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JISC-SHIBBOLETH  July 2008

JISC-SHIBBOLETH July 2008

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Subject:

Re: A federation trust Q

From:

Ian Young <[log in to unmask]>

Reply-To:

Discussion list for Shibboleth developments <[log in to unmask]>

Date:

Mon, 21 Jul 2008 15:52:34 +0100

Content-Type:

text/plain

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Alistair Young wrote:

> Would it ever be likely that, say, an IdP could have the same entityID in
> two different federations but each federation used the shibboleth method
> of trust, i.e. the federation metadata for both federations would contain
> the KeyAuthority extensions for root CAs. However, fed1 was the uk
> federation, which trusts a lot of root CAs but fed2 is a high security
> federation, say medical image sharing and it only trusts one CA, itself.
> It issues its own certificates to entities.

This does already happen.  InCommon issues its own certificates, for 
example, and doesn't currently accept anyone else's.  An entity that 
works in both InCommon and the UK federation has to do one of:

1) use different credentials for different sets of partners

2) use a different entity name when talking to different sets of partners

3) persuade the UK federation to publish the credentials acquired for 
InCommon

The question of who issues certificates is largely a red herring, by the 
way.  What's important is the nature of the process by which keys and 
certificates are bound to entities.

> Is this ever likely to be seen in the wild?

All three of the above solutions have been used in appropriate 
situations.  If you look carefully in the UK federation metadata, you 
can see a number of cases where we've done quite tailored things for 
particular entities to work round issues in this and other areas.

In the longer term, I'd like to think the technical consensus in most 
places is moving towards using long-lived, self-signed certificates for 
trust purposes rather than federation-issued or commercial certificates. 
  This move away from the Shibboleth-invented extensions should give 
better interoperability in the long run, as well as addressing the 
problem you're describing.  Again, we've done this with selected 
entities in the UK federation when it has been the most appropriate way 
to solve a particular member's deployment issues.

> Or should an entity, such as
> an IdP, identify itself differently in different federations? i.e. have a
> different entityID (providerId) for each federation?

In general, it makes sense for an entity to use the same name in all 
contexts, because federations don't really exist at the protocol level.

There are problems that can occur if an IdP and SP both belong to 
multiple federations with the same name and have different metadata in 
each.  Given that IdPs don't appear in multiple federations nearly as 
much as SPs do, the easiest way to avoid this is to have IdPs in this 
situation either have identical metadata in every federation, or to have 
different entity names in each federation.  There are other techniques too.

The far more common case is of service providers, which frequently serve 
customers in multiple federations.  It's still best for them to have a 
single entity name and identical metadata in every federation (some 
software can't cope with anything more complicated than that) but 
because all the IdPs see of an SP at run-time is the certificate used 
for authenticating attribute requests (unlike an IdP, they don't need to 
have TLS-protected SOAP endpoints) things usually just work anyway for 
an SP.

	-- Ian

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