ietf-dkim
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Re: [ietf-dkim] New canonicalizations

2011-05-17 10:28:56

On 16 May 2011, at 14:26, Alessandro Vesely wrote:



Yes, http://www.opendkim.org/stats/report.html#hdr_canon says

Header canonicalization use:
canonicalization      count   domains passed
simple                  653688        6786    591938
relaxed                 3940377       56621   3640854

It does, but how does one interpret that? Certainly the weight of relaxed 
versus simple passes implies a user desire for relaxed canonicalisation.

However, the 90% versus 92% is meaningless without making certain assumptions. 
If all these messages were originally properly signed, then the 2% represents a 
20% reduction in false negatives, but only if we assume that canonicalisation 
method was selected at random or that choice of canonicalisation method was 
statistically independent of the likelihood of breakage - the latter might be 
plausible.

However if some of the messages were never properly signed (whether failed 
attempts to spoof, or administrative or technical failure), then that 20% must 
be higher. It could even represent 100% reduction in false negatives due to 
(otherwise benign) in-flight modifications.

Although they only differ by 2% (90% simple vs 92% relaxed), such
percentages would be superb for tools like Spamassassin.  I'd expect
at least 99% from a cryptographic tool.

-- 
Ian Eiloart
Postmaster, University of Sussex
+44 (0) 1273 87-3148


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