Re: [TLS] Rethink TLS 1.3

Daniel Kahn Gillmor <dkg@fifthhorseman.net> Mon, 24 November 2014 20:02 UTC

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Date: Mon, 24 Nov 2014 15:02:00 -0500
From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
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Subject: Re: [TLS] Rethink TLS 1.3
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On 11/23/2014 04:40 PM, Jeffrey Walton wrote:
> In fact, the IETF seem to accommodate interception in its standards,
> which makes me wonder if its an unwritten agenda. For example, Public
> Key Pinning opaquely accommodates interception by allowing attackers
> to break pinsets (cf. Section 2.7 of
> https://tools.ietf.org/html/draft-ietf-websec-key-pinning-21). And the
> ability to surreptitiously break a pinset is not listed in security
> considerations.

https://tools.ietf.org/html/draft-ietf-websec-key-pinning-21#section-2.7

reads:

2.7.  Interactions With Preloaded Pin Lists

   UAs MAY choose to implement additional sources of pinning
   information, such as through built-in lists of pinning information.
   Such UAs should allow users to override such additional sources,
   including disabling them from consideration.

   The effective policy for a Known Pinned Host that has both built-in
   Pins and Pins from previously observed PKP header response fields is
   implementation-defined.

Can you explain how this can be used by an attacker to break a pinset?

	--dkg