Subject: Re: [idn] Debunking the ACE myth

From: Dan Oscarsson <[email-masked]>
Date: Mon, 23 Jul 2001 13:40:58 +0200 (MEST)

D. J. Bernstein said:

>
>Wrong again. UTF-8 poses no problems for DNS servers. As Mark Andrews
>says: ``UTF8 does not require a server upgrade.''
>

No that is not correct. For both ACE and UTF-8 there are two
ways that it can be done:
1) All names are transmitted in a form/semantic insensitive format
   (that is what nameprep is for) so that names can be compared
   using binary matching.
   
   In this case a server upgrade is NOT required.
   
2) Names are transmitted with form retained (that is any form, though
   they should be normalised).
   In this case the applications that do name comparing need to to
   convert them into the form/semantic insensitive format before comparing
   them (or do it on the fly while comparing them).
   
   In this case the DNS servers need to be upgraded.

1) Is the IDNA case and also in Microsofts draft-skwan-utf8-dns.
   This results in that for example upper case characters cannot be
   used in responses from DNS. Probably very irritating some people
   who have spent a lot of mony on their nice company name which uses
   mixed case and will break some programs expecting mixed case
   in PTR responses.

   Dan

---

From: "Adam M. Costello" <[email-masked]>
Date: Tue, 24 Jul 2001 00:19:14 +0000

Dan Oscarsson <[email-masked]> wrote:

> For both ACE and UTF-8 there are two ways that it can be done:
>
> (that is what nameprep is for) so that names can be compared using
> binary matching.
>
> 1) is the IDNA case and also in Microsofts draft-skwan-utf8-dns.  This
> results in that for example upper case characters cannot be used in
> responses from DNS.

For the UTF-8 case, as I've pointed out before, it is not necessary
for DNS queries and DNS responses to use the same rules.  It would
be perfectly reasonable to use nameprep'd UTF-8 in queries and
non-nameprep'd UTF-8 in responses.

For the ACE case, as I've pointed out before, mixed-case ACE can easily
be used to represent mixed-case Unicode.  You would lose things like
circled-digit-one (which becomes a regular digit-one), but mixed case
can be conveyed in ACE.

By the way, it would be pointless to combine ACE with option 2 (no
nameprep).

AMC

---

From: David Hopwood <[email-masked]>
Date: Mon, 23 Jul 2001 23:24:51 +0100

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Dan Oscarsson wrote:
> 1) [names on the wire are always canonicalised]
>    is the IDNA case and also in Microsofts draft-skwan-utf8-dns.

What programs will break in this case? That doesn't sound remotely
plausible to me. If it turns out to be difficult to support case
preservation then that would be the first thing I'd discard: other
properties are far more important.

- -- 
David Hopwood <[email-masked]>

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