Am Di, den 04.05.2004 schrieb Gary Stainburn um 14:43:
However, if you search the net, you will find MANY documents telling you why you should not do this. PPTP is a VERY insecure method.
Hey, I never told anybody to use PPTP. In fact, I usually tell people to use OpenVPN or IPSec.
(Sorry bit I can't cite anything specific here as it's a while since I investigated this stuff - I decided on the more restrictive but more secure port forwarding over SSH. (Other methods are available. No guarantee is provided either implied..........you know what I mean)).
short: http://www.schneier.com/pptp.html long: http://www.schneier.com/paper-pptpv2.html
Quote: "7 Conclusions Microsoft has improved PPTP to correct the major security weaknesses described in [SM98]. However, the fundamental weakness of the authentication and encryption protocol is that it is only as secure as the password chosen by the user."
Ok, it all depends on the password (and not on keys or certs). Now take
a look at: http://mopo.informatik.uni-freiburg.de/pptp_mschapv2/pptp_mschapv2.html
Quote:
"Conclusions
While testing this software, we used a dictionary of about three
gigabytes containing about 74 million words. Equipped with this, we were
able to derive all passwords used in our test network in about four
hours.
It is true that dictionary attacks tend to fail on good passwords, but it is enough to have one password to break into a system. The step to gaining root access (or doing any other kind of abuse) from there is small."
So I fully agree with you, Garry: Everybody, please do not use pptp. It might be sufficient for a dialup with your laptop, but I would not dare using it for a production system.
Christoph
You failed to quote one very important assumption, and missed off a major conclusion:
"The next step is to audit a valid authentication. To do this, you need an IEEE 802.11b compatible wireless device, available in the computer store of your choice. Equipped with this, you can immediately audit all wireless network traffic if WEP encryption isn't used."
"With this said, it is clear why we believe Microsoft's PPTP implementation isn't suitable for securing wireless networks."
Their analysis and conclusions are only valid for a wireless network *without WEP*, or a network where network sniffers can be employed to access a valid authentication sequence and obtain a suitable challenge/response.
-- Nigel Wade, System Administrator, Space Plasma Physics Group, University of Leicester, Leicester, LE1 7RH, UK E-mail : nmw@xxxxxxxxxxxx Phone : +44 (0)116 2523548, Fax : +44 (0)116 2523555
