On Thu, Aug 17, 2017 at 5:22 PM, Brandon Long <bl...@fiction.net> wrote:
> We went down the path of including a diff of the message in the headers, > but you run up against more complicated changes that make that > challenging. Ie, mailing lists which strip attachments. If all we cared > about were subject munging and footers, there probably would have been a > practical solution there. > I wrote a draft a while ago that would allow a DKIM-Signature to include an annotation indicating that the signing ADMD did one or more of a specific set of small but well-defined message changes (e.g., add a footer, add a Subject tag). Knowing what those are, a verifier could undo them and attempt validation of earlier signatures in the handling chain. Presumably if no other modifications were made, the original content is thus discoverable, and you could then produce a chain of custody of the actual content before you that makes sense. If that's worthy of consideration now I could certainly revivify it. -MSK
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