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Re: [dkim-ops] FYI: protecting subdomains in signature with dkimproxy

2009-02-02 13:30:31
On Sun, 1 Feb 2009, Byung-Hee HWANG wrote:
Authentication-Results: mx.google.com; (...)
smtp(_dot_)mail=smith(_at_)cs(_dot_)dkim(_dot_)edu; dkim=pass (test mode) 
header(_dot_)i=smith(_at_)dkim(_dot_)edu
(...)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed; d=dkim.edu;
       h=message-id:date:from:mime-version:to:subject:content-type:
      content-transfer-encoding; s=student.cs; 
i=smith(_at_)cs(_dot_)dkim(_dot_)edu;
         (...)

Did you invent this example or actually try it?  If it's real, the i= part 
of "Authentication-Results" Google is reporting is wrong, since that's not 
the i= value in the signature.

RFC4871 does not force "i=" tag's implementation in signature. However 
Several company (eg., port25.com) try to match headers each 2822-From 
and "i=" tag. That's somewhat dangerous (at least to me using subdomains 
often). At reflector of port25.com, the result is *not* "pass" whenever 
i send email with subdomains. So to Jason i suggested to make a way 
protecting subdomains. And now, i see "DKIM Result: pass" at refelector 
of port25.com. Let's go with dkimproxy. Now it's safe with 
subdomains..;;

I'm not sure I agree that adding a feature which tricks the local policy 
of a verifier, or a broken verifier, is something that can be described as 
"safe".  RFC4871 doesn't make a connection between the i= or d= values and 
From:, so this is a local policy choice they've made (or perhaps a 
hold-over from DomainKeys which did try to make that connection).

At any rate, there are other signing agents which provide this service, so 
it's a common option.
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