Re: [TLS] draft-green-tls-static-dh-in-tls13-01

Tony Arcieri <bascule@gmail.com> Sat, 08 July 2017 16:11 UTC

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From: Tony Arcieri <bascule@gmail.com>
Date: Sat, 8 Jul 2017 09:11:26 -0700
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To: Richard Barnes <rlb@ipv.sx>
Cc: Matthew Green <matthewdgreen@gmail.com>, "<tls@ietf.org>" <tls@ietf.org>
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Subject: Re: [TLS] draft-green-tls-static-dh-in-tls13-01
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On Fri, Jul 7, 2017 at 6:02 AM, Richard Barnes <rlb@ipv.sx>; wrote:

> You could avoid changing how the DH works altogether by simply exporting
> the DH private key, encrypted with a key shared with the monitoring device,
> in a server extension.  (Not in EncryptedExtensions, obviously.)  This
> would also have the benefit of explicitly signaling when such monitoring is
> in use.  The only real challenge here is that the client would have to
> offer the extension in order for the server to be able to send it, which I
> expect things like browsers would be unlikely to do.  However, given that
> the target of this draft seems to be intra-data-center TLS, perhaps this is
> a workable requirement?
>

I very much like the property that by using an extension, the client must
consent to being MitMed.

But in this case, why not just keywrap the session master secret with a
preshared KEK as opposed to exfiltrating the DH private key?

-- 
Tony Arcieri