Kerberos Feature Request
Henry B. Hotz
hotz at jpl.nasa.gov
Thu Feb 12 14:37:10 EST 2004
At 8:43 AM +0000 2/12/04, Tim Alsop wrote:
>Thankyou for the examples. This helps understand your requirements.
>Comments below prefixed with Tim>
I don't know if I'd call them "requirements" yet, if ever.
>From: Henry B. Hotz [<mailto:hotz at jpl.nasa.gov>mailto:hotz at jpl.nasa.gov]
>Sent: 11 February 2004 23:01
>To: Tim Alsop; krbdev at mit.edu; heimdal-discuss at sics.se;
>darwin-development at lists.apple.com
>Cc: Dj Byrne
>Subject: RE: Kerberos Feature Request
>Use case 1: I need to control access to some information based on
>ITAR (US Export) regulations. There is an existing LDAP attribute
>listing whether each kerberos user is a "US Person".
> KDC queries LDAP for each ticket request for that attribute
>to see if it's true. If so put the info in the authorization data.
>If not, or if LDAP is down, then leave it blank or set it false.
>Services that care need to check it.
>Tim> The KDC does not have to query the LDAP directory - this can be
>done after authentication has taken place using a pam module (for
>example) or an authorisation exit/module in the application/service.
>This approach is commonly used thoughout the Kerberos community. The
>confusion is introduced because Microsoft have chosen to transport
>authorisation data inside Kerberos tickets, but this has
>disadvantages and is not considered by some as being the best
>architecture. We find that most people want to use Kerberos to
>authenticate a user to an applicationk and then once they know who
>the user is, they should determine whether that user can access the
>application by using a standard LDAP lookup ... If the LDAP
>directory supports Kerberos binding (ie. SASL/GSS/Kerberos) then the
>forwarded Kerberos credentials available at the application can be
>used to bind with the directory to securely read the authorisation
You're describing how people could do it now (which is fine!). I
think I'm describing a simple example of how the optional
authorization data was originally intended to be used.
>Use case 3: I don't want to pay Microsoft all the fees for their server.
> Tap into all the open information about how to set up the
>windows information on an open LDAP server. Then proceed as in case
>2. (Alternatively you could construct a PAC attribute ahead of time
>on the LDAP side and just copy it into the ticket.)
>Tim> This is a clear potential requirement, but as I commented
>before - do you realy think Microsoft would allow such a product to
>exist ? If it did, then they would loose sales of Active Directory
>and would likely do their best to kill the product concerned ???
>Just my opinion - maybe being over cautious !!
I suspect Microsoft wouldn't like it at all. OTOH what can they do?
They are already tinkering with the LDAP schema as much as they
There are already lots of people inspecting the AD LDAP schema so it
can be duplicated on an Open LDAP server. Apple already bundles an
LDAP server with a Kerberos server to provide AD functionality.
Adding correctly-formatted PAC data to the Kerberos tickets is a
pretty small piece of the puzzle, and only provides an incremental
improvement in compatibility AFAIK. (I'm not a Windows expert.)
The opinions expressed in this message are mine,
not those of Caltech, JPL, NASA, or the US Government.
Henry.B.Hotz at jpl.nasa.gov, or hbhotz at oxy.edu
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