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Re: [EAI] Localpart normalization (was Re: Downgrade Design Team Discussion Results Released)

John C Klensin <klensin@jck.com> Fri, 19 March 2010 04:59 UTC

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Date: Fri, 19 Mar 2010 00:59:43 -0400
From: John C Klensin <klensin@jck.com>
To: Peter Saint-Andre <stpeter@stpeter.im>, ima@ietf.org
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Subject: Re: [EAI] Localpart normalization (was Re: Downgrade Design Team Discussion Results Released)
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--On Thursday, March 18, 2010 22:14 -0600 Peter Saint-Andre
<stpeter@stpeter.im> wrote:

>> Alexey, FWIW, RFC 5198 suggests NFC and explains why.  Unless
>> there is a really strong reason to do something else, my
>> recommendation is that all three of these specs conform to
>> that recommendation.
> 
> Unfortunately, both Nodeprep (RFC 3920) and SASLprep (RFC
> 4013) used NFKC, not NFC.

So did Nameprep.  Unfortunately, NFKC is _very_ dangerous.  It
combines several different transformations, some quite
reasonable and obvious and some that are basically the UTC's
revenge on people who made them add characters they didn't want
to add.    The latter part results in characters being mapped
together that those who wanted them in Unicode think are
separate.

     john

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