Subject: OCSP Problem

From: Philipp Gühring <[email-masked]>
Date: Fri, 6 Apr 2007 02:18:06 +0200

Hi,

The OCSP RFC says that a OCSP request can contain several queries for 
different certificates. 
Those queries can be for certificates from different CA´s  (/Sub-CAs).
Additionally, the RFC demands that the OCSP response has to be signed by the 
OCSP Server certificate that corresponds to the CA of the certificate that 
was asked for in the request.
According to the RFC, the whole OCSP response has to be digitally signed.

Now what happens if a client asks for several different certificates from 
different CA´s? Which corresponding OCSP server certificate should be used to 
sign the whole response?

* The one of the first certificate request?
* The one of the last certificate request?
* Any of the certificate requests?

Is it a security hole, that the digital signature can´t cover the other 
certificates in that case?

Or is it prohibited to ask for certificates from different (Sub-)CA´s in a 
OCSP request?

I couldn´t find anything in the RFC mentioning that issue.

Best regards,
Philipp Gühring

---

From: "Santosh Chokhani" <[email-masked]>
Date: Thu, 5 Apr 2007 18:29:10 -0700

The responder should have certificates signed by each of the CAs that it services.  The Responder should send all the certificates that are relevant to the request.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Philipp Gühring
Sent: Thursday, April 05, 2007 8:18 PM
To: [email-masked]
Subject: OCSP Problem

Hi,

Best regards,
Philipp Gühring

---

From: Ryan Hurst <[email-masked]>
Date: Thu, 5 Apr 2007 19:16:28 -0700

OCSP allows for several trust models (although not explicitly called out).

I generally refer to them as:
VA Direct - I trust the OCSP responder to sign for any CA.
VA Delegated - I trust the OCSP responder to delegate its signing ability to any of its sub-Vas.
CA signed - Signed by the same ca/key that signed the certificate.
CA delegated - Signed by a OCSP responder delegated by the CA to sign responses on its behalf.

The most common deployed trust model is the CA delegated trust model.

In your case (a OCSP request for multiple certificates issued by multiple CAs) the responder could have a certificate from each of the CAs its delegated for where each of these certificates are bound to the same key pair therefore the signature would still be valid and the bag in the response could contain each of these certificates.

With that being said it is uncommon for a client to generate requests for more than one certificate at a time.

Ryan

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Philipp Gühring
Sent: Thursday, April 05, 2007 5:18 PM
To: [email-masked]
Subject: OCSP Problem

Hi,

Best regards,
Philipp Gühring