ietf-dkim
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Re: [ietf-dkim] Broken signature analysis (was: Proposed new charter)

2010-02-24 11:31:13
On Feb 24, 2010, at 5:51 AM, Michael Thomas wrote:

I'm sort of dubious about this. Unless you're using z=, your chances  
of
figuring out why something broke are slim to none. With z=, your  
chances
of figuring it out are merely slim.

Mike, with far too much experience at that

It got a luke-warm response a few years back, but now that a lot more  
people are having to deal with "why did the verify failed", is it  
worth re-vivifying the DKIM-Trace stuff, or whatever it was called  
back then? We found it very useful for our early days of interop  
testing.

The idea is pretty simple: The signer adds a header that characterizes  
the content before and after canonicalization. The verifier performs  
the same characterization and compares the differences. The  
characterizations we used at the time were simple character counts  
represented in a relatively compressed form (27 a's, 60 b's, 40LFs,  
50spaces, etc)

The form we used is kinda ugly as 
http://www.ietf.org/mail-archive/web/ietf/current/msg39488.html 
  shows, but it was very illuminating as things like mis-match of  
white-space counts, or case-conversions, etc, identified what changed  
and where it changed (canonicalization vs transit).


Mark.

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