Subject: RE: Associating symmetric algorithms with a public key

From: "Trevor Freeman (Exchange)" <[email-masked]>
Date: Tue, 16 Nov 1999 17:19:46 -0800

Hi Steve,

I am sympathetic to being careful as to what is in a certificate. 
The main reason for saying they are a hint is that in the final analysis,
this kind of thing can never be more than a hint with asynchronous
protocols, so it really is a reality check. I am equally hesitant to yet
again build a dependency on the directory, and I am equally unconvinced that
it makes sense in this case to duplicate this information. This defined
mechanism also give a clean package  of self contained data - wherever the
certificate goes, so does the information regarding the associated symmetric
algorithms. RFC2459 supports the use of directory attributes, this is a
directory attribute so all we are doing in reality is clarifying and
highlighting a potential application of this specific attribute. Adding it
to the certificate also simplifies the semantics because key usage and
policy are now inherited from the certificate so are not needed in the
extension.

Trevor

-----Original Message-----
From: Stephen Kent [mailto:[email-masked]]
Sent: Tuesday, November 16, 1999 4:14 PM
To: Trevor Freeman (Exchange)
Cc: Pkix List (E-mail)
Subject: RE: Associating symmetric algorithms with a public key

Trevor,

I hate to see extra attributes added to certs. I appreciate the 
desire to give hints to a user re what symmetric algorithms that user 
might employ when communicating with a target user, identified by the 
certificate in question.  However, I'd rather see the LDAP & X.500 
folks provide better data structures for this in the directory, 
rather than adding a field that has only heuristic value to a cert. 
If these are only hints, not proscriptive, then we don't seem to be 
making a string security statement about them anyway.

Even if we agree that Steve's Rule of Revocation is closer to linear 
or log than quadratic, the principle still applies ...

Steve

---

From: Stephen Kent <[email-masked]>
Date: Wed, 17 Nov 1999 10:54:20 -0500

Trevor,

Yes, 2459 does carry over the 509 facility for inclusion of directory 
attributes, but we recommend against its use.  So, if one wants to 
take advantage of that facility, it is "legal," but it also is 
clearly discouraged.  For the reasons I cited in my message, and 
seconded by others, I don't think we should encourage use of this 
facility and thus I don't believe that we ought to make any comments 
about this specific case relative to our current characterization of 
this certificate attribute.

Steve