RE: German Key Usage

["Eugene C. (Gene) Williams" <williams@xxxxxxxxxxxxxxxxxxxxx>]

On the surface Paul's comments seem logical, however, I'm wondering why any
process which authenticates privileges and access would not demand
non-repudiation???  If a key, which has been copied for encryption key
recovery purposes, is used for digital signatures associated with I&A as
well as for encryption, it seems that we're back to the basic reason for not
making copies of keys used for digital signatures.  Maybe I'm missing
something...

v.r.

Gene

-----Original Message-----
     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

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