Network Working Group P. Saint-Andre Internet-Draft Cisco Systems, Inc. Obsoletes: 3454 (if approved) M. Blanchet Intended status: Standards Track Viagenie Expires: September 13, 2012 March 12, 2012 PRECIS Framework: Handling Internationalized Strings in Protocols draft-ietf-precis-framework-02 Abstract Application protocols using 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). This document defines a framework enabling application protocols to use various classes of strings in a way that depends on the properties of Unicode code points. A specification using this framework can either directly use the base string classes or can subclass the base string classes as needed. This framework uses an approach similar to 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 application technologies other than the Domain Name System (DNS). This document obsoletes the previous framework, named Stringprep, as defined in 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 September 13, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. Saint-Andre & Blanchet Expires September 13, 2012 [Page 1] Internet-Draft PRECIS Framework March 2012 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. String Classes . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. NameClass . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1.2. Disallowed . . . . . . . . . . . . . . . . . . . . . . 7 3.1.3. Unassigned . . . . . . . . . . . . . . . . . . . . . . 7 3.1.4. Directionality . . . . . . . . . . . . . . . . . . . . 7 3.1.5. Case Mapping . . . . . . . . . . . . . . . . . . . . . 7 3.1.6. Normalization . . . . . . . . . . . . . . . . . . . . 7 3.2. FreeClass . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. Disallowed . . . . . . . . . . . . . . . . . . . . . . 8 3.2.3. Unassigned . . . . . . . . . . . . . . . . . . . . . . 8 3.2.4. Directionality . . . . . . . . . . . . . . . . . . . . 8 3.2.5. Case Mapping . . . . . . . . . . . . . . . . . . . . . 9 3.2.6. Normalization . . . . . . . . . . . . . . . . . . . . 9 4. Use of PRECIS String Classes . . . . . . . . . . . . . . . . . 9 4.1. Principles . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2. Subclassing . . . . . . . . . . . . . . . . . . . . . . . 10 4.3. Registration . . . . . . . . . . . . . . . . . . . . . . . 10 5. Code Point Properties . . . . . . . . . . . . . . . . . . . . 10 6. Category Definitions Used to Calculate Derived Property Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . . 13 6.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . . 13 6.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 13 6.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 13 6.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . . 13 6.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . . 15 6.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 15 6.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 16 6.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . . 16 6.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . . 16 Saint-Andre & Blanchet Expires September 13, 2012 [Page 2] Internet-Draft PRECIS Framework March 2012 6.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . . 16 6.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 17 6.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . . 17 6.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 17 6.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 17 6.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 17 7. Calculation of the Derived Property . . . . . . . . . . . . . 18 8. Code Points . . . . . . . . . . . . . . . . . . . . . . . . . 19 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 9.1. PRECIS Derived Property Value Registry . . . . . . . . . . 19 9.2. PRECIS Usage Registry . . . . . . . . . . . . . . . . . . 19 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 10.1. General Issues . . . . . . . . . . . . . . . . . . . . . . 20 10.2. Local Character Set Issues . . . . . . . . . . . . . . . . 20 10.3. Visually Similar Characters . . . . . . . . . . . . . . . 20 10.4. Security of Passwords and Passphrases . . . . . . . . . . 22 11. Interoperability Considerations . . . . . . . . . . . . . . . 23 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 12.1. Normative References . . . . . . . . . . . . . . . . . . . 23 12.2. Informative References . . . . . . . . . . . . . . . . . . 24 Appendix A. Codepoints 0x0000 - 0x10FFFF . . . . . . . . . . . . 26 A.1. Codepoints in Unicode Character Database (UCD) format . . 26 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 Saint-Andre & Blanchet Expires September 13, 2012 [Page 3] Internet-Draft PRECIS Framework March 2012 1. Introduction As described in [I-D.ietf-precis-problem-statement], many IETF protocols use the Stringprep [RFC3454] framework as the basis for preparing and comparing protocol strings that contain Unicode code points [UNICODE]. The Stringprep framework was defined during work on the original technology for internationalized domain names (IDNs), IDNA2003 [RFC3490], as a way to enable other protocols to use the same or similar method by defining a Stringprep profile to prepare and compare strings and identifiers in these protocols. Nameprep [RFC3491] was such a profile for the IDN case. Since then, issues were documented [RFC4690] related to the IDN and Nameprep cases. The new IDN specifications, named IDNA2008 ([RFC5890], [RFC5891], [RFC5892], [RFC5893], [RFC5894]), do not use Stringprep and Nameprep anymore. 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 [I-D.ietf-precis-problem-statement]. This document defines 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 and free-form strings. 2. Define each base string class in terms of Unicode code points and their properties, specifying whether each code point or character category is valid, disallowed, or unassigned. 3. Enable application protocols to subclass the base string classes, mainly to disallow particular code points that are currently disallowed in the relevant application protocol (e.g., characters with special or reserved meaning, such as "@" and "/" when used as separators within identifiers). 4. Leave various mapping operations (e.g., case preservation or lowercasing, Unicode normalization, right-to-left characters) as the responsibility of application protocols, as was done for IDNA2008 via [RFC5895]. It is expected that this framework will yield the following benefits: Saint-Andre & Blanchet Expires September 13, 2012 [Page 4] Internet-Draft PRECIS Framework March 2012 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 software libraries. o End users will be able to acquire 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 application protocols will be more predictable and coherent. Although this framework is similar to IDNA2008 and borrows some of the character categories defined in [RFC5892], it defines additional string classes and character categories to meet the needs of common application protocols. 2. Terminology Many important terms used in this document are defined in [I-D.ietf-precis-problem-statement], [RFC6365], [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 define a string class for domain names, and application protocols are strongly encouraged to use IDNA2008 as the appropriate method to prepare domain names and hostnames.) We propose the following additional base string classes for use in application protocols: NameClass: a sequence of letters, numbers, and symbols that is used to identify or address a network entity such as a user account, a venue (e.g., a chatroom), an information source (e.g., a data feed), or a collection of data (e.g., a file). Saint-Andre & Blanchet Expires September 13, 2012 [Page 5] Internet-Draft PRECIS Framework March 2012 FreeClass: a sequence of letters, numbers, symbols, spaces, and other code points that is used for free-form strings, including passwords and passphrases as well as display elements such as a human-friendly nickname in a chatroom. The following subsections discuss these string classes in more detail, with reference to the dimensions described in Section 3 of [I-D.ietf-precis-problem-statement]. Each string class is defined by the following behavioral rules: Valid: defines which code points and character categories are treated as valid input to preparation of the string. Disallowed: defines which code points and character 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 (instead of case preservation), 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 9.2. 3.1. NameClass Most application technologies need a special class of strings that can be used to refer to, include, or communicate things like usernames, file names, data feed names, and chatroom names. We group such things into a bucket called "NameClass" having the following features. 3.1.1. Valid Saint-Andre & Blanchet Expires September 13, 2012 [Page 6] Internet-Draft PRECIS Framework March 2012 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 Ignorable characters, i.e., the PrecisIgnorableProperties ("M") category defined under Section 6.13. 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. 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 the NameClass. 3.1.4. Directionality The directionality rule MUST be specified by each application protocol that uses or subclasses the NameClass. 3.1.5. Case Mapping The casemapping rule MUST be specified by each application protocol that uses or subclasses the NameClass. 3.1.6. Normalization The normalization form MUST be specified by each application protocol that uses or subclasses the NameClass. However, in accordance with [RFC5198], normalization form C (NFC) is RECOMMENDED. Saint-Andre & Blanchet Expires September 13, 2012 [Page 7] Internet-Draft PRECIS Framework March 2012 3.2. FreeClass Some application technologies need a special class of strings that can be used in a free-form way, e.g., as a passphrase in an authentication exchange (see [I-D.melnikov-precis-saslprepbis] or a nickname in a chatroom (see [I-D.saintandre-precis-nickname]). We group such things into a bucket called "FreeClass" having the following features. NOTE: Consult Section 10.4 for relevant security considerations when strings conforming to the FreeClass, or a subclass thereof, are used as passwords or passphrases. 3.2.1. 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. 3.2.2. Disallowed o Control characters, i.e., the Controls ("L") category defined under Section 6.12. o Ignorable characters, i.e., the PrecisIgnorableProperties ("M") category defined under Section 6.13. 3.2.3. Unassigned Any code points that are not yet assigned in the Unicode character set SHALL be considered Unassigned for purposes of the FreeClass. 3.2.4. Directionality The directionality rule MUST be specified by each application protocol that uses or subclasses the FreeClass. Saint-Andre & Blanchet Expires September 13, 2012 [Page 8] Internet-Draft PRECIS Framework March 2012 3.2.5. Case Mapping The casemapping rule MUST be specified by each application protocol that uses or subclasses the FreeClass. In general, case preservation is NOT RECOMMENDED for application protocols that perform case-insensitive comparison of internationalized strings; instead, application protocols SHOULD either (a) not preserve case but perform case-insensitive matching or (b) preserve case but perform case-sensitive comparison. In order to maximize entropy, it is NOT RECOMMENDED for application protocols to map uppercase and titlecase code points to their lowercase equivalents when strings conforming to the FreeClass, or a subclass thereof, are used in passwords or passphrases; instead, it is RECOMMENDED to preserve the case of all code points contained in such strings. 3.2.6. Normalization The normalization form MUST be specified by each application protocol that uses or subclasses the FreeClass. However, in accordance with [RFC5198], normalization form C (NFC) is RECOMMENDED. 4. Use 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 some other 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. Saint-Andre & Blanchet Expires September 13, 2012 [Page 9] Internet-Draft PRECIS Framework March 2012 Normalization: Which Unicode normalization form (D, KD, C, or KC) is to be applied (see [UAX15] for background information); in accordance with [RFC5198], NFC is RECOMMENDED. 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 character 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. Registration Application protocols that use the PRECIS string classes MUST register with the IANA as described under Section 9.2. This is especially important for protocols that subclass the PRECIS string classes. 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 code point properties. 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. 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. Saint-Andre & Blanchet Expires September 13, 2012 [Page 10] Internet-Draft PRECIS Framework March 2012 PROTOCOL VALID Those code points that are allowed to be used in any PRECIS string class (NameClass and FreeClass). 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 remainder of this document. SPECIFIC CLASS PROTOCOL VALID Those code points 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 remainder of this document, the abbreviated term *_PVAL is used, where * = (NAME | FREE), i.e., either FREE_PVAL or NAME_PVAL. CONTEXTUAL RULE REQUIRED Some characteristics of the character, such as its being invisible in certain contexts or problematic in others, require 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 remainder 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). DISALLOWED Those code points that must not be included in any string class. Code points with this property value are not permitted in any string class. SPECIFIC CLASS DISALLOWED Those code points 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 in others. In the remainder of this document, the abbreviated term *_DIS is used, where * = (NAME | FREE), i.e., either FREE_DIS or NAME_DIS. 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 6.1 depending on the category, since some categories in this document are reused from IDNA2008 and therefore were defined at the time of Unicode 5.2). 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. Saint-Andre & Blanchet Expires September 13, 2012 [Page 11] Internet-Draft PRECIS Framework March 2012 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. PRECIS does not define its own contextual rules, but instead re-uses the contextual rules defined for IDNA2008; 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 either (1) based on core properties defined by the Unicode Standard or (2) by treating the code point as an exception and addressing the code point as its code point value. These categories are not mutually exclusive. 2. Set operations are used with these categories to determine the values for a property that is specific to a given string class. 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 and "Ll" for the Lowercase_Letter property value of the gc property.) In the following specification of character categories, the operation that returns the value of a particular Unicode character property for a code point is designated by using the formal name of that property (from the Unicode PropertyAliases.txt [1]) followed by '(cp)' for "code point". 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 reused 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. Saint-Andre & Blanchet Expires September 13, 2012 [Page 12] Internet-Draft PRECIS Framework March 2012 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 PRECIS identifiers. 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 PRECIS identifiers. 6.6. Exceptions (F) NOTE: This category is defined in [RFC5892] and might be used in a future version of this specification. Saint-Andre & Blanchet Expires September 13, 2012 [Page 13] Internet-Draft PRECIS Framework March 2012 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 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 Saint-Andre & Blanchet Expires September 13, 2012 [Page 14] Internet-Draft PRECIS Framework March 2012 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. Because of how the PRECIS string classes are defined, only changes that would result in code points being added to or removed from the LetterDigits ("A") category would result in backward-incompatible modifications to code point assignments. Therefore, management of this category is handled via the processes specified in [RFC5892]. G: cp is in {} This category includes the code points for which 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. 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. Saint-Andre & Blanchet Expires September 13, 2012 [Page 15] Internet-Draft PRECIS Framework March 2012 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 PRECIS-specific category exempts most characters in the ASCII-7 range 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. K: cp is in {0021..007E} 6.12. Controls (L) L: Control(cp) = True Saint-Andre & Blanchet Expires September 13, 2012 [Page 16] Internet-Draft PRECIS Framework March 2012 6.13. PrecisIgnorableProperties (M) This PRECIS-specific 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 the DerivedCoreProperties.txt [2] file, and at the time of Unicode 6.1 is as follows: Other_Default_Ignorable_Code_Point + Cf (Format characters) + Variation_Selector - White_Space - FFF9..FFFB (Annotation Characters) - 0600..0604, 06DD, 070F, 110BD (exceptional Cf characters that should be visible) 6.14. Spaces (N) This PRECIS-specific category is used to group code points that are space characters. N: General_Category(cp) is in {Zs} 6.15. Symbols (O) This PRECIS-specific category is used to group code points that are symbols. O: General_Category(cp) is in {Sm, Sc, Sk, So} 6.16. Punctuation (P) This PRECIS-specific category is used to group code points that are punctuation characters. P: General_Category(cp) is in {Pc, Pd, Ps, Pe, Pi, Pf, Po} 6.17. HasCompat (Q) This PRECIS-specific 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 Saint-Andre & Blanchet Expires September 13, 2012 [Page 17] Internet-Draft PRECIS Framework March 2012 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 NAME_PVAL o FREE_PVAL o CONTEXTJ o CONTEXTO o DISALLOWED o NAME_DIS o FREE_DIS o UNASSIGNED NOTE: In some instances, the value of the derived property calculated depends on the string class (e.g., if an identifier used in an application protocol is defined as using or subclassing the PRECIS NameClass, then a space character would be assigned to NAME_DIS). The algorithm to calculate the value of the derived property is as follows. (NOTE: Use of the name of a rule (such as "Exception") implies the set of code points that the rule defines, whereas the same name as a function call (such as "Exception(cp)") implies the value that the code point has in the Exceptions table.) 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 NAME_DIS or FREE_PVAL; Else If .cp. .in. Symbols Then NAME_DIS or FREE_PVAL; Else If .cp. .in. Punctuation Then NAME_DIS or FREE_PVAL; Else If .cp. .in. HasCompat Then NAME_DIS or FREE_PVAL; Else DISALLOWED; Saint-Andre & Blanchet Expires September 13, 2012 [Page 18] Internet-Draft PRECIS Framework March 2012 8. Code Points The Categories and Rules defined in Section 6 and Section 7 apply to all Unicode code points. The table in Appendix A 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 Appendix A is non- normative. Instead, the rules defined by Section 6 and Section 7 are normative, and any tables are derived from the rules. 9. IANA Considerations 9.1. PRECIS Derived Property Value Registry IANA is requested to create a PRECIS-specific registry with the Derived Properties for the versions of Unicode that are released after (and including) version 6.1. 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 Appendix A. If during this process (creation of the table of derived property values) followed by a designated expert review, either backward- incompatible changes to the table of derived properties are discovered, or otherwise problems arise during the creation of the table, 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 Usage Registry IANA is requested to create a registry of application protocols that use the base string classes. The registry will include one entry for each use (e.g., if a protocol uses both the NameClass and the FreeClass then the specification for that protocol would submit two registrations). In accordance with [RFC5226], the registration policy is "First Come First Served". The registration template is as follows: Application Protocol: [the application protocol that is using or subclassing the PRECIS string class] Saint-Andre & Blanchet Expires September 13, 2012 [Page 19] Internet-Draft PRECIS Framework March 2012 Base Class: [which base class is being used] Subclassing: [whether the base class is being subclassed and, if so, where documentation of the subclassing can be found] 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] Specification: [a pointer to relevant documentation, such as an RFC or Internet-Draft] 10. Security Considerations 10.1. General Issues The security of applications that use this framework can depend in part on the proper preparation and comparison of internationalized strings. For example, such strings can be used to make authentication and authorization decisions, and the security of an application could be compromised if an entity providing a given string is connected to the wrong account or online resource based on different interpretations of the string. Specifications of application protocols that use this framework are encouraged to describe how internationalized strings are used in the protocol, including the security implications of any false positives and false negatives that might result from various comparison operations. For some helpful guidelines, refer to [I-D.iab-identifier-comparison], [RFC5890], [UTR36], and [UTR39]. 10.2. Local Character Set Issues When systems use local character sets other than ASCII and Unicode, these specifications leave the problem of converting between the local character set and Unicode up to the application or local system. If different applications (or different versions of one application) implement different rules for conversions among coded character sets, they could interpret the same name differently and contact different application servers or other network entities. This problem is not solved by security protocols, such as Transport Layer Security (TLS) [RFC5246] and the Simple Authentication and Security Layer (SASL) [RFC4422], that do not take local character sets into account. 10.3. Visually Similar Characters Some characters are visually similar and thus can cause confusion among humans. Such characters are often called "confusable Saint-Andre & Blanchet Expires September 13, 2012 [Page 20] Internet-Draft PRECIS Framework March 2012 characters" or "confusables". The problem of confusable characters is not necessarily caused by the use of Unicode code points outside the US-ASCII range. For example, in some presentations and to some individuals the string "ju1iet" (spelled with the Arabic numeral one as the third character) might appear to be the same as "juliet" (spelled with the lowercase version of the letter "L"), especially on casual visual inspection. This phenomenon is sometimes called "typejacking". However, the problem is made more serious by introducing the full range of Unicode code points into protocol strings. For example, the characters U+13DA U+13A2 U+13B5 U+13AC U+13A2 U+13AC U+13D2 from the Cherokee block look similar to the US-ASCII characters "STPETER" as they might look when presented in a "creative" font. In some examples of confusable characters, it is unlikely that the average human could tell the difference between the real string and the fake string. (Indeed, there is no programmatic way to distinguish with full certainty which is the fake string and which is the real string; in some contexts, the string formed of Cherokee characters might be the real string and the string formed of US-ASCII characters might be the fake string.) Because PRECIS-compliant strings can contain almost any properly encoded Unicode code point, it can be relatively easy to fake or mimic some strings in systems that use the PRECIS framework. The fact that some strings are easily confused introduces security vulnerabilities of the kind that have also plagued the World Wide Web, specifically the phenomenon known as phishing. Despite the fact that some specific suggestions about identification and handling of confusable characters appear in the Unicode Security Considerations [UTR36], it is also true (as noted in [RFC5890]) that "there are no comprehensive technical solutions to the problems of confusable characters". Because it is impossible to map visually similar characters without a great deal of context (such as knowing the fonts used), the PRECIS framework does nothing to map similar- looking characters together, nor does it prohibit some characters because they look like others. However, specifications for application protocols that use this framework MUST describe how confusable characters can be used to compromise the security of systems that use the protocol in question, and any protocol-specific suggestions for overcoming those threats. In particular, software implementations and service deployments that use PRECIS-based technologies are strongly encouraged to define and implement consistent policies regarding the registration, storage, and presentation of visually similar characters. The following Saint-Andre & Blanchet Expires September 13, 2012 [Page 21] Internet-Draft PRECIS Framework March 2012 recommendations are appropriate: 1. An application service SHOULD define a policy that specifies the scripts or blocks of characters that the service will allow to be registered (e.g., in an account name) or stored (e.g., in a file name). Such a policy SHOULD be informed by the languages and scripts that are used to write registered account names; in particular, to reduce confusion, the service SHOULD forbid registration or storage of stings that contain characters from more than one script and to restrict registrations to characters drawn from a very small number of scripts (e.g., scripts that are well-understood by the administrators of the service, to improve manageability). 2. User-oriented application software SHOULD define a policy that specifies how internationalized strings will be presented to a human user. Because every human user of such software has a preferred language or a small set of preferred languages, the software SHOULD gather that information either explicitly from the user or implicitly via the operating system of the user's device. Furthermore, because most languages are typically represented by a single script or a small set of scripts, and because and most scripts are typically contained in one or more blocks of characters, the software SHOULD warn the user when presenting a string that mixes characters from more than one script or block, or that uses characters outside the normal range of the user's preferred language(s). (Such a recommendation is not intended to discourage communication across different communities of language users; instead, it recognizes the existence of such communities and encourages due caution when presenting unfamiliar scripts or characters to human users.) 10.4. Security of Passwords and Passphrases One goal of passwords and passphrases is to maximize the amount of entropy, for example by allowing a wide range of code points and by ensuring that secrets are not prepared in such a way that code points are compared aggressively. Therefore, it is NOT RECOMMENDED for application protocols to subclass the FreeClass for use in passwords and passphrases in a way that removes entire categories (e.g., by disallowing symbols or punctuation). Furthermore, it is NOT RECOMMENDED for application protocols to map uppercase and titlecase code points to their lowercase equivalents in such strings; instead, it is RECOMMENDED to preserve the case of all code points contained in such strings. That said, software implementers need to be aware that there exist tradeoffs between entropy and usability. For example, allowing a Saint-Andre & Blanchet Expires September 13, 2012 [Page 22] Internet-Draft PRECIS Framework March 2012 user to establish a password containing "uncommon" code points might make it difficult for the user to access an application when using an unfamiliar or constrained input device. Some application protocols use passwords and passphrases directly, whereas others reuse technologies that themselves process passwords (one example is the Simple Authentication and Security Layer [RFC4422]). Moreover, passwords are often carried by a sequence of protocols with backends authentication systems or data storage systems such as RADIUS [RFC2865] and LDAP [RFC4510]. Developers of application protocols are encouraged to look into reusing these profiles instead of defining new ones, so that end-user expectations about passwords are consistent no matter which application protocol is used. 11. Interoperability Considerations Although strings that are consumed in PRECIS-based application protocols are often encoded using UTF-8 [RFC3629], the exact encoding is a matter for the using protocol, not the PRECIS framework. It is known that some existing systems are unable to support the full Unicode character set, or even any characters outside the US-ASCII range. If two (or more) applications need to interoperate when exchanging data (e.g., for the purpose of authenticating a username or password), they will naturally need have in common at least one coded character set (as defined by [RFC6365]). Establishing such a baseline is a matter for the using protocol, not the PRECIS framework. 12. References 12.1. 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, . Saint-Andre & Blanchet Expires September 13, 2012 [Page 23] Internet-Draft PRECIS Framework March 2012 12.2. Informative References [I-D.iab-identifier-comparison] Thaler, D., "Issues in Identifier Comparison for Security Purposes", draft-iab-identifier-comparison-00 (work in progress), July 2011. [I-D.ietf-precis-problem-statement] Sullivan, A. and M. Blanchet, "Stringprep Revision Problem Statement", draft-ietf-precis-problem-statement-04 (work in progress), January 2012. [I-D.ietf-xmpp-6122bis] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Address Format", draft-ietf-xmpp-6122bis-00 (work in progress), November 2011. [I-D.melnikov-precis-saslprepbis] Melnikov, A. and P. Saint-Andre, "Username and Password Preparation Algorithms", draft-melnikov-precis-saslprepbis-00 (work in progress), March 2012. [I-D.saintandre-precis-nickname] Saint-Andre, P., "Preparation and Comparison of Nicknames", draft-saintandre-precis-nickname-00 (work in progress), March 2012. [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [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. [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)", RFC 3491, March 2003. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. Saint-Andre & Blanchet Expires September 13, 2012 [Page 24] Internet-Draft PRECIS Framework March 2012 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol (LDAP): Technical Specification Road Map", RFC 4510, 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, May 2008. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 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. [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in Internationalization in the IETF", BCP 166, RFC 6365, September 2011. [UAX15] The Unicode Consortium, "Unicode Standard Annex #15: Unicode Normalization Forms", September 2010, . Saint-Andre & Blanchet Expires September 13, 2012 [Page 25] Internet-Draft PRECIS Framework March 2012 [UAX9] The Unicode Consortium, "Unicode Standard Annex #9: Unicode Bidirectional Algorithm", September 2010, . [UTR36] The Unicode Consortium, "Unicode Technical Report #36: Unicode Security Considerations", August 2010, . [UTR39] The Unicode Consortium, "Unicode Technical Report #39: Unicode Security Mechanisms", August 2010, . URIs [1] [2] Appendix A. Codepoints 0x0000 - 0x10FFFF To follow. If one applies the rules (Section 7) to the code points 0x0000 to 0x10FFFF to Unicode 6.1, 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 necessarily the formal name of the code point (as defined in [UNICODE]). There are differences, for example with regard to 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. However, for many code points, what you see is the official name. A.1. Codepoints in Unicode Character Database (UCD) format In progress... 0000..001F ; DISALLOWED # 0020 ; FREE_PVAL, NAME_DIS # SPACE 0021..007E ; PVALID # EXCLAMATION MARK .. TILDE 007F..009F ; DISALLOWED # 00A0..00A9 ; FREE_PVAL, NAME_DIS # NO-BREAK SPACE .. COPYRIGHT SIGN 00AA ; PVALID # FEMININE ORDINAL INDICATOR 00AB..00AC ; FREE_PVAL, NAME_DIS # NO-BREAK SPACE .. NOT SIGN 00AD ; DISALLOWED # SOFT HYPHEN 00AE..00B6 ; FREE_PVAL, NAME_DIS # REGISTERED SIGN .. PILCROW SIGN Saint-Andre & Blanchet Expires September 13, 2012 [Page 26] Internet-Draft PRECIS Framework March 2012 00B7 ; CONTEXTO # MIDDLE DOT 00B8..00BF ; FREE_PVAL, NAME_DIS # CEDILLA..INVERTED QUESTION IND 00C0..00D6 ; PVALID # LAT CAP LET A W GRAV..LAT CAP O 00D7 ; FREE_PVAL, NAME_DIS # MULTIPLICATION SIGN 00D8..00F6 ; PVALID # LAT CAP LET O W STROKE..LAT SM 00F7 ; FREE_PVAL, NAME_DIS # DIVISION SIGN 00F8..0131 ; PVALID # LAT SM LET O W STROKE..LAT SM LET 0132..0133 ; FREE_PVAL, NAME_DIS # LAT CAP LIG IJ..LAT SM LIB IJ 0134..013E ; PVALID # LAT CAP LET J W CIRCUM..LAT SM LET 013F..0140 ; FREE_PVAL, NAME_DIS # LAT CAP LET L W MID DOT..LAT SM LET 0141..0148 ; PVALID # LAT CAP LET L W STROKE..LAT SM LET 0149 ; FREE_PVAL, NAME_DIS # LAT SM LET N PRECEDED BY APOSTROPHE 014A..017E ; PVALID # LAT CAP LET ENG..LAT SM LET Z W CA 017F ; FREE_PVAL, NAME_DIS # LATIN SMALL LETTER LONG S 0180..01C3 ; PVALID # LAT SM LET B W STROKE..LAT LET RETR 01C4..01CC ; FREE_PVAL, NAME_DIS # LAT CAP LET DZ W CARON..LATIN SM 01CD..01F0 ; PVALID # LAT CAP LET A W CARON..LAT SM LET J 01F1..01F3 ; FREE_PVAL, NAME_DIS # LAT CAP LET DZ..LAT SM LET DZ 01F4..02AF ; PVALID # LAT CAP LET G WITH ACUTE..LAT SM 02B0..02B8 ; FREE_PVAL, NAME_DIS # MOD LET SM H..MOD LET SM Y 02B9..02C1 ; PVALID # MOD LET PRIME..MOD LET REV GLOT ST 02C2..02C5 ; FREE_PVAL, NAME_DIS # MOD LET L ARROW..MOD LET D ARROW 02C6..02D1 ; PVALID # MOD LET CIRCUM ACC..MOD LET HALF TR 02D2..02EB ; FREE_PVAL, NAME_DIS # MOD LET CENT R HALF RING..MOD LET Y 02EC ; PVALID # MODIFIER LETTER VOICING 02ED ; FREE_PVAL, NAME_DIS # MODIFIER LETTER UNASPIRATED 02EE ; PVALID # MODIFIER LETTER DOUBLE APOSTROPHE 02EF..02FF ; FREE_PVAL, NAME_DIS # MOD LET LOW D ARR..MOD LET LOW L AR 0300..0374 ; PVALID # COMB GRAVE ACCENT..GREEK NUM SIGN 0375 ; CONTEXTO # GREEK LOWER NUMERAL SIGN 0376..0377 ; PVALID # GR CAP LET PAMPHYLIAN DIGAMMA..GR S 0378..0379 ; UNASSIGNED # .. 037A..037D ; PVALID # GR YPOGEGRAMMENI..GR SM REV DOT LUN 037E ; FREE_PVAL, NAME_DIS # GREEK QUESTION MARK 037F..0383 ; UNASSIGNED # .. 0384..0385 ; FREE_PVAL, NAME_DIS # GREEK TONOS..GREEK DIALYTIKA TONOS 0386 ; PVALID # GR CAP LET ALPHA WITH TONOS 0387 ; FREE_PVAL, NAME_DIS # GREEK ANO TELEIA 0388..038A ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP 038B ; UNASSIGNED # 038C ; PVALID # GR CAP LET OMICRON WITH TONOS 038D ; UNASSIGNED # 038E..03A1 ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP 03A2 ; UNASSIGNED # 03A3..03CF ; PVALID # GREEK CAPITAL LETTER SIGMA..GR CAP 03D0..03D2 ; FREE_PVAL, NAME_DIS # GR BETA SYMBOL..GR UPSILON W HOOK 03D3..03D4 ; PVALID # GR UPSILON W ACUTE AND HOOK..GR UP 03D5..03D6 ; FREE_PVAL, NAME_DIS # GR PHI SYMBOL..GR PI SYMBOL Saint-Andre & Blanchet Expires September 13, 2012 [Page 27] Internet-Draft PRECIS Framework March 2012 03D7..03EF ; PVALID # GR KAI SYMBOL..COPTIC SM LET DEI 03F0..03F2 ; FREE_PVAL, NAME_DIS # GR KAPPA SYMBOL..GR LUNATE SIGMA 03F3 ; PVALID # GREEK LETTER YOT 03F4..03F6 ; FREE_PVAL, NAME_DIS # GR CAP THETA..GR REV LUNATE EPSILON 03F7..03F8 ; PVALID # GR CAP LET SHO..GR SM LET SHO 03F9 ; FREE_PVAL, NAME_DIS # GREEK CAPITAL LUNATE SIGMA SYMBOL 03FA..0481 ; PVALID # GR CAP LET SAN..CYR SML LET KOPPA 0482 ; FREE_PVAL, NAME_DIS # CYRILLIC THOUSANDS SIGN 0483..0487 ; PVALID # COMB CYR TITLO..COMB CYRILLIC POK 0488..048A ; FREE_PVAL, NAME_DIS # COMB CYR HUNDRED THOUSANDS SIGN..C 048B..0527 ; PVALID # CYR SM LET SHORT I WITH TAIL..CYR S 0528..0530 ; UNASSIGNED # .. 0531..0556 ; PVALID # ARM CAP LET AYB..ARM CAP LET FEH 0557..0558 ; UNASSIGNED # .. 0559 ; PVALID # ARM MOD LET LEFT HALF RING 055A..055F ; FREE_PVAL, NAME_DIS # ARM APOS..ARM ABBREV 0560 ; UNASSIGNED # 0561..0586 ; PVALID # ARM SM LET AYB..ARMENIAN SMALL LE 0587 ; FREE_PVAL, NAME_DIS # ARM SM LIGATURE ECH YIWN 0588 ; UNASSIGNED # 0589..058A ; FREE_PVAL, NAME_DIS # ARMENIAN FULL STOP..ARMENIAN HYPHEN 058B..058E ; UNASSIGNED # .. 058F ; FREE_PVAL, NAME_DIS # ARMENIAN DRAM SIGN 0590 ; UNASSIGNED # 0591..05BD ; PVALID # HEBR ACC ETNAHTA..HEBR PNT ME 05BE ; FREE_PVAL, NAME_DIS # HEBR PUNCT MAQAF 05BF ; PVALID # HEBR PNT RAFE 05C0 ; FREE_PVAL, NAME_DIS # HEBR PUNCT PASEQ 05C1..05C2 ; PVALID # HEBR PNT SHIN DOT..HEBR PNT SIN DOT 05C3 ; FREE_PVAL, NAME_DIS # HEBR PUNCT SOF PASUQ 05C4..05C5 ; PVALID # HEBR MARK UP DOT..HEBR MARK LOW DOT 05C6 ; FREE_PVAL, NAME_DIS # HEBR PUNCT NUN HAFUKHA 05C7 ; PVALID # HEBR PNT QAMATS QATAN 05C8..05CF ; UNASSIGNED # .. 05D0..05EA ; PVALID # HEBR LET ALEF..HEBR LET TAV 05EB..05EF ; UNASSIGNED # .. 05F0..05F2 ; PVALID # HEBR LIG YIDDISH DOUBLE VAV..HEBR L 05F3..05F4 ; CONTEXTO # HEBR PUNCT GERESH..HEBR PUNCTUATIO 05F5..05FF ; UNASSIGNED # .. 0600..0604 ; DISALLOWED # ARABIC NUMBER SIGN..ARABIC SIGN SAM 0605 ; UNASSIGNED # .. 0606..060F ; FREE_PVAL, NAME_DIS # AR-IND CUBE ROOT..ARABIC SIGN MISRA 0610..061A ; PVALID # ARABIC SIGN SALLALLAHOU ALAYHE ..AR 061B ; FREE_PVAL, NAME_DIS # ARABIC SEMICOLON 061C..061D ; UNASSIGNED # .. 061E..061F ; FREE_PVAL, NAME_DIS # ARABIC TRIPLE DOT PUNCT MARK..ARABI 0620 ; UNASSIGNED # 0621..063F ; PVALID # ARABIC LET HAMZA..ARABIC LET FARSI Saint-Andre & Blanchet Expires September 13, 2012 [Page 28] Internet-Draft PRECIS Framework March 2012 0640 ; DISALLOWED # ARABIC TATWEEL 0641..065F ; PVALID # ARABIC LET FEH..ARABIC WAVY HAMZA B 0660..0669 ; CONTEXTO # AR-IND DIG ZERO..AR-IND DIG 066A..066D ; FREE_PVAL, NAME_DIS # ARABIC PCT SIGN..ARABIC FIVE PNTED 066E..0674 ; PVALID # ARABIC LET DOTLESS BEH..ARABIC LET 0675..0678 ; FREE_PVAL, NAME_DIS # ARABIC LET HIGH HAMZA ALEF..ARABIC 0679..06D3 ; PVALID # ARABIC LET TTEH..ARABIC LET YEH BAR 06D4 ; FREE_PVAL, NAME_DIS # ARABIC FULL STOP 06D5..06DC ; PVALID # ARABIC LET AE..ARABIC SM HIGH SEEN 06DD ; DISALLOWED # ARABIC END OF AYAH 06DE ; FREE_PVAL, NAME_DIS # ARABIC START OF RUB EL HIZB 06DF..06E8 ; PVALID # ARABIC SM HIGH ROUNDED ZERO..ARABI 06E9 ; FREE_PVAL, NAME_DIS # ARABIC PLACE OF SAJDAH 06EA..06EF ; PVALID # ARABIC EMPTY CENTRE LOW STOP..ARABI 06F0..06F9 ; CONTEXTO # EXT AR-IND DIG ZERO..EXT A 06FA..06FF ; PVALID # ARABIC LET SHEEN W DOT BEL..ARABIC 0700..070D ; FREE_PVAL, NAME_DIS # SYR END OF PARA..SYR HARKLEAN AST 070E ; UNASSIGNED # 070F ; DISALLOWED # SYR ABBR MARK 0710..07B1 ; PVALID # SYR LET ALAPH..THAANA LET N 07B2..07BF ; UNASSIGNED # .. 07C0..07F5 ; PVALID # NKO DIG ZERO..NKO LOW TONE APOS 07F6..07FA ; FREE_PVAL, NAME_DIS # NKO SYMBOL OO DENNEN..NKO LAJANYA 07FB..07FF ; UNASSIGNED # .. 0800..082D ; PVALID # SAMAR LET ALAF..SAMAR MARK NEQUDA 082E..082F ; UNASSIGNED # .. 0830..083E ; FREE_PVAL, NAME_DIS # SAMAR PUNCT NEQUDAA..SAMAR PUN 083F ; UNASSIGNED # 0840..085B ; PVALID # MANDAIC LET HALQA..MANDAIC GEM 085C..085D ; UNASSIGNED # .. 085E ; FREE_PVAL, NAME_DIS # MANDAIC PUNCTUATION 08A0..08AC ; PVALID # ARABIC LET BEH W SM V BEL..ARABIC 08AD..08E3 ; UNASSIGNED # .. 08E4..08FE ; PVALID # ARABIC CURLY FATHA..ARABIC DAMMA W 08FF ; UNASSIGNED # 0900..0963 ; PVALID # DEVAN SIGN INV CANDRABINDU..DEVAN V 0964..0965 ; FREE_PVAL, NAME_DIS # DEVAN DANDA..DEVAN DOUBLE DANDA 0966..096F ; PVALID # DEVAN DIG ZERO..DEVAN DIG NINE 0970 ; FREE_PVAL, NAME_DIS # DEVAN ABBR SIGN 0971..097F ; PVALID # DEVAN SIGN HIGH SPACING DOT..DEVAN 0980 ; UNASSIGNED # 0981..0983 ; PVALID # BENG SIGN CANDRABINDU..BENG SIGN V 0984 ; UNASSIGNED # 0985..098C ; PVALID # BENG LET A..BENG LET VOCALIC L 098D..098E ; UNASSIGNED # .. 098F..0990 ; PVALID # BENG LET E..BENG LET AI 0991..0992 ; UNASSIGNED # .. 0993..09A8 ; PVALID # BENG LET O..BENG LET NA Saint-Andre & Blanchet Expires September 13, 2012 [Page 29] Internet-Draft PRECIS Framework March 2012 09A9 ; UNASSIGNED # 09AA..09B0 ; PVALID # BENG LET PA..BENG LET RA 09B1 ; UNASSIGNED # 09B2 ; PVALID # BENG LET LA 09B3..09B5 ; UNASSIGNED # .. 09B6..09B9 ; PVALID # BENG LET SHA..BENG LET HA 09BA..09BB ; UNASSIGNED # .. 09BC..09C4 ; PVALID # BENG SIGN NUKTA..BENG VOWEL SIGN VO 09C5..09C6 ; UNASSIGNED # .. 09C7..09C8 ; PVALID # BENG VOWEL SIGN E..BENG VOWEL SIGN 09C9..09CA ; UNASSIGNED # .. 09CB..09CE ; PVALID # BENG VOWEL SIGN O..BENG LET KHANDA 09CF..09D6 ; UNASSIGNED # .. 09D7 ; PVALID # BENG AU LENGTH MARK 09D8..09DB ; UNASSIGNED # .. 09DC..09DD ; PVALID # BENG LET RRA..BENG LET RHA 09DE ; UNASSIGNED # 09DF..09E3 ; PVALID # BENG LET YYA..BENG VOWEL SIG 09E4..09E5 ; UNASSIGNED # .. 09E6..09F1 ; PVALID # BENG DIG ZERO..BENG LET RA W L 09F2..09F3 ; FREE_PVAL, NAME_DIS # BENG RUPEE MARK..BENG RUPEE SIGN 09F4..09FB ; DISALLOWED # BENG CURR NUM ONE..BENG GANDA MARK 09FC..0A00 ; UNASSIGNED # .. 0A01..10FFFF; TBD! Appendix B. Acknowledgements The authors would like to acknowledge the comments and contributions of the following individuals: David Black, Mark Davis, Alan DeKok, Martin Duerst, Patrik Faltstrom, Ted Hardie, Joe Hildebrand, Paul Hoffman, Jeffrey Hutzelman, Simon Josefsson, John Klensin, Alexey Melnikov, Yoav Nir, Mike Parker, Pete Resnick, Andrew Sullivan, Dave Thaler, and Yoshiro Yoneya. Some algorithms and textual descriptions have been borrowed from [RFC5892]. Some text regarding security has been borrowed from [RFC5890] and [I-D.ietf-xmpp-6122bis]. Saint-Andre & Blanchet Expires September 13, 2012 [Page 30] Internet-Draft PRECIS Framework March 2012 Authors' Addresses Peter Saint-Andre Cisco Systems, Inc. 1899 Wynkoop Street, Suite 600 Denver, CO 80202 USA Phone: +1-303-308-3282 Email: psaintan@cisco.com Marc Blanchet Viagenie 246 Aberdeen Quebec, QC G1R 2E1 Canada Email: Marc.Blanchet@viagenie.ca URI: http://www.viagenie.ca/ Saint-Andre & Blanchet Expires September 13, 2012 [Page 31]