RE: Question about 3280bis keyUsage and extKeyUsage consistency

["Manger, James H" <James.H.Manger@xxxxxxxxxxxxxxxx>]

The id-kp-clientAuth extended key usage indicates that a public key can be used for "TLS WWW client authentication" [RFC 3280, page 41], ie https connections using mutual authentication.  This is not the same purpose as an IPSec VPN connection.

Some extended key usage OIDs where defined for IPSec, but later deprecated.

Theoretically, a PKIX-compliant IPSec system MUST recognize keyUsage & extendedKeyUsage extensions [RFC 3280, 4.2, page 25].  An IPSec system should only reject a certificate based on the keyUsage extension if:
* the extension is present; and
* the digitalSignature bit is not set;
Any other combination should be acceptable (eg no ku, ku with dig.Sig & nonRep., ku with just dig.Sig., ku with every bit set, ...).
An IPSec system should only reject a certificate based on the extendedKeyUsage extension if:
* the extension is present; and
* doesn't contain anyExtendedKeyUsage or any of the deprecated IPSec OIDs.
Any other combination should be acceptable (eg no eku, eku with any.EKU. & id-kp-codeSigning, ...).

If I was writing IPSec software I would probably make the list of acceptable extendedKeyUsage OIDs easily configurable so things such as id-kp-clientAuth could be added for interoperability even though it is not strictly correct.

P.S. I am not an expert on IPSec or the vagaries of various IPSec products.


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From: owner-ietf-pkix@xxxxxxxxxxxx [mailto:owner-ietf-pkix@xxxxxxxxxxxx] On Behalf Of Eric Grenier (egrenier)
Sent: Thursday, 2 June 2005 5:04 AM
To: ietf-pkix@xxxxxxx
Subject: Question about 3280bis keyUsage and extKeyUsage consistency

...
The follow-up question...  In a situation where an IPSec VPN client
application uses end entity certificates for user authentication
purposes to a head-end device.  Which combinations of keyUsage and
extKeyUsage would be most correct?  My interpretation of the draft
suggests a keyUsage of digitalSignature and nonRepudiation as minimum
requirements along with an optional extKeyUsage of clientAuth.

An issue has arisen where a cert does not have the nonRepudiation bit
asserted but it does have digitalSignature and clientAuth.  Given that
the nature of IPSec VPNs provides a non-repudiation service is requiring
the nonRepudiation bit to be set reasonable even if the cert has an
extKeyUsage of clientAuth?

Appreciate any insight,