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Subject: BTG sequence diagram
This is to respond to David Chadwick's notes [1] and [2] and to try to explain what I believe is the correct sequence of a BTG episode. In [1], David describes three evaluation scenarios: 1. "If action = read and role=Doctor and resource=medical record and BTGstate = True then grant access" No problem here--it corresponds to the last user interaction in attached sequence diagram. 2. "If Action=SetBTG and .... then grant with obligation set BTGstate to True in StateDB." I guess it could work this way, but if we identify a "GlassManager" service, the user would request the GlassManager to break the glass, who in turn would make an authorization request, verify permission, and take the action, and return an appropriate message (perhaps including obligations) to the user. 3. "If Action=ResetBTG and .... then grant with obligation set BTGstate to False in StateDB" I did not show this interaction, but it would look like the illustrated interaction for "breakGlass". Now, more generally, to respond to [2], refer to the attached sequence diagram, which represents a rather purified view of the components and their interactions. Many variations on this are possible, but the variations I do not want to sanction with a standard are the ones that would have the PEP, PDP, or PIP doing things that degrade their functional independence or extend their specified behavior, or that would overload the XACML request/response mechanism with additional meanings. David's last formal proposal [3] has all of these risks, although subsequent discussion has mitigated some of them. One feature of that proposal that has not been discussed much is the initial BTG obligation (section 2.1). This would require the PDP not only to apply the policy to the original request (for data), but also to find and apply a policy to a hypothetical request to break the glass. I don't know of a policy feature to induce this behavior, nor any type of stanard request that could do this. The policy could return the state of the glass as an obligation attribute, but that is all it could do using standard features. Maybe if we can agree on the scenarios we want to support (using sequence diagrams for common understanding) we would have a better chance of identifying opportunities for standardization around BTG. Regards, --Paul [1] http://lists.oasis-open.org/archives/xacml/201104/msg00031.html [2] http://lists.oasis-open.org/archives/xacml/201104/msg00033.html [3] http://lists.oasis-open.org/archives/xacml/201102/msg00017.html
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