maradydd: (money)
maradydd ([personal profile] maradydd) wrote2010-01-26 11:22 pm
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YHBW.

Observation just now from Radu Sion during the FC rump session: in the cloud, it costs about $5 million to brute-force 64 bits of symmetric key.

[identity profile] jrtom.livejournal.com 2010-01-27 09:05 pm (UTC)(link)
That's what I'd expect, yes. But what I expect is not always what is true, so it's good to have data that confirm (or deny) my understanding. Also, I'm not a cryptanalyst, so I don't know whether there are any nuances to the "double per extra bit" rule of thumb.
vatine: Generated with some CL code and a hand-designed blackletter font (Default)

[personal profile] vatine 2010-01-28 01:58 pm (UTC)(link)
I think the right answer is "roughly". It depends on how much the extra key space influences the actual encryption. A typical example would be 3DES, with triple the number of key bits, for squaring the amount of effort to brute-force (as to exactly why that is, ask a cryptographer, I can sorta see it but not explain it).