On Sun, 23 Sep 2001, Mike Hicks wrote: > Scott Dier <dieman+tclug at ringworld.org> wrote: > > > > /me wonders if you know the exact plain text and the encrypted text, how > > 'hard' is it to extract the secret key? This would fall into the category of a "known plaintext attack." Strong encryption algorithms are pretty safe from this these days. These sorts of attacks were crucial in WWII. > This is certainly what happens when small keys (these days, <64 bits) are > used. I wouldn't be surprised if the NSA can crack this size key pretty > easily > (within hours or days). > > Most people, when using PGP or GPG, make keys of 1024 or 2048 bits. This > is 2^960 (9.7e288) to 2^1984 (? - probably somewhere around 10^600) times > harder to calculate. Be careful to distinguish between symmetric and asymmetric cryptography. A 64 bit AES key is still pretty good. Asymmetric algorithms like the kind used for public key cryptography require much longer keys to be secure. For anyone who's interested in a nice discussion of the role of cryptography in history and a good description of public key cryptography I would recommend Simon Singh's "The Codebreakers." A very entertaining piece of geek writing. -Tim -- Tim Wilson | Visit Sibley online: | Check out: Henry Sibley HS | http://www.isd197.org | http://www.zope.com W. St. Paul, MN | | http://slashdot.org wilson at visi.com | <dtml-var pithy_quote> | http://linux.com