Comments on draft-ietf-idnabis-defs-10

[Paul Hoffman]

At 2:32 PM -0400 8/30/09, John C Klensin wrote:
>Suggested fix?  Do I need to put a "force lower case for
>undecorated Latin (ASCII) characters" into the conversation step
>from A-labels to U-labels?

Lower-casing the A-label before conversion is one possibility. The other is to do case-preserving comparisons when comparing A-labels for equivalence. I think the latter is a smaller change at this late date and also more robust. If you choose case-preserving comparisons, I think the following changes are sufficient.

idnabis-defs 2.3.2.4:

   In IDNA, equivalence of labels is defined in terms of the A-labels.
   If the A-labels are equal in a case-independent comparison, then the
s/case-independent/case-preserving/
   labels are considered equivalent, no matter how they are represented.
   Because of the isomorphism of A-labels and U-labels in IDNA2008, it
   is possible to compare U-labels directly; see [IDNA2008-Protocol] for
   details.  Traditional LDH labels already have a notion of
   equivalence: within that list of characters, upper case and lower
   case are considered equivalent.  The IDNA notion of equivalence is an
Remove the whole sentence "Traditional LDH ... considered equivalent."
   extension of that older notion but, because there is no mapping, the
   only equivalents are:

   o  Exact (bit-string identity) matches between a pair of U-labels.

   o  Matches between a pair of A-labels, using normal DNS matching
      rules.
s/normal DNS/exact character/

   o  Equivalence between a U-label and an A-label determined by
      translating the U-label form into an A-label form and then testing
      for an exact match between the A-labels.

. . .

idnabis-defs 4.4:
. . .
   [IDNA2008-Protocol].  For labels already in ASCII form, the proper
   comparison reduces to the same case-insensitive ASCII comparison that
   has always been used for ASCII labels although IDNA-aware
   applications are expected to look up only A-labels and NR-LDH-labels,
   i.e., to avoid looking up R-LDH-labels that are not A-labels.
. . .
Change "reduces to...ASCII labels although" to "(case-preserving), although...".

idnabis-protocol 3.1:
. . .
                                                        A pair of
       A-labels MUST be compared as case-insensitive ASCII (as with all
       comparisons of ASCII DNS labels).
Change to:
                                                        A pair of
       A-labels MUST be compared using a case-preserving comparison.

I think the WG owes a hearty thanks to Wil for finding this bug in the spec and for being persistent in pointing it out after we forgot his earlier postings.