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Subject: [xacml] resource-id Attribute proposal

Summary of the issue:

  During the TC conference call on 29 August 2002, we discussed
  whether a Request <Resource> MUST contain an Attribute with

  Polar argued that the resource might be identified by a more
  general attribute, such as classification level: the <Subject>
  is requesting access to all documents with the given
  classification level.

  Hal argued that this semantic implies that the PEP is doing its
  own finer-grained access control, which is not part of the
  XACML model, and that the specific resource to which access is
  being requested MUST be specified by its id.  Hal also argued
  that there was a security problem if resource-id is not listed,
  since the policy might grant access to resources it did not


  I propose that we make minOccurs on <Resource> <Attribute>
  equal to 0, and use the following wording in describing
  <Resource> <Attribute>:

  "At least one Attribute must be present for the <Resource> if
  <ResourceContent> is not present.  Typically, an Attribute with
  AttributeId equal to
  "urn:oasis:names:tc:xacml:1.0:resource:resource-id" will be
  present to identify the resource to which access is being


  I do not think Hal's security issue holds up: if a policy wants
  to grant access only according to resource-id, then its target
  or conditions will always reference the resource-id attribute.
  In that case, if the attribute is not present, the policy will
  not apply or will be indeterminate.

  My proposal allows for several models of access control.  It is
  up to a policy writer to determine which models the policies
  conform to.  It is up to a PEP to know which attributes must be
  supplied for a given policy: one way to communicate this is
  through a "missing-attributes" status code in the <Response> to
  an initial <Request> that may contain minimal attributes.
  XACML does not need to specify the model for access control or
  the model for how required attributes are determined.

Anne Anderson
Anne H. Anderson             Email: Anne.Anderson@Sun.COM
Sun Microsystems Laboratories
1 Network Drive,UBUR02-311     Tel: 781/442-0928
Burlington, MA 01803-0902 USA  Fax: 781/442-1692

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