INTERNET-DRAFT S. Legg draft-legg-ldap-gser-abnf-01.txt Adacel Technologies Intended Category: Informational January 10, 2002 Common Elements of GSER Encodings Copyright (C) The Internet Society (2002). All Rights Reserved. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Distribution of this document is unlimited. Comments should be sent to the LDAPEXT working group mailing list or to the author. This Internet-Draft expires on 10 July 2002. 1. Abstract The Generic String Encoding Rules (GSER) defined in draft-legg- ldapext-component-matching-xx.txt (a work in progress) describe a human readable text encoding for an ASN.1 value of any ASN.1 type. Specifications making use of GSER may wish to provide an equivalent ABNF description of the GSER encoding for a particular ASN.1 type as a convenience for implementors. This document supports such specifications by providing equivalent ABNF for the GSER encodings for ASN.1 types commonly occuring in LDAP syntaxes. Legg Expires 10 July 2002 [Page 1] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1]. 2. Table of Contents 1. Abstract .................................................... 1 2. Table of Contents ........................................... 2 3. Introduction ................................................ 2 4. Separators .................................................. 2 5. ASN.1 Built-in Types ........................................ 3 6. ASN.1 Restricted String Types ............................... 6 7. Directory ASN.1 Types ....................................... 8 8. Security Considerations ..................................... 9 9. Normative References ........................................ 9 10. Informative References ..................................... 10 11. Intellectual Property Notice ............................... 10 12. Copyright Notice ........................................... 11 13. Author's Address ........................................... 11 3. Introduction The Generic String Encoding Rules (GSER) defined in Section 8 of [10] define a human readable text encoding, based on ASN.1 [7] value notation, for an ASN.1 value of any ASN.1 type. Specifications making use of GSER may wish to provide a non-normative equivalent ABNF [3] description of the GSER encoding for a particular ASN.1 type as a convenience for implementors unfamiliar with ASN.1. This document supports such specifications by providing equivalent ABNF for the GSER encodings for ASN.1 types commonly occuring in LDAP [9] or X.500 [11] attribute and assertion syntaxes, as well as equivalent ABNF for the GSER encodings for the ASN.1 built-in types. The ABNF given in this document does not replace or alter GSER in any way. If there is a discrepancy between the ABNF specified here and the encoding defined by GSER in [10] then [10] is to be taken as definitive. 4. Separators Certain separators are commonly used in constructing equivalent ABNF for SET and SEQUENCE types. sp = *%x20 ; zero, one or more space characters msp = 1*%x20 ; one or more space characters Legg Expires 10 July 2002 [Page 2] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 sep = [ "," ] The rule is used in the ABNF description of the encoding for ASN.1 SET or SEQUENCE types where all the components are either OPTIONAL or DEFAULT. It encodes to an empty string if and only if the immediately preceding character in the encoding is "{", i.e. it is only empty for the first optional component actually present in the SET or SEQUENCE value being encoded. 5. ASN.1 Built-in Types This section describes the GSER encoding of values of the ASN.1 built-in types, except for the restricted character string types. The rule describes the GSER encoding of values of the BIT STRING type without a named bit list. BIT-STRING = bstring / hstring If the number of bits in a BIT STRING value is a multiple of four the form of MAY be used. The form of is used otherwise. The rule encodes each bit as the character "0" or "1" in order from the first bit to the last bit. The rule encodes each group of four bits as a hexadecimal number where the first bit is the most significant. An odd number of hexadecimal digits is permitted. hstring = squote *hexadecimal-digit squote %x48 ; '...'H hexadecimal-digit = %x30-39 / ; "0" to "9" %x41-46 ; "A" to "F" bstring = squote *binary-digit squote %x42 ; '...'B binary-digit = "0" / "1" squote = %x27 ; ' (single quote) The rule describes the GSER encoding of values of the BOOLEAN type. BOOLEAN = %x54.52.55.45 / ; "TRUE" %x46.41.4C.53.45 ; "FALSE" The rule describes the GSER encoding of values of the associated type for the unrestricted CHARACTER STRING type. CHARACTER-STRING = "{" sp id-identification msp Identification "," sp id-data-value msp OCTET-STRING Legg Expires 10 July 2002 [Page 3] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 sp "}" id-identification = %x69.64.65.6E.74.69.66.69.63.61.74.69.6F.6E ; "identification" id-data-value = %x64.61.74.61.2D.76.61.6C.75.65 ; "data-value" Identification = ( id-syntaxes ":" Syntaxes ) / ( id-syntax ":" OBJECT-IDENTIFIER ) / ( id-presentation-context-id ":" INTEGER ) / ( id-context-negotiation ":" ContextNegotiation ) / ( id-transfer-syntax ":" OBJECT-IDENTIFIER ) / ( id-fixed ":" NULL ) id-syntaxes = %x73.79.6E.74.61.78.65.73 ; "syntaxes" id-syntax = %x73.79.6E.74.61.78 ; "syntax" id-presentation-context-id = %x70.72.65.73.65.6E.74.61.74.69.6F.6E.2D %x63.6F.6E.74.65.78.74.2D.69.64 ; "presentation-context-id" id-context-negotiation = %x63.6F.6E.74.65.78.74.2D.6E.65.67.6F.74 %x69.61.74.69.6F.6E ; "context-negotiation" id-transfer-syntax = %x74.72.61.6E.73.66.65.72.2D.73.79.6E.74 %x61.78 ; "transfer-syntax" id-fixed = %x66.69.78.65.64 ; "fixed" Syntaxes = "{" sp id-abstract msp OBJECT-IDENTIFIER "," sp id-transfer msp OBJECT-IDENTIFIER sp "}" id-abstract = %x61.62.73.74.72.61.63.74 ; "abstract" id-transfer = %x74.72.61.6E.73.66.65.72 ; "transfer" ContextNegotiation = "{" sp id-presentation-context-id msp INTEGER "," sp id-transfer-syntax msp OBJECT-IDENTIFIER sp "}" The rule describes the GSER encoding of values of the INTEGER type without a named number list. The rule describes the GSER encoding of values of the constrained type INTEGER (0..MAX). The rule describes the GSER encoding of values of the constrained type INTEGER (1..MAX). INTEGER = "0" / positive-number / ("-" positive-number) INTEGER-0-MAX = "0" / positive-number INTEGER-1-MAX = positive-number positive-number = non-zero-digit *decimal-digit decimal-digit = %x30-39 ; "0" to "9" non-zero-digit = %x31-39 ; "1" to "9" Legg Expires 10 July 2002 [Page 4] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 The rule describes the GSER encoding of values of the associated type for the EMBEDDED PDV type. EMBEDDED-PDV = "{" sp id-identification msp Identification [ "," sp id-data-value-descriptor msp ObjectDescriptor ] "," sp id-data-value msp OCTET-STRING sp "}" id-data-value-descriptor = %x64.61.74.61.2D.76.61.6C.75.65.2D.64.65 %x73.63.72.69.70.74.6F.72 ; "data-value-descriptor" The rule describes the GSER encoding of values of the associated type for the EXTERNAL type. EXTERNAL = "{" sp id-identification msp E-Identification [ "," sp id-data-value-descriptor msp ObjectDescriptor ] "," sp id-data-value msp OCTET-STRING sp "}" E-Identification = ( id-syntax ":" OBJECT-IDENTIFIER ) / ( id-presentation-context-id ":" INTEGER ) / ( id-context-negotiation ":" ContextNegotiation ) The rule describes the GSER encoding of values of the NULL type. NULL = %x4E.55.4C.4C ; "NULL" The rule describes the GSER encoding of values of the OBJECT IDENTIFIER type. OBJECT-IDENTIFIER = numeric-oid / descr numeric-oid = oid-component 1*( "." oid-component ) oid-component = "0" / positive-number An OBJECT IDENTIFIER value is encoded using either the dotted decimal representation or an object descriptor name, i.e. . The rule is described in [4]. An object descriptor name is potentially ambiguous and should be used with care. The rule describes the GSER encoding of values of the OCTET STRING type. OCTET-STRING = hstring Legg Expires 10 July 2002 [Page 5] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 The octets are encoded in order from the first octet to the last octet. Each octet is encoded as a pair of hexadecimal digits where the first digit corresponds to the four most significant bits of the octet. If the hexadecimal string does not have an even number of digits the four least significant bits in the last octet are assumed to be zero. The rule describes the GSER encoding of values of the REAL type. REAL = "0" ; zero / PLUS-INFINITY ; positive infinity / MINUS-INFINITY ; negative infinity / realnumber ; positive base 10 REAL value / ( "-" realnumber ) ; negative base 10 REAL value / real-sequence-value ; non-zero base 2 or 10 REAL value PLUS-INFINITY = %x50.4C.55.53.2D.49.4E.46.49.4E.49.54.59 ; "PLUS-INFINITY" MINUS-INFINITY = %x4D.49.4E.55.53.2D.49.4E.46.49.4E.49.54.59 ; "MINUS-INFINITY" realnumber = mantissa exponent mantissa = (positive-number [ "." *decimal-digit ]) / ( "0." *("0") positive-number ) exponent = "E" ( "0" | ([ "-" ] positive-number)) real-sequence-value = "{" sp id-mantissa msp INTEGER "," sp id-base msp ( "2" / "10" ) "," sp id-exponent msp INTEGER sp "}" id-mantissa = %x6D.61.6E.74.69.73.73.61 ; "mantissa" id-base = %x62.61.73.65 ; "base" id-exponent = %x65.78.70.6F.6E.65.6E.74 ; "exponent" A value of the REAL type MUST be encoded as "0" if it is zero. The rule describes the GSER encoding of values of the RELATIVE-OID type. RELATIVE-OID = oid-component *( "." oid-component ) 6. ASN.1 Restricted String Types This section describes the GSER encoding of values of the ASN.1 restricted character string types. The characters of a value of a restricted character string type are always encoded as a UTF8 character string between double quotes. For some of the ASN.1 string Legg Expires 10 July 2002 [Page 6] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 types this requires a translation to or form the UTF8 encoding. Some of the ASN.1 string types permit only a subset of the characters representable in UTF8. Any double quote characters in the character string, where allowed by the character set, are escaped by being repeated. The rule describes the GSER encoding of values of the UTF8String type. The characters of this string type do not require any translation before being encoded. UTF8String = StringValue StringValue = dquote *SafeUTF8Character dquote dquote = %x22 ; " (double quote) SafeUTF8Character = %x00-21 / %x23-7F / ; ASCII minus dquote dquote dquote / ; escaped double quote %xC0-DF %x80-BF / ; 2 byte UTF8 character %xE0-EF 2(%x80-BF) / ; 3 byte UTF8 character %xF0-F7 3(%x80-BF) / ; 4 byte UTF8 character %xF8-FB 4(%x80-BF) / ; 5 byte UTF8 character %xFC-FD 5(%x80-BF) ; 6 byte UTF8 character The , , , , , and rules describe the GSER encoding of values of the correspondingly named ASN.1 types. The characters of these string types are compatible with UTF8 and do not require any translation before being encoded. The GeneralizedTime and UTCTime types use the VisibleString character set, but have a strictly defined format. NumericString = dquote *(decimal-digit / space) dquote space = %x20 PrintableString = dquote *PrintableCharacter dquote PrintableCharacter = decimal-digit / space / %x41-5A ; A to Z / %x61-7A ; a to z / %x27-29 ; ' ( ) / %x2B-2F ; + , - . / / %x3A ; : / %x3D ; = / %x3F ; ? ISO646String = VisibleString VisibleString = dquote *SafeVisibleCharacter dquote SafeVisibleCharacter = %x20-21 / %x23-7E ; printable ASCII minus dquote / dquote dquote ; escaped double quote Legg Expires 10 July 2002 [Page 7] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 IA5String = dquote *SafeIA5Character dquote SafeIA5Character = %x00-21 / %x23-7F ; ASCII minus dquote / dquote dquote ; escaped double quote UTCTime = dquote 10 decimal-digit [2 decimal-digit] [ "Z" | u-differential ] dquote u-differential = ( "-" / "+" ) 4 decimal-digit GeneralizedTime = dquote 10 decimal-digit *2(2 decimal-digit) fraction [ "Z" | g-differential ] dquote fraction = ( "." / "," ) 1*decimal-digit g-differential = ( "-" / "+" ) 1*2(2 decimal-digit) The and rules describe the GSER encoding of values of the BMPString and UniversalString types respectively. BMPString (UCS-2) and UniversalString (UCS-4) values are translated into UTF8 [6] character strings before being encoded according to . BMPString = StringValue UniversalString = StringValue The , , , , and rules describe the GSER encoding of values of the correspondingly named ASN.1 types. Values of these string types are translated into UTF8 character strings before being encoded according to . The ObjectDescriptor type uses the GraphicString character set. TeletexString = StringValue T61String = StringValue VideotexString = StringValue GraphicString = StringValue GeneralString = StringValue ObjectDescriptor = GraphicString 7. Directory ASN.1 Types This section describes the GSER encoding of values of selected ASN.1 types defined for LDAP and X.500. The ABNF rule names beginning with uppercase letters describe the GSER encoding of values of the ASN.1 type with the same name. AttributeType = OBJECT-IDENTIFIER The characters of a DirectoryString are translated into UTF8 characters as required before being encoded between double quotes with any embedded double quotes escaped by being repeated. Legg Expires 10 July 2002 [Page 8] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 DirectoryString = dquote *SafeUTF8Character dquote The rule describes the GSER encoding of values of the RDNSequence type, which is syntactically equivalent to the DistinguishedName and LocalName types. The rule encodes a name as an LDAPDN character string between double quotes. The character string is first derived according to the rule in Section 3 of [5], and then it is encoded between double quotes with any embedded double quotes escaped by being repeated. DistinguishedName = RDNSequence LocalName = RDNSequence RDNSequence = dquote *SafeUTF8Character dquote The rule describes the GSER encoding of values of the RelativeDistinguishedName type that are not part of an RDNSequence value. The rule encodes an RDN as a double quoted string containing the RDN as it would appear in an LDAPDN character string. The character string is first derived according to the rule in Section 3 of [6], and then any embedded double quote characters are escaped by being repeated. This resulting string is output between double quotes. RelativeDistinguishedName = dquote *SafeUTF8Character dquote The rule encodes an X.400 address as an IA5 character string between double quotes. The character string is first derived according to Section 4.1 of [2], and then any embedded double quotes are escaped by being repeated. This resulting string is output between double quotes. ORAddress = dquote *SafeIA5Character dquote 8. Security Considerations GSER, and therefore the ABNF encodings described in this document, do not necessarily enable the exact octet encoding of values of the TeletexString, VideotexString, GraphicString or GeneralString types to be reconstructed, so a transformation from DER to GSER and back to DER may not reproduce the original DER encoding. This has consequences for the verification of digital signatures. 9. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Legg Expires 10 July 2002 [Page 9] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 Levels", BCP 14, RFC 2119, March 1997. [2] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME", RFC 2156, January 1998. [3] Crocker, D., Overell, P., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [4] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight Directory Access Protocol (v3): Attribute Syntax Definitions", RFC 2252, December 1997. [5] Wahl, M., Kille, S. and T. Howes, "Lightweight Directory Access Protocol (v3): UTF-8 String Representation of Distinguished Names", RFC 2253, December 1997. [6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [7] ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998 Information Technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation 10. Informative References [8] Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process", BCP 11, RFC 2028, October 1996. [9] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access Protocol (v3)", RFC 2251, December 1997. [10] Legg, S., "LDAP & X.500 Component Matching Rules", draft-legg- ldapext-component-matching-xx.txt, a work in progress, January 2002. [11] ITU-T Recommendation X.500 (1993) | ISO/IEC 9594-1:1994, Information Technology - Open Systems Interconnection - The Directory: Overview of concepts, models and services 11. Intellectual Property Notice The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it Legg Expires 10 July 2002 [Page 10] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. [8] Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 12. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 13. Author's Address Steven Legg Legg Expires 10 July 2002 [Page 11] INTERNET-DRAFT Common Elements of GSER Encodings January 10, 2002 Adacel Technologies Ltd. 405-409 Ferntree Gully Road Mount Waverley, Victoria 3149 AUSTRALIA Phone: +61 3 9451 2107 Fax: +61 3 9541 2121 EMail: steven.legg@adacel.com.au Legg Expires 10 July 2002 [Page 12]