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Network Working Group T. Howes Request for Comments: 1778 University of Michigan Obsoletes: 1488 S. Kille Category: Standards Track ISODE Consortium

                                                              W. Yeong
                                     Performance Systems International
                                                            C. Robbins
                                                            NeXor Ltd.
                                                            March 1995

      The String Representation of Standard Attribute Syntaxes

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) 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 X.500 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 1778 Syntax Encoding March 1995

2. 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, with the string value being the BER-encoded version of
 the value.

2.2. Case Ignore String

 A string of type caseIgnoreStringSyntax is encoded as the string
 value itself.

Howes, Kille, Yeong & Robbins [Page 2] RFC 1778 Syntax Encoding March 1995

2.3. 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 1778 Syntax Encoding March 1995

2.11. 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
 character

2.15. 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 the

Howes, Kille, Yeong & Robbins [Page 4] RFC 1778 Syntax Encoding March 1995

 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*('$' <ttx-parm>)

   <ttx-param> ::= <ttx-key> ':' <ttx-value>

   <ttx-key> ::= 'graphic' | 'control' | 'misc' | 'page' | 'private'

   <ttx-value> ::= <octetstring>

 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.

Howes, Kille, Yeong & Robbins [Page 5] RFC 1778 Syntax Encoding March 1995

2.19. Facsimile Telephone Number

 Values of type FacsimileTelephoneNumber are encoded according to the
 following BNF:

<fax-number> ::= <printablestring> [ '$' <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>

<criteria-set> ::= [ '(' ] <criteria> '&' <criteria-set> [ ')' ] |

                 [ '(' ] <criteria> '|' <criteria-set> [ ')' ]

<criteria-item> ::= [ '(' ] <attributetype> '$' <match-type> [ ')' ]

<match-type> ::= "EQ" | "SUBSTR" | "GE" | "LE" | "APPROX"

Howes, Kille, Yeong & Robbins [Page 6] RFC 1778 Syntax Encoding March 1995

2.23. Postal Address

 Values 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.

2.24. 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> ::= <version> '#' <serial> '#' <signature-algorithm-id>
                   '#' <issuer> '#' <validity> '#' <subject>
                   '#' <public-key-info> '#' <encrypted-sign-value>

   <version> ::= <integervalue>

   <serial> ::= <integervalue>

   <signature-algorithm-id> ::= <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-sign-value>

   <encrypted-sign-value> ::= <hex-string> | <hex-string> '-' <d>

   <algorithm-id> ::= <oid> '#' <algorithm-parameters>

Howes, Kille, Yeong & Robbins [Page 7] RFC 1778 Syntax Encoding March 1995

   <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:

<certificate-list> ::= <signature-algorithm-id> '#' <issuer> '#' <utc-time>

                      [ '#' <revoked-certificates> ]
                      '#' <signature-algorithm-id>
                      '#' <encrypted-sign-value>

<revoked-certificates> ::= 1*( '#' <revoked-certificate> )

                      <signature-algorithm-id> '#' <encrypted-sign-value>

<revoked-certificate> ::= <signature-algorithm-id> '#' <issuer> '#'

                      <serial> '#' <utc-time>

 The syntactic components <signature-algorithm-id>, <issuer>,
 <encrypted-sign-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> ::= <forward> '#' <reverse>
                           | <forward>
                           | <reverse>

   <forward> ::= 'forward:' <certificate>

   <reverse> ::= 'reverse:' <certificate>

Howes, Kille, Yeong & Robbins [Page 8] RFC 1778 Syntax Encoding March 1995

 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 String

 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].

Howes, Kille, Yeong & Robbins [Page 9] RFC 1778 Syntax Encoding March 1995

2.34. Distribution List Submit Permission

 Values of type DLSubmitPermission are encoded as strings, according
 to the following BNF:

   <dlsubmit-perm> ::= <dlgroup_label> ':' <dlgroup-value>
                           | <dl-label> ':' <dl-value>

   <dlgroup-label> ::= 'group_member'

   <dlgroup-value> ::= <name>

   <name> ::= an encoded Distinguished Name

   <dl-label> ::= 'individual' | 'dl_member' | 'pattern'

   <dl-value> ::= <orname>

   <orname> ::= <address> '#' <dn>
          |  <address>

   <address> ::= <add-label> ':' <oraddress>

   <dn> ::= <dn-label> ':' <name>

   <add-label> = 'X400'

   <dn-label> = 'X500'

 where <oraddress> is as defined in RFC 1327.

2.35. 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].

2.36. Fax

 Values of type Fax are encoded as if they were octet strings
 containing Group 3 Fax images as defined in [7].

Howes, Kille, Yeong & Robbins [Page 10] RFC 1778 Syntax Encoding March 1995

3. Security Considerations

 Security issues are not discussed in this memo.

4. Acknowledgements

 Many of the attribute syntax encodings defined in this document are
 adapted from those used in the QUIPU X.500 implementation. The
 contributions of the authors of the QUIPU implementation in the
 specification of the QUIPU syntaxes [4] are gratefully acknowledged.

5. 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.

 [5] Kille, S., "A String Representation of Distinguished Names", RFC
     1779, ISODE Consortium, March 1995.

 [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 1777, Performance Systems International,
     University of Michigan, ISODE Consortium, March 1995.

[10] Alvestrand, H., Kille, S., Miles, R., Rose, M., and S.  Thompson,
     "Mapping between X.400 and RFC-822 Message Bodies", RFC 1495,
     SINTEF DELAB, ISODE Consortium, Soft*Switch, Inc., Dover Beach
     Consulting, Inc., Soft*Switch, Inc., August 1993.

Howes, Kille, Yeong & Robbins [Page 11] RFC 1778 Syntax Encoding March 1995

6. 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
     UK

Howes, Kille, Yeong & Robbins [Page 12]