Network Working Group
Request for Comments: 1488
 T. Howes
University of Michigan
S. Kille
ISODE Consortium
W. Yeong
Performance Systems International
C. Robbins
NeXor Ltd.
July 1993
 
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The X.500 String Representation of Standard Attribute Syntaxes

Status 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. 



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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. 


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*( '$' <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> ]



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 <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 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. 



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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> ::= <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: 



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     <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 String



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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. 



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[5] Kille, S., "A String Representation of Distinguished Names", RFC 1485, 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 and RFC 822", RFC 1327, University College London, May 1992. 


5 Security Considerations
Security issues are not discussed in this memo. 



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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: 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 



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