Subject: Re: Differences between Kerbeors revisions and PKINIT

From: Jeffrey Altman <[email-masked]>
Date: Fri, 4 Aug 2000 20:04:05 EDT

Thanks Bob.  :-)

I want to point out one other thing about the use of UTF-8.  UTF-8
representations are not unique.  Many Unicode code points can be
represented by multiple UTF-8 representations.  UTF-8 MUST not be used
as a means for processing and comparing Unicode strings.  To compare
two Unicode strings you must convert from UTF-8 to UCS2 and compare
the values.  This is a separate issue from the fact that many
characters are represented by multiple code points and/or by multiple
orderings of base character and modifiers.

If we are going to reuse the GeneralString as a UTF8 string we have to
agree upon a set of canonicalization rules for the interpretation.
This applies not just to the princial names for the Revisions document
but the PKINIT stuff as well.  Has the appropriate thought been put
into this?  I'm not sure.

> > It would be useful if sites could scan their databases and report the
> > number of principals that use 8-bit characters (if there are any).
> 
> The person at UW responsible for this reports:
> 
>   All our principals use 8 bit characters.  The top bit, however, is zero
>   in all cases.
> 
> 8^)
> 
>  - RL "Bob"

                  Jeffrey Altman * Sr.Software Designer
                 The Kermit Project * Columbia University
               612 West 115th St * New York, NY * 10025 * USA
     http://www.kermit-project.org/ * [email-masked]

---

From: Russ Allbery <[email-masked]>
Date: 04 Aug 2000 20:17:55 -0700

Jeffrey Altman <[email-masked]> writes:

> as a means for processing and comparing Unicode strings.  To compare two
> Unicode strings you must convert from UTF-8 to UCS2 and compare the
> values.  This is a separate issue from the fact that many characters are
> represented by multiple code points and/or by multiple orderings of base
> character and modifiers.

How so?  According to RFC 2279:

   1) Determine the number of octets required from the character value
      and the first column of the table above.  It is important to note
      that the rows of the table are mutually exclusive, i.e. there is
      only one valid way to encode a given UCS-4 character.

There's supposed to be a one-to-one mapping between UTF-8 and UCS-4.  Is
UCS-4 also not a unique representation?  You seem to imply above that
UCS-2 is, which would imply that UCS-4 would be.

Or is RFC 2279 in error?

-- 
Russ Allbery ([email-masked])             <http://www.eyrie.org/~eagle/>