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Re: [TLS] Summarizing identity change discussion so far

David-Sarah Hopwood <david-sarah@jacaranda.org> Sat, 19 December 2009 04:07 UTC

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Date: Sat, 19 Dec 2009 04:06:51 +0000
From: David-Sarah Hopwood <david-sarah@jacaranda.org>
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Subject: Re: [TLS] Summarizing identity change discussion so far
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Blumenthal, Uri - 0662 - MITLL wrote:
> Kyle Hamilton wrote:
>> On Tue, Dec 8, 2009 at 1:13 AM,  <Pasi.Eronen@nokia.com> wrote:
>>> (wearing Area Director hat)
>>>
>>> - We recommend that TLS libraries SHOULD provide identity matching
>>> (with memcmp, abort handshake if changed) functionality to
>>> applications, and SHOULD allow applications to enable/disable this
>>> functionality.
>> No, identity matching SHOULD be done in accordance with PKIX.
> 
> Strongly disagree. If implementations try to do identity matching that
> is any more complicated than memcmp then they *will* get it wrong; see
> <http://www.ioactive.com/pdfs/PKILayerCake.pdf> for evidence.
>
> My strong conviction is that the fact of non-zero probability to get
> (e.g.) PKIX identity matching wrong - does NOT invalidate the need for
> something more powerful and usable than memcmp. I'm not convinced that
> MD5 collision exploitation justifies restriction of matching to memcmp.

There are numerous independent bugs related to name matching described
in that paper; I wasn't referring specifically to the MD5 issue.

-- 
David-Sarah Hopwood  ⚥  http://davidsarah.livejournal.com

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