Re: [TLS] TLS Proxy Server Extension

Martin Rex <mrex@sap.com> Fri, 29 July 2011 06:21 UTC

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From: Martin Rex <mrex@sap.com>
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To: matt@mattmccutchen.net (Matt McCutchen)
Date: Fri, 29 Jul 2011 08:21:38 +0200 (MEST)
In-Reply-To: <1311915090.2035.36.camel@localhost> from "Matt McCutchen" at Jul 29, 11 00:51:30 am
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Cc: pgladstone@cisco.com, mcgrew@cisco.com, tls@ietf.org
Subject: Re: [TLS] TLS Proxy Server Extension
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Matt McCutchen wrote:
> 
> > and that also enables the clients
> > to clearly limit who is able to read the traffic.
> 
> Huh?  The proxy's ability to pass decrypted data to someone else is no
> different than if it were bridging two TLS connections.

No, that is entirely different.

Revealing the traffic **encryption** keys to the proxy requires cooperation
of the client, so a sensible client implementation can ask for consent
and the user may deny consent, whereas a proxy with a super-CA-cert
can subvert any connection for that client, no matter where that
client goes--and MitM all connections any time, including those that do
not traverse that proxy.


> 
> > No super-CA-equivalent
> > keys would need to be on the malware-scanning Proxy.
> 
> You speak as if that were in a whole different class of badness, but the
> actual effect is simply to give up integrity as well as confidentiality
> to the proxy.

You would not reveal the MAC keys, of course. only the encryption keys.

There is no need to allow the proxy to modify the traffic.  If the
proxy doesn't like some of the data, it should not pass it along and
terminate the connection.

-Martin