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From Rob Stradling <>
Subject Re: mod_ssl patch: use new OpenSSL features to autofix cert chains
Date Thu, 27 Mar 2014 22:23:09 GMT
On 27/03/14 17:11, Emilia Kasper wrote:
> Right. So this particular case could be handled by carefully
> constructing the shortest possible chain from all AIA information
> available (system store, p7c, crt).

In that particular case, yes, I suppose so.  However, our "older" 
AddTrust/UTN roots have also cross-certified some of our "newer" roots. 
  So, in some cases, shortest possible chain (to a known, trusted root) 
would be too short!

> But I agree that it's gnarly, a
> bunch of ugly code, and hugely undeterministic (what if the .crt
> responds but the .p7c request errors out?).


> Would you agree that it's safe to do a one-hop AIA-autocorrection for
> leaves only, i.e. certs with NO intermediates configured? My hunch is
> that this would fix the bulk of misconfigured chains while leaving the
> ugly cross-signing cornercases alone.

I think it's probably "safe" in the sense that it wouldn't cause 
additional misconfiguration (and would sometimes cause correct 

But I'm in two minds about whether or not it's a good idea.  IMHO, AIA 
chasing bears much of the blame for the problem we're trying to fix 
here.  Why?  Because when a site administrator tests their site in a 
browser that does AIA chasing (such as Internet Explorer), it "works", 
so they don't notice and fix the misconfiguration.

One-hop AIA-autocorrection might well make the configuration less broken 
(e.g. a missing intermediate is added), but still not correct (e.g. a 
missing cross-certificate is not added).  Being less broken would mean 
that the remaining brokenness is less likely to be detected and corrected.

So if the goal is to maximize the % of servers that are 100% correctly 
configured, one-hop AIA-autocorrection might actually be counterproductive.

Rob Stradling
Senior Research & Development Scientist
COMODO - Creating Trust Online

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