Re: [TLS] TLS and middleboxes again

Philip Gladstone <> Wed, 07 September 2011 12:28 UTC

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Date: Wed, 07 Sep 2011 08:30:07 -0400
From: Philip Gladstone <>
Organization: Cisco Systems, Inc
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Subject: Re: [TLS] TLS and middleboxes again
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On 8/26/2011 4:45 PM, Daniel Kahn Gillmor wrote:
> Since HTTP redirects can only be done in an HTTP header, the middlebox
> would need to buffer all HTTP content before relaying it to the User
> Agent, in case "bad" material was found at the end.
> I don't think either of these use cases are valuable, certainly not
> valuable enough to warrant allowing middleboxes to violate the integrity
> guarantees of TLS.

The problem with not allowing modification of the data stream is that 
the middlebox only has one choice left -- to abort the connection. This 
provides a less than satisfactory experience to the end user -- and some 
file transfer managers will simply retry the connection (as they think 
that the connection was accidentally aborted).

There is another reason to release the authentication keys -- and that 
is to prove to the middlebox that the correct encryption key was 
released. Otherwise, the client can release a bogus encryption key, and 
the middlebox has no way of determining what is being transferred. [Of 
course, the client would release the correct key initially to cover the 
HTTP request, and would then rekey the connection with the server and 
release an incorrect key for the response body. ]


Philip Gladstone
Distinguished Engineer
Product Development
Phone: +1 978-ZEN-TOAD (+1 978 936 8623)
Google: +1 978 800 1010
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