On Mon, 12 Feb 2001, Ben Nagy wrote:
> > On Mon, 12 Feb 2001, Mark Jones wrote:
> >
> > > I am trying to find some information on the following
> > > PPTP
> >
> > Some real good information on ptpp can be found at
> > http://www.counterpane.com/.
> >
> > It explains why you do not want to use it. (Both versions are
> > very broken
> > in some amazing ways.)
>
> Steady on there.
>
> Unless I've missed some new work PPTPv2 isn't _very_ broken. With the high
> encryption pack the only real crypto problem was that the shared-key relied
> on the user password, making it vulnerable to a password guessing attack.
> That's hardly 'broken'. Kerberos, for example, is in widespread use and it's
> vulnerable to password guessing as well. It's just a risk one needs to
> understand.
My understanding is that you can get PPTP v2 to fall back to PPTP v1. If
this happens, then you have a problem.
> Yes, I would rather see the protocol _not_ derive session keys from the
> passwords, but I think that saying "the MPPE keys are as weak as the user
> passwords" is a much better way of assessing the protcol than saying "It's
> broken, it's eeeevil, it will give you cancer".
I did not quite say that. I should have added the "as implemented by
Microsoft" warning label as well. PPTP v2 has supposedly been done right
by others.
> I still recommend IPSec over PPTP, but I don't rate PPTP as unuseable. With
> strong user passwords and for low threat sites I have recommended it a few
> times. PPTP has some good points. It's NATable, for one.
>
> Note that IPSec is hardly the VPN Messiah - I'm just waiting for the first
> boneheaded implementation error to surface. It's a very complex protocol
> with a few useless bits and pieces - someone _will_ screw it up.
My experience with IPSec is that it tends to not work well with other
implementations. I have heard of too many cases where verious
implementations do not negotiate well with other implementations.
Hopefully these will get hammered out, but they are still a problem. (This
was a year or so ago. It may have improved since them.)
> People may find the the Counterpane "PPTP FAQ" floating around - you should
> be aware (and it's not mentioned in the document) that this FAQ applies ONLY
> to PPTPv1. PPTPv1 was indeed truly broken in some very spectacular ways.
Actually they examined PPTP v2 as well. They said it was better, but
there were still problems. (The fall-back problem the worst of the lot.)
http://www.counterpane.com/pptpv2-paper.html for more info on the
brokenness of PPTP v2.
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