RE: German Key Usage

["Friedrichs, Paul" <friedrip@xxxxxxxxxxxx>]

     All,
     
     I agree. What's wrong with one key/cert for 
     keyExchange/Encipherment *and* digitalSignature and a second for 
     nonRepudiation? 
     
     Still two keys/certs: The first is used for privileges/access to 
     resources either encrypted or protected by some AC mechanism 
     requiring remote I&A. The second is used for consciously created 
     signatures that may have to stand up in court. 
     
     This would appear to be the most fundamental distinction of 
     services from the user's or replying party's perspective.
     
     keyUsage is an assertion by the CA, so this split makes sense from 
     the PKI's perspective, as well: The primary functional difference 
     from the CA's point of view is the promise to support 
     non-repudiation by archiving certs/CRLs beyond all statutes of 
     limitations and that it has not archived a copy of the associated 
     private key. 
     
     What I hope disappears is any possibility of interpreting 
     nonRepudiation "service" as applying to notaries and timestamps! 
     These are applications which require nonRepudiation keyUsage like 
     anybody else.
     
     Paul 
     
      


______________________________ Reply Separator
_________________________________
Subject: RE: German Key Usage
Author:  lars.gu.johansson@posten.se [SMTP:lars.gu.johansson@posten.se]  at 
DISAHUB
Date:    8/13/98 10:14 AM


Key users,
     
Seems to me that everyone agrees that it is essential
to separate the two security services authentication and 
non-repudiation by using different keys. That's why I've 
previously supported the idea of never mix these key 
usages (DS and NR) in the same certificate.
     
However, if the intepretation of the bits, as some of you 
point out, should be that digitalSignature (DS) indicates a 
MECHANISM wheras nonRepudiation (NR) is a SERVICE,
then indeed can there be a good reason for having both 
bits set.
     
In order to still achieve the separation of the authantication 
and non-repudiation service, I would propose the addition
of yet another key usage bit, namely the authentication (A) 
SERVICE bit!
     
That could make sense: either the keyUsage field of the 
certificate has DS+A set, indicating an authentication 
service based on a digital signature mechanism. Or the 
certificate would have the keyUsage field set to DS+NR, 
indicating a non-repudiation service based on a digital 
signature mechanism.
     
(Thinking of it: Wouldn't it also be possible to implement an 
authentication service based on an data-encipherment 
mechanism? If so, then the keyUsage would be DE+A)
     
The drawback of this aproach is that it adds further complexity 
to an already quite complex concept. My only concern is that
we can agree on ONE solution that everyone interpret the same 
way. Perhaps it's better to stick to the original idea of never 
combining the DS and NR bits? Opinions?
     
/Lars Johansson