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Subject: Re: [xacml] Updated policy template wiki


On 5/10/2012 6:03 PM, Erik Rissanen wrote:

I put in one such example on the wiki page. Search for "on-permit-apply-second" and you will find it.

This strategy only works if there is one policy template data for the
policy template. In general, there may be many policy template data per
policy template. The example in the wiki has two: TAA-1.1 and TAA-1.2.

Although you didn't do it, I assume you meant to replace the parameters
in the condition with attribute designators as well, i.e., designators
for "organizations", "nationals" and "workEfforts".

The policy needs to be evaluated twice. The first time the attribute
designator for PolicyIdOnResource needs to return "urn:curtiss:ba:taa:taa-1.1",
the designator for "organizations" needs to return the bag of { "Curtiss",
"Packard" }, the designator for "nationals" needs to return the bag
of { "US", "GB" }, and "workEfforts" needs to return { "DetailedDesign",
"Simulation" }. The second time, PolicyIdOnResource needs to return
"urn:curtiss:ba:taa:taa-1.2", "organizations" needs to return { "Curtiss",
"Spad" }, "nationals" needs to return { "US", "FR" } and "workEfforts"
needs to return { "Integration", "Simulation" }.

Of course, we don't currently have a way to cause a policy to be evaluated
multiple times with the attribute designators returning different bags each
time. For one thing, the result of an attribute designator is fixed for
the entire duration of the processing of an authorization request. The
expansion of the policy template into a policy template instance for each
policy template data achieves the same end.

The use of on-permit-apply-second is a good idea for removing the need
for any special processing of parameters in targets.


Best regards,

On 2012-10-04 23:01, Jean-Paul Buu-Sao wrote:


Apologies for missing the call today, as I was in a TSCP event, together with Gerry and David of Axiomatics.

I have been much interested in the last findings, and agree that if the “template” property that we are
(all, I think) looking for could be achieved with standard the <AttributeDesignator> construct, rather
than introducing new concepts, then this would be for the better.

May I suggest that, in order to verify this assertion (so to speak), some folks, such as Erik or Danny,
would be kind enough to propose an alternate proposal to the sample found on our Wiki
(https://wiki.oasis-open.org/xacml/Policy%20Template%20Profile%20Examples)? By the way, as a word of
caution, please disregard the in-correctness of the XCAML 3.0 of section 1. of the example (yes the devil
is in the details, and David shown me how this example could be made compliant).

Thanks in advance,


*From:*xacml@lists.oasis-open.org [mailto:xacml@lists.oasis-open.org] *On Behalf Of *Danny Thorpe
*Sent:* Thursday, October 04, 2012 20:11
*To:* Erik Rissanen; xacml@lists.oasis-open.org
*Subject:* RE: [xacml] Updated policy template wiki

When the original proposal for policy templates was brought forward, I noted that simply replacing a
single AttributeValue element with a list of values from the policy template <Parameter> would fail in
<Match> expressions, since <Match> is very explicit about one value, one designator/selector.  I offered a
transform to help produce valid match expressions.

AttributeDesignator does provide similar “insert-multiple-values-here” operations to the policy template
substitution behavior, but I believe the suggestion of policy parameterization came up because of
situations in which AttributeDesignator cannot be used. Comparing an  attribute against a static list of
test values (specific to an organization or location and applied to a generic policy), for example, is a
many-to-many comparison, but cannot be expressed in a <Match> element.

As we discussed on the TC call today, we’re finding more difficulties with parameter substitution the
deeper we dig. Steven Legg noted in an earlier email that some Xacml functions that take single
<AttributeValue> won’t work if multiple values are dropped in to replace the <AttributeValue>. This means
some sort of expression transform will be necessary in condition expressions as well to move policy
templates forward.

In light of these increasing complexities and challenges, I’m beginning to agree with you that perhaps the
policy template use case can better be addressed using the existing <AttributeDesignator>.

This would mean:

1.Giving up parameterization behavior in <Match> expressions and moving that logic into conditions using
<AttributeDesignator> to reference an attribute ID representing the parameterization data.

2.Moving parameterization data from a static policy generator step to a PIP to fill <AttributeDesignator>
references to a particular attribute ID with parameterization data in the PDP at auth request evaluation time.

Using <AttributeDesignator> instead of policy templates does impact the use case quite a bit because
populating PIP data is not part of the Xacml spec.  Policies could be shared between organizations per the
use case, but how the parameterization data is applied to those policies would become a vendor-specific
implementation detail.

I can see the attraction of parameterizing policies to allow up-front synthesis of specific policies, but
as we say “the devil is in the details.” The details are winning. :/


*Danny Thorpe *

Authorization Architect

Dell | Identity & Access Management, Quest Software

Quest Software is not part of Dell.

*From:*xacml@lists.oasis-open.org <mailto:xacml@lists.oasis-open.org> [mailto:xacml@lists.oasis-open.org]
<mailto:[mailto:xacml@lists.oasis-open.org]> *On Behalf Of *Erik Rissanen
*Sent:* Thursday, October 04, 2012 4:42 AM
*To:* xacml@lists.oasis-open.org <mailto:xacml@lists.oasis-open.org>
*Subject:* Re: [xacml] Updated policy template wiki


I still fail to see why this is useful.

If you take a policy template, and replace each <Parameter> with an appropriate <AttributeDesignator>,
then you get a regular XACML policy, and the PEP/PDP can "fill in" the "template" at runtime using normal
XACML attributes.

Why do we need a new standard? In particular I would be opposed to "implementation option C", that is a
PDP would construct the policy from the template at runtime. That's lots of heavy machinery for no gain.

Best regards,

On 2012-09-20 20:25, Danny Thorpe wrote:

    I’ve updated the policy template wiki (https://wiki.oasis-open.org/xacml/Policy%20Template%20Profile)
    with text about required Match expression rewriting in parameter substitution and optional use of
    AttributeDesignators and AttributeSelectors in Parameter data in dynamic policy template reduction


    *Danny Thorpe *

    Product Architect | | *Quest Software*- /Now including the people and products of BiTKOO/ |
    www.quest.com <http://www.quest.com>

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