[OGSA-AUTHZ] Draft XACML/SAML Protocol Profile

[David Chadwick]

Hi Chad

from your long response I do believe that you are confusing integrity 
with authenticity. Can you tell me which integrity mechanism you are 
thinking of that provides message integrity without any ability for the 
recipient to determine who the sender is.

regards

David

Chad La Joie wrote:
> Let me address confidentiality and integrity requirements separately.
> 
> XACML authorization decision requests *and* responses may carry XACML 
> request contexts.  These contexts can contain sensitive information 
> about individuals.  Such information can not be distinguished by 
> requester/responder software.  The only way then to ensure the 
> protection of such information is to always require that some form of 
> confidentiality be in place.  This is also why the requester/responder 
> is not allowed to forward assertion onto parties for which it was not 
> intended.
> 
> Likewise the policy response may contain sensitive information, in most 
> cases the sensitivity will likely stem from the ability to examine and 
> exploit the policy under which the PDP will operate, but other issues 
> may be present as well.  While we certainly hope that deployers won't 
> have holes in their policies, the complexity of XACML makes it likely 
> that such holes will occur.  Providing all the information necessary for 
> an attacker to take advantage of such holes posses an unnecessary risk; 
> a risk that is easily mitigated by confidentiality requirements.
> 
> Integrity is required within the authorization decision request so that 
> an attacker can not manipulate the content of the request in order to 
> produce a positive authorization decision.  While a PEP may be able to 
> detect this if the XACML request context is returned by the PDP it is 
> unlikely that the context will be returned in the response.  The 
> authorization decision response needs to be protected because the 
> response may simply be a "yes" or a "no".  The PEP has no way to 
> determine if the message was changed in transit.  Also, note, that even 
> if the responder did return the request context, allowing the PEP to 
> verify that the request was not altered, such a check is meaningless 
> without response integrity checking.
> 
> An integrity mechanism is required on a policy request to prevent a 
> third party from intercepting the request and altering the policy 
> requirements such that a more lax policy is returned.  It is required on 
> the response to prevent that the policy itself from being altered.
> 
> Tom Scavo wrote:
>> On Dec 10, 2007 12:37 AM, Chad La Joie <chad.lajoie at switch.ch> wrote:
>>> Tom Scavo wrote:
>>>> I'm sure you know this but if you change all the normative language
>>>> regarding <saml:Issuer> from SHOULD to MUST, you essentially end up
>>>> with the Assertion Query/Request Profile in section 6 of the SAML V2.0
>>>> Profiles spec:
>>>>
>>>> http://docs.oasis-open.org/security/saml/v2.0/saml-profiles-2.0-os.pdf
>>> Yes, it's supposed to be very similar to the query/request profile.
>>>
>>>> So the obvious question is why did you change the language regarding
>>>> <saml:Issuer>?
>>> The responder needs to know who is making the request.
>> Well, this is straightforward query, so your profile can (and probably
>> should) build on the Assertion Query/Request Profile (which requires
>> <saml:Issuer>).  In that case, the profile reduces to little more than
>> section 3.
>>
>>>> Overall, your profile is a curious blend of more restrictive / less
>>>> restrictive language with respect to the profiles it depends on.  The
>>>> stated requirements on <saml:Issuer> are an example of the latter.
>>>> The security requirements in section 3 seem to be an example of the
>>>> former.  In particular, I find it odd that integrity and
>>>> confidentiality are MUSTs, yet authentication is SHOULD.  Can you say
>>>> a few words about that (beyond what's already written in the
>>>> document)?
>>> Why would you find it odd that security requests/responses require
>>> integrity and confidentiality mechanisms?  They are required because not
>>> doing them makes the request/response completely untrustwothy.
>>>
>>> In regards to authentication, this one I went back and forth on.  I
>>> personally think the requester and responder should always be mutually
>>> authenticated, but I could imagine cases where deployers had a more lax
>>> view, especially on the policy request.  So, I just left it as a SHOULD
>>> so that individual deployments could choose not to do it, if they wanted.
>> Section 6.1 of [SAMLSecure] addresses the security implications of the
>> SAML SOAP Binding. In addition, section 3.1.2 of the SAML Bindings
>> specification [SAMLBind] provides further security guidelines
>> regarding SAML bindings.  Taken together, these security
>> considerations adequately address this use case, I think.  Additional
>> requirements with respect to integrity and confidentiality have not
>> been justified.
>>
>> Tom
> 

-- 

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David W. Chadwick, BSc PhD
Professor of Information Systems Security
The Computing Laboratory, University of Kent, Canterbury, CT2 7NF
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