sharp s (Eszett)

[Martin Duerst]

At 07:26 08/03/08, John C Klensin wrote:

>You are correct.  The document basically assumes that all
>validity checking gets done on the U-labels (or as part of the
>U-label definition).  "Rationale" essentially assumes that
>A-labels that can't be obtained from valid U-labels are invalid
>and vice versa, but the current text of "Protocol" doesn't
>enforce that assumption.    In particular, that leaves a hole if
>someone creates a funky A-label that could not have been formed
>via the U-label process. I think that hole that needs to be
>plugged,

Why? Whom are we trying to protect, against what?


>but am troubled about the case of non-IDNA-aware
>applications in which it is impossible to state, much less
>enforce, any sort of validity checks on A-labels.

Very good point. An A-label is just a domain name label.
A label starting with xn-- is just a domain name label.
There is nothing that I know of that currently prevents
me from creating
xn--nothueshc235987495783neouhtnethu.sw.it.aoyama.ac.jp.
I control sw.it.aoyama.ac.jp, and nothueshc235987495783neouhtnethu
is a random string and so I hope it converts to an illegal
U-label (if not, choose a different one).

The point where this has to be checked is when it gets transformed
to an U-label. If it's not legal, it should not be transformed,
but left alone, or produce some error.

Regards,    Martin.



#-#-#  Martin J. Du"rst, Assoc. Professor, Aoyama Gakuin University
#-#-#  http://www.sw.it.aoyama.ac.jp       mailto:duerst at it.aoyama.ac.jp