I read the "WYTM" thread with great interest because it dovetailed nicely with some 
research I am
currently involved in.  But I would like to branch this topic onto something specific, 
to see what
everyone here thinks.

As far as I can glean, the general consensus in WYTM is that MITM attacks are very low 
inconsequential) probability.  Is this *really* true?  I came across this paper last 
year, at the
SANS reading room:


I found it both fascinating and disturbing, and I have since confirmed much of what it 
describing.  This leads me to think that an MITM attack is not merely of academic 
interest but one
that can occur in practice.  With sufficiently simplified tools this type of attack 
can readily be
launched by "script kiddies" or someone only just slightly higher on the hacker 
evolutionary scale.

Having said that then, I would like to suggest that one of the really big flaws in the 
way SSL is
used for HTTP is that the server rarely, if ever, requires client certs.  We all seem 
to agree that
convincing server certs can be crafted with ease so that a significant portion of the 
Web population
can be fooled into communicating with a MITM, especially when one takes into account 
Schneier's observations of legitimate uses of server certs (as quoted by Bryce 
O'Whielacronx).  But
as long as servers do *no* authentication on client certs (to the point of not even 
asking for
them), then the essential handshaking built into SSL is wasted.

I can think of numerous online examples where requiring client certs would be a good 
thing: online
banking and stock trading are two examples that immediately leap to mind.  So the 
question is, why
are client certs not more prevalent?  Is is simply an ease of use thing?  Since the 
"Internet threat
model" upon which SSL is based makes the assumption that the channel is *not* secure, 
why is MITM
not taken more seriously?  Why, if SSL is designed to solve a problem that can be 
solved, namely
securing the channel (and people are content with just that), are not more people 
jumping up and
down yelling that it is being used incorrectly?

Am I missing something obvious here?  I look forward to any comments you might have.

-- Tom Otvos

"Don't think you are. Know you are." - Morpheus

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