Rob Stradling rob.stradling at comodo.com
Wed Oct 23 19:13:11 UTC 2013

On 23/10/13 18:07, W-Mark Kubacki wrote:
> Hi,
> As someone about to purchase two certificates please allow me to
> weight in an outside perspective:


> On 2013-10-22 12:09 UTC Maxim Dounin wrote:
>> An unwanted side effect would be that this will allow client
>> certificate authentication to use certs from a server's
>> certificate chain.  Probably not something we want to happen.
> On 2013-10-22 13:31 UTC Rob Stradling replied:
>> Yes, that's a potentially unwanted side effect.  But unfortunately,
>> AFAICT, putting the intermediates into the "trusted certificates
>> store" is the only way to implement this feature with OpenSSL
>> <1.0.2.
> Just drop the backwards-compatibility and require OpenSSL 1.0.2 or
> later for that feature, just like a particular version of OpenSSL is
> needed for TLS-SNI.

Apache httpd can do RSA+DSA+ECC with OpenSSL 1.0.0, and OCSP Stapling 
works correctly (in recent OpenSSL versions anyway - see [1] ;-) ).

Why wouldn't Nginx want to offer the same compatibility?

CAs are already starting to sell ECC certs.  OpenSSL 1.0.2 isn't even 
released yet, so most sites will be stuck on <1.0.2 for quite some time.

Most sites don't use TLS client authentication, so they wouldn't be 
affected by the "unwanted side effect" anyway.

> On 2013-10-23 00:25 UTC Maxim Dounin wrote:
>> Given the number of problems, it might be easier to assume the
>> [certificate-]chains must be the same. […]
> • When you are about to get two certificates, most likely RSA+ECC, you
> go for a ECC-only and a RSA-only chain: The former because clients
> support ECC anyway, all the way up to the CA. If not, then the latter
> »classic« RSA-chain would be used.
> • Additionally, it enables you to purchase from more than one CA —
> which is good if a visitor with a recent browser doesn't want to trust
> a CA anymore.

I agree.

> I would disable OCSP for now in such cases and implement it later.

Why's that?


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

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