Subject: RE: CMP Interoperability Question

From: Frank Balluffi <[email-masked]>
Date: Wed, 10 Apr 2002 05:57:33 -0700

Al Arsenault asked:

>     For those who have implemented CMP, the question is: Does 
> your implementation support CAs who sign CMP messages (e.g., 
> cp, ip, ...) using a different key than they use to sign certificates?

Yes. It is possible to configure our validation authority product to accept
a CMP revocation request signed with a key other than the CA's certificate
signing key. For example, it is possible to configure the system to accept
requests signed by a local administrator.

Frank

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From: [email-masked] (Peter Gutmann)
Date: Thu, 11 Apr 2002 01:26:43 +1200 (NZST)

Al Arsenault <[email-masked]> writes:

>For those who have implemented CMP, the question is: Does your implementation
>support CAs who sign CMP messages (e.g., cp, ip, ...) using a different key
>than they use to sign certificates?

Sure.  If it didn't, it wouldn't be possible to use an RA which proxies for a
CA.  I'd be surprised if there were implementations which didn't allow this...
no hang on, after having taken part in CMP interop testing I wouldn't be
surprised if there were implementations which reformatted the hard drive or
played an MPEG of a cat :-).

>- signed with a key without keyUsage set to some magic value?

keyUsage = signature or nonrepudiation would be useful (there's a Norwegian CA
which believes that a keyUsage extension is unnecessary in its root cert, and
obviously I'm not going to be able to check anything signed with that).

Peter.

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From: Carlisle Adams <[email-masked]>
Date: Fri, 12 Apr 2002 10:33:06 -0400

Hi Al,

> ----------
> From: 	Al Arsenault[SMTP:[email-masked]]
> Sent: 	Wednesday, April 10, 2002 7:52 AM
> To: 	[email-masked]
> Cc: 	Alfred Arsenault
> Subject: 	CMP Interoperability Question
> 
>     The reason for asking this: we tend to believe that they private
> signing key used to sign certificates and revocation information (CRLs,
> OCSP responses) should ONLY be used for that purpose.  The CA has a
> separate key to use for secure communications, including signing CMP
> responses. (I can't find anything in the spec - either RFC2510 or
> son-of-2510 - that addresses this at all. My apologies if I just missed a
> section.)
 
The spec mentions the concept of a "protocol encryption key" and I was sure
it also mentioned the concept of a "protocol signing key" somewhere, but I
just took a look and I can't find it...

In any case, there was never any assumption in our minds that the key used
to sign CMP responses would be the same one as used to sign certificates,
CRLs, etc..  I always thought in terms of a protocol signing key (whose
public key was put into a certificate signed by the regular cert-signing key
so that the EE would be able to trust it).

As far as I am aware, this issue never came up during the CMP interop
testing.  In particular, we always used a separate key to sign CMP responses
and were able to successfully interoperate with the other participants.

Carlisle.