Identifiers

[Iljitsch van Beijnum <iljitsch@muada.com>]

Looking at the proposed solutions, it seems that we have been 
gravitating towards locator agility without explicit identifiers. While 
that's certainly a valid approach, I think we should take a few moments 
to consider identifier issues.

The main reason to forego having identifiers is that it is hard to 
determine if a correspondent is rightfully using an identifier. 
However, this is not the case for two classes of potential identifiers:

1. Identifiers with a cryptographic nature, such as the ones proposed 
for HIP. Since the identifier is a hash of a public key, proving 
ownership is trivial given a few round trips and CPU cycles.

2. FQDNs with a certificate that leads back to a trusted authority. 
These are in relative wide use today for SSL.

It stands to reason that future developments will lead to new types of 
verifyable identifiers. I think this invalidates the assumption that 
verifying the authenticity of identifiers is too hard a priori. Rather, 
the question should be whether we are willing to accept the necessary 
complexity to allow extensible identifier authentication in our multi6 
solution of choice. In this regard, it should be interesting to see 
what the MOBIKE people are up to.

Personally, I think the best choice would be to remain agnostic about 
the identifier issue for now, but build our negotiation protocol such 
that they can be added easily later. For now, we build a "no 
identifier" type solution. Solving the problem of how a correspondent 
proves ownership of an identifier can then be deferred until such time 
that someone actually wants to extend the multi6 solution to support 
identifiers. So the only thing we have to do now is make sure the 
protocols are flexible enough to allow such extensions.

Thoughts?