Subject: FYI: Unicode proposal to break NFKC backwards compatibility

From: Simon Josefsson <[email-masked]>
Date: Tue, 25 Jan 2005 00:14:15 +0100

I have not seen this apparently IETF related Unicode news mentioned
here, so FYI:

If anyone is interested in Unicode normalization issues, especially
wrt to Stringprep or Internationalized Domain Names (IDN), you might
be interested in a current public review issue in the UTC:

  Issue #61 Proposed Update UAX #15 Unicode Normalization Forms
  A proposed update to UAX #15 for Unicode 4.1.0 is available at the
  link above. The proposed changes are listed in the Modifications
  section of the document.

The UTC accept comments from the public until January 31th.  The above
abstract isn't informative, but when you look at the proposed changes:

http://www.unicode.org/reports/tr15/tr15-24.html

It is clear that this is the next step of the backwards incompatible
NFC/NFKC normalization change first discussed in:

http://www.unicode.org/review/pr-29.html

That change affect all StringPrep profile that uses NFKC
normalization.  The change may imply interoperability problems, or at
worst security problems, when/if IETF wants to use Unicode 4.1 or
later in StringPrep.  As far as I am aware, the IETF has not given
implementors advice on whether to follow the proposed UTC change or
not.  My experience is that deployed IDN implementations are not
implemented the same way.

Regards,
Simon

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