Network Working Group J. Klensin Internet-Draft November 2, 2007 Obsoletes: 3490 (if approved) Intended status: Standards Track Expires: May 5, 2008 Internationalizing Domain Names in Applications (IDNA): Protocol draft-klensin-idnabis-protocol-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 5, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document supplies the protocol definition for a revised and updated specification for internationalized domain names. The rationale for these changes and relationship to the older specification and some new terminology is provided in other documents. This document specifies a standard method using characters outside the ASCII repertoire in domain names. This document defines internationalized domain names (IDNs) and a Klensin Expires May 5, 2008 [Page 1] Internet-Draft IDNA200X Protocol November 2007 mechanism called Internationalizing Domain Names in Applications (IDNA) for handling them in a standard fashion. IDNs use characters drawn from a large subset of the Unicode repertoire, but IDNA allows the non-ASCII characters to be represented using only the ASCII characters already allowed in so-called host names today. This backward-compatible representation is required in existing protocols like DNS, so that IDNs can be introduced with no changes to the existing infrastructure. IDNA is only meant for processing domain names, not free text. Klensin Expires May 5, 2008 [Page 2] Internet-Draft IDNA200X Protocol November 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Requirements and Applicability . . . . . . . . . . . . . . . . 5 3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 5 3.2.1. DNS Resource Records . . . . . . . . . . . . . . . . . 5 3.2.2. Non-domain-name Data Types Stored in Domain Names . . 6 4. Registration Protocol . . . . . . . . . . . . . . . . . . . . 6 4.1. Proposed label . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 6 4.3. Permitted Character Identification . . . . . . . . . . . . 6 4.4. Additional Character String Checking and Processing . . . 7 4.5. Registry Restrictions . . . . . . . . . . . . . . . . . . 7 4.6. Punycode Conversion . . . . . . . . . . . . . . . . . . . 8 4.7. Insertion in the Zone . . . . . . . . . . . . . . . . . . 8 5. Domain Name Resolution (Lookup) Protocol . . . . . . . . . . . 8 5.1. User input . . . . . . . . . . . . . . . . . . . . . . . . 8 5.2. Conversion to Unicode . . . . . . . . . . . . . . . . . . 8 5.3. User Interface Character Changes . . . . . . . . . . . . . 9 5.4. Pre-Normalization Validation and Character List Testing . 9 5.5. Normalization . . . . . . . . . . . . . . . . . . . . . . 10 5.6. Post-Normalization Processing . . . . . . . . . . . . . . 10 5.7. Punycode Conversion . . . . . . . . . . . . . . . . . . . 10 5.8. DNS Name Resolution . . . . . . . . . . . . . . . . . . . 10 6. Entry and Display in Applications . . . . . . . . . . . . . . 10 7. Name server Considerations . . . . . . . . . . . . . . . . . . 11 7.1. Processing Non-ASCII Strings . . . . . . . . . . . . . . . 11 7.2. DNSSEC Authentication of IDN Domain Names . . . . . . . . 12 7.3. Root Server Considerations . . . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 13 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 12.1. Normative References . . . . . . . . . . . . . . . . . . . 14 12.2. Informative References . . . . . . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 17 Klensin Expires May 5, 2008 [Page 3] Internet-Draft IDNA200X Protocol November 2007 1. Introduction This document supplies the protocol definition for a revised and updated specification for internationalized domain names. The rationale for these changes and relationship to the older specification and some new terminology is provided in other documents, notably [IDNA200X-issues]. IDNA works by allowing applications to use certain ASCII string labels (beginning with a special prefix) to represent non-ASCII name labels. Lower-layer protocols need not be aware of this; therefore IDNA does not depend on changes to any infrastructure. In particular, IDNA does not depend on any changes to DNS servers, resolvers, or protocol elements, because the ASCII name service provided by the existing DNS is entirely sufficient for IDNA. IDNA is applied only to DNS labels. Standards for combining labels into fully-qualified domain names and parsing labels out of those names are covered in the base DNS standards [RFC1035]. An application may, of course, apply locally-appropriate conventions to the presentation forms of domain names as discussed in Section 6 and [IDNA200X-issues]. A good deal of the background material that appeared in RFC 3490 has been removed from this update. That material is either of historical interest only or has been covered from a more recent perspective in RFC 4690 [RFC4690] and [IDNA200X-issues]. [[anchor2: This version of this draft, and the corresponding version of the issues/rationale document, mark the first step in separating protocol-specific materials about IDNA from discussions of rationale and user interface issues. The documents are intermediate works in progress with a number of loose ends, some but not all of which are explicitly identified. They are posted for the convenience of the community and to solicit the community's help in identifying the boundary between materials that should correctly be in each document. A revised set of drafts can be anticipated significantly before IETF 70.]] 2. Terminology General terminology applicable to IDNA, but with meanings familiar to those who have worked with Unicode or other character set standards and the DNS, appears in [IDNA200X-issues]. Terminology that is an integral, normative, part of the IDNA definition appears in that document as well. Familiarity with the terminology materials in that document is assumed for reading this one. Klensin Expires May 5, 2008 [Page 4] Internet-Draft IDNA200X Protocol November 2007 [[anchor3: May want to copy some definitions from "issues" back to here to avoid or reduce normative dependencies. But, of course, that would risk the two sets of definitions becoming inconsistent. Tradeoff...]] The key words "MUST", "SHALL", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119]. 3. Requirements and Applicability 3.1. Requirements IDNA conformance means adherence to the following requirements: 1. Whenever a domain name is put into an IDN-unaware domain name slot (see Section 2 and [IDNA200X-issues]), it MUST contain only ASCII characters (i.e., must be either an A-label, an LDH-label, or a label associated with a DNS application that is not subject to IDNA. 2. Comparing two labels MUST be done on the A-label form, using an ASCII case-insensitive comparison. 3.2. Applicability IDNA is applicable to all domain names in all domain name slots except where it is explicitly excluded. It is not applicable to domain name slots which do not use the LDH syntax rules. This implies that IDNA is applicable to many protocols that predate IDNA. Note that IDNs occupying domain name slots in those protocols MUST be in A-label form. 3.2.1. DNS Resource Records IDNA applies only to domain names in the NAME and RDATA fields of DNS resource records whose CLASS is IN. There are currently no other exclusions on the applicability of IDNA to DNS resource records; it depends entirely on the CLASS, and not on the TYPE. This will remain true, even as new types are defined, unless there is a compelling reason for a new type to complicate matters by imposing type-specific rules. It is worth noting that the special naming conventions applicable to SRV records are precisely such type-specific rules. Klensin Expires May 5, 2008 [Page 5] Internet-Draft IDNA200X Protocol November 2007 3.2.2. Non-domain-name Data Types Stored in Domain Names Although IDNA enables the representation of non-ASCII characters in domain names, that does not imply that IDNA enables the representation of non-ASCII characters in other data types that are stored in domain names. For example, an email address local part is sometimes stored in a domain label (hostmaster@example.com would be represented as hostmaster.example.com in the RDATA field of an SOA record). IDNA does not update the existing email standards, which allow only ASCII characters in local parts. Other work is under development to define internationalization for email addresses [RFC4952], but changes to that part of the SOA RDATA would require action in other standards. 4. Registration Protocol This section defines the procedure for registering an IDN. The procedure is implementation-independent; any sequence of steps that produces exactly the same result for all labels is considered a valid implementation. 4.1. Proposed label The registrant submits a request for an IDN. The user typically produces the request string by the keyboard entry of a character sequence. 4.2. Conversion to Unicode Some system routine, or a localized front-end to the IDNA process, ensures that the proposed label is a Unicode string. As a local implementation choice, the implementation may choose to map some forbidden characters to permitted characters (for instance mapping uppercase characters to lowercase ones), displaying the result to the user, and allowing processing to continue. 4.3. Permitted Character Identification The Unicode string is examined to prohibit characters that IDNA does not permit in input. Those characters are identified in the "never" list that is discussed in [IDNA200X-issues] and [IDNA200X-Permitted]. In addition to what is explicitly identified in those documents, characters or sequences that are unassigned in Unicode MUST NOT be part of labels registered in the DNS. [[anchor9: The previous sentence should be redundant with the text in the tables and issues documents, but I want to leave it here until we are sure those are stable --JcK]] Klensin Expires May 5, 2008 [Page 6] Internet-Draft IDNA200X Protocol November 2007 4.4. Additional Character String Checking and Processing All characters produced as output of the preceding step are then verified for permissibility by IDNA. Conceptually, these tests are, in order: 1. Each code point is verified to be assigned in the version of Unicode in use (See [IDNA200X-issues]). 2. Each code point is checked for its presence as "Always permitted" in the table of included characters for registration or, if appropriate for the specific registry, as "Maybe permitted" (see [IDNA200X-Permitted]). 3. Each code point is checked for its presence as "Context Required" in the table of included characters for registration. If that indication appears, the table of contextual rules is checked for a rule for that character. If no rule is found, the proposed label is rejected. If one is found, it is applied (typically as a test on the entire label or adjacent characters). If the application of the rule does not conclude that the character is valid in context, the proposed label must be rejected. (See the IANA Considerations: IDNA Context Registry section of [IDNA200X-issues]). 4. Additional special tests for right-to-left strings are applied (See [IDNA200X-BIDI]. Strings that have been produced by the steps above, and whose contents pass the above tests, are U-labels. To summarize, tests are made here for invalid combinations of characters, and for labels that are invalid even if the individual characters they contain are all valid. For example, labels containing invisible ("zero-width") characters may be permitted in context with characters whose presentation forms are significantly changed by the presence or absence of the zero-width characters, while other labels in which zero-width characters appear may be rejected. Additional transformations that do not occur as the result of the steps above may be specified at this point by IDNA200x. As the list of characters permitted to be registered expands, new rules, similar to those suggested for zero-width characters, may accompany them. 4.5. Registry Restrictions Registries at all levels of the DNS, not just the top level, are expected to establish policies about the labels that may be Klensin Expires May 5, 2008 [Page 7] Internet-Draft IDNA200X Protocol November 2007 registered, and for the processes associated with that action. As discussed in [IDNA200X-issues]), such restrictions have always existed in the DNS. The string produced by the above steps is checked and processed as appropriate to local registry restrictions. Application of those registry restrictions may result in the rejection of some labels or the application of special restrictions to others. 4.6. Punycode Conversion The resulting U-label is converted to an A-label (i.e., the encoding of that label according to the Punycode algorithm [RFC3492] with the prefix included, i.e., the "xn--..." form). 4.7. Insertion in the Zone The A-label is then registered in the DNS by insertion into a zone. 5. Domain Name Resolution (Lookup) Protocol Resolution is conceptually different from registration and different tests are applied on the client. The resolution-side tests are more permissive and rely heavily on the assumption that names that are present in the DNS are valid. Among other things, this distinction facilitates expansion of the permitted character lists to include new scripts and accommodate new version of Unicode. 5.1. User input The user supplies a string in the local character set, typically by typing it or clicking on, or cutting and pasting, a resource identifier, e.g., a URI [RFC3986] or IRI [RFC3987]. Processing in this step and the next two are local matters, to be accomplished prior to actual invocation of IDNAbis, but at least this one and the next one must be accomplished in some way. 5.2. Conversion to Unicode The local character set, character coding conventions, and, as necessary, display and presentation conventions, are converted to Unicode (without surrogates), paralleling the process above (Section 4.2). Klensin Expires May 5, 2008 [Page 8] Internet-Draft IDNA200X Protocol November 2007 5.3. User Interface Character Changes The Unicode string MAY then be processed, in a way specific to the local environment, to make the result of the IDNA processing match user expectations. For instance, at this step, it would be reasonable to case-fold all upper case characters to lower case, if this makes sense in the user's environment. Other examples of processing for localization that might be applied, if appropriate, at this point (but even further outside the scope of this specification) include interpreting the KANA MIDDLE DOT to separate domain name components from each other, standardizing different "width" forms of the same character, or giving special treatment to characters whose presentation forms are dependent only on placement in the label. Because these transformations are local, it is important that domain names that might be passed between systems (e.g., in IRIs) be U-labels or A-labels and not forms that might be accepted locally as a consequence of this step. This step is not standardized, and not specified further here. 5.4. Pre-Normalization Validation and Character List Testing In parallel to the registration procedure, the Unicode string is checked to verify that all characters that appear in it are valid for IDNA resolution input. As discussed in [IDNA200X-issues], the resolution check is more liberal than that of the registration one: characters that fall into the "Maybe" (see [IDNA200X-issues]) categories in the inclusion tables do not lead to label rejection on resolution. Putative labels containing code points with any of the following characteristics MUST BE rejected prior to DNS lookup: o Code points that are unassigned in the version of Unicode being used by the application. o Prohibited code points, i.e., those that are assigned to the "Never" category in the permitted character table. o Code points that are shown in the permitted character table as requiring a contextual rule, but for which no such rule appears in the table of rules. For all other strings, the resolver MUST rely on the presence or absence of labels in the DNS to determine the validity of those labels and the validity of the characters they contain: if they are registered, they are presumed to be valid; if they are not, their possible validity is not relevant. Klensin Expires May 5, 2008 [Page 9] Internet-Draft IDNA200X Protocol November 2007 5.5. Normalization The validated Unicode string is normalized (using NFC); no case- mapping is performed. If a code point unassigned in the current version of Unicode is actually assigned in a later version, the resolver and the application containing it and calling it should be upgraded when possible; the protocol cannot automatically provide that upgrade. See [IDNA200X-issues] for more discussion on this issue. 5.6. Post-Normalization Processing Any necessary processing or filtering is applied to the normalized output string produced by the above. In the cases that can be anticipated, this step will be null. It is included in the model in case, e.g., full-label checks are needed on lookup. 5.7. Punycode Conversion The validated string, a U-label, is converted to an A-label. 5.8. DNS Name Resolution The A-label is looked up in the DNS, using normal DNS procedures. 6. Entry and Display in Applications [[anchor12: It may be appropriate to move this entire section to "issues". Opinions welcome.]] Applications can accept domain names using any character set or sets desired by the application developer, and can display domain names in any charset. That is, the IDNA protocol does not affect the interface between users and applications. An IDNA-aware application can accept and display internationalized domain names in two formats: the internationalized character set(s) supported by the application (i.e., an appropriate local representation of a U-label), and as an A-label. Applications MAY allow input from, and display to, the user of A-labels, but are not encouraged to do so except as an interface for special purposes, possibly for debugging, or to cope with display limitations. A-labels are opaque and ugly, and, where possible, should thus only be exposed to users who absolutely need them. Because IDN labels can be rendered either as the A-labels or U-labels, the application may reasonably have an option for the user to select the preferred method of display; if it does, rendering the U-label should normally not be Klensin Expires May 5, 2008 [Page 10] Internet-Draft IDNA200X Protocol November 2007 the default. Domain names are often stored and transported in many places. For example, they are part of documents such as mail messages and web pages. They are transported in many parts of many protocols, such as both the control commands and the RFC 2822 body parts of SMTP, and the headers and the body content in HTTP. It is important to remember that domain names appear both in domain name slots and in the content that is passed over protocols. In protocols and document formats that define how to handle specification or negotiation of charsets, labels can be encoded in any charset allowed by the protocol or document format. If a protocol or document format only allows one charset, the labels MUST be given in that charset. Of course, not all charsets can properly represent all labels. If a U-label cannot be displayed in its entirety, the only choice (without loss of information) may be to display the A-label. In any place where a protocol or document format allows transmission of the characters in internationalized labels, internationalized labels SHOULD be transmitted using whatever character encoding and escape mechanism that the protocol or document format uses at that place. All protocols that use domain name slots already have the capacity for handling domain names in the ASCII charset. Thus, A-labels can inherently be handled by those protocols. 7. Name server Considerations 7.1. Processing Non-ASCII Strings Existing DNS servers do not know the IDNA rules for handling non- ASCII forms of IDNs, and therefore need to be shielded from them. All existing channels through which names can enter a DNS server database (for example, master files (as described in RFC 1034) and DNS update messages [RFC2136]) are IDN-unaware because they predate IDNA. Other sections of this document provide the needed shielding by ensuring that internationalized domain names entering DNS server databases through such channels have already been converted to their equivalent ASCII A-label forms. It is imperative that there be only one ASCII encoding for a particular domain name. Because of the design of the U-label and A-label definitions and transformations, there are no ACE labels that decode to ASCII labels (LDH or otherwise), and therefore name servers Klensin Expires May 5, 2008 [Page 11] Internet-Draft IDNA200X Protocol November 2007 cannot contain multiple ASCII encodings of the same domain name. [RFC2181] explicitly allows domain labels to contain octets beyond the ASCII range (0..7F), and this document does not change that. Note, however, that there is no defined interpretation of octets 80..FF as characters. If labels containing these octets are returned to applications, unpredictable behavior could result. The A-label (ASCII) form, which cannot contain those characters, is the only standard representation for internationalized labels in the current DNS protocol. 7.2. DNSSEC Authentication of IDN Domain Names DNS Security [RFC2535] is a method for supplying cryptographic verification information along with DNS messages. Public Key Cryptography is used in conjunction with digital signatures to provide a means for a requester of domain information to authenticate the source of the data. This ensures that it can be traced back to a trusted source, either directly, or via a chain of trust linking the source of the information to the top of the DNS hierarchy. IDNA specifies that all internationalized domain names served by DNS servers that cannot be represented directly in ASCII must use the A-label form. Conversion to A-labels must be performed prior to a zone being signed by the private key for that zone. Because of this ordering, it is important to recognize that DNSSEC authenticates a domain name containing A-labels or conventional LDH-labels, not U-labels. In the presence of DNSSEC, no form of a zone file or query response that contains a U-label may be signed or validated against. One consequence of this for sites deploying IDNA in the presence of DNSSEC is that any special purpose proxies or forwarders used to transform user input into IDNs must be earlier in the resolution flow than DNSSEC authenticating nameservers for DNSSEC to work. 7.3. Root Server Considerations IDNs are likely to be somewhat longer than current domain names, so the bandwidth needed by the root servers is likely to go up by a small amount. Also, queries and responses for IDNs will probably be somewhat longer than typical queries today, so more queries and responses may be forced to go to TCP instead of UDP. 8. Security Considerations The general security principles and issues for IDNA appear in [IDNA200X-issues]. The comments below are specific to this protocol, Klensin Expires May 5, 2008 [Page 12] Internet-Draft IDNA200X Protocol November 2007 but should be read in the context of that material and the specifications, identified there, on which this one depends. This memo describes an algorithm which encodes characters that are not valid according to the base DNS specifications (STD13 [RFC1034] [RFC1035] and Host Requirements [RFC1123]) into octet values that are valid. No security issues such as string length increases or new allowed values are introduced by the encoding process or the use of these encoded values, apart from those introduced by the ACE encoding itself. Domain names (or portions of them) are sometimes compared against a set of privileged or anti-privileged domains. In such situations it is especially important that the comparisons be done properly, as specified in requirement 2 of Section 3.1. 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. The introduction of IDNA means that any existing labels that start with the ACE prefix would be construed as U-labels, at least until they failed one of the relevant tests, whether or not that was the intent of the zone administrator or registrant. There is no evidence that this has caused any practical problems since RFC 3490 was adopted, but the risk still exists in principle. 9. IANA Considerations IANA actions for this version of IDNA are specified in [IDNA200X-issues]. 10. Contributors While the listed editor held the pen, this document represents the joint work and conclusions of an ad hoc design team consisting of the editor and, in alphabetic order, Harald Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. This document draws significantly on the original version of IDNA [RFC3490] both conceptually and for specific text. This second-generation version would not have been possible without the work that went into that first version and its authors, Patrik Faltstrom, Paul Hoffman, and Adam Costello. While Faltstrom was actively involved in the creation of this version, Hoffman and Costello were not and should not be held responsible for any errors or omissions. Klensin Expires May 5, 2008 [Page 13] Internet-Draft IDNA200X Protocol November 2007 11. Acknowledgements This revision to IDNA would have been impossible without the accumulated experience since RFC 3490 was published and resulting comments and complaints of many people in the IETF, ICANN, and other communities, too many people to list here. Nor would it have been possible without RFC 3490 itself and the efforts of the Working Group that defined it. Those people whose contributions are acknowledged in RFC 3490, [RFC4690], and [IDNA200X-issues] were particularly important. 12. References 12.1. Normative References [IDNA200X-BIDI] Alvestrand, H. and C. Karp, "An IDNA problem in right-to- left scripts", October 2006, . [IDNA200X-issues] Klensin, J., Ed., "Internationalizing Domain Names for Applications (IDNA): Issues and Rationale", November 2007. [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC1123] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)", RFC 3492, March 2003. 12.2. Informative References [ASCII] American National Standards Institute (formerly United States of America Standards Institute), "USA Code for Information Interchange", ANSI X3.4-1968, 1968. ANSI X3.4-1968 has been replaced by newer versions with Klensin Expires May 5, 2008 [Page 14] Internet-Draft IDNA200X Protocol November 2007 slight modifications, but the 1968 version remains definitive for the Internet. [IDNA200X-Permitted] Faltstrom, P., "The Unicode Codepoints and IDN", February 2007, . A version of this document, is available in HTML format at http://stupid.domain.name/idnabis/ draft-faltstrom-idnabis-tables-02.txt [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. [RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997. [RFC2535] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005. [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and Recommendations for Internationalized Domain Names (IDNs)", RFC 4690, September 2006. [RFC4952] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", RFC 4952, July 2007. [Unicode] The Unicode Consortium, "The Unicode Standard, Version 5.0", 2007. Boston, MA, USA: Addison-Wesley. ISBN 0-321-48091-0 Klensin Expires May 5, 2008 [Page 15] Internet-Draft IDNA200X Protocol November 2007 Author's Address John C Klensin 1770 Massachusetts Ave, Ste 322 Cambridge, MA 02140 USA Phone: +1 617 245 1457 Fax: Email: john+ietf@jck.com URI: Klensin Expires May 5, 2008 [Page 16] Internet-Draft IDNA200X Protocol November 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Klensin Expires May 5, 2008 [Page 17]