Network Working Group M. Blanchet Internet-Draft Viagenie Obsoletes: 3454 (if approved) P. Saint-Andre Intended status: Standards Track Cisco Expires: November 18, 2011 May 17, 2011 PRECIS Framework: Handling Internationalized Strings in Protocols draft-blanchet-precis-framework-01 Abstract Application protocols that make use of Unicode code points in protocol strings need to prepare such strings in order to perform comparison operations (e.g., for purposes of authentication or authorization). In general, this problem has been labeled the "preparation and comparison of internationalized strings" or "PRECIS". This document defines a framework that enables application protocols to prepare various classes of strings in a way that depends on the properties of Unicode code points. Because this framework does not depend on large tables of Unicode code points as in stringprep (RFC 3454), it is more agile with regard to changes in the underlying Unicode database and thus provides improved flexibility to application protocols. A specification that reuses this framework either can directly use the base string classes defined in this document or can subclass the base string classes as needed. This framework uses an approach similar to that of the revised internationalized domain names in applications (IDNA) technology (RFC 5890, RFC 5891, RFC 5892, RFC 5893, RFC 5894) and thus adheres to the high-level design goals described in RFC 4690, albeit for non-IDNA technologies. This document obsoletes RFC 3454. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on November 18, 2011. Blanchet & Saint-Andre Expires November 18, 2011 [Page 1]
Internet-Draft PRECIS Framework May 2011 Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Blanchet & Saint-Andre Expires November 18, 2011 [Page 2]
Internet-Draft PRECIS Framework May 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. String Classes . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Nameything . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1.2. Disallowed . . . . . . . . . . . . . . . . . . . . . . 7 3.1.3. Unassigned . . . . . . . . . . . . . . . . . . . . . . 8 3.1.4. Directionality . . . . . . . . . . . . . . . . . . . . 8 3.1.5. Case Mapping . . . . . . . . . . . . . . . . . . . . . 8 3.1.6. Normalization . . . . . . . . . . . . . . . . . . . . 8 3.2. Wordything . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. Disallowed . . . . . . . . . . . . . . . . . . . . . . 9 3.2.3. Unassigned . . . . . . . . . . . . . . . . . . . . . . 9 3.2.4. Directionality . . . . . . . . . . . . . . . . . . . . 9 3.2.5. Case Mapping . . . . . . . . . . . . . . . . . . . . . 9 3.2.6. Normalization . . . . . . . . . . . . . . . . . . . . 9 3.3. Stringything . . . . . . . . . . . . . . . . . . . . . . . 10 3.3.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 10 3.3.2. Disallowed . . . . . . . . . . . . . . . . . . . . . . 10 3.3.3. Unassigned . . . . . . . . . . . . . . . . . . . . . . 10 3.3.4. Directionality . . . . . . . . . . . . . . . . . . . . 10 3.3.5. Case Mapping . . . . . . . . . . . . . . . . . . . . . 10 3.3.6. Normalization . . . . . . . . . . . . . . . . . . . . 10 4. Reuse of PRECIS String Classes . . . . . . . . . . . . . . . . 11 4.1. Principles . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Subclassing . . . . . . . . . . . . . . . . . . . . . . . 11 4.3. Template . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.4. Registration . . . . . . . . . . . . . . . . . . . . . . . 11 5. Code Point Properties . . . . . . . . . . . . . . . . . . . . 12 6. Category Definitions Used to Calculate Derived Property Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . . 14 6.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . . 14 6.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 14 6.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 15 6.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . . 15 6.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . . 16 6.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 17 6.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 17 6.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . . 17 6.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . . 17 6.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . . 18 6.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 18 6.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . . 18 Blanchet & Saint-Andre Expires November 18, 2011 [Page 3]
Internet-Draft PRECIS Framework May 2011 6.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 18 6.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 18 6.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 19 7. Calculation of the Derived Property . . . . . . . . . . . . . 19 8. Code Points . . . . . . . . . . . . . . . . . . . . . . . . . 20 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 9.1. PRECIS Derived Property Value Registry . . . . . . . . . . 20 9.2. PRECIS Contextual Rules Registry . . . . . . . . . . . . . 21 10. Security Considerations . . . . . . . . . . . . . . . . . . . 21 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21 12. Codepoints 0x0000 - 0x10FFFF . . . . . . . . . . . . . . . . . 21 12.1. Codepoints in Unicode Character Database (UCD) format . . 22 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 13.1. Normative References . . . . . . . . . . . . . . . . . . . 22 13.2. Informative References . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 Blanchet & Saint-Andre Expires November 18, 2011 [Page 4]
Internet-Draft PRECIS Framework May 2011 1. Introduction A number of IETF application technologies use stringprep [RFC3454] as the basis for comparing protocol strings that contain Unicode characters or "code points" [UNICODE]. Since the publication of [RFC3454] in 2002, the Internet community has gained much more experience with internationalization, some of it reflected in [RFC4690]. In particular, the IETF's technology for internationalized domain names (IDNs) has changed significantly: IDNA2003 [RFC3490], which was based on stringprep, has been superseded by IDNA2008 ([RFC5890], [RFC5891], [RFC5892], [RFC5893], [RFC5894]), which does not use stringprep. This migration away from stringprep for internationalized domain names has prompted other "customers" of stringprep to consider new approaches to the preparation and comparison of internationalized strings ("PRECIS"), as described in [PROBLEM]. This document proposes a technical framework for a post-stringprep approach to the preparation and comparison of internationalized strings in application protocols. The framework is based on several principles: 1. Define a small set of base string classes appropriate for common application protocol constructs such as usernames, passwords, and free-form identifiers. 2. Define each base string class in terms of Unicode code points and their properties, specifying whether each code point or category of code points is valid, disallowed, or unassigned. 3. Enable application protocols to subclass the base string classes. 4. Mapping operations (e.g., case preservation or lowercasing, Unicode normalization, right-to-left characters) are the responsibility of application protocols, as was done for IDNA2008 via [RFC5895]. It is expected that this framework will yield the following benefits: o Application protocols will be more version-agile with regard to the Unicode database. o Implementers will be able to share code point tables and software code across application protocols, most likely by means of code libraries. o End users will be able to build more accurate expectations about the code points that are acceptable in various contexts. Given this more uniform set of string classes, it is also expected that copy/paste operations between software implementing different Blanchet & Saint-Andre Expires November 18, 2011 [Page 5]
Internet-Draft PRECIS Framework May 2011 application protocols will be more predictable and coherent. Although this framework is similar to IDNA2008, it defines additional string classes to meet the needs of common application protocols. 2. Terminology Many important terms used in this document are defined in [PROBLEM], [I18N-TERMS], [RFC5890], and [UNICODE]. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. String Classes IDNA2008 essentially defines a base string class of internationalized domain name, although it does not use the term "string class". (This document does not redefine a string class for domain names, and application protocols are strongly encouraged to IDNA2008 as the appropriate method to prepare domain names and hostnames.) We propose the following additional base string classes for use in application protocols: Nameything: a word or set of words that is used to identify or address a network entity such as a user, an account, a venue (e.g., a chatroom), an information source (e.g., a data feed), or a collection of data (e.g., a file). Wordything: a sequence of letters, numbers, and symbols that is used as a secret for access to some resource on a network (e.g., a password or passphrase). Stringything: a sequence of letters, numbers, symbols, spaces, and other code points that is used for more expressive purposes in an application protocol (e.g., a nickname in a chatroom). The following subsections discuss these string classes in more detail, with reference to the dimensions described in Section 3 of [PROBLEM]. Each string class is defined by the following behavioral rules: Blanchet & Saint-Andre Expires November 18, 2011 [Page 6]
Internet-Draft PRECIS Framework May 2011 Valid: defines which code points and code point categories are treated as valid input to preparation of the string. Disallowed: defines which code points and code point categories are treated as disallowed during preparation of the string. Unassigned: defines application behavior in the presence of code points that are unassigned, i.e. unknown for the version of Unicode the application is built upon. Directionality: defines application behavior in the presence of code points that have directionality, in particular right-to-left code points as defined in the Unicode database (see [UAX9]. Casemapping: defines if case mapping is used for this class, and how the mapping is done. Normalization: defines which Unicode normalization form (D, KD, C, or KC) is to be applied (see [UAX15]). This document defines the valid, disallowed, and unassigned rules. Application protocols that use the PRECIS string classes MUST define the directionality, casemapping, and normalization rules, as further described under Section 4. 3.1. Nameything Most application technologies need a special class of strings that can be used to refer to, include, or communicate things like usernames, chatroom names, file names, and data feed names. We group such things into a bucket called "nameythings" having the following features. 3.1.1. Valid o Letters and numbers, i.e., the LetterDigits ("A") category first defined in [RFC5892] and listed here under Section 6.1. o Code points in the range U+0021 through U+007E, i.e., the ASCII7 ("K") rule defined under Section 6.11. These code points are valid even if they would otherwise be disallowed according to the property-based rules specified in the next section. 3.1.2. Disallowed o Control characters, i.e., the Controls ("L") category defined under Section 6.12. o Space characters, i.e., the Spaces ("N") category defined under Section 6.14. o Symbol characters, i.e., the Symbols ("O") category defined under Section 6.15. o Punctuation characters, i.e., the Punctuation ("P") category defined under Section 6.16. Blanchet & Saint-Andre Expires November 18, 2011 [Page 7]
Internet-Draft PRECIS Framework May 2011 o Any character that has a compatibility equivalent, i.e., the HasCompat ("Q") category defined under Section 6.17. These code points are disallowed even if they would otherwise be valid according to the property-based rules specified in the previous section. 3.1.3. Unassigned Any code points that are not yet assigned in the Unicode character set shall be considered Unassigned for purposes of PRECIS string classes. 3.1.4. Directionality To be defined by application protocols. 3.1.5. Case Mapping To be defined by application protocols. 3.1.6. Normalization To be defined by application protocols. ### OPEN ISSUE: Perhaps recommend that application protocols use NFC, in accordance with [RFC5198], normalization form C (NFC) is RECOMMENDED. ### 3.2. Wordything Many application technologies need a special class of strings that can be used to communicate secrets of the kind that are typically used as passwords or passphrases. We group such things into a bucket called "wordythings" having the following features. NOTE: Some application protocols use passwords and passphrases directly, whereas others reuse technologies that process passwords (e.g., the Simple Authentication and Security Layer [RFC4422]). Moreover, passwords are often carried by a sequence of protocols with backends such as RADIUS or LDAP. Developers of application protocols are encouraged to look into reusing these profiles instead of defining new ones, so that expectations for passwords by end-users are consistent no matter what application protocol is used. 3.2.1. Valid Blanchet & Saint-Andre Expires November 18, 2011 [Page 8]
Internet-Draft PRECIS Framework May 2011 o Letters and numbers, i.e., the LetterDigits ("A") category first defined in [RFC5892] and listed here under Section 6.1. o Code points in the range U+0021 through U+007E, i.e., the ASCII7 ("K") rule defined under Section 6.11. These code points are valid even if they would otherwise be disallowed according to the property-based rules specified in the next section. o Any character that has a compatibility equivalent, i.e., the HasCompat ("Q") category defined under Section 6.17. 3.2.2. Disallowed o Control characters, i.e., the Controls ("L") category defined under Section 6.12. o Space characters, i.e., the Spaces ("N") category defined under Section 6.14. o Symbol characters, i.e., the Symbols ("O") category defined under Section 6.15. o Punctuation characters, i.e., the Punctuation ("P") category defined under Section 6.16. ### OPEN ISSUE: Why not allow symbols and punctuation characters in wordythings? ### 3.2.3. Unassigned Any code points that are not yet assigned in the Unicode character set shall be considered Unassigned for purposes of PRECIS string classes. 3.2.4. Directionality To be defined by application protocols. 3.2.5. Case Mapping To be defined by application protocols. ### OPEN ISSUE: Perhaps recommend that application protocols map uppercase and titlecase code points to their lowercase equivalents, in order to maximize the entropy of passwords and passphrases. ### 3.2.6. Normalization To be defined by application protocols. ### OPEN ISSUE: Perhaps recommend that application protocols use NFC, in accordance with [RFC5198], normalization form C (NFC) is RECOMMENDED. ### Blanchet & Saint-Andre Expires November 18, 2011 [Page 9]
Internet-Draft PRECIS Framework May 2011 3.3. Stringything Some application technologies need a special class of strings that can be used in a free-form way (e.g., a nickname in a chatroom). We group such things into a bucket called "stringythings" having the following features. 3.3.1. Valid o Letters and numbers, i.e., the LetterDigits ("A") category first defined in [RFC5892] and listed here under Section 6.1. o Code points in the range U+0021 through U+007E, i.e., the ASCII7 ("K") rule defined under Section 6.11. o Any character that has a compatibility equivalent, i.e., the HasCompat ("Q") category defined under Section 6.17. o Space characters, i.e., the Spaces ("N") category defined under Section 6.14. o Symbol characters, i.e., the Symbols ("O") category defined under Section 6.15. o Punctuation characters, i.e., the Punctuation ("P") category defined under Section 6.16. 3.3.2. Disallowed o Control characters, i.e., the Controls ("L") category defined under Section 6.12. 3.3.3. Unassigned Any code points that are not yet assigned in the Unicode character set shall be considered Unassigned for purposes of PRECIS string classes. 3.3.4. Directionality To be defined by application protocols. 3.3.5. Case Mapping To be defined by application protocols. 3.3.6. Normalization To be defined by application protocols. ### OPEN ISSUE: Perhaps recommend that application protocols use NFC, in accordance with [RFC5198], normalization form C (NFC) is RECOMMENDED. ### Blanchet & Saint-Andre Expires November 18, 2011 [Page 10]
Internet-Draft PRECIS Framework May 2011 4. Reuse of PRECIS String Classes 4.1. Principles This document defines the valid, disallowed, and unassigned rules. Application protocols that use the PRECIS string classes MUST define the directionality, casemapping, and normalization rules. Such definitions MUST at a minimum specify the following: Directionality: Whether any instance of the class that contains a right-to-left code point is to be considered a right-to-left string, or whether a more complex rule is to be applied (e.g., the "Bidi Rule" from [RFC5893]). Casemapping: Whether uppercase and titlecase code points are to be (a) preserved or (b) mapped to lowercase. Normalization: Which Unicode normalization form (D, KD, C, or KC) is to be applied (see [UAX15] for background information and [RFC5198] for relevant considerations). 4.2. Subclassing Application protocols are allowed to subclass the base string classes specified in this document. As the word "subclass" implies, a subclass MUST NOT add as valid any code points or code point categories that are disallowed by the base string class. However, a subclass MAY do either of the following: 1. Exclude specific code points that are included in the base string class. 2. exclude characters matching certain Unicode properties (e.g., math symbols) that are included in the base string class. 4.3. Template The following template can be used by application protocols that reuse the PRECIS string classes. Base Class: [which base class is being reused] Subclassing: [whether the base class is being subclassed] Directionality: [the behavioral rule for handling of right-to-left code points] Casemapping: [the behavioral rule for handling of case] Normalization: [which Unicode normalization form is applied] 4.4. Registration ### OPEN ISSUE: Perhaps define an IANA registry for application protocols that reuse the PRECIS string classes. Blanchet & Saint-Andre Expires November 18, 2011 [Page 11]
Internet-Draft PRECIS Framework May 2011 5. Code Point Properties In order to implement the string classes described above, this document does the following: 1. Reviews and classifies the collections of code points in the Unicode character set by examining various properties of the code points. 2. Defines an algorithm for determining a derived property value, which can vary depending on the string class being used by the relevant application protocol. NOTE: This document specifies a procedure that can be applied to code points, and not a table of code points, so that the algorithm can be used to determine code point sets independent of the version of Unicode that is in use. This document is not intended to specify precisely how derived property values are to be applied in protocol strings. That information should be defined in the protocol specification that uses or subclasses a base string class from this document. The value of the property is to be interpreted as follows. o PROTOCOL VALID: Those that are allowed to be used in any PRECIS string class (nameything, wordything, and stringything). Code points with this property value are permitted for general use in any string class. The abbreviated term PVALID is used to refer to this value in the rest of this document. o SPECIFIC CLASS PROTOCOL VALID: Those that are allowed to be used in specific string classes. Code points with this property value are permitted for use in specific string classes. In the rest of this document, the abbreviated term *_PVALID is used, where * = (NAMEY, WORDY, STRINGY). o CONTEXTUAL RULE REQUIRED: Some characteristics of the character, such as it being invisible in certain contexts or problematic in others, requires that it not be used in labels unless specific other characters or properties are present. The abbreviated term CONTEXT is used to refer to this value in the rest of this document. There are two subdivisions of CONTEXTUAL RULE REQUIRED, the first for Join_controls (called CONTEXTJ) and the second for other characters (called CONTEXTO). o DISALLOWED: Those that must not be included in any string class. Code points with this property value are not permitted in any string class. o SPECIFIC CLASS DISALLOWED: Those that are not to be included in a specific string class. Code points with this property value are not permitted in one of the string classes but might be permitted Blanchet & Saint-Andre Expires November 18, 2011 [Page 12]
Internet-Draft PRECIS Framework May 2011 in others. In the rest of this document, the abbreviated term *_DISALLOWED is used, where * = (NAMEY, WORDY, STRINGY). o UNASSIGNED: Those code points that are not designated (i.e. are unassigned) in the Unicode Standard. The mechanisms described here allow determination of the value of the property for future versions of Unicode (including characters added after Unicode 5.2 or 6.0 depending on the category, since some categories in this document are re-used from IDNA2008). Changes in Unicode properties that do not affect the outcome of this process do not affect this framework. For example, a character can have its Unicode General_Category value [UNICODE] change from So to Sm, or from Lo to Ll, without affecting the algorithm results. Moreover, even if such changes were to result, the BackwardCompatible list (Section 6.7) can be adjusted to ensure the stability of the results. ### OPEN ISSUE: How to handle a backward compatible list on the level of PRECIS string classes or sub-classes. ### Some code points need to be allowed in exceptional circumstances, but should be excluded in all other cases; these rules are also described in other documents. The most notable of these are the Join Control characters, U+200D ZERO WIDTH JOINER and U+200C ZERO WIDTH NON- JOINER. Both of them have the derived property value CONTEXTJ. A character with the derived property value CONTEXTJ or CONTEXTO (CONTEXTUAL RULE REQUIRED) is not to be used unless an appropriate rule has been established and the context of the character is consistent with that rule. It is invalid to generate a string containing these characters unless such a contextual rule is found and satisfied. Please see Appendix A of [RFC5892] for more information. 6. Category Definitions Used to Calculate Derived Property Value The derived property obtains its value based on a two-step procedure: 1. Characters are placed in one or more character categories based on either core properties defined by the Unicode Standard or by treating the code point as an exception and addressing the code point by its code point value. These categories are not mutually exclusive. 2. Set operations are used with these categories to determine the values for an string class specific property. These operations are specified under Section 7. (NOTE: Unicode property names and property value names might have short abbreviations, such as gc for the General_Category property, Blanchet & Saint-Andre Expires November 18, 2011 [Page 13]
Internet-Draft PRECIS Framework May 2011 and Ll for the Lowercase_Letter property value of the gc property.) In the following specification of categories, the operation which returns the value of a particular Unicode character property for a code point is designated by using the formal name of that property (from PropertyAliases.txt) followed by '(cp)'. For example, the value of the General_Category property for a code point is indicated by General_Category(cp). The first ten categories (A-J) shown below were previously defined for IDNA2008 and are copied directly from [RFC5892]. Some of these categories are re-used in PRECIS and some of them are not; however, the lettering of categories is retained to prevent overlap and to ease implementation of both IDNA2008 and PRECIS in a single software application. The next seven categories (K-Q) are specific to PRECIS. 6.1. LetterDigits (A) NOTE: This category is defined in [RFC5892] and copied here for use in PRECIS. A: General_Category(cp) is in {Ll, Lu, Lo, Nd, Lm, Mn, Mc} These rules identify characters commonly used in mnemonics and often informally described as "language characters". For more information, see section 4.5 of [UNICODE]. The categories used in this rule are: o Ll - Lowercase_Letter o Lu - Uppercase_Letter o Lo - Other_Letter o Nd - Decimal_Number o Lm - Modifier_Letter o Mn - Nonspacing_Mark o Mc - Spacing_Mark 6.2. Unstable (B) NOTE: This category is defined in [RFC5892] but not used in PRECIS. 6.3. IgnorableProperties (C) NOTE: This category is defined in [RFC5892] but not used in PRECIS. See the "PrecisIgnorableProperties (M)" category below for a more inclusive category used in non-IDN identifiers. Blanchet & Saint-Andre Expires November 18, 2011 [Page 14]
Internet-Draft PRECIS Framework May 2011 6.4. IgnorableBlocks (D) NOTE: This category is defined in [RFC5892] but not used in PRECIS. 6.5. LDH (E) NOTE: This category is defined in [RFC5892] but not used in PRECIS. See the "ASCII7 (K)" category below for a more inclusive category used in non-IDN identifiers. 6.6. Exceptions (F) NOTE: This category is defined in [RFC5892] and might be used in a future version of this specification. F: cp is in {00B7, 00DF, 0375, 03C2, 05F3, 05F4, 0640, 0660, 0661, 0662, 0663, 0664, 0665, 0666, 0667, 0668, 0669, 06F0, 06F1, 06F2, 06F3, 06F4, 06F5, 06F6, 06F7, 06F8, 06F9, 06FD, 06FE, 07FA, 0F0B, 3007, 302E, 302F, 3031, 3032, 3033, 3034, 3035, 303B, 30FB} This category explicitly lists code points for which the category cannot be assigned using only the core property values that exist in the Unicode standard. The values are according to the table below: PVALID -- Would otherwise have been DISALLOWED 00DF; PVALID # LATIN SMALL LETTER SHARP S 03C2; PVALID # GREEK SMALL LETTER FINAL SIGMA 06FD; PVALID # ARABIC SIGN SINDHI AMPERSAND 06FE; PVALID # ARABIC SIGN SINDHI POSTPOSITION MEN 0F0B; PVALID # TIBETAN MARK INTERSYLLABIC TSHEG 3007; PVALID # IDEOGRAPHIC NUMBER ZERO CONTEXTO -- Would otherwise have been DISALLOWED 00B7; CONTEXTO # MIDDLE DOT 0375; CONTEXTO # GREEK LOWER NUMERAL SIGN (KERAIA) 05F3; CONTEXTO # HEBREW PUNCTUATION GERESH 05F4; CONTEXTO # HEBREW PUNCTUATION GERSHAYIM 30FB; CONTEXTO # KATAKANA MIDDLE DOT CONTEXTO -- Would otherwise have been PVALID 0660; CONTEXTO # ARABIC-INDIC DIGIT ZERO 0661; CONTEXTO # ARABIC-INDIC DIGIT ONE 0662; CONTEXTO # ARABIC-INDIC DIGIT TWO Blanchet & Saint-Andre Expires November 18, 2011 [Page 15]
Internet-Draft PRECIS Framework May 2011 0663; CONTEXTO # ARABIC-INDIC DIGIT THREE 0664; CONTEXTO # ARABIC-INDIC DIGIT FOUR 0665; CONTEXTO # ARABIC-INDIC DIGIT FIVE 0666; CONTEXTO # ARABIC-INDIC DIGIT SIX 0667; CONTEXTO # ARABIC-INDIC DIGIT SEVEN 0668; CONTEXTO # ARABIC-INDIC DIGIT EIGHT 0669; CONTEXTO # ARABIC-INDIC DIGIT NINE 06F0; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT ZERO 06F1; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT ONE 06F2; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT TWO 06F3; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT THREE 06F4; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT FOUR 06F5; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT FIVE 06F6; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT SIX 06F7; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT SEVEN 06F8; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT EIGHT 06F9; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT NINE DISALLOWED -- Would otherwise have been PVALID 0640; DISALLOWED # ARABIC TATWEEL 07FA; DISALLOWED # NKO LAJANYALAN 302E; DISALLOWED # HANGUL SINGLE DOT TONE MARK 302F; DISALLOWED # HANGUL DOUBLE DOT TONE MARK 3031; DISALLOWED # VERTICAL KANA REPEAT MARK 3032; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK 3033; DISALLOWED # VERTICAL KANA REPEAT MARK UPPER HALF 3034; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK UPPER HA 3035; DISALLOWED # VERTICAL KANA REPEAT MARK LOWER HALF 303B; DISALLOWED # VERTICAL IDEOGRAPHIC ITERATION MARK 6.7. BackwardCompatible (G) NOTE: This category is defined in [RFC5892] and copied here for use in PRECIS. G: cp is in {} This category includes the code points that property values in versions of Unicode after 5.2 have changed in such a way that the derived property value would no longer be PVALID or DISALLOWED. If changes are made to future versions of Unicode so that code points might change property value from PVALID or DISALLOWED, then this table can be updated and keep special exception values so that the property values for code points stay stable. Blanchet & Saint-Andre Expires November 18, 2011 [Page 16]
Internet-Draft PRECIS Framework May 2011 6.8. JoinControl (H) NOTE: This category is defined in [RFC5892] and copied here for use in PRECIS. H: Join_Control(cp) = True This category consists of Join Control characters (i.e., they are not in LetterDigits (Section 6.1)) but are still required in strings under some circumstances. 6.9. OldHangulJamo (I) NOTE: This category is defined in [RFC5892] and copied here for use in PRECIS. I: Hangul_Syllable_Type(cp) is in {L, V, T} This category consists of all conjoining Hangul Jamo (Leading Jamo, Vowel Jamo, and Trailing Jamo). Elimination of conjoining Hangul Jamos from the set of PVALID characters results in restricting the set of Korean PVALID characters just to preformed, modern Hangul syllable characters. Old Hangul syllables, which must be spelled with sequences of conjoining Hangul Jamos, are not PVALID for string classes. 6.10. Unassigned (J) NOTE: This category is defined in [RFC5892] and copied here for use in PRECIS. J: General_Category(cp) is in {Cn} and Noncharacter_Code_Point(cp) = False This category consists of code points in the Unicode character set that are not (yet) assigned. It should be noted that Unicode distinguishes between 'unassigned code points' and 'unassigned characters'. The unassigned code points are all but (Cn - Noncharacters), while the unassigned *characters* are all but (Cn + Cs). 6.11. ASCII7 (K) This category exempts most "ASCII7" characters from other rules that might be applied during PRECIS processing, on the assumption that these code points are in such wide use that disallowing them would be counter-productive. Blanchet & Saint-Andre Expires November 18, 2011 [Page 17]
Internet-Draft PRECIS Framework May 2011 K: cp is in {0021..007E} 6.12. Controls (L) L: Control(cp) = True 6.13. PrecisIgnorableProperties (M) This category is used to group code points that are not recommended for use in PRECIS string classes. M: Default_Ignorable_Code_Point(cp) = True or Noncharacter_Code_Point(cp) = True The definition for Default_Ignorable_Code_Point can be found in DerivedCoreProperties.txt [1] and at the time of Unicode 6.0 is as follows: Other_Default_Ignorable_Code_Point + Cf (Format characters) + Variation_Selector - White_Space - FFF9..FFFB (Annotation Characters) - 0600..0603, 06DD, 070F (exceptional Cf characters that should be visible) 6.14. Spaces (N) This category is used to group code points that are space characters. N: General_Category(cp) is in {Zs} 6.15. Symbols (O) This category is used to group code points that are symbols. O: General_Category(cp) is in {Sc} 6.16. Punctuation (P) This category is used to group code points that are punctuation marks. P: General_Category(cp) is in {Pi} Blanchet & Saint-Andre Expires November 18, 2011 [Page 18]
Internet-Draft PRECIS Framework May 2011 6.17. HasCompat (Q) This category is used to group code points that have compatibility equivalents as explained in Chapter 2 and Chapter 3 of [UNICODE]. Q: toNFKC(cp) != cp The toNFKC() operation returns the code point in normalization form KC. For more information, see Section 5 of [UAX15]. 7. Calculation of the Derived Property Possible values of the derived property are: o PVALID o NAMEY_VALID o WORDY_VALID o STRINGY_VALID o CONTEXTJ o CONTEXTO o DISALLOWED o NAMEY_DISALLOWED o WORDY_DISALLOWED o STRINGY_DISALLOWED o UNASSIGNED In some instances, the value of the derived property calculated depends on the string class. The algorithm to calculate the value of the derived property is as follows. (NOTE: If the name of a rule (such as Exception) is used, that implies the set of code points that the rule define, while the same name as a function call (such as Exception(cp)) imply the value cp has in the Exceptions table.) Blanchet & Saint-Andre Expires November 18, 2011 [Page 19]
Internet-Draft PRECIS Framework May 2011 If .cp. .in. Exceptions Then Exceptions(cp); Else If .cp. .in. BackwardCompatible Then BackwardCompatible(cp); Else If .cp. .in. Unassigned Then UNASSIGNED; Else If .cp. .in. ASCII7 Then PVALID; Else If .cp. .in. JoinControl Then CONTEXTJ; Else If .cp. .in. PrecisIgnorableProperties Then DISALLOWED; Else If .cp. .in. Controls Then DISALLOWED; Else If .cp. .in. OldHangulJamo Then DISALLOWED; Else If .cp. .in. LetterDigits Then PVALID; Else If .cp. .in. Spaces Then NAMEY_DISALLOWED or WORDY_DISALLOWED or STRINGY_VALID; Else If .cp. .in. Symbols Then NAMEY_DISALLOWED or WORDY_DISALLOWED or STRINGY_VALID; Else If .cp. .in. Punctuation Then NAMEY_DISALLOWED or WORDY_DISALLOWED or STRINGY_VALID; Else If .cp. .in. HasCompat Then NAMEY_DISALLOWED or WORDY_VALID or STRINGY_VALID; Else DISALLOWED; 8. Code Points The Categories and Rules defined in Section 6 and Section 7 apply to all Unicode code points. The table in Section 12 shows, for illustrative purposes, the consequences of the categories and classification rules, and the resulting property values. The list of code points that can be found in Section 12 is non- normative. Section 6 and Section 7 are normative. 9. IANA Considerations 9.1. PRECIS Derived Property Value Registry IANA is to create a PRECIS-specific registry with the Derived Properties for the versions of Unicode that are released after (and including) version 6.0. The derived property value is to be calculated in cooperation with a designated expert [RFC5226] according to the specifications in Section 6 and Section 7, and not by copying the non-normative table found in Section 12. If during this process (creation of the table of derived property values) followed by a designated expert review, either non-backward Blanchet & Saint-Andre Expires November 18, 2011 [Page 20]
Internet-Draft PRECIS Framework May 2011 compatible changes to the table of derived properties are discovered, or otherwise problems during the creation of the table arises, that is to be flagged to the IESG. Changes to the rules (as specified in Section 6 and Section 7) require IETF Review, as described in [RFC5226]. 9.2. PRECIS Contextual Rules Registry For characters that are defined in the IDNA derived property value registry as CONTEXTO or CONTEXTJ and that therefore require a contextual rule, IANA will create and maintain a list of approved contextual rules. Additions or changes to these rules require IETF Review, as described in [RFC5226]. Appendix A (TBD) contains further discussion and a table from which that registry can be initialized. 10. Security Considerations This section has yet to be defined. However, the security considerations provided in [RFC5890] provide a good starting point. 11. Acknowledgements The authors would like to acknowledge the comments and contributions of the following people: David Black, Mark Davis, Alan DeKok, Martin Duerst, Patrik Faltstrom, Ted Hardie, Joe Hildebrand, Paul Hoffman, Jeffrey Hutzelman, Simon Josefsson, John Klensin, Alexey Melnikov, Pete Resnick, Andrew Sullivan, and Dave Thaler. Some algorithms and textual descriptions have been borrowed from [RFC5892]. 12. Codepoints 0x0000 - 0x10FFFF If one applies the rules (Section 7) to the code points 0x0000 to 0x10FFFF to Unicode 6.0, the result is as follows. NOTE: This list is non-normative, and only included for illustrative purposes. Specifically, what is displayed in the third column is not the formal name of the code point (as defined in [UNICODE]). The differences exists for example for the code points that have the code point value as part of the name (example: CJK UNIFIED IDEOGRAPH-4E00) and the naming of Hangul syllables. For many code points, what you see is the official name. Blanchet & Saint-Andre Expires November 18, 2011 [Page 21]
Internet-Draft PRECIS Framework May 2011 12.1. Codepoints in Unicode Character Database (UCD) format 0000..10FFFF; TBD! 13. References 13.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network Interchange", RFC 5198, March 2008. [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 6.0", 2010, <http://www.unicode.org/versions/Unicode6.0.0/>. 13.2. Informative References [I18N-TERMS] Hoffman, P. and J. Klensin, "Terminology Used in Internationalization in the IETF", draft-hoffman-rfc3536bis-02 (work in progress), April 2011. [PROBLEM] Blanchet, M. and A. Sullivan, "Stringprep Revision Problem Statement", draft-ietf-precis-problem-statement-02 (work in progress), March 2011. [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("stringprep")", RFC 3454, December 2002. [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003. [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and Recommendations for Internationalized Domain Names (IDNs)", RFC 4690, September 2006. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, Blanchet & Saint-Andre Expires November 18, 2011 [Page 22]
Internet-Draft PRECIS Framework May 2011 May 2008. [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, August 2010. [RFC5891] Klensin, J., "Internationalized Domain Names in Applications (IDNA): Protocol", RFC 5891, August 2010. [RFC5892] Faltstrom, P., "The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)", RFC 5892, August 2010. [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for Internationalized Domain Names for Applications (IDNA)", RFC 5893, August 2010. [RFC5894] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Background, Explanation, and Rationale", RFC 5894, August 2010. [RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008", RFC 5895, September 2010. [UAX15] The Unicode Consortium, "Unicode Standard Annex #15: Unicode Normalization Forms", September 2010, <http://unicode.org/reports/tr15/>. [UAX9] The Unicode Consortium, "Unicode Standard Annex #9: Unicode Bidirectional Algorithm", September 2010, <http://unicode.org/reports/tr9/>. URIs [1] <http://unicode.org/Public/UNIDATA/DerivedCoreProperties.txt> Blanchet & Saint-Andre Expires November 18, 2011 [Page 23]
Internet-Draft PRECIS Framework May 2011 Authors' Addresses Marc Blanchet Viagenie 2600 boul. Laurier, suite 625 Quebec, QC G1V 4W1 Canada Email: Marc.Blanchet@viagenie.ca URI: http://www.viagenie.ca Peter Saint-Andre Cisco 1899 Wyknoop Street, Suite 600 Denver, CO 80202 USA Phone: +1-303-308-3282 Email: psaintan@cisco.com Blanchet & Saint-Andre Expires November 18, 2011 [Page 24]