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Subject: Re: [xacml] Redaction by Multiple Decisions

Hi David,

On 24/09/2015 6:48 PM, David Brossard wrote:
Hi Steven,

Interesting idea. I have also seen a similar trend in the insurance industry. The redaction is particularly useful in any industry where there is a strong standardization body which standardizes document structures (e.g. EHR, EMR...).

Using obligations is an OK approach but it hides away authorization semantics inside obligations which means you cannot easily audit your policies or even ask the simpler questions. Also it makes your PEP logic much thicker. And it poses the question of how you combine multiple obligations together.

Also you say that it would be faster to run a single request + obligations. I think an MDP would be equally efficient (the bulk of time spent is on the request-response not on evaluation). It makes enforcement easier.

You would typically ask:

  * Can user Alice view medical record X... and field SSN... and field name... and field address...?

I wasn't thinking of such highly structured documents. This sort of thing is what
I would usually call fine-grained access control, where users are given rights to
perform specific actions on specific fields (columns, properties, attributes, ...)
with little or no regard for the contents of the fields.

For redaction, I was thinking about documents with only basic structure (chapters ->
sections -> paragraphs -> sentences -> words) where arbitrary passages of text
might carry classifications (top secret, etc) or other markings (Australian Eyes
Only, ANZUS Eyes Only) or might have annotations applied by tools that are looking
for certain kinds of sensitive information in the text. Individual words might
need to be redacted but processing an authorization request for every single word
would be time consuming.


To which the PDP would reply Permit, Permit, Deny...

It makes the PEP easy to implement: all you have to do is enforce a Permit or Deny. It also means you probably want to integrate with a PEP capable of processing the type of document we are dealing with. If it is an XML document, then an API / XML gateway would be a great PEP.



On Thu, Sep 24, 2015 at 8:00 AM, Steven Legg <steven.legg@viewds.com <mailto:steven.legg@viewds.com>> wrote:

    On the last TC conference call Hal mentioned using multiple authorization requests
    to redact a document. Basically asking for each discrete piece of the document
    whether it is visible. This is the obvious way to do it but it is also expensive,
    even using the Multiple Decision and Hierarchical Resource profiles.

    The redaction solution I sketched out was the result of looking for a faster way
    to do redaction. One request determines whether access to the document is permitted
    and simultaneously returns the instructions for redacting the document, as
    obligations, if access is permitted.

    A profile for redaction could talk about both methods.

    Mohammad mentioned interest in redaction for health documents so I was wondering
    if there might be existing marking schemes and vocabularies for health records that
    might feed into some XACML attribute definitions and concrete examples for a
    redaction profile. Anything similar in the military sphere would be interesting too.


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