Subject: RE: [idn] stringprep comment 1

From: Yves Arrouye <[email-masked]>
Date: Fri, 1 Feb 2002 09:56:10 -0800

> To repeat, the loose vs strict approach works as follows:
> 
> Suppose the client is Unicode 3.1 and the server is Unicode 4.0. As
> long as the client produces names that are only 3.1, no problem.
> Stringprep on the client will produce results that the server accepts.
> 
> Suppose the user has characters that are unassigned in 3.1 (but are in
> 4.0). As long as the user (manually) picks lowercase characters (in
> the right canonical form), those names will be accepted by the 4.0
> server. While it is not as easy as when the software does it for the
> user, it will work for any new characters.
> 
> This is important for another scenario. Client A is on Unicode 4.0,
> client B is on Unicode 3.1, and the server is on Unicode 4.0. Client A
> namepreps a string, sends to client B. Client B sends the string on to
> the server. Everything works. It even works if client B re-namepreps
> the string.

The interesting scenario is: Server S is on Nameprep-08 (where a deletion
mapping has been introduced for codepoint U+XXXXX), Client A is on
Nameprep-07 but his OS supports Unicode 4.0 and its IME generates U+XXXXX.
Client A will then pas U+XXXXX unchanged (since it was unassigned when
Nameprep-07's tables were generated) and Server S won't find a match, since
its stored strings do not have U+XXXXX. Same for case mapping, if that were
to happen. The user has no clue what is happening to her.

YA

---

From: Paul Hoffman / IMC <[email-masked]>
Date: Fri, 1 Feb 2002 10:48:47 -0800

At 9:56 AM -0800 2/1/02, Yves Arrouye wrote:
>its stored strings do not have U+XXXXX.

That scenario will happen, and it is *supposed* to happen. It is 
identical to if Nameprep-08 mapped U+XXXX to U+XYZX. The client must 
not get a positive response to a query that includes characters that 
are not allowed in the version on the authoritative server.

>  Same for case mapping, if that were

Correct. It is identical to a user accidentally entering a Greek 
capital Alpha instead of a Latin capital A. Or, even if we didn't do 
IDN, the user accidentally enters numeral 0 instead of Latin capital 
O. The DNS matching scheme will simply say "no match". In other 
words, these failure scenarios are not a criticism of the versioning 
method, they are a criticism of the simple matching in DNS.

--Paul Hoffman, Director
--Internet Mail Consortium