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Re: FOAF and trust and certificates

From: Graham Klyne <GK@NineByNine.org>
Date: Thu, 17 Oct 2002 15:45:32 +0100
Message-Id: <>
To: Dave Reynolds <der@hplb.hpl.hp.com>
Cc: SWAD-E public discussion <public-esw@w3.org>

I hadn't thought of SPKI in this context.  I agree the directness and 
relative simplicity appeals, especially when the additional metadata 
carried in X.509 certs might be supplied as signed RDF.

But ... I was of the impression that SPKI is not widely used:  do you know 
otherwise?  Do you think it's a serious contender in the public key 
security space?


At 10:31 AM 10/17/02 +0100, Dave Reynolds wrote:

>I've always felt that SPKI/SDSI [1] is a very interesting model of security
>which fits rather nicely with the semantic web:
>  o Rights certificates are bound directly to keys ("principals") not to
>identities. x.509 effectively maps rights to identities but SDSI separates
>these. This leads to a decentralized design where everyone can be a sort of
>certification authority, no need for a global hierarchy. This separation also
>means you can have some level of privacy and yet still exercise certified
>  o The notion of local namespaces that map from "principals" (i.e. keys) 
> to some
>name or identity is very consistent with foaf. First you could use
>foaf/vCard/person-ont to associate your own names and contact information for
>principals that you know. This could be either informal or formally done 
>by SDSI
>identity certificates. Secondly the SDSI principle of addressing people via
>chains of names in linked local namespaces would fit very nicely with 
>using FOAF
>"knows" links.
>  o The delegation certificate machinery is a good base for allowing
>authoritative sources to delegate their authority. It could be an interesting
>way of approaching the semantic web trust layer so that when a package of
>assertions is signed it can signed on behalf of some delegation chain giving a
>traceback mechanism.
>[1] http://theory.lcs.mit.edu/~cis/sdsi.html
>Graham Klyne wrote:
> >
> > Maybe this has already been considered ... it's obvious enough, but the
> > thought has only just struck me.
> >
> > It occurs to me that the FOAF experiment of Dan Brickley and friends (and
> > FOAFs) might have some relevance to some aspects of trust modelling.  I'm
> > scratching some words about public key certificates and CA chaining, and
> > got to this point:
> > [[
> >            <t>So X.509 employs the idea of certificate chains, where
> >              each CA's public key is itself signed by a "higher" CA,
> >              and so on until a trusted "root" CA is encountered.
> >              Thus, a chain of certificates can link the holder of
> >              some key and a user of the corresponding public key
> >              to a common point of trust.  Set against this, the
> >              longer the certificate chain the more scope there is
> >              for compromise of any one of the CA signing keys, which
> >              would effectively nullify the basis for trust in the
> >              end user keys thus protected.</t>
> > ]]
> >
> > This describes the X.509 hierarchical CA chaining model.  PGP, on the other
> > hand, employs a more grassroots based web of trust, in which any keyholder
> > can express degrees of trust in another.  In his book "Applied
> > Crytography", Bruce Schneier puts it like this:
> > [[
> > There are no key certification authorities;   PGP instead supports a "web
> > of trust".  Every user generates and distributes his own public key.  Users
> > sign each other's public keys, creating an interconnected community of PGP
> > users.
> > ]]
> >
> > All of which has strong resonances with FOAF.  I'm thinking in 
> particular that:
> > (a) FOAF might be used to model PGP webs-of-trust.
> > (b) FOAF might be able to supply additional information about
> > relationships, which could be used to guide trust decisions in a PGP
> > web-of-trust.
> > (c) with a FOAF model and trust strategies modelled as rules on RDF data,
> > some PGP trust decisions might be automated that otherwise are made 
> manually.
> >
> > Hmmm... I must pay more attention to the next IETF key-signing party.
> >
> > #g
> >
> > -------------------
> > Graham Klyne
> > <GK@NineByNine.org>

Graham Klyne
Received on Thursday, 17 October 2002 10:34:24 UTC

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