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Re: Certificates Field in Signed Data

1997-01-27 14:00:51

At 11:06 PM 1/23/97 +0000, David Chadwick wrote: 

It also seems
likely that people are going to want to push other certificates than the 
ones that are required to validate the signature or signing certificate 
trust (in the case of a dual key model where the signing and enveloping 
certificates are separate, you may want to push both the signing and
enveloping certificates and their respective chains). 

This is an arguement for a SET OF SEQUENCES in my opinion

Presently, PKCS #7 provides a heap of certificates that might be useful to 
the recipient.  PKCS #7 does not constrain the originator in the contets of 
the heap.  The originator can include any certificates that might be useful 
to the recipient, including certificates for key management.  I do not see 
any reason why the originator cannot piggy back key management certificates 
on a signed only message in the current syntax.

I think that the current wording of the use of
ExtendedCertificatesAndCertificates in the S/MIME implementation guide is 
appropriate -- the sender should put in the signing certificate and
certificate chain, and the receiver should be prepared to accept anything 
in any order, but other stuff can go in there also if it's useful.

Being too restrictive in this case will probably hurt, especially in the 
dual key model that I mentioned before.

But being too loose creates work for the receiver, does it not?

The additional authorization information needs to be transfered somewhere.  
These certificates containing authorization information do not make the 
recipient's job overly onerous.

In our case, we maintain a
local cache database that has certificates indexed by issuerAndSerialNumber 
and also by subject, and root keys that are indexed by subject.  Finding
the chain is a matter of doing lookups by issuerAndSerialNumber and by
subject (by issuerAndSerialNumber for the signing cert, and then looking up 
root keys or certificates by subject, keeping in mind that multiple
certificates can have the same subject). 

Yes, but if you have a local database, you dont really need any 
certificates to be passed to you do you? Except to add more to your 
database. I think that the certificates in the message are for 
receivers who dont have a general certificate database, but who only 
have a very small set of trusted root keys. And to help them, one or 
more chains of certificates seems to be the best.

The certificates must be passed in the message or obtained from some server 
(perhaps a Directory or Web Server).  They do not appear in the local cache 
without being sent or fetched.  Also, most implementations of local 
certificate stores limit their size, so certificate key flushed 


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