Re: [idn] length restrictions on IDN label

[Mark.Andrews@isc.org]

> Mark.Andrews@isc.org wrote:
> 
> >>The restriction orginated from RFC1035 affects all  label 
> >>creation/validations.
> >>And "octet(ToASCII(X)) <= 63" seems to loosen the restrictions about
> >>8bit labels. That is why i think RFC1035 restriction is about to be 
> >>obsoleted.
> >>    
> >>
> >
> >	There is nothing new with the number of octets in presentation
> >	form being greater those presented on the wire.  In RFC
> >	1034 0x00 is presented as "\000", 0x5c as "\\" or  "\093",
> >	0x2e as "\." or "\046".
> >
> UTF8-form of a label may be used as protocol elements , in addition to
> presentation forms.
> In the latter case, there will be no problem as you said above: just
> display it.
> 
> But, in the former case of being used as protocols elements, utf8-form
> label length limit is
> of our concern. IDNA drafts does not rule out that utf-8 form of labels
> may be used as protocol
> elements. This will clairfy my point.

	The restrictions have always derived from the DNS wire format.
	Each individual presentation format will have its own maximum
	number of octets however just because a string fits within
	that number of octets doesn't mean that it will be valid.

	Invalid 
	0123456789012345678901234567890123456789012345678901234567891234

	Valid
	\048\049\050\051\052\053\054\055\056\057\048\049\050\051\052\053

	Both of the above presentation strings are 64 octets long.  Only
	one is a legal label, both are < 252 octets that you would have
	to allow to convert a arbitary label from wire format to
	to RFC 1034 presentation format.  Similar things will happen
	with UTF-8 as a presentation format.  Only after you have attempted
	to covert to wire format can you determine if a arbitarty string
	of UTF-8 characters that is less than the maximum number of octets
	long will fit.

	Mark

> Thanks.
> 
> Soobok Lee
> 
> 
> 
--
Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews@isc.org