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Re: Counterpane PPTP paper
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Re: Counterpane PPTP paper

  • To: NTBUGTRAQLISTSERV.NTBUGTRAQ.COM
  • Subject: Re: Counterpane PPTP paper
  • From: Alan Ramsbottom <acrals.co.uk>
  • Date: Mon, 1 Jun 1998 22:48:52 +0100
  • Comments: cc: Aleph One <aleph1nationwide.net>
  • Reply-To: acrals.co.uk
  • Sender: Windows NT BugTraq Mailing List <NTBUGTRAQLISTSERV.NTBUGTRAQ.COM>
On 1 Jun 98, at 11:04, Aleph One wrote:

> 1) Breaking MS-CHAP. The fact that you can crack the challenge/responce
> via a dictionary attack has been know for a while. I mentioned in my posts
> to the list. What the paper shows is that it is easier than normal. In the
> case of MS-CHAP the the LANMAN hash is broken into three pieces. These
> three pieces can be cracked independently, just like the two sections of
> the LANMAN hash.

Presumably you're referring to "The Cryptoanalysis Of MS-CHAP" section?
This too has been known for a while e.g. I wrote lots about three
variants on that theme 12 months ago.

Note: I'm certainly **NOT** claiming any credit for any discovery ..by
that time the concept had already figured in two distinct IE attacks
implemented by Paul Ashton and Aaron Spangler respectively. The third
variant was my musings on the screamingly obvious NT authentication
protocol attack. I believe that was more or less the same approach
Aaron had taken and it was similar to the implementation that showed up
later in L0phtCrack 1.5(?).

> They fail to mention the latest version of the software has the
> ability to not send the LANMAN based hash.

Curious considering there are several other references to the revised
MPPE spec. Whatever, I think this particular point of the new
functionality is worth discussing from the International point of view:

Firstly, outside North America we only get the (not-quite) 40-bit
version of PPTP which IMO is a fairly good reason for not touching it
with a 10-foot pole.

Secondly, this weekends PPTP fix to prevent the LANMAN hashes being
sent only works when (not-quite) 128-bit authentication is enabled on
the client ..so I guess we don't get that either.

OTOH we did get the LM-fix to disable the transmission of LANMAN hashes
during normal NT authentication, so I find the latter a teeny bit
inconsistent. Am I missing something blindingly obvious or is this MS's
way of agreeing with me on the first point?

--Alan--
acrals.co.uk