Hi Erik,
Responses inline:
On 5/16/2011 11:42 AM, Erik Rissanen wrote:
4DD145FB.6000509@axiomatics.com" type="cite">
Hi Rich,
I am about to post a new draft, but I noticed I need to get some
clarifications on your comments before I do that.
See inline.
On 2011-05-11 16:43, rich levinson wrote:
4DCAA0A5.3010808@oracle.com" type="cite">
Hi Erik,
Yes, I am referring to WD-19, when I am saying "leave it as it
is".
However (sorry), that being said, I do think there is some
additional "clean-up"
required on this overall issue.
There is also an additional unrelated typo we found in section
A.13.
I will just list the following "clarifications" to WD-19 and
Erik's current email:
- "from the appendix to section 9" ?? I think you mean
section 7.13 (or earlier (see below)).
Yes.
<Rich>
ok
</>
4DD145FB.6000509@axiomatics.com" type="cite">
4DCAA0A5.3010808@oracle.com" type="cite">
- Since we are introducing Ind{P,D,DP} in section 7, I think
it needs to also be included
in Table 4 for Rule evaluation, and possibly other places.
Yes, to make it clearer. Though, the text in appendix C (to be
moved to Section 7) does contain the base case for the rule
already, but it's better to put in the table to avoid confusion.
<Rich>
That's what I was thinking as well, except possibly even more so,
because one of the effects
of this change is that, at least for this type of processing
(analyzing the Indeterminate to
determine D, P, or DP), the Rule, Policy, and PolicySet processing
is now the same, which
I believe makes the whole thing easier to understand, although it
becomes more abstract
by no longer differentiating between these element types. But I
think the next bullet is the
more important one to discuss, so let's leave this more
"philosophical" aspect until later.
</>
4DD145FB.6000509@axiomatics.com" type="cite">
4DCAA0A5.3010808@oracle.com" type="cite">
- I think we also need to consider having more explanation
in the old C.1 section about
the "extended Inds", which describes the underlying cause:
which imo is that when
you have an "-overrides" type comb-alg, the relative
"weight" of the return values
suddenly has a "precedence" that would otherwise not be
there, namely:
- for example for a "deny-overrides Policy:
Ind{P} < P < Ind{D} < D
which means if a Rule that evaluates to D is encountered,
the processing for
the policy can end, since that is the final answer, no
matter what follows.
However, until a D is encountered processing must
continue.
When all Rules are processed, the "answer" is the greatest
value in the
precedence chain above.
I am not sure about this. I don't want to fill up the normative
sections with long examples. We could say something short like
"The extended Indeterminate values allow combining algorithms to
treat Indeterminate smarter, so that in some cases an
Indeterminate can be ignored when the extended Indeterminate value
shows that the section of the policy which produced the
Indeterminate could not have influenced the final decision even
when there would not have been an Indeterminate." And clearly mark
this non-normative.
<Rich>
This is somewhat subjective in terms of how to best explain the
situation, and I was considering
writing a separate email totally focused on that since w the
resolution of the Policy/Target concept
of Indeterminate, I think I can explain it all fairly concisely in a
systematic way.
To add to what's above:
- For "biased" combining algorithms:
- deny-biased or deny-overrides:
- N/A < Ind{P} < P < Ind{D} < D
- permit-biased or permit-overrides:
- N/A < Ind{D} < D < Ind{P} < P
- non-biased (ex. first-applicable):
- ( N/A = Ind {*} ) < ( D = P )
(i.e. (D = P) means either one that comes first is good, and
both
of them override either N/A or Ind{*})
While these statements might at first be confusing, I think that
ultimately they dictate
the processing algorithm and so from that perspective can provide a
sanity check on
both the p-code and the text.
But, again, this falls into the "explanatory" category, the
significant point I think is in the
next bullet.
</>
4DD145FB.6000509@axiomatics.com" type="cite">
4DCAA0A5.3010808@oracle.com" type="cite">
- Also, considering the above bullet, I think the current
algorithms should be modified
back to look more like the original 2.0 algs. For example
compare the
"denyOverridesCombiningAlgorithm" of section C.2 (new) w
C.10 (legacy):
- In C.2 the parameter to the algorithm is "Decision[]
decisions", where as
in C.10 the parameter to the algorithm is "Rule[] rules".
- Also, in section C.10, within the loop, the first thing
is:
decision = evaluate(rules[i]);
if (decision == Deny) return Deny;
- I think it is important to retain this logic so it can
be shown where the breakout
occurs, which cuts off unnecessary evaluation of
subsequent rules.
- Also, we can retain the criteria for choosing Ind{d} vs
Ind{p} where the
if (effect(rules[i]) ...
is evaluated.
Is this just to refactor the algorithms to look prettier, or are
there actual errors in them? If there are no errors, could we just
keep them as they are, so we don't risk breaking them?
This is not just to refactor the algorithms. When I looked over the
new algorithms in
detail, I noticed there was a quantitative difference between them.
i.e. comparing C.10 and C.2:
- In C.10 (legacy deny-overrides), line 6131, there is a loop
that begins:
- for (i=0; i<lenghtOf(rules); i++ ) {
decision = evaluate(rules[i])
if (decision == Deny)
return Deny;
...
}
- With the new algorithms, this logic also applies to Policies
as well as rules.
Furthermore, starting from the top of the PolicySet tree, and
working down,
this logic is recursive, and the processing should be identical
for PolicySet,
Policy, and Rule (although the "evaluate" function will be
different for each).
- A second important point here is that it is significant that
the first "if" stmt
causes a "return" as opposed to the subsequent "if" stmts that
set various
booleans, but allow the loop to continue processing.
The importance is that in a biased algorithm, if the decision to
which the
algorithm is biased is found, then processing of the loop can
end right there,
and there is no need to evaluate the rest of the rules,
policies, or policysets,
within the current node. i.e. if I am in a deny-overrides node,
if, when I
evaluate the next node, it returns a Deny, I am done.
Clearly in the case of Policy and PolicySet, there is no ability
to get either
a Permit or Deny until the leaf Rules are processed. However, if
I am in a
deny-overrides PolicySet, and there are 10 child Policy
elements, for example,
and I "evaluate" the first Policy and it in turn evaluates its
child Rules, if its
first, or any other, rule returns a Deny, then the first Policy
will return a Deny,
and there is no need to "evaluate" the other 9 Policy elements
since the
decision will be a Deny regardless of what they return.
- Therefore, I think a better algorithm would look like this for
C.2 (note the
"evaluate" operation in the first line of the for loop which is
not currently
in C.2):
- Decision denyOverridesCombiningAlgorithm(Node[] nodes) {
...
for ( i=0; i<lengthOf(nodes); i++ ) {
Decision decision = evaluate(nodes[i]);
if (decision == Deny) {
return Deny;
}
// I believe the rest of the logic remains the same as
currently in C.2:
...
} // end for loop
// logic should also be same as C.2 after loop
} // end algorithm
- Now, if we look again at C.10, and try to see how it relates
to the new algorithms,
I think it would go something like this, where Rule is subclass
of Node:
- Decision denyOverridesRuleCombiningAlgorithm(Node[] nodes) {
Boolean atLeastOneError = false;
Boolean atLeastOneErrorD = false;
Boolean atLeastOneErrorP = false;
Boolean atLeastOneErrorDP = false;
Boolean atLeastOnePermit = false;
for ( i=0; i<lengthOf(rules); i++ ) {
Decision decision = evaluate(nodes[i]);
if (decision==Deny) {
return Deny;
}
// the next 2 "if"s are the same as C.10:
if (decision==Permit) {
atLeastOnePermit = true;
continue; // i.e. skip the rest of the logic
current iteration of loop
// and start next iteration
}
if (decision==NotApplicable) {
continue;
}
if (decision==Indeterminate) { // this can only be
returned for rules
if ( effect((Rule)nodes[i])==Deny) ) { // cast to
Rule to get effect
atLeastOneErrorD = true;
}
else {
atLeastOneErrorP = true;
}
continue;
}
// the following is same as C.2 and will evaluate the
3 types
// of Indeterminate, which can only be returned for
Policy and PolicySet
... same as lines 5762->5776 (not repeated here)
} // end for loop
if (atLeastOneErrorD==true &&
(atLeastOneErrorP==true || atLeastOnePermit==true) {
atLeastOneErrorDP = true;
}
if (atLeastOneErrorDP==true) {
return Indeterminate(DP);
if (atLeastOneErrorD==true) {
return Indeterminate(D);
}
if (atLeastOnePermit==true) {
return Permit;
}
if (atLeastOneErrorP == true) {
return Indeterminate(P);
}
return NotApplicable;
} // end algorithm
- The representation above clearly shows:
N/A < Ind{P} < P < Ind{D} < D
by simple following the "return" statements up the algorithm.
- I think the above algorithm also shows the origin of D,P,DP
coming
from the effect of the rules, and then being percolated thru
Policy
and PolicySet.
So, basically, although the above algorithm may look a little more
complicated than
the current C.2, I think it retains 2 things from C.10 that the
current C.2 drops:
- It retains the break of the loop when the biased Decision is
returned
- It retains the logic that creates the breakout of
Indeterminate to Ind(D,P,DP)
Comments?
Thanks,
Rich
</>
4DD145FB.6000509@axiomatics.com" type="cite">
4DCAA0A5.3010808@oracle.com" type="cite">
- Finally, rather than passing in (Rule[] rules), or
(Policy[] policies), we might want to
consider using a neutral term, such as (Node[] nodes) or
(Child[] children) where
Node or Child could refer to either a Rule or Policy.
- And, finally, the typo in section A.3.14, under
rfc822Name-match:
In cs-01 line 4992 (next to last para), the phrase: "matches
a value in the first argument"
should say "matches a value in the second argument".
I think this is just a typo, esp when
compared w the next para.
Yes, this is a typo. I will fix it.
4DCAA0A5.3010808@oracle.com" type="cite">
Thanks,
Rich
On 5/11/2011 5:37 AM, Erik Rissanen wrote:
4DCA58DB.4080406@axiomatics.com"
type="cite">
Hi All,
Rich, when you say "leave it as it is", I assume you mean the
new working draft which evaluates the children of policy sets.
If so, I think everybody is in agreement.
I will still post an updated draft which moves the definitions
of the text from the appendix to section 9, so everything is
in one place.
Best regards,
Erik
On 2011-05-09 06:27, rich levinson wrote:
4DC76D48.7030208@oracle.com" type="cite">
Hi again, Paul, Erik, Hal, and TC:
I have spent some additional time looking at this problem
and I am now leaning
toward leaving the spec as is, at least as far as I have
analyzed it.
For anyone interested, my reassessment is based on the
following:
The intention has always been to maintain consistency with
XACML 2.0, while at
the same time enabling the "D" and "P" types of
Indeterminates to propagate up
the PolicySet hierarchy in addition to the "DP" which was
all that was propagated
up in 2.0, despite the fact that D and P were determined and
used on the first
hop up, they were unnecessarily cut off at that point and
information was lost.
It appears that I inadvertently lost sight of this big
picture when looking at the
details from the top down. However, in order to go from the
top down one
has to allow the existing algorithms on the bottom level to
remain the same,
and obviously by assuming that the Rules do not need to be
evaluated is a
direct contradiction with the existing XACML 2.0 algorithms
which first evaluate
the Rule, then look directly at the effect later if there
was an indeterminate.
Bottom line: I withdraw this sidebar issue, about not
needing to evaluate the
Rules when the Policy or PolicySet Target produces an
Indeterminate. In 2.0 the
spec was able to say that because it did not propagate the D
and P properties up,
however, to do the complete job of propagating all the D and
P properties, we
do need to evaluate the Rules, and the changes in the spec
to this effect I believe
are correct.
Thanks,
Rich
On 5/6/2011 11:06 PM, rich levinson wrote:
4DC4B750.2070402@oracle.com"
type="cite">
Hi Paul and TC,
I think the toothpaste is out of the tube on this one:
i.e. I think too much has been
invested in the analysis for one member to unilaterally
shut down the issue by
"withdrawal". In any event, that's my opinion, but,
regardless, based on
yesterday's mtg, I believe there is more to be said on
this issue, and hopefully
we can channel it to a clean resolution.
That being said, following is additional analysis I have
done and some conclusions that
I believe we can reach agreement on, and that I think I
can describe in terms that everyone
can follow (for "clarity" I will just add an "s" for the
plural of "Policy"). There are 2 arguments
I would like to make.
Argument 1:
- First, there are 3 "types" of Policys:
- Policys{P} where all Rules have Effect="Permit"
and therefore
these Policys can never return a "Deny".
- Policys{D} where all Rules have Effect="Deny" and
therefore
these Policys can never return a "Permit"
- Policys{DP} where there are a mix of Rules, some
of which are "Permit",
and some of which are "Deny", and therefore, there
is no apriori way
to look at such a Policy and know whether or not it
can return either
a Permit or a Deny.
- Therefore, the 3 types of Policys each have an
inherent property, which
can be determined simply by inspection of the Policy
w/o regard to
evaluation of any Attributes.
- In fact, 2 out of 3 of the types retain their
"property" regardless of
evaluation of the attributes.
i.e. Policy{P} is always Policy{P}, it can never
change its property and
become either Policy{D} or Policy{DP}
i.e. same can be said for Policy{D}
I would therefore refer to these as "static
properties"
- The third type Policy{DP} has a run-time
characteristic, where if
current values of the Attributes happen to exclude
all the Rules
of either D or P, then the current run-time
"property" of the Policy{DP}
for a single evaluation can effectively become
either Policy{P} or Policy{D}.
On subsequent evaluations the Policy{DP} can again
by happenstance
become any one of the 3 types.
I would therefore consider this a "runtime property"
if we allow its
definition to be subject to Attribute evaluation.
Therefore, I think we can say that the problem we are
discussing reduces to only the
evaluation of Policy{DP} elements.
We can then ask whether we want our combining algorithms
to be subject to runtime
values of Attributes that on any given evaluation can
cause a Policy{DP} to become a
Policy{D} or a Policy{P}, thus rendering the property of
the Policy indeterminate
until runtime values are plugged in.
I would also suggest that it is this indeterminacy, which
would cause Policys not to
be comparable for "equivalence", because the Policys
themselves have a built-in
uncertainty depending on how one regards this property.
I would also suggest that for the purpose of "equivalence"
this runtime characteristic could
be considered a "performance optimization", which could be
a property of the Policy Engine,
whereas the inherent D and P properties can be considered
a Policy language characteristic
independent of runtime, which could be included in an
equivalence algorithm.
Argument 2:
There is one additional argument I would like to add for
consideration. In XACML 2.0,
there is a statement in section 7.10 for Policy
Evaluation, which says:
'If the target value is "No-match" or
“Indeterminate” then the policy value SHALL be
“NotApplicable” or “Indeterminate”, respectively,
regardless of the value of the rules.
For these cases, therefore, the rules need not be
evaluated.'
By comparison, in XACML 3.0, WD 19, the corresponding
statement in section 7.11 has
been modified to say:
'If the target value is "No-match" then the
policy value SHALL be
"NotApplicable", regardless of the value of the rules.
For this case, therefore, the rules need not be
evaluated.'
The "Indeterminate" part of this statement has been
modified to say:
'If the target value is "Indeterminate", then
the policy value SHALL be
determined as specified in Table 7, in section 7.13.'
Therefore, the "meaning" of the spec has been changed,
because in order to select
an entry in Table 7, now the rules do have to be
evaluated, which is not obvious
unless one does a very careful and complete reading of the
changes that are
being proposed.
Additional Consideration:
One other side effect that I think is of concern, is that
if we allow the Policy property
(P, D, or DP) to be subject to runtime determination then
when an Indeterminate is
obtained at the top of the tree, then it would be
necessary to evaluate the complete
subtree in order to determine what this property is. By
comparison, the static property
can be determined at any time by processing the tree once
and recording the property
for all subsequent evaluations.
My Conclusions:
Bottom line: my recommendation is that we define the
D,P,DP property in such a way
that it is a static characteristic of the Policy
definition, which presumably allow it to
be used in "equivalence" determinations. I would also
recommend that runtime
optimization be a configurable option, and it will be
clear that if this option is activated,
that any presumption of equivalence should be disregarded
as far as runtime behavior
would be concerned.
Comments, suggestions welcome.
Thanks,
Rich
On 5/6/2011 12:51 PM, Tyson, Paul H wrote:
3898C40CCD069D4F91FCD69C9EFBF096064B3D1C@txamashur004.ent.textron.com"
type="cite">
I withdraw my objection to the Section 7 changes made by Erik in the 3.0
core spec wd-19.
I'm still concerned that the policy evaluation specification (in section
7) may cause unexpected variations in the results from two seemingly
"equivalent" policies, but I need to produce some theoretical or
empirical evidence to demonstrate this (or to relieve my concern). In
any case, the wd-19 changes probably do not make this any better or
worse.
Regards,
--Paul
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