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From: "Steven M. Bellovin" <smb@research.att.com> To: "nanog@nanog.org" <nanog@nanog.org> Date: Sun, 26 Jan 2003 10:53:34 -0500 Errors-To: owner-nanog-outgoing@merit.edu In message <Pine.LNX.4.44.0301260529320.29298-100000@www.everquick.net>, "E.B. Dreger" writes: > >AR> Date: Sun, 26 Jan 2003 00:22:02 -0500 (Eastern Standard Time) >AR> From: Alex Rubenstein > > >AR> Agreed. And, even if it is super encrypted, who cares? Enough >AR> CPU and time will take care of that. > >Articles about "1000 years to crack using brute force" are a bit >disconcerting if someone has access to 10,000x compromised hosts. >While we're on the subject: root certificates, anybody? > >Each worm seems to prove the availability of CPU and time. This is practical against, say, DES, with its 56-bit keys. In fact, it's been done; see http://www.virusbtn.com/resources/viruses/indepth/opaserv.xml for an example. But the fact that DES is insecure has been known for years; it doesn't take a worm to underscore that point. Let's look at AES or 3DES instead. Suppose there are 1,000,000,000 infected hosts. Let's further assume that each one can check a single key in .1 nanoseconds. (That's a gross exageration, I might add, for a general-purpose machine -- and we're not talking about 1,000,000,000 NSA code-crackers being infected.) AES uses 128-bit keys; there are therefore 340282366920938463463374607431768211456 possibilities. Call it 3*10^38. Divide that by 10^9 hosts, and 10^10 tries per second per host. That gives us 3*10^19 tries per second. There are ~10^5 seconds/day, and 3*10^2 seconds/year, meaning that it would take 10^12 years for this scenario. 3DES? Well, 3DES may be using 112-bit keys, so we can cut the time by 2^16. Call that 10^5 -- so we'll only have to wait 10^7 years for a single result.... Yes, with enough CPU and enough time, it's possible to crack modern ciphers by brute force. But "enough" is quite a large number. --Steve Bellovin, http://www.research.att.com/~smb (me) http://www.wilyhacker.com (2nd edition of "Firewalls" book)
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