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Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: draft-ietf-idnabis-protocol has been published as RFC 5891 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Resnick 3 Internet-Draft Qualcomm Incorporated 4 Intended status: Informational P. Hoffman 5 Expires: October 15, 2010 VPN Consortium 6 April 13, 2010 8 Mapping Characters in IDNA2008 9 draft-resman-idna2008-mappings-00 11 Abstract 13 In the original version of the Internationalized Domain Names in 14 Applications (IDNA) protocol, any Unicode code points taken from user 15 input were mapped into a set of Unicode code points that "made 16 sense", and then encoded and passed to the domain name system (DNS). 17 The IDNA2008 protocol presumes that the input to the protocol comes 18 from a set of "permitted" code points, which it then encodes and 19 passes to the DNS, but does not specify what to do with the result of 20 user input. This document describes the actions that can be taken by 21 an implementation between user input and passing permitted code 22 points to the new IDNA protocol. 24 Status of this Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on October 15, 2010. 41 Copyright Notice 43 Copyright (c) 2010 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. 53 1. Introduction 55 This document describes the operations that can be applied to user 56 input in order to get it into a form acceptable by the 57 Internationalized Domain Names in Applications (IDNA) protocol 58 [IDNA2008protocol]. It includes a general implementation procedure 59 for mapping. 61 It should be noted that this document does not specify the behavior 62 of a protocol that appears "on the wire". It describes an operation 63 that is to be applied to user input in order to prepare that user 64 input for use in an "on the network" protocol. As unusual as this 65 may be for a document concerning Internet protocols, it is necessary 66 to describe this operation for implementors who may have designed 67 around the original IDNA protocol, which conflates this user input 68 operation into the protocol. 70 It is very important to note that there are many potential valid 71 mappings of characters from user input. The mapping described in 72 this document is the basis for other mappings, and is not likely to 73 be useful without modification. Any useful mapping will have 74 features designed to reduce the surprise for users and is likely to 75 be slightly (or sometimes radically) different depending on the 76 locale of the user, the type of input being used (such as typing, 77 copy-and-paste, voice, and so on), the type application used, etc. 78 Although most common mappings will probably produce similar results 79 for the same input, there will be subtle differences between 80 applications. 82 1.1. The Dividing Line between User Interface and Protocol 84 The user interface to applications is much more complicated than most 85 network implementers think. When we say "the user enters an 86 internationalized domain name in the application", we are talking 87 about a very complex process that encompasses everything from the 88 user formulating the name and deciding which symbols to use to 89 express that name, to the user entering the symbols into the computer 90 using some input method (be it a keyboard, a stylus, or even a voice 91 recognition program), to the computer interpreting that input (be it 92 keyboard scan codes, a graphical representation, or digitized sounds) 93 into some representation of those symbols, through finally 94 normalizing those symbols into a particular character repertoire in 95 an encoding recognizable to IDNA processes and the domain name 96 system. 98 Consideration for user interface for internationalized domain names 99 involves taking into account culture, context, and locale for any 100 given user. A simple and well-known example is the lowercasing of 101 the letter Latin capital letter I (U+0049) when it is used in the 102 Turkish and other languages. A capital "I" in Turkish is properly 103 lowercased to a lowercase dotless "i" (U+0131), not to a Latin small 104 letter i (U+0069). This lowercasing is clearly dependent on the 105 locale of the system and/or the locale of the user. Using a single 106 context-free mapping without considering the user interface 107 properties has the potential of doing exactly the wrong thing for the 108 user. 110 The original version of IDNA conflated user interface processing and 111 protocol. It took whatever characters the user produced in whatever 112 encoding the application used, assumed some conversion to Unicode 113 code points, and then without regard to context, locale, or anything 114 about the user's intentions, mapped them into a particular set of 115 other characters, and then re-encoded them in Punycode, in order have 116 the entire operation be contained within the protocol. This made for 117 a much simpler implementation, making it it significantly less 118 complicated for the application developer, but at the expense of 119 minimizing "user surprise" for consumers and producers of domain 120 names. 122 In IDNA2008, the dividing line between "user interface" and 123 "protocol" is clear. The IDNA2008 specification defines the protocol 124 part of IDNA: it explicitly does not deal with the user interface. 125 Mappings such as the one described in this document explicitly deal 126 with the user interface and not the protocol. That is, a mapping is 127 only to be applied before a string of characters is treated as a 128 domain name (in the "user interface") and is never to be applied 129 during domain name processing (in the "protocol"). 131 1.2. The Design of this Mapping 133 The user interface mapping in this document is a set of expansions to 134 IDNA2008 that are meant to be sensible and friendly and mostly 135 obvious to people throughout the world when using typical 136 applications with domain names that are entered by hand. It is also 137 designed to let applications be mostly backwards compatible with 138 IDNA2003. By definition, it cannot meet all of those design goals 139 for all people, and in fact is known to fail on some of those goals 140 for quite large populations of people. 142 A good mapping in the real world might use the "sensible and friendly 143 and mostly obvious" design goal but come up with a different 144 algorithm. Many algorithms will have results that are close to what 145 is described here, but will differ in assumptions about the users' 146 way of thinking or typing. Having said that, it is likely that some 147 mappings will be significantly different. For example, a mapping 148 might apply to a spoken user interface instead of a typed one. 149 Another example is that a mapping might be different for users typing 150 than for users using copy-and-paste from different applications. 152 2. The General Procedure 154 This section defines a general algorithm that applications ought to 155 implement in order to produce Unicode code points that will be valid 156 under the IDNA protocol. An application might implement the full 157 mapping as described below, or can choose a different mapping. This 158 mapping is very general and was designed to be very acceptable to the 159 widest user community, but as stated above, it does not take into 160 account any particular context, culture, or locale. 162 The general algorithm that an application (or the input method 163 provided by an operating system) ought to use is relatively 164 straightforward: 166 1. Upper case characters are mapped to their lower case equivalents 167 by using the algorithm for mapping case in Unicode characters. 168 This step was chosen because the output will behave more like 169 ASCII host names behave. 171 2. Full-width and half-width characters (those defined with 172 Decomposition Types and ) are mapped to their 173 decomposition mappings as shown in the Unicode character 174 database. This step was chosen because many input mechanisms, 175 particularly in Asia, do no allow you to easily enter characters 176 in the form used by IDNA2008. Even if they do allow the correct 177 character form, the user might not know which form they are 178 entering. 180 3. All characters are mapped using Unicode Normalization Form C 181 (NFC). This step was chosen because it maps combinations of 182 combining characters into canonical composed form. As with the 183 full-width/half-width mapping, users are not generally aware of 184 the particular form of characters that they are entering, and 185 IDNA2008 requires that only the canonical composed forms from NFC 186 are used. 188 4. [IDNA2008protocol] is specified such that the protocol acts on 189 the individual labels of the domain name. If an implementation 190 of this mapping is also performing the step of separation of the 191 parts of a domain name into labels by using the FULL STOP 192 character (U+002E), the IDEOGRAPHIC FULL STOP (U+3002) character 193 can be mapped to the FULL STOP before label separation occurs. 194 There are other characters that are used as "full stops" that one 195 could consider mapping as label separators, but their use as such 196 has not been investigated thoroughly. This step was chosen 197 because some input mechanisms do not allow the user to easily 198 enter proper label separators. Only the IDEOGRAPHIC FULL STOP 199 (U+3002) character is added in this mapping because the authors 200 have not fully investigated the applicability of other characters 201 and the environments where they should and should not be 202 considered domain name label separators. 204 Note that the steps above are ordered. 206 Definitions for the rules in this algorithm can be found in 207 [Unicode52]. Specifically: 209 o Unicode Normalization Form C can be found in Annex #15 of 210 [Unicode52]. 212 o In order to map upper case characters to their lower case 213 equivalents (defined in section 3.13 of [Unicode52]), first map 214 characters to the "Lowercase_Mapping" property (the "" 215 entry in the second column) in 216 , if any. 217 Then, map characters to the "Simple_Lowercase_Mapping" property 218 (the fourteenth column) in 219 , if any. 221 o In order to map full-width and half-width characters to their 222 decomposition mappings, map any character whose 223 "Decomposition_Type" (contained in the first part of of the sixth 224 column) in 225 is either "" or "" to the "Decomposition_Mapping" of 226 that character (contained in the second part of the sixth column) 227 in . 229 o The Unicode Character Database [TR44] has useful descriptions of 230 the contents of these files. 232 If the mappings in this document are applied to versions of Unicode 233 later than Unicode 5.2, the later versions of the Unicode Standard 234 should be consulted. 236 These form a minimal set of mappings that an application should 237 strongly consider doing. Of course, there are many others that might 238 be done. 240 3. Implementing This Mapping 242 If you are implementing a mapping for an application or operating 243 system by using exactly the four steps in Section 2, the authors of 244 this document have a request: please don't. We mean it. Section 2 245 does not describe a universal mapping algorithm because, as we said, 246 there is no universally-applicable mapping algorithm. 248 If you read the material in Section 2 without reading Section 1, go 249 back and carefully read all of Section 1; in many ways, Section 1 is 250 more important than Section 2. Further, you can probably think of 251 user interface considerations that we did not list in Section 1. If 252 you did read Section 1 but somehow decided that the algorithm in 253 Section 2 is completely correct for the intended users of your 254 application or operating system, you are probably not thinking hard 255 enough about your intended users. 257 4. IANA Considerations 259 This memo includes no request to IANA. 261 5. Security Considerations 263 This document suggests creating mappings that might cause confusion 264 for some users while alleviating confusion in other users. Such 265 confusion is not covered in any depth in this document (nor in the 266 other IDNA-related documents). 268 6. Acknowledgements 270 This document is the product of many contributions from numerous 271 people in the IETF. 273 7. Normative References 275 [IDNA2008protocol] 276 Klensin, J., "Internationalized Domain Names in 277 Applications (IDNA): Protocol", 278 draft-ietf-idnabis-protocol (work in progress), 279 January 2010. 281 [TR44] The Unicode Consortium, "Unicode Character Database", 282 Unicode Standard Annex 44, 2009. 284 [Unicode52] 285 The Unicode Consortium, "The Unicode Standard, Version 286 5.2.0", 2009. 288 defined by: The Unicode Standard, Version 5.0, Boston, MA, 289 Addison-Wesley, 2007, ISBN 0-321-48091-0, as amended by 290 Unicode 5.2.0 291 (). 293 Authors' Addresses 295 Peter W. Resnick 296 Qualcomm Incorporated 297 5775 Morehouse Drive 298 San Diego, CA 92121-1714 299 US 301 Phone: +1 858 651 4478 302 Email: presnick@qualcomm.com 303 URI: http://www.qualcomm.com/~presnick/ 305 Paul Hoffman 306 VPN Consortium 307 127 Segre Place 308 Santa Cruz, CA 95060 309 US 311 Phone: 1-831-426-9827 312 Email: paul.hoffman@vpnc.org