Internationalized Domain Names in Applications, Revised
Internationalized Domain Names in Applications, Revised WG
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The original Internationalized Domain Name (IDN) WG specified rules for
the use of characters other than Latin A(a)-Z(z), digits 0-9 and the
hyphen (-) in domain names in RFC3490, RFC3491 and RFC3492 in 2002
(published in 2003 and often referenced collectively as "IDNA2003").
These documents depend on RFC 3454 and were tied to Unicode version
3.2. An update to the current version (5.x) is required to accommodate
additional scripts. In addition, experience has shown that significant
improvements could be made in the protocol as presently specified.
This WG is chartered to decouple IDNA from specific versions of Unicode
using algorithms that define validity based on Unicode properties. It
is recognized that some explicit exceptions may be necessary in any
case, but attempts will be made to minimize these exceptions.
- Separate requirements for valid IDNs at registration time (insertion
of names into DNS zone files), vs. at resolution time (looking up those
- Review, and if necessary revise, the algorithms and rules for
handling right to left character sequences in an IDN context to allow
labels based on additional scripts and languages and to make presentation
as predictable as reasonably possible.
- Permit use of some scripts that were inadvertently excluded by the
- Ensure practical stability of validity algorithms for IDNs.
The constraints of the original IDN WG still apply to IDNABIS, namely
to avoid disturbing the current use and operation of the domain name
system, and for the DNS to continue to allow any system to resolve any
domain name in a consistent way. The client-based approach of the
original IDN work will be maintained -- substantially new protocols or
mechanisms are not in scope. In particular, IDNs continue to use the
"xn--" prefix and the same ASCII-compatible encoding, and the
bidirectional algorithm follows the same basic design.
The specifications are initially organized as four documents: overview
and rationale, protocol, table algorithm, and improvements to the
bidirectional algorithm. These documents are to be used as the basis
for the discussion of the general direction of the work.
This working group will be providing extended public review of the
output of a design team that has been working on improvement of the
This review-based approach is being used in part because of the way the
work was undertaken by the team; in particular, the design team has
been working with IETF visibility and has solicited and received
significant amounts of technical review already from IETF participants
and from others including experts in the Unicode specifications and the
use of scripts in languages. If the public review provided by this
Working Group confirms the basic method outlined in the input documents,
it is expected that the working group will be able to respond with any
needed changes and close in a short period of time. If technical issues
arise that indicate a fundamentally different approach must be taken
from the one outlined above, it is anticipated that this working group
would close, and a new one with an appropriate charter would be
This work is intended to specify an improved means to produce and use
stable and unambiguous IDN identifiers.
There are a variety of generally unsolvable problems, notably the
problem of characters that are confusingly similar in appearance (often
known as the "phishing" problem) that are not specifically part of the
scope of the WG although some of the preliminary results of the design
team suggest that the improvements contemplated in the specifications
might mitigate some of the ways in which the current IDNA specifications
can be abused for phishing purposes.
While it is referenced from the original IDNA2003 package, the original
Stringprep specification, RFC 3454, is not formally part of the IDNA
package and will not be altered by this work.
The work will update or obsolete RFC 3490. It is not expected to
continue to use Nameprep (RFC 3491). Nameprep is used by other
specifications; determining how (or whether) to update those
specifications and, consequently, the long-term status of Nameprep,
are not part of this effort. The method for ASCII-compatible ("ACE")
encoding of IDNs, "Punycode" (RFC 3492) will not be revised by this WG.
Subject to the more general constraints described above, the WG is
permitted to consider changes that are not strictly backwards-
compatible. For any such change that is recommended, it is expected to
document the reasons for the change, the characters affected, and
possible transition strategies.
The assumptions outlined above are considered critical to the WG
constituted by this charter. The WG will stop work and recommend that
a new charter be generated if it concludes that any of the following are
necessary to meet its goals:
(i) A change to the "punycode" algorithm or to the ACE approach to
encoding names in the DNS.
(ii) A change to the ACE prefix from "xn--"
(iii) A change to the basic approach taken in the design team
documents (Namely: independence from Unicode version and reduction of
dependency on character mapping )