Re: pre-shared key v RSA encryption or RSA signature authentication modes

[Joern Sierwald <joern@f-secure.com>]

At 16:10 21.03.2002 +0300, you wrote:
> > Dear ipsec-list,
> >
> > I just have a quick question for which I could not find any answers yet.
> > Can someone tell whether the security strength of pre-shared key IKE
> > authentication mode has been proven weaker than RSA-enc or RSA-sig IKE
> > authentication mode ?
> > Links would be much appreciated ...
> >
> > Many thanks,
> >
> > Claudine
> >

Well. the big plus with RSA is that RSA keys are generated mostly in a 
correct way.
What I mean is, there is randomness in them and they are long enough.

pre-shared keys are often not. Most software on the market do not
use bit strings for the PSK, but ASCII strings. And there is no minimum length
requirement.

That means you can use a dictionary attack or an exhaustive search.
If the GW doesn't notice the load and the number of failed Phase 1
connections, you might get authenticated.

So. If you use PSKs with 128 bits or more (just to print a number here)
of randomness in them, there is nothing really wrong with it.
But in real life......

(This doesn't really answer your question. I'm aware.)

J–rn Sierwald