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Network Working Group                                         T. HowesRequest for Comments: 1488                      University of Michigan                                                              S. Kille                                                      ISODE Consortium                                                              W. Yeong                                     Performance Systems International                                                            C. Robbins                                                            NeXor Ltd.                                                             July 1993The X.500 String Representation of Standard Attribute SyntaxesStatus of this Memo   This RFC specifies an IAB standards track protocol for the Internet   community, and requests discussion and suggestions for improvements.   Please refer to the current edition of the "IAB Official Protocol   Standards" for the standardization state and status of this protocol.   Distribution of this memo is unlimited.Abstract   The Lightweight Directory Access Protocol (LDAP) [9] requires that   the contents of AttributeValue fields in protocol elements be octet   strings.  This document defines the requirements that must be   satisfied by encoding rules used to render Directory attribute   syntaxes into a form suitable for use in the LDAP, then goes on to   define the encoding rules for the standard set of attribute syntaxes   defined in [1,2] and [3].1.  Attribute Syntax Encoding Requirements   This section defines general requirements for lightweight directory   protocol attribute syntax encodings. All documents defining attribute   syntax encodings for use by the lightweight directory protocols are   expected to conform to these requirements.   The encoding rules defined for a given attribute syntax must produce   octet strings.  To the greatest extent possible, encoded octet   strings should be usable in their native encoded form for display   purposes. In particular, encoding rules for attribute syntaxes   defining non-binary values should produce strings that can be   displayed with little or no translation by clients implementing the   lightweight directory protocols.Howes, Kille, Yeong & Robbins                                   [Page 1]

RFC 1488                 X.500 Syntax Encoding                 July 19932.  Standard Attribute Syntax Encodings   For the purposes of defining the encoding rules for the standard   attribute syntaxes, the following auxiliary BNF definitions will be   used:     <a> ::= 'a' | 'b' | 'c' | 'd' | 'e' | 'f' | 'g' | 'h' | 'i' |             'j' | 'k' | 'l' | 'm' | 'n' | 'o' | 'p' | 'q' | 'r' |             's' | 't' | 'u' | 'v' | 'w' | 'x' | 'y' | 'z' | 'A' |             'B' | 'C' | 'D' | 'E' | 'F' | 'G' | 'H' | 'I' | 'J' |             'K' | 'L' | 'M' | 'N' | 'O' | 'P' | 'Q' | 'R' | 'S' |             'T' | 'U' | 'V' | 'W' | 'X' | 'Y' | 'Z'     <d> ::= '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'     <hex-digit> ::= <d> | 'a' | 'b' | 'c' | 'd' | 'e' | 'f' |                      'A' | 'B' | 'C' | 'D' | 'E' | 'F'     <k> ::= <a> | <d> | '-'     <p> ::= <a> | <d> | ''' | '(' | ')' | '+' | ',' | '-' | '.' |             '/' | ':' | '?' | ' '     <CRLF> ::= The ASCII newline character with hexadecimal value 0x0A     <letterstring> ::= <a> | <a> <letterstring>     <numericstring> ::= <d> | <d> <numericstring>     <keystring> ::= <a> | <a> <anhstring>     <anhstring> ::= <k> | <k> <anhstring>     <printablestring> ::= <p> | <p> <printablestring>     <space> ::= ' ' | ' ' <space>2.1.  Undefined   Values of type Undefined are encoded as if they were values of type   Octet String.2.2.  Case Ignore String   A string of type caseIgnoreStringSyntax is encoded as the string   value itself.Howes, Kille, Yeong & Robbins                                   [Page 2]

RFC 1488                 X.500 Syntax Encoding                 July 19932.3.  Case Exact String   The encoding of a string of type caseExactStringSyntax is the string   value itself.2.4.  Printable String   The encoding of a string of type printableStringSyntax is the string   value itself.2.5.  Numeric String   The encoding of a string of type numericStringSyntax is the string   value itself.2.6.  Octet String   The encoding of a string of type octetStringSyntax is the string   value itself.2.7.  Case Ignore IA5 String   The encoding of a string of type caseIgnoreIA5String is the string   value itself.2.8.  IA5 String   The encoding of a string of type iA5StringSyntax is the string value   itself.2.9.  T61 String   The encoding of a string of type t61StringSyntax is the string value   itself.2.10.  Case Ignore List   Values of type caseIgnoreListSyntax are encoded according to the   following BNF:     <caseignorelist> ::= <caseignorestring> |                          <caseignorestring> '$' <caseignorelist>     <caseignorestring> ::= a string encoded according to the rules                             for Case Ignore String as above.Howes, Kille, Yeong & Robbins                                   [Page 3]

RFC 1488                 X.500 Syntax Encoding                 July 19932.11.  Case Exact List   Values of type caseExactListSyntax are encoded according to the   following BNF:     <caseexactlist> ::= <caseexactstring> |                          <caseexactstring> '$' <caseexactlist>     <caseexactstring> ::= a string encoded according to the rules for                            Case Exact String as above.2.12.  Distinguished Name   Values of type distinguishedNameSyntax are encoded to have the   representation defined in [5].2.13.  Boolean   Values of type booleanSyntax are encoded according to the following   BNF:     <boolean> ::= "TRUE" | "FALSE"   Boolean values have an encoding of "TRUE" if they are logically true,   and have an encoding of "FALSE" otherwise.2.14.  Integer   Values of type integerSyntax are encoded as the decimal   representation of their values, with each decimal digit represented   by the its character equivalent. So the digit 1 is represented by the   character2.15.  Object Identifier   Values of type objectIdentifierSyntax are encoded according to the   following BNF:     <oid> ::= <descr> | <descr> '.' <numericoid> | <numericoid>     <descr> ::= <keystring>     <numericoid> ::= <numericstring> | <numericstring> '.' <numericoid>   In the above BNF, <descr> is the syntactic representation of an   object descriptor. When encoding values of type   objectIdentifierSyntax, the first encoding option should be used in   preference to the second, which should be used in preference to theHowes, Kille, Yeong & Robbins                                   [Page 4]

RFC 1488                 X.500 Syntax Encoding                 July 1993   third wherever possible. That is, in encoding object identifiers,   object descriptors (where assigned and known by the implementation)   should be used in preference to numeric oids to the greatest extent   possible. For example, in encoding the object identifier representing   an organizationName, the descriptor "organizationName" is preferable   to "ds.4.10", which is in turn preferable to the string "2.5.4.10".2.16.  Telephone Number   Values of type telephoneNumberSyntax are encoded as if they were   Printable String types.2.17.  Telex Number   Values of type telexNumberSyntax are encoded according to the   following BNF:     <telex-number> ::= <actual-number> '$' <country> '$' <answerback>     <actual-number> ::= <printablestring>     <country> ::= <printablestring>     <answerback> ::= <printablestring>   In the above, <actual-number> is the syntactic representation of the   number portion of the TELEX number being encoded, <country> is the   TELEX country code, and <answerback> is the answerback code of a   TELEX terminal.2.18.  Teletex Terminal Identifier   Values of type teletexTerminalIdentifier are encoded according to the   following BNF:     <teletex-id> ::= <printablestring> 0*( '$' <printablestring>)   In the above, the first <printablestring> is the encoding of the   first portion of the teletex terminal identifier to be encoded, and   the subsequent 0 or more <printablestrings> are subsequent portions   of the teletex terminal identifier.2.19.  Facsimile Telephone Number   Values of type FacsimileTelephoneNumber are encoded according to the   following BNF: <fax-number> ::= <printablestring> [ '$' <faxparameters> ]Howes, Kille, Yeong & Robbins                                   [Page 5]

RFC 1488                 X.500 Syntax Encoding                 July 1993 <faxparameters> ::= <faxparm> | <faxparm> '$' <faxparameters> <faxparm> ::= 'twoDimensional' | 'fineResolution' | 'unlimitedLength' |               'b4Length' | 'a3Width' | 'b4Width' | 'uncompressed'   In the above, the first <printablestring> is the actual fax number,   and the <faxparm> tokens represent fax parameters.2.20.  Presentation Address   Values of type PresentationAddress are encoded to have the   representation described in [6].2.21.  UTC Time   Values of type uTCTimeSyntax are encoded as if they were Printable   Strings with the strings containing a UTCTime value.2.22.  Guide (search guide)   Values of type Guide, such as values of the searchGuide attribute,   are encoded according to the following BNF:     <guide-value> ::= [ <object-class> '#' ] <criteria>     <object-class> ::= an encoded value of type objectIdentifierSyntax     <criteria> ::= <criteria-item> | <criteria-set> | '!' <criteria>     <criteria-set> ::= [ '(' ] <criteria> '&' <criteria-set> [ ')' ] |                        [ '(' ] <criteria> '|' <criteria-set> [ ')' ]     <criteria-item> ::= [ '(' ] <attributetype> '$' <match-type> [ ')' ]     <match-type> ::= "EQ" | "SUBSTR" | "GE" | "LE" | "APPROX"2.23.  Postal AddressValues of type PostalAddress are encoded according to the following BNF:     <postal-address> ::= <t61string> | <t61string> '$' <postal-address>   In the above, each <t61string> component of a postal address value is   encoded as a value of type t61StringSyntax.Howes, Kille, Yeong & Robbins                                   [Page 6]

RFC 1488                 X.500 Syntax Encoding                 July 19932.24.  User Password   Values of type userPasswordSyntax are encoded as if they were of type   octetStringSyntax.2.25.  User Certificate   Values of type userCertificate are encoded according to the following   BNF: <certificate> ::= <signature> '#' <issuer> '#' <validity> '#' <subject>                   '#' <public-key-info> <signature> ::= <algorithm-id> <issuer> ::= an encoded Distinguished Name <validity> ::= <not-before-time> '#' <not-after-time> <not-before-time> ::= <utc-time> <not-after-time> ::= <utc-time> <algorithm-parameters> ::=  <null> | <integervalue> |                             '{ASN}' <hex-string> <subject> ::= an encoded Distinguished Name <public-key-info> ::= <algorithm-id> '#' <encrypted-value> <encrypted-value> ::= <hex-string> | <hex-string> '-' <d> <algorithm-id> ::= <oid> '#' <algorithm-parameters> <utc-time> ::= an encoded UTCTime value <hex-string> ::= <hex-digit> | <hex-digit> <hex-string>2.26.  CA Certificate   Values of type cACertificate are encoded as if the values were of   type userCertificate.2.27.  Authority Revocation List   Values of type authorityRevocationList are encoded according to the   following BNF:Howes, Kille, Yeong & Robbins                                   [Page 7]

RFC 1488                 X.500 Syntax Encoding                 July 1993     <certificate-list> ::= <signature> '#' <issuer> '#'                            <utc-time> [ '#' <revoked-certificates> ]     <revoked-certificates> ::= <algorithm> '#' <encrypted-value>                                [ '#' 0*(<revoked-certificate>) '#']     <revoked-certificates> ::= <subject> '#' <algorithm> '#'                                <serial> '#' <utc-time>   The syntactic components <algorithm>, <issuer>, <encrypted-value>,   <utc-time>, <subject> and <serial> have the same definitions as in   the BNF for the userCertificate attribute syntax.2.28.  Certificate Revocation List   Values of type certificateRevocationList are encoded as if the values   were of type authorityRevocationList.2.29.  Cross Certificate Pair   Values of type crossCertificatePair are encoded according to the   following BNF:     <certificate-pair> ::= <certificate> '|' <certificate>   The syntactic component <certificate> has the same definition as in   the BNF for the userCertificate attribute syntax.2.30.  Delivery Method   Values of type deliveryMethod are encoded according to the following   BNF:     <delivery-value> ::= <pdm> | <pdm> '$' <delivery-value>     <pdm> ::= 'any' | 'mhs' | 'physical' | 'telex' | 'teletex' |               'g3fax' | 'g4fax' | 'ia5' | 'videotex' | 'telephone'2.31.  Other Mailbox   Values of the type otherMailboxSyntax are encoded according to the   following BNF:     <otherMailbox> ::= <mailbox-type> '$' <mailbox>     <mailbox-type> ::= an encoded Printable String     <mailbox> ::= an encoded IA5 StringHowes, Kille, Yeong & Robbins                                   [Page 8]

RFC 1488                 X.500 Syntax Encoding                 July 1993   In the above, <mailbox-type> represents the type of mail system in   which the mailbox resides, for example "Internet" or "MCIMail"; and   <mailbox> is the actual mailbox in the mail system defined by   <mailbox-type>.2.32.  Mail Preference   Values of type mailPreferenceOption are encoded according to the   following BNF: <mail-preference> ::= "NO-LISTS" | "ANY-LIST" | "PROFESSIONAL-LISTS"2.33.  MHS OR Address   Values of type MHS OR Address are encoded as strings, according to   the format defined in [10].2.34.  Photo   Values of type Photo are encoded as if they were octet strings   containing JPEG images in the JPEG File Interchange Format (JFIF), as   described in [8].2.35.  Fax   Values of type Fax are encoded as if they were octet strings   containing Group 3 Fax images as defined in [7].3.  Acknowledgements   Many of the attribute syntax encodings defined in this document are   adapted from those used in the QUIPU X.500 implementation. The   contribu- tions of the authors of the QUIPU implementation in the   specification of the QUIPU syntaxes [4] are gratefully acknowledged.4.  Bibliography   [1] The Directory: Selected Attribute Syntaxes.  CCITT,       Recommendation X.520.   [2] Information Processing Systems -- Open Systems Interconnection --       The Directory: Selected Attribute Syntaxes.   [3] Barker, P., and S. Kille, "The COSINE and Internet X.500 Schema",RFC 1274, University College London, November 1991.   [4] The ISO Development Environment: User's Manual -- Volume 5:       QUIPU.  Colin Robbins, Stephen E. Kille.Howes, Kille, Yeong & Robbins                                   [Page 9]

RFC 1488                 X.500 Syntax Encoding                 July 1993   [5] Kille, S., "A String Representation of Distinguished Names",RFC1485, July 1993.   [6] Kille, S., "A String Representation for Presentation Addresses",RFC 1278, University College London, November 1991.   [7] Terminal Equipment and Protocols for Telematic Services -       Standardization of Group 3 facsimile apparatus for document       transmission.  CCITT, Recommendation T.4.   [8] JPEG File Interchange Format (Version 1.02).  Eric Hamilton, C-       Cube Microsystems, Milpitas, CA, September 1, 1992.   [9] Yeong, W., Howes, T., and S. Kille, "Lightweight Directory Access       Protocol",RFC 1487, Performance Systems International,       University of Michigan, ISODE Consortium, July 1993.  [10] Kille, S., "Mapping between X.400(1988)/ISO 10021 andRFC 822",RFC 1327, University College London, May 1992.5.  Security Considerations   Security issues are not discussed in this memo.Howes, Kille, Yeong & Robbins                                  [Page 10]

RFC 1488                 X.500 Syntax Encoding                 July 19936.  Authors' Addresses   Tim Howes   University of Michigan   ITD Research Systems   535 W William St.   Ann Arbor, MI 48103-4943   USA   Phone: +1 313 747-4454   EMail: tim@umich.edu   Steve Kille   ISODE Consortium   PO Box 505   London   SW11 1DX   UK   Phone: +44-71-223-4062   EMail: S.Kille@isode.com   Wengyik Yeong   PSI, Inc.   510 Huntmar Park Drive   Herndon, VA 22070   USA   Phone: +1 703-450-8001   EMail: yeongw@psilink.com   Colin Robbins   NeXor Ltd   University Park   Nottingham   NG7 2RD   UKHowes, Kille, Yeong & Robbins                                  [Page 11]