[ietf-dkim] RFC4871bis - whether to drop -- l= and x=

[John Levine]

>> Both l= and x= are bad for interoperability, because it is utterly
>> unclear what a recipient will do with them.  Whevever I ask, the
>> answer is they might do this and they could do that.  If I put a
>> really long x= into a signature, will recipient systems accept a
>> stale message that otherwise they wouldn't?  If I sign the first
>> 100 bytes of a 10K message, will recipient systems accept it, and
>> if so, what will users see?  There's no way to tell, because
>> everyone just makes something up.

>I would argue that your specification of l=100 when the actual
>message size is 10K is intentional breakage of your own signature.

I mean that the body hash covers the first 100 bytes of the body, and
doesn't cover the other 9900 bytes.

The question remains: given a message with such a signature, which is
entirely valid in the current DKIM, what will a recipient system do
with it?  What will users see?  Ask ten people, get ten answers, which
is about as far from interoperable as you can get.

R's,
John