Question: Yadis Service URIs in the OpenID Auth case

Johannes Ernst at
Fri Aug 25 04:25:55 UTC 2006

Ah. So Drummond, you are saying that while Yadis does not define  
this, the larger XRI framework makes the assumption that each service  
that's advertised in the XRDS file is advertised on behalf of exactly  
one provider, and it does not make sense, really, to have multiple  
service endpoints in the same service element that are operated by  
different providers.

I wasn't aware of that, and that's good to know. (Anybody want to  
write this up somewhere?)

That makes it much more possible to share D-H secrets between  
multiple endpoints within the same service element. But is that what  
we think should be the normal case?

Specifically, if I negotiate a shared secret with
will I be able to use that same shared secret with
     httpS:// ?

I would probably argue that we should not assume that they use the  
same secret, but negotiate separately. For example, it would be  
rather difficult to share the same secret between
both of which are endpoints operated on behalf of a

On Aug 24, 2006, at 12:22, Drummond Reed wrote:

> To slightly tweak Kevin's feedback, I think Johanne's assumption #2  
> (that
> the URIs are maintained by the same organization) is 100% valid if a
> non-empty ProviderID element is present in the service endpoint (SEP).
> The ProviderID value is the only SEP element with a cardinality of
> zero-or-one, so all the URIs in a SEP are associated with only one  
> provider.
> This is important because if the ProviderID value is itself  
> resolvable to an
> XRDS describing the Provider, it makes it easy to discover ProviderID
> metadata that applies to all their SEPs.
> If the SEP has no ProviderID value, there's nothing technically to  
> prevent
> different URIs in the SEP from going to different service  
> providers, but
> it's clearly not a good practice.
> =Drummond
> -----Original Message-----
> From: yadis-bounces at [mailto:yadis- 
> bounces at]
> On Behalf Of Kevin Turner
> Sent: Thursday, August 24, 2006 12:04 PM
> To: yadis at
> Subject: Re: Question: Yadis Service URIs in the OpenID Auth case
> On Wed, 2006-08-23 at 17:54 -0700, Johannes Ernst wrote:
>> Am I correct that it would be false to assume that:
>>   - the two service URIs reside on the same server;
>>   - are maintained by the same organization;
>>   - use the same negotiated D-H secret (aka I negotiate with one
>> service URI, but successfully use it with the other), even if they
>> are very similar URIs.
> I think you are correct; none of those are 100% safe assumptions to
> make.  Some of those might be sane conventions to establish, i.e.
> "everything under a single Service tag is maintained by one provider,"
> but I don't think we can count on that.  And even if you could  
> count on
> that one, the other two wouldn't necessarily follow.

Johannes Ernst
NetMesh Inc.

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