Re: [TLS] Please discuss: draft-housley-evidence-extns-00 - brokerage illustration

Eric Rescorla <ekr@networkresonance.com> Fri, 12 January 2007 18:53 UTC

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To: Mark Brown <mark@redphonesecurity.com>
Subject: Re: [TLS] Please discuss: draft-housley-evidence-extns-00 - brokerage illustration
References: <003a01c73678$b9ee0df0$6801a8c0@rps.local>
From: Eric Rescorla <ekr@networkresonance.com>
Date: Fri, 12 Jan 2007 10:53:42 -0800
In-Reply-To: <003a01c73678$b9ee0df0$6801a8c0@rps.local> (Mark Brown's message of "Fri, 12 Jan 2007 12:37:34 -0600")
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"Mark Brown" <mark@redphonesecurity.com> writes:
> Let me retrace Eric's line of thought first, using his broker illustration:
>
> 1) 100's of fetches to accomplish a trade:  In HTTP the TCP/IP session gets
> torn down after every fetch.

Uh, not in any modern HTTP stack, no. I refer you to RFC 2616 S 8.1.


> This TLS client configuration line identifies one DNS name and port number
> for which the client will always ClientHello using TLS Evidence.

It does what??? I need to hard-configure some list of names and ports?
That scales how?


> To one of Eric's concerns, in this illustration there really is no change
> required for either the TLS client or the TLS server APIs (i.e. how the
> application interacts programmatically with the TLS layer).

No. The server *still* needs to check that he's actually getting
evidence. I.e., that the client is coming in through the right
virtual server (unless you're proposing that I rearchitect
all my server apps to split every kind of transaction into
two different servers), and there's still the relative inefficiency
of your signature mechanism, which is conservatively a factor of 2-4
slower than app-level signatures.

So, you've had to modify both client and server, you quite
possibly had to substantially rearchitect the server, and the
client has to have some semi-manual configuration settings to
determine when it offers evidence. None of this seems
particularly convenient. 

To uplevel a moment, I'm not arguing that you can't make some proposal
along the lines you indicate sort of work. What I am arguing is that
it isn't substantially simpler than the application-level signature
alternatives, that it offers inferior semantics, and that it doesn't
fit well with the TLS architecture. None of this discussion has
changed my views on that point.

-Ekr


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