From: Eric Murray <ericm@lne.com>
Date: Thu, 13 Nov 1997 02:04:17 +0800
To: Doug_Tygar@cs.cmu.edu
Subject: Re: SET
In-Reply-To: <2325.879351741@tygar.trust.cs.cmu.edu>
Message-ID: <199711121751.JAA01757@slack.lne.com>
MIME-Version: 1.0
Content-Type: text/plain



Doug_Tygar@cs.cmu.edu writes:
> 
> rah@shipwright.com wrote:
> 
> >At Doug Tygar's talk at Harvard last week, he claimed to have found a way
> >to crack it. I, um, forgot to press him on this. Has anyone heard about
> >this, or what it might be?
> 
> Actually, I did not claim to break SET.  What I said was:
> 
> (a)  because SET is such a complicated protocol, I am certain that it
>      does have flaws;
> (b)  SET does not have a clear design philosophy -- for example, it has
>      modes in which a consumer's credit card number is hidden from a
>      merchant and modes when it is given to a merchant.  These ambiguous
>      design points in the protocol make the protocol vulnerable to misuse.

I agree completely.  The people involved in the SET "standards effort" 
seem to have relatively little concern about security compared to
say the TLS working group.  There are smart security-aware people
involved but the process is controlled by non-security-aware
card company VPs.

 
> I have not made a serious effort to crack SET, yet.

Neither have I, but I've already found a significant privacy problem
which would allow merchants to determine who else a cardholder has
made purchases from.  When I posted details to the set-discuss list
the response from the SET czars was "so what?".

[details: according to the spec the cardholder sends to the merchant
thumbs (SHA1 hashes) of all the certs in the cardholder's cert cache.
Since this will contain certs from merchants the cardholder has
made purchases from in the past, a merchant could simply match up
those merchant cert thumbs with cert thumbs he obtains from other
merchants, allowing him to build a list of merchants the cardholder has
attempted to make purchases from].

When the right people do make an effort to crack SET 1.0, it's quite likely
to be broken.


Sorry to sound so negative, but I just got back from a SET meeting
and those always seem to make me especially cynical.


-- 
Eric Murray  Chief Security Scientist  N*Able Technologies  www.nabletech.com
(email:  ericm  at  lne.com   or   nabletech.com)          PGP keyid:E03F65E5