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Re: [Asrg] DNS-based Email Sender Authentication Mechanisms: a Critical Review

John Levine <johnl@taugh.com> Wed, 27 May 2009 21:53 UTC

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Date: Wed, 27 May 2009 21:55:10 -0000
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From: John Levine <johnl@taugh.com>
To: asrg@irtf.org
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Subject: Re: [Asrg] DNS-based Email Sender Authentication Mechanisms: a Critical Review
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>Title: DNS-based Email Sender Authentication Mechanisms: a Critical Review

Dave is right -- this misunderstands what DKIM does.  The only validated
identity is the signer, which need bear no relationship to any other header
domain, e.g.

 DKIM-Signature: ... d=rbn.ru; ...
 From: Bank of America Security <security@paypal.com>

The From: header is signed, but the only domain that DKIM
authenticates here is rbn.ru.  It doesn't say anything about the
legitimacy or lack thereof of the address security@paypal.com, or of
the string "Bank of America Security" which is what a whole lot of
MUAs will actually display.

Even if the d= domain matches the domain on the From: line, it still
doesn't promise that the address is "real".  This is an important
point that a lot of people misunderstand.

R's,
John

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