Re: Certificate requests for encryption keys

[Anne Anderson - Sun Microsystems <aha@xxxxxxxxxxxx>]

I would like to see any Subject, including an End-Entity, be able to 
issue certificates for encryption keys (and possibly other types as
well).

Justification:

1. CAs have the task of certifying identity.  There does not need to
   be a new identity certification in certifying keys other than
   those used for certifying or verifying identity.

2. End-Entities may need to change encryption keys frequently.  Many 
   CAs are not designed for frequent updates.

3. A CA can still have a policy of not signing end-entity
   certificates that allow certification of non-identity keys, if
   that CA wants to certify all end-entity keys.

4. A verifier can still have a policy of not accepting end-entity
   certificates that are used to certify non-identity keys, if that
   verifying wants a "CA" to verify all keys.

5. It is generally simpler for an End-Entity to manage the
   certificates used for purposes other than identity.

So REQUIRING non-identity keys to be certified by a CA seems to rule 
out reasonable and useful models for the use of certificates.

Supporting this model will require agreement on what combination of
BasicConstraints values and KeyUsage values are permitted in
certification paths.

One way to do this follows:

End-Entities could be issued certificates by a CA for keys with
KeyUsage of keyCertSign, but certification paths would accept these
keys only when used to sign certificates for the same End-Entity
where keyUsage is digitalSignature, nonRepudiation?,
keyEncipherment, dataEncipherment, or keyAgreement.

Example:

Certificate 1:
   Issuer:  X
   Subject: Y
   SubjectPublicKey: <Y's keyCertSign key>
   BasicConstraints: CA
   KeyUsage: keyCertSign
   Signed by: <X's keyCertSign key>

Certificate 2:
   Issuer: Y
   Subject: Z
   SubjectPublicKey: <Z's keyCertSign key>
   BasicConstraints: EE
   KeyUsage: keyCertSign
   Signed by: <Y's keyCertSign key>

Certificate 3:
   Issuer: Z
   Subject: Z
   SubjectPublicKey: <Z's keyEncipherment key>
   KeyUsage: keyEncipherment
   Signed by: <Z's keyCertSign key>

Other solutions include a new KeyUsage type corresponding to
"keyCertSign", but used only for End-Entities.

Anne Anderson
-- 
Anne H. Anderson  ECI#712-KC Email: aha@acm.org
Sun Microsystems Laboratories   or: aha@east.sun.com
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