[foaf-dev] for more information please log in

Story Henry henry.story at bblfish.net
Mon Jan 14 10:03:24 GMT 2008

On 14 Jan 2008, at 10:44, Peter Williams wrote:

> Lets address the application of the bloom filter to access control  
> in specifically a FOAF setting:-
> If we assume that one authenticates optionally and only for a  
> purpose that is FOAF-specific (i.e. FOAF is not a general purpose  
> cache of distributed directory data, but targets the assertion of  
> personal friend relationship and personal expectations of privacy)  
> then authentication exists to assert friendship in order to obtain  
> friendship privileges in accordance with the limits of the class of  
> friendship/acquaintance.
> If the bloom filter allows one to test whether one is probably a  
> member of the FOAF-object's friend/acquaintaince list with the  
> implied right of the FOAF-subject to query private friendship  
> relations,  lets now assume that authentication exists to now (1)  
> "assert" that status seeking a session; and a resulting login   
> should then (2) "entitle" one to exploit various query rights about  
> the subject's and others' relations with the person whose PPD is  
> being addressed.
> Upon login with strength S, the authorization cookie assigned to the  
> FOAF-subject's web session will be assigned various access mode  
> rights as a function of S and after the session manager possibly  
> tests additional bloom filters that guard whether you the subject  
> ought to be assigned privilege P - where Pi compute particular  
> classes of friend-based inferences. For example, strength S of  
> "publickey" may gate access to inference about the pubkeys of  
> Henry's friends. If strengh S' is "openid from provider #myOP", then  
> this may gate query rights to the pubkeys of Henrys friends whose  
> openids are asserted by #myOP. In general S => P.

Yes. I think we are agreeing on that.

> So, in one embodiment, std xml encryption would be applied as the  
> entire FOAF file as is being streamed out by the webserver hosting  
> the FOAF file, where those query rights would identify which  
> (syntactic) elements of the xml/rdf should be masked. Those parts of  
> the stream that should be masked for the particular FOAF subject UA  
> would be encrypted using std xml element selection principles built  
> into the xml encryption transform. The various groups of parts  
> identified udner the transform would each be encrypted using a  
> particular key generated now for this purpose - a key which could  
> subsequeently be shared with those doing authorized FOAF file  
> aggregation of particular classes of relations that the PPD owner  
> select, when removing his/her expecation of privacy.

That would be an option, but the least likely to get traction it seems  
to me. I don't think we are speaking about encrypting pieces of the  
xml or n3. That could be done, but it seems more than is needed.  
Currently I was suggesting that one publish only what the viewer is  
allowed to see. No need to send him information that is encrypted.  
There are two solutions currently for this:

   1. the same URL could return different representations (different  
content) depending on who is viewing the file, as determined by  
   2. the URL always returns the same representation, but has  
conditional pointers to other files where more information can be  
found for those who are authenticated

In both cases there needs to be a way to tell the consumer of the  
initial representation that he may find more information if he is a  
member of a certain group. This group could indeed be specified in a  
number of ways (including not at all). One of these ways may be to  
specify a group via a bloom filter. Another way may be via some family  
relation. This is a topic I have not thought about. It seems useful to  
specify the group, so that agents don't always need to log in whenever  
they come across a foaf file. But perhaps not. That was just a thought.

> Ignoring my fanciful embodiment, have I got the general thrust of  
> the idea?

I think so.


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