Association Handles and Service URIs

Kevin Turner kevin at
Fri Aug 25 00:17:09 UTC 2006

On Thu, 2006-08-24 at 15:24 -0700, Marius Scurtescu wrote:
> The RP URI (or the Trust Root) could be sent by the RP with the  
> "associate" request.

It could, but if there's no way of validating that information, it isn't
reliable, and is then misleading at best.  The RP can pass its URI in
checkid requests because we know that if *that* URI is invalid, the RP
will not receive the redirect response.  The same is not true in
associate requests, as the answer just goes back through the tcp
connection, not tied to any URI.

> > In contrast, an RP will be aware of which IdP it requested an
> > association from.
> So the RP does not really need this handle then, right?

The RP needs that handle to distinguish between other associations
issued by that IdP, as associations may expire or be otherwise

The RP also needs that handle because that's the only way it can talk to
the IdP about which handle to use.  (because, as discussed above, the
IdP cannot look up a handle from a return_to or trust root.)

> Yes, but 'now' is relative. Between the time an association is  
> created by the IdP (IdP's now) and the time it is sent back and  
> parsed by the RP (RP's now) there is a gap. In most cases this gap is  
> negligible, but it can create borderline issues.

one might argue that the gap created by transmitting and processing a
TCP packet is in fact more negligible than the clock skew between any
given couple of servers on the network.

(Yes, I know we have the infrastructure available to synchronize all
computers on the Internet to within an imperceptible differences from
meticulously maintained atomic clocks.  I also know that not everyone
takes advantage of that, and even on systems that do, it can fail and
nobody notices for weeks.)

There are fall-back cases in the protocol that take care of any
borderline issues that may arise from this particular problem.  An
especially apprehensive RP may also shave a bit off the association
lifetime to avoid playing things too close to the line, with no ill

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