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Subject: RE: [xri] Trust (was: Re: [xri] Re: The elements formerly known as TargetAuthority and TargetSubject)

Nat Sakimura wrote on 2009-07-15:
>> Truly distributing signing authority essentially requires a PKI of some
>> kind. That's one of the reasons I'm not a big fan of discovery based on
>> endpoints signing their own information. It's basically making trust
>> somebody else's problem. Instead, I would prefer to rely on "XRD (or SAML
>> metadata) signing services" that essentially work like CAs but can be
>> implemented more flexibly and don't rely on DN naming and other vestiges
>> that simply haven't been deployed.
> I have not fully grasped this. Could you elaborate a little more please?

It relates to the answer you gave at the end about representing ownership of
keys. I was not under the impression that the only signer for an XRD was
supposed to be the Subject itself.

So what I was saying was that I was envisioning the ability to rely on third
party registration authorities to sign XRDs, because there are ways to
create trust in those authorities that don't presume PKIX validation, and
don't rely on the use of DNs as the only means of connecting things

The problem with DNs is that they don't work. They've been misused and
turned into meaningless garbage and at this point they do more harm than
good anywhere they show up. Look at the craziness of subjectAltName and SSL
server name validation, just to get around the fact that certificates are
wedded to DNs.

> Well, yes, there has been, and it still is, as far as I know.
> XRD/ds:Signature/ds:KeyInfo is supposed to be expressing the
> keys controlled by the Subject.

That was not at all clear to me, but it essentially says that XRDs have to
be signed by their Subject. That seems questionable to me. One reason being
that in general, authentication of the XRD should be interchanageable at the
transport or message layers. If I host something unsigned at an
SSL-protected site, the "signer" of the XRD is the owner of the SSL
certificate, and that doesn't seem to make sense to me in light of what
you're saying above.

You also have the problem that a Signature can only carry a single key, and
as we discussed, supporting multiple keys is important for key management.

But it is certainly true that recognizing that the signer and the subject
don't have to be the same introduces a much more complex set of scenarios.
That's why I've been asking all the questions, because I was proceeding from
that assumption.

-- Scott

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