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Re: [ietf-dkim] Corner cases and loose ends, was , draft-vesely-dkim-joint-sigs

2010-09-28 13:04:25
On 28/Sep/10 12:59, Ian Eiloart wrote:
--On 27 September 2010 19:26:37 +0200 Alessandro 
Vesely<vesely(_at_)tana(_dot_)it>
wrote:

 Now the MLM does its editing job.  It knows the original message was
 signed, so it makes sense to verify if the signature is still good
 after any changes have been applied.  In case verification fails, it
 shouldn't try to distribute an adsp-breaking message, so it can either
 send back a bounce or drop it.

Oh, but I already know that my MLM is going to break any message with a
signed body. UK law practically mandates the addition of unsubscription
information in a message footer. We certainly require it locally.

Signatures may still survive if they use l=.  Probably, the best 
method for determining whether a signature has been broken is to 
simply verify it again.  BTW, running OpenDKIM testsuite, it seems 
that verifying is an order of magnitude faster than signing.  Thus, an 
extra verification shouldn't hurt.

As a curiosity, I've noted that MLMs usually avoid duplicating the 
subject-tag (possibly even if it was present twice in the original.) 
However, they almost invariably duplicate the footer, if it's already 
present.
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