On 2/10/2018 7:50 AM, John Levine wrote:
The idea with DKIM v=2 is that there are things that you cannot say in
a v=1 signature, no matter how many new tags you add, so you need some
way to tell verifiers what they need to understand. How about this?
We rebrand the v= tag to be a feature list so the syntax is now roughly
v= word (, word)*
where each word describes a semantic feature. Feature tag "1" is all
the stuff in RFC6376. My feature is mandatory to understand tags,
feature name "mandatory", so the signatures start
The listing of 'authorized' features makes sense when the usage may
occur later in the session, as it does with ESMTP, for giving the other
side permission to use those features. It makes no sense at all for a
unilateral exchange where one side uses whatever it feels like and the
other side -- getting all this later -- either likes it or doesn't.
That is there are no contingent behaviors in the exchange.
In a unilateral activity like DKIM, the mere presence of the usage
"featurex=..." serves to flag that featurex is used. There is no
incremental benefit into moving the flag elsehwere.
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