I was reviewing the DKIM specification the other day and realized that my
implementation has got something wrong. Granularity checking should be
case-sensitive. Here's my rationale:
- RFC 4871 section 3.2 says all tag values, unless otherwise specified,
are case-sensitive.
- RFC 4871 section 3.6.1 describes the granularity (g=) tag, but says
nothing about case-sensitivity.
- Therefore, the granularity checking of a public key record should be
case-sensitive.
Agree?
Well, I checked this point on various responders by constructing a message
that tests this specific issue... Here's what I found:
the following responders are NOT case-sensitive:
dkimtest.jason.long.name
sendmail.net
dk.elandsys.com
blackops.org
the following responders ARE case-sensitive:
altn.com - responded with (:DKIM_SELECTOR_GRANULARITY_MISMATCH)
verifier.port25.com - responded with (key granularity "jl*g" doesn't
match local part "JLong")
So, which is it? Should granularity be case-sensitive?
Jason
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