Re: [TLS] Update spec to match current practices for certificate chain order

Watson Ladd <watsonbladd@gmail.com> Tue, 12 May 2015 16:31 UTC

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Date: Tue, 12 May 2015 09:31:15 -0700
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From: Watson Ladd <watsonbladd@gmail.com>
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Subject: Re: [TLS] Update spec to match current practices for certificate chain order
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On Tue, May 12, 2015 at 9:24 AM, Viktor Dukhovni <ietf-dane@dukhovni.org> wrote:
> On Fri, May 08, 2015 at 08:51:49PM -0700, Ryan Sleevi wrote:
>
>> I know nothing I say will dissuade you from calling it "unsafe path
>> discovery", even though I rather vehemently disagree with you. I will
>> simply point out, however, that were it not for this "unsafe path
>> discovery", we would not finally be moving to a place where we might be
>> able to turn off 1024-bit RSA keys used in intermediate and root
>> certificates, because the PKI is hard and the Internet involves multiple
>> stakeholders.
>
> FWIW, OpenSSL does no path discovery.  Whatever certificates the
> server sends, there is a linearly ordered subset[1] of these that
> achieves the same validation result as the original heap of certs
> for all OpenSSL-based clients.  So sending something other than a
> linearly ordered list has no value.
>
> With OpenSSL 1.0.2 recently tweaked to do trust-store look-asides
> for nodes in the middle of the provided linear list, as also noted
> by Martin cross-signing with SHA256 or RSA 2048, ... works just
> fine.

So the actual requirement is for a linearization of the DAG of certs,
and this will produce the same results as considering all chains in
the DAG? Or am I misunderstanding you?

Sincerely,
Watson Ladd

>
> --
>         Viktor.
>
> [1] If we assign ordinals to the heap elements in order of appearance,
> the equivalent linear list is the chain (successor == issuer of
> predecessor) that sorts lexically first.  That is for each chain
> element, the issuer with the smallest heap ordinal is chosen and
> no other issuers from the heap are considered.
>
> This is augmented with look-aside at each chain layer into the
> trust store, to identify a locally trusted alternative issuer.
>
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