OCSP Stapling w/ Delegated Signers

[Tom Ritter]

I have what may be a well tread topic in the nuances of OCSP Stapling
- but after having it posed to me I realized I did not know the
answer. Thus, I ask publicly in the hope that there is a simple
answer I can point to in the future.

If a CA uses a delegated signer for OCSP, and a website delivers an
OCSP Staple... How does the user (talking only to the website) get

- The Delegated Signing Cert (which is presumably an Intermediate off
a Trust Root)
- The revocation information for *that* Intermediate cert

thanks,
tom

[Kai Engert]

See the definition of an OCSPResponse in RFC 2560.

An OCSPResponse may contain an optional sequence of additional
certificates. This is the place to transport the delegated signing cert.

In my understanding, if you request status for a certificate C1, which
was signed by a CA1, and the CA1 choses to use a delegated signing cert
C2, then both C1 and C2 must have been signed by the same CA1.

Although an OCSP response can contain only information related to one
CA, the signed data inside the OCSPResponse contains a sequence of one
or more entries of type SingleResponse. It guess this sequence could
contain status entries for both C1 and C2.

I wonder if an OCSP responder using a delegated signing cert should
always include status information for the delegated signing cert, too.

Kai

[Rob Stradling]

On 27/04/13 18:37, Tom Ritter wrote:
> I have what may be a well tread topic in the nuances of OCSP Stapling
> - but after having it posed to me I realized I did not know the
> answer. Thus, I ask publicly in the hope that there is a simple
> answer I can point to in the future.
>
> If a CA uses a delegated signer for OCSP, and a website delivers an
> OCSP Staple... How does the user (talking only to the website) get
>
> - The Delegated Signing Cert (which is presumably an Intermediate off
> a Trust Root)
> - The revocation information for *that* Intermediate cert

Tom, RFC2560 deals with this issue (see section 4.2.2.2.1).

Public CAs that use delegated OCSP signing should follow the CABForum
Baseline Requirements (section 13.2.5):
"the OCSP signing Certificate MUST contain an extension of type
id-pkix-ocsp-nocheck, as defined by RFC2560."

Delegated OCSP signing certificates are end-entity certs, not
Intermediate certs.

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