radish wrote: > How does the amount of entropy affect the crack time for brute force, > provided there's a trivial amount so the key isn't in a dictionary?
This is getting OT, and complicated. First, it depends on the cipher and the amount of ciphertext you have access to. With WiFi, its easy to get huge amounts of cipher text and you can get some known clear text. For example, if the user checks his email every 10 minutes, you can see traffic, which will have known text as he does the POP3 access to the ISP. With better ciphers, every bit in the key changes every byte of output. But you don't know, without doing a lot of serious post-doc-level analysis, if changing the key from "Bonjour" to "Bonj0ur" changes it completely, or if you can do partial attacks. Birthday paradox become a big deal with sufficient amounts of ciphertext. You also don't know how the attack works. For example, with a cable modem or DSL line, a little work wearing all black can let you plug in a 'butt set' to pick up the clear text. With both clear text and cipher text, a lot of attacks are much easier. Its all about how paranoid you want to be. Remember, just because you are paranoid, it doesn't mean that they are not out to get you. > in so he has to test those all the same. Now he may be smart and think > that I'm probably an idiot and have a really small character set, so > statistically he's better off hitting the lower-case-only keys first, > but you get my point. If you look at the serious research, you find that even folks using what they think are good passphrases use the same, weak ones. There are about 30,000 words in a typical college educated English speaker's vocabulary. That is a trivial number to push through a dictionary attack. Even if you change from Englist to LeetSpeak, its still a fairly small number in crypto terms. Check out the reference to a CERT advisory (Cert advisory CA-2003-08) on lame passwords. Its sad. http://www.pfarrell.com/technotes/lamepasswords.html > Agreed. The easiest way to break into WPA is probably to attack a node > on the network directly (via a trojan for example) and get the PSK from > an OS vulnerability. Social engineering is how most cracks are done. With the popularity of wireless keyboards, it doesn't take much to just capture the key strokes and skip all the WiFi stuff complete. -- Pat Farrell http://www.pfarrell.com/ _______________________________________________ discuss mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/discuss
