion keys. Assuming that you can check one thousand trillion keys per second, it would take about 9,583,696,565,945,500 years to find the secret key. Stated differently, 128 bit keys are way long enough to protect against such attacks, even using the best supercomputers today, and for many many years to come. (Of course, if a weakness is found in the encryption scheme, then it becomes a completely different ballgame.)

Meanwhile, don't worry about your encryption scheme. If you're using a standard algorithm with a long enough key, then you're safe there. Unfortunately, this doesn't mean that you're really safe, because there's much more to a secure solution than a secure cryptographic algorithm; crypto is where it starts (and this is far from where it ends).

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Cryptography

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7/25/2008

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9/27/2008

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