On 01.05.2011 14:13, John R. Levine wrote:
I don't think we actually understand all the ways that l= allows you to
shoot yourself in the foot, so I would prefer not to give the impression
that if people avoid a few cases we describe, they're safe.
-1, I agree we don't know all the ways DKIM can be fooled. Neither we
actually saw real attacks in the wild. We don't even state how to
react to multiple Froms. Presumably, the wider the DKIM deployment,
the more we'll learn on handling attacks. However, hiding the few
things we know doesn't seem to be a good start toward such watchful
cooperative deployment.
The message should be don't use l= if you care about your signature.
I mostly agree on that. However, the way it is stated in version -09, it may
be overlooked. IME, your message [1] prompted me to conceive an actual
example, which in turn makes me want to amend my signer's configuration.
Thus, I believe the current text requires some extra diligence to have the
desired effect.
[1] http://mipassoc.org/pipermail/ietf-dkim/2011q2/016002.html
I don't think we yet have consensus to take out l= but it is quite clear
that the problems it causes are far greater than whatever problems it
might solve.
As Hector notes, it is required by non-DKIM aware MLMs. The point is that
relaying MTAs seldom know whether the target is a MLM, let alone whether
DKIM-aware.
Perhaps reasoning should go like this: Let's assume we can sign according to
the target, then what would we do with a non-aware MLM? If the answer is to
avoid signing in such cases, then omitting l= and letting the signature break
is just equivalent --except for aesthetic considerations...
Please consider the environment before printing the header of this e-mail
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