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.






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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.




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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.






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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



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  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.




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2.19.  Facsimile Telephone Number

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

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

<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"









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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>



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    <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>




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  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].











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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].










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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.





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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: [email protected]


      Steve Kille
      ISODE Consortium
      PO Box 505
      London
      SW11 1DX
      UK

      Phone: +44-71-223-4062
      EMail: [email protected]


      Wengyik Yeong
      PSI Inc.
      510 Huntmar Park Drive
      Herndon, VA 22070
      USA

      Phone: +1 703-450-8001
      EMail: [email protected]


      Colin Robbins
      NeXor Ltd
      University Park
      Nottingham
      NG7 2RD
      UK











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