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Graphs vs. Authorities vs. Warrants vs. Authentication vs. Certification etc.

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Fri, 19 Mar 2004 09:33:09 +0200
Message-Id: <AB7B8C86-7977-11D8-A9CA-000A95EAFCEA@nokia.com>
To: ext Jeremy Carroll <jjc@hpl.hp.com>, Jeremy Carroll <jjc@hplb.hpl.hp.com>, Pat Hayes <phayes@ihmc.us>, "<www-archive@w3.org> <www-archive@w3.org>" <www-archive@w3.org>, ext Chris Bizer <chris@bizer.de>


Our recent interchanges about signatures, certificates, certification 
authorities,
etc. as well as the realization that multiple authorities may 
publish/assert the same
graph jointly yet use different certification schemes has led me to 
think that we are
blurring a necessary distinction between qualifications of the graph 
versus characteristics
of particular warrants which are used to verify/authenticate a graph.

So, I've massaged/expanded the swp vocabulary a bit with the goal of 
making warrants
distinct objects which are associated with a graph, and inferring the 
origin and/or
asserting authorities of a graph from those (presumably valid) warrants.

I.e.: (feel free to skip down first to the concrete examples)

swp:Authority
    a rdfs:Class ;
    rdfs:comment "An authority, or origin, of a graph; such as a person 
or company." .

swp:Warrant
    a rdfs:Class ;
    rdfs:comment "A bundle of essential information needed to 
authenticate a graph." .

swp:Signature
    a rdfs:Class ;
    rdfs:comment "A signature used to authenticate a graph." .

swp:Certificate
    a rdfs:Class ;
    rdfs:comment "A digital object by which an authority can be 
authenticated." .

swp:CertificationAuthority
    a rdfs:Class ;
    rdfs:comment "An authority which issues certificates." .

swp:warrant
    a rdf:Property ;
    rdfs:comment "The object is a warrant by which the subject graph can 
be authenticated and
                  its assertional status and asserting or originating 
authority determined." ;
    rdfs:domain rdfg:Graph ;
    rdfs:range swp:Warrant .

swp:authority
    a rdf:Property ;
    rdfs:comment "The object is the authority, or origin, of the graph 
with which the
                  subject warrant is associated." ;
    rdfs:domain swp:Warrant ;
    rdfs:range swp:Authority ;
    owl:cardinality "1"^^xsd:nonNegativeInteger .

swp:assertingAuthority
    a rdf:Property ;
    rdfs:subPropertyOf swp:authority ;
    rdfs:comment "The object is the asserting authority of the graph 
with which the
                  subject warrant is associated." ;
    rdfs:domain swp:Warrant ;
    rdfs:range swp:Authority .

swp:signature
    a rdf:Property ;
    rdfs:comment "The object is the signature to be used to authenticate 
the graph with
                  which the subject warrant is associated." ;
    rdfs:domain swp:Warrant ;
    rdfs:range swp:Signature ;
    owl:cardinality "1"^^xsd:nonNegativeInteger .

swp:certificate
    a rdf:Property ;
    rdfs:comment "The object is a certificate by which the authority can 
be authenticated." ;
    rdfs:domain swp:Warrant ;
    rdfs:range swp:Certificate ;
    owl:maxCardinality "1"^^xsd:nonNegativeInteger .

swp:certificationAuthority
    a rdf:Property ;
    rdfs:comment "The object is the certification authority issuing the 
certificate specified using swp:certificate." ;
    rdfs:domain swp:Warrant ;
    rdfs:range swp:CertificationAuthority ;
    owl:maxCardinality "1"^^xsd:nonNegativeInteger .

swp:origin
    a rdf:Property ;
    rdfs:comment "The object is the origin of the subject graph." ;
    rdfs:domain swp:Graph ;
    rdfs:range swp:Authority .

swp:assertedBy
    a rdf:Property ;
    rdfs:subPropertyOf swp:authority ;
    rdfs:comment "The object asserts the subject graph." ;
    rdfs:domain rdfg:Graph ;
    rdfs:range swp:Authority .


Note the cardinality constraints defined for swp:authority and 
swp:signature. A
warrant for a graph must have one and only one of each.

The ability to explicitly specify a certificate and certification 
authority for
the authority of the warrant is simply a convenience, so that agents 
need not
have to go out and discover such information themselves based on the 
URI denoting
the authority -- though some paranoid agents may choose to do that 
anyway, just
to be sure.

--

OK, here's a concrete example:

Graph G is published by four authorities with distinct authentication 
credentials,
one of which (Bill) is not asserting the claims expressed in the graph, 
only sharing
authorship/publication, and one warrant being external to the graph 
itself:

:G (

      some:resource some:property some:value .

      :G swp:warrant [
         a swp:Warrant ;
         swp:assertingAuthority ex:Bob ;
         swp:signature "..."^^sig:PGPSignature .
         swp:certificate "..." .
         swp:certificationAuthority <http://www.certificates-R-us.com> .
      ]

      :G swp:warrant [
         a swp:Warrant ;
         swp:authority ex:Bill ;
         swp:signature "..."^^sig:X509Signature .
      ]

      :G swp:warrant [
         a swp:Warrant ;
         swp:assertingAuthority ex:Mary ;
         swp:signature "..."^^xyz:XYZSignature ;
         xyz:policy xyz:blargh .
      ]

      :G swp:warrant 
<http://www.foo.bar.com/us282uss82wsauia9whjrui.wnt> .

    )

Note how datatypes are used to differentiate the type of signatures 
used.

Note that in the third warrant, for Mary, an authentication scheme is
used which requires explicit specification of a particular 
authentication
policy to successfuly authenticate the graph (and, no, I'm not going to
suggest what that policy might be or why it would be required -- the 
point
is that this approach allows for extensibility where additional 
information
can be provided in the warrant which is specific to the authentication
machinery and doesn't directly describe the graph itself).

Note also that in the case of the external warrant, the agent is going
to have to *first* validate/authenticate that external warrant before
it can reliably apply it to the graph in question; so while this 
approach
allows for reference to external warrants, it has a higher operational
cost.

 From the above graph, if all of the warrants are valid (and let's 
presume
the external warrant contains [ swp:assertingAuthority ex:Jane ]), one 
can
apply the following two closure rules:

IF   :G swp:warrant ?warrant .
AND  ?warrant swp:assertingAuthority ?authority .
THEN :G swp:assertedBy ?authority .

and

IF   :G swp:warrant ?warrant .
AND  ?warrant swp:authority ?authority .
THEN :G swp:origin ?authority .

along with the relevant RDFS closure rules to infer that

    :G swp:assertedBy ex:Bob .
    :G swp:assertedBy ex:Mary .
    :G swp:assertedBy ex:Jane .
    :G swp:origin     ex:Bob .
    :G swp:origin     ex:Bill .
    :G swp:origin     ex:Mary .
    :G swp:origin     ex:Jane .

by which one can then apply ones trust policies to make determinations
about whether to trust graph G.

E.g.

IF   ?graph swp:assertedBy ?authority .
AND  ?authority rdf:type trust:TrustedAuthority .
THEN ?graph rdf:type trust:TrustedGraph .

etc.

with all queries then being constrained to statements made within
trusted graphs.

Eh?

Patrick

--

Patrick Stickler
Nokia, Finland
patrick.stickler@nokia.com
Received on Friday, 19 March 2004 02:44:51 UTC

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