[cap-talk] Delegating Responsibility in Digital Systems:Horton's "Who Done It?"

[Jed Donnelley]

At 12:51 AM 6/8/2007, Toby Murray wrote:
>On Fri, 2007-06-08 at 00:52 +0000, Karp, Alan H wrote:
> > > Scribit Karp, Alan H dies 07/06/2007 hora 15:47:
> > > > Each request from a different responsible party comes through a
> > > > different forwarder under Carol's control.  That provides Carol
> > > > undeniable authentication.  However, Carol can't prove that
> > > to anyone
> > > > else because the forwarder is under her control.  For example, she
> > > > could have sent the request herself.
> > >
> > > So if I understand this correctly, for the authentication to be
> > > undeniable to other subjects than Carol, the forwarder must
> > > be under the
> > > control of a third party trusted by those subjects, and not under
> > > Carol's control, mustn't it?
> >
> > Or signed by the sender.
>
>Using a key that everyone can authenticate, which may require a TTP
>anyway to authenticate the key.

It's important that it doesn't require a trusted third party.
What do you mean by "authenticate the key"?  Are you referring
to the business of developing a relationship with the key (e.g.
web of trust, organizational database - e.g. LDAP), or is there
something more to your "authenticate the key" requirement?

Using the public/private key model, if Carol can produce a message
signed by the private key, then the 'proof' of the responsibility
of the identity is as good as the cryptography.  The meaning/relevance
of the identity (who the heck is this "Bob") I see as a separate issue.

--Jed  http://www.webstart.com/jed-signature.html