Subject: [OCSP] are several requests for different CAs at once valid ?

From: "Julien Stern" <[email-masked]>
Date: Wed, 10 Sep 2003 18:25:09 +0200

Hi all,

I was wondering if it was ok to send an OSCPRequest containing
requests for several certificates issued by different CAs ?

In case this is ok, more specifically, when trying to figure out whether
the signer should be trusted, OCSP defines three models:

i)   Directly signed by the CA
ii)  Signed by a specific certificate with the correct extension directly
     issued by the CA
iii) Signed by a certificate which is directly trusted by the user

My first question obviously does not make sense in case i) as there
is only one signature per response. It is simple in case iii) as there
is no relationship any more between the certs to be checked and the OCSP
responder.

A more problematic case is ii). One could imagine that several
certificates with the "OCSP delegation extension" are delivered to
an OSCP responder by different CAs. In that case, these certificates
should either have the same name, or the same public key, depending
on how the OSCP responder chooses to identify itself. It this setting
valid ? SHOULD/MUST it be supported ?

And while I'm at it, I would also be interested by knowing what the
existing implementations return in the optional "certs" field of the
BasicOCSPResponse depending on the aforementionned trust model, if
anyone has a clue ...

Thanks a lot.

--
Julien Stern

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From: "Miguel Rodriguez" <[email-masked]>
Date: Wed, 10 Sep 2003 14:15:23 -0500

Hi, responses are inline
> valid ? SHOULD/MUST it be supported ?
In this setting the client is expecting the OCSP responder's certificate
issued by the CA that issued the target certificate.  

> BasicOCSPResponse depending on the aforementionned trust model, if

Most implementations return the OCSP responder certificate in this
field. Also the standard practice is that an OCSP responder works for a
single CA. When a client is validating a certificate chain it usually
goes in a "one by one" fashion, sending an OCSP request for each
certificate.

Miguel A Rodriguez
SeguriDATA
Mexico

---

From: "Ambarish Malpani" <[email-masked]>
Date: Wed, 10 Sep 2003 22:31:26 -0700

Hi Julian,
    Responses inline of the behavior of the Valicert responder.

Regards,
Ambarish

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of Julien Stern
> Sent: Wednesday, September 10, 2003 9:25 AM
> To: [email-masked]
> Subject: [OCSP] are several requests for different CAs at once valid ?
> 
> 
> 
> Hi all,
> 

This works fine. The server responds for all certs in the request.
For servers it doesn't have information for, it returns unknown.

> valid ? SHOULD/MUST it be supported ?

The Valicert responder could be configured to respond by name/key or
to respond by key only if the names of all the certs issued to
it by various CAs didn't match.

> BasicOCSPResponse depending on the aforementionned trust model, if

The responder's cert(s). Could have more than one, if you have
delegated certs from multiple CAs.

---

From: "Julien Stern" <[email-masked]>
Date: Thu, 11 Sep 2003 12:07:01 +0200

On Wed, Sep 10, 2003 at 06:25:09PM +0200, Julien Stern wrote:
> [Many answers snipped]

Many thanks to all of you for your very valuable answers.
I'm starting to have a really good idea of the behavior
that OCSP clients (just send one cert at a time) and OCSP
servers (deal with utterly complex requests) should have ;)

When the OCSP can answer for several CAs, I guess that attribute
certificates would be more appropriate than having different
certificates with the same public key signed by several CAs,
but that would clearly make the clients and the servers much more
complex, so I'm fairly happy with the way it is ...

Thanks again.

--
Julien Stern