On 11/29/2017 02:40 PM, Grant Taylor via NANOG wrote:
On 11/29/2017 03:24 PM, Michael Thomas wrote:
Message footers and subject lines can be dealt with. That's already been proven within the current DKIM spec.
Please humor my ignorance and explain how a subject line (which is (over)signed) can be dealt with in the current DKIM spec?
I get how footers can be dealt with, read appended. At least as long as DKIM only signs a given amount of the (original) body. (Though HTML (read: MIME structures) can complicate this.) - Or are you referring to something else?
You know what the original header was via the signature. You can take the delta of the current subject line and remove any additions and validate the signature. Whether you're happy with the additions is a different concern, If I were constructing a spam filter out of it, I'd give a lot of prejudice to anything added, but that's outside of what you can do within the bounds of the spec. Mike