Sorry, didn't send this to the whole list. -------- Original Message -------- Subject: Re: [OGSA-AUTHZ] Draft XACML/SAML Protocol Profile Date: Wed, 12 Dec 2007 14:59:03 +0100 From: Chad La Joie <chad.lajoie@switch.ch> Organization: SWITCH To: David Chadwick <d.w.chadwick@kent.ac.uk> References: <475418B0.5050003@switch.ch> <ea2af9bd0712091902p1b5547efv2d25c40e2b6b535c@mail.gmail.com> <475CD07F.1050307@switch.ch> <ea2af9bd0712100636l7f2c4ce4je88a6ecdd01194f2@mail.gmail.com> <475D6EF7.504@switch.ch> <475EBFCE.5030300@kent.ac.uk> No, no confusion. I was referring to a very specific requirement, integrity, which is orthagonal to authentication. It happens that the most common mechanism we use for confidentiality and integrity, SSL/TLS, *may* also provide a means for authenticating the client as well. It is not required and it not doing does not change the integrity properties of that mechanism. David Chadwick wrote:

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:

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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:

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Tom Scavo wrote:

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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.

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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

On Dec 10, 2007 12:37 AM, Chad La Joie <chad.lajoie@switch.ch> wrote: section 3.

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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

-- SWITCH Serving Swiss Universities -------------------------- Chad La Joie, Software Engineer, Security Werdstrasse 2, P.O. Box, 8021 Zurich, Switzerland phone +41 44 268 15 75, fax +41 44 268 15 68 chad.lajoie@switch.ch, http://www.switch.ch -- SWITCH Serving Swiss Universities -------------------------- Chad La Joie, Software Engineer, Security Werdstrasse 2, P.O. Box, 8021 Zurich, Switzerland phone +41 44 268 15 75, fax +41 44 268 15 68 chad.lajoie@switch.ch, http://www.switch.ch