From: Valdis.Kletnieks@vt.edu [mailto:Valdis.Kletnieks@vt.edu]
Sent: Tuesday, July 31, 2001 3:10 PM> You are probably aware, but EFF published the DES crack. I
understand that
> it is now an issue of cracking DES in less than 12 hours.
3DES is better
> but it only amounts to DES with a 128-bit key.Actually, 3DES has a 112 bit effective key. However,
although that's only
double the key length, the *difficulty* is a bit more than
twice as much.
Assuming a brute-force of a 56-bit key in 12 hours, then a 112 bit key
will take (given the same resources) 2**56 * 12 hours, which is about
864,691,128,455,135,232 hours which works out to
98,709,032,928,668 years,
which is about 4,000 times the current estimated age of the universe.This analysis of course assumes that the EFF crack is a brute-force,
and not a result of differential cryptanalysis or exploitation of a
flaw in the DES S-boxes or similar. Schneier's 'Applied Cryptography'
lists an attack that's around 2**47 rather than 2**56,
assuming you can
get the victim to encrypt several gigabytes of text of your
choosing with
his key....
... and then they load it on www.distributed.net