[ietf-dkim] DKIM vs. MIME
sm at resistor.net
Sat Apr 24 23:45:22 PDT 2010
At 21:22 24-04-10, Murray S. Kucherawy wrote:
>Someone on the opendkim-users list has pointed out that DKIM
>signatures are being invalidated when re-mailed through one
>particular MLM that rewrites Content-Type: so that its value is all
>lowercase. Obviously this is a problem for DKIM since even
>"relaxed" requires nothing other than spacing changes in header
>field values; however RFC2045 says that the interpretation of
>Content-Type: values is case-insensitive. Thus, at least to
>consumers of that header field, DKIM is doing something "wrong". In
>any case, it was suggested on that list that "relaxed" header
>canonicalization be adjusted to accommodate this.
If I am not mistaken, it's a MTA and not a MLM that did that modification.
>The response is probably obvious: DKIM operates at a level below the
>semantics of the header fields it signs, i.e. closer to SMTP than to
>MIME, and so it hasn't, and shouldn't have, knowledge about header
>field interpretation. I suspect this isn't something we consider a
>problem that needs fixing in the spec.
I would categorize it as operating close to the (signer/verifier)
boundaries to get around in-transit modifications to the mail format.
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