Re: Evaluation: draft-ietf-pkix-wlan-extns-04.txt

[Russ Housley <housley@vigilsec.com>]

Ted:

The Security Considerations section does address this concern.  It says:

   SSID values are unmanaged; therefore SSIDs may not be unique.  Hence,
   multiple client certificates may contain the same SSID.  In this
   case, automatic selection of the certificate SHOULD fail, and the
   implementation will require help from the user to choose the correct
   certificate.  If the implementation chooses to automatically select
   the client certificate and choose the incorrect one, then information
   such as the list of SSIDs may be disclosed.

If your concern is implementations that do not have human operators, then 
sequentially trying the certificates may be necessary.

Whether the implementation has a human user associated with it or not, the 
sequential attempt with each certificate only needs to be done once if a 
cache of AP MAC addresses with which the certificate has successfully 
authenticated.  I think this is a good addition to the document.  I propose 
the following text:

   The Wireless LAN (WLAN) System Service identifiers (SSIDs) public key
   certificate extension is always non-critical.  It contains a list of
   SSIDs.  When more than one certificate includes an extended key usage
   extension indicating that the certified public key is appropriate for
   use with the EAP in the LAN environment, the list of SSIDs MAY be
   used to select the correct certificate for authentication in a
   particular WLAN.

   Since SSID values are unmanaged, the same SSID can appear in
   different certificates that are intended to be used with different
   WLANs.  When this occurs, automatic selection of the certificate
   SHOULD fail, and the implementation will require help from the user
   to choose the correct certificate.  However, by maintaining a cache
   of Access Point (AP) MAC addresses with which the certificate has
   successfully authenticated, user involvement can be minimized.

I have CCed my coauthor to give him an opportunity to review my proposed 
text as well.

Russ

At 10:34 AM 8/4/2003 -0700, hardie@qualcomm.com wrote:
> Ted Hardie           [   ]     [   ]     [ x  ]     [   ]
>
> Since there is no guarantee of uniqueness for  SSIDs,
> it seems like there may be a separate step needed
> when you have the "every SSID is called CORP" problem.
> This text, in particular:
>
>    The Wireless LAN (WLAN) System Service identifiers (SSIDs) public key
>    certificate extension is always non-critical.  It contains a list of
>    SSIDs.  When more than one certificate includes an extended key usage
>    extension indicating that the certified public key is appropriate for
>    use with the EAP in the LAN environment, the list of SSIDs MAY be
>    used to select the correct certificate for authentication in a
>    particular WLAN.
>
> may need to contain text on what to do if more than one certificate
> contains the same octet string as an SSID.  Given that the whole
> thing is a "MAY" the answer may well be "try them in turn" or
> something very basic, but a note of the problem and what to do
> would be useful.
>                         thanks,
>                                 Ted