[ietf-dkim] RFC4871bis - whether to drop -- l= and x=
johnl at iecc.com
Tue Jun 2 13:56:31 PDT 2009
>> 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.
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