Re: Cracking preshared keys

[daw () mozart cs berkeley edu (David Wagner)]

Michael Thumann  wrote:
> we would like to announce the publication of a proof of concept paper 'PSK 
> cracking using IKE Aggressive Mode'. Paper can be downloaded from 
> www.ernw.de/download/pskattack.pdf .
[...]
> 4. Of course the psk must be weak to crack it in an acceptable amount of time

Well, what did you expect?  In your example, the pre-shared key was
derived from the ``secret'' string "cisco".  Of course, if you choose
a key that the attacker can guess, the system won't be secure.  Surprise!

What do you expect IPSec to do if you give it an insecure, guessable key?
Noone claimed it would be secure in such a situation.

I find your recommendations hard to take seriously.  This is not a
vulnerability in IPSec, a good reason to disable vpn access, or anything
like that.  Just use some common sense in how you use the crypto.  If you
must use pre-shared keys, choose strong keys; or, use public keys instead
of pre-shared keying.  Surely you agree?

User: "Doctor, doctor, it hurts when I use insecure crypto keys."
Doctor: "Don't do that, then."