Subject: RE: I-D ACTION:draft-deacon-xkms-aia-00.txt [SCVP-AIA]

From: Peter Sylvester <[email-masked]>
Date: Wed, 3 Sep 2003 19:34:59 +0200 (MEST)

> 
> But, I'd like to know what use the local server would make of the 
> pointers in one or more AIA extensions.  I've seen too many examples 
> of "let's allow X to be put here because maybe there will be some 
> good use for it that we will figure out later" to be comfortable 
> going down this path without a better understanding of what purpose 
> is served. 

Scenario 1:

- A client asks his local server to validate a cert. 

- The local server has a policy/configuration indicating that
  for the cert in question the AIA of an CA operated DPV
  service is populated and should be contacted.

- The local server does so and authenticates the response
  in whatever way is indicated in the policy. 

Now, one can ask whether the ee-cert needs an AIA. Indeed,
it may be better to have an SIA extension in a CA cert
saying that in order to obtain a paricular information 
containing certificates issued by this authority.

A SIA in a CA cert for OCSP also makes sense to me BTW. 

Scenario 2:

- The same client wants a pointer to his local server; 
  this can be done in different ways; the client would
  never use an IA in any of the certificate in the
  chain to be validated. but would use an extension
  in one certificate of a chain usable to authenticate
  its local server.

---

From: Stephen Kent <[email-masked]>
Date: Fri, 5 Sep 2003 13:51:09 -0400

>   service is populated and should be contacted.

How might this be specified? certainly it would be impractical to 
specify this on a per cert basis.  do you envision specifying this on 
a per CA basis?

>   in whatever way is indicated in the policy.

SCVP requires a signature on every server response, other than an 
error response. if we don't use the signature for validation, I have 
no idea what it might take to trick the server. it also was not clear 
to me that there was a policy configuration item for this, i.e., that 
one could specify non-signature means of verifying server responses 
on a per server basis. can you point me to the part of SCVP that 
indicates this?

>A SIA in a CA cert for OCSP also makes sense to me BTW.

we should defer arguing about the choice of extension until we 
understand how the extension is used and what the the benefits and 
pitfalls.

>   in one certificate of a chain usable to authenticate

I don't understand this example. are you saying that use of an 
extension to identify an SCVP server is a good means of configuring 
this info for a client? you mention a cert chain for the client 
containing this info, but the presumption for DPV is that the client 
may not be able to verify cert chains, and even for DPD that the 
client may not be prepared to fetch and revocation info for chains. 
thus any reference to a cert chain used by a client to verify the 
public key and determine the name for an SCVP server seems 
problematic, in that many of the contexts for which we cretaed SCVP 
would not be able to make use of such a chain.

Steve