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> ]
<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"
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>
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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>
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
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