[ietf-dkim] Modified Introduction text for rfc4871-errata (resend)

[Murray S. Kucherawy]

> OK, so now I guess I'm confused.  My understanding is that if "i=" isn't
> specified it takes the value of "d=", so I'm not clear how it can be undefined?

Maybe the wording of the errata draft could be improved (I'll propose new text shortly if I can), but here's my understanding:

I believe you're confusing the semantics of the DKIM signature with the definition of the DKIM interface.

Again, think of this in terms of an API definition.  Let's say you're building a DKIM library to sell or give away.  Obviously you need to know what outputs are required, i.e. what application developers will expect from you.

The errata draft is attempting to state clearly that the output of your library has to include the yes/no result of the verification and the "d=" value.  It can include other stuff at your discretion (you might even find that most assessors, the consumers of your library, want a lot more than that), but that's the minimum you have to provide to a consumer in order to be able to claim you are DKIM compliant.

It's not stating at all what the implicit value of "i=" is relative to "d=".  In this context, that fact is irrelevant.

Think of another example, like the socket interface to TCP vs. the TCP protocol itself.  There's what's going on in the protocol stack and then there's what's going on in the C libraries we actually use.  Could be that the language used in RFC4871 and the errata draft don't make that distinction clear, but I believe that's what we're trying to achieve here.

-MSK