Comments on draft-ietf-idnabis-defs-10

Wil Tan wil at
Tue Sep 1 16:40:05 CEST 2009

On Wed, Sep 2, 2009 at 12:36 AM, Andrew Sullivan <ajs at> wrote:

> On Tue, Sep 01, 2009 at 02:14:37PM +1000, James Mitchell wrote:
> >
> > Punycode does not require output to be in any particular case.  I
> > have copied from RFC3492 Page 8 below for convenience
> >
> > 'An encoder SHOULD output only uppercase forms or only lowercase
> > forms, unless it uses mixed-case annotation'
> >
> > Therefore KGBECHTV and kgbechtv are both valid outputs of the
> > punycode algorithm.
> Hrm, so actually it is possible that all ASCII characters in an
> A-label are upper case, even though the input from the U-label is not
> allowed to have upper case in them.  This seems to be bad, because the
> returned result from the Punycode decoding could make the U-label
> ASCII characters upper case, right?
Yes, that's indeed a good catch, James.

I haven't encountered any implementation that encodes using uppercase
characters as output, though I can't claim to have seen them all.

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