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Re: [TLS] Summarizing identity change discussion so far

David-Sarah Hopwood <david-sarah@jacaranda.org> Sat, 19 December 2009 04:47 UTC

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Sender: David-Sarah Hopwood <djhopwood@googlemail.com>
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Date: Sat, 19 Dec 2009 04:46:43 +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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[I messed up the attributions in the previous post -- fixed below.]

Blumenthal, Uri - 0662 - MITLL wrote:
> David-Sarah Hopwood 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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