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Edit File: draft-legg-ldap-transfer-xx.txt

INTERNET-DRAFT                                                   S. Legg
draft-legg-ldap-transfer-03.txt                      Adacel Technologies
Intended Category: Standards Track                          16 June 2004
Updates: RFC 2252bis

Lightweight Directory Access Protocol (LDAP):
                       Transfer Encoding Options

Status of this Memo

This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress".

The list of current Internet-Drafts can be accessed at
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This document is intended to be, after appropriate review and
   revision, submitted to the RFC Editor as a Standard Track document.
   Distribution of this document is unlimited.  Technical discussion of
   this document should take place on the IETF LDAP Revision Working
   Group (LDAPbis) mailing list <ietf-ldapbis@openldap.org>.  Please
   send editorial comments directly to the editor
   <steven.legg@adacel.com.au>.

This Internet-Draft expires on 16 December 2004.

Abstract

Each attribute stored in a Lightweight Directory Access Protocol
   (LDAP) directory has a defined syntax (i.e., data type).  A syntax

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definition specifies how attribute values conforming to the syntax
   are normally represented when transferred in LDAP operations.  This
   representation is referred to as the LDAP-specific encoding to
   distinguish it from other methods of encoding attribute values.  This
   document introduces a new category of attribute options, called
   transfer encoding options, which can be used to specify that the
   associated attribute values are encoded according to one of these
   other methods.

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Table of Contents

1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions. . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Transfer Encoding Options. . . . . . . . . . . . . . . . . . .  4
   4.  Defined Transfer Encoding Options. . . . . . . . . . . . . . .  5
   5.  Attributes Returned in a Search. . . . . . . . . . . . . . . .  6
   6.  Syntaxes Requiring Binary Transfer . . . . . . . . . . . . . .  7
   7.  Security Considerations. . . . . . . . . . . . . . . . . . . .  7
   8.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . .  8
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
       9.1.  Normative References . . . . . . . . . . . . . . . . . .  9
       9.2.  Informative References . . . . . . . . . . . . . . . . . 10
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 10

1.  Introduction

Each attribute stored in a Lightweight Directory Access Protocol
   (LDAP) directory [ROADMAP] has a defined syntax (i.e., data type)
   which constrains the structure and format of its values.

The description of each syntax [SYNTAX] specifies how attribute or
   assertion values [MODELS] conforming to the syntax are normally
   represented when transferred in LDAP operations [PROT].  This
   representation is referred to as the LDAP-specific encoding to
   distinguish it from other methods of encoding attribute values.

This document introduces a new category of attribute options
   [MODELS], called transfer encoding options, that allow attribute and
   assertion values to be transferred using an alternative method of
   encoding.  This document defines several transfer encoding options
   which can be used in an attribute description [MODELS] in an LDAP
   operation to specify that the associated attribute values or
   assertion value are, or are requested to be, encoded according to
   specific Abstract Syntax Notation One (ASN.1) [X680] encoding rules,
   instead of the usual LDAP-specific encoding.  One option in
   particular allows Extensible Markup Language (XML) [XML] encodings.

2.  Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and  "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [KEYWORD].

This specification makes use of definitions from the XML Information
   Set (Infoset) [ISET].  In particular, information item property names

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are presented per the Infoset, e.g., [local name].

3.  Transfer Encoding Options

Transfer encoding options enable attribute and assertion values to be
   transferred using an alternative method of encoding to the default
   LDAP-specific encoding.  In fact, some attribute and assertion
   syntaxes do not have a defined LDAP-specific encoding in which case
   the only way values of those syntaxes can be transferred is by using
   an alternative encoding.

The binary option [BINARY] is not formally regarded as a transfer
   encoding option, though it has much in common with transfer encoding
   options.  The requirements governing the use of transfer encoding
   options do not apply to the binary option.  The requirements
   governing the use of the binary option are described elsewhere
   [BINARY].

In terms of the protocol [PROT], a transfer encoding option specifies
   that the contents octets of an associated AttributeValue or
   AssertionValue OCTET STRING are a complete encoding of the relevant
   value according to the encoding method specified by the option.

Where a transfer encoding option is present in an attribute
   description the associated attribute values or assertion value MUST
   be encoded according to the encoding method corresponding to the
   option.  Note that it is possible for a syntax to be defined such
   that its LDAP-specific encoding is exactly the same as its encoding
   according to some transfer encoding option (e.g., the LDAP-specific
   encoding might be defined to be the same as the BER encoding).

Transfer encoding options are mutually exclusive.  An attribute
   description SHALL NOT contain more than one transfer encoding option,
   and SHALL NOT contain both a transfer encoding option and the binary
   option.

Transfer encoding options are not tagging options [MODELS] so the
   presence of a transfer encoding option does not specify an attribute
   subtype.  An attribute description containing a transfer encoding
   option references exactly the same attribute as the same attribute
   description without the transfer encoding option.  The
   supertype/subtype relationships of attributes with tagging options
   are not altered in any way by the presence or absence of transfer
   encoding options.

An attribute description SHALL be treated as unrecognized if it
   contains a transfer encoding option and the syntax of the attribute
   does not have an associated ASN.1 type [SYNTAX], or if the nominated

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encoding is not supported for that type.

The presence or absence of a transfer encoding option only affects
   the transfer of attribute and assertion values in protocol; servers
   store any particular attribute value in a single format of their
   choosing.

4.  Defined Transfer Encoding Options

The attribute option string "transfer-ber" specifies that the
   associated attribute values or assertion value are (to be) encoded
   according to the Basic Encoding Rules [X690] of ASN.1.  This option
   is similar to the binary option [BINARY], however servers are more
   restricted in when they can use "transfer-ber" which leads to more
   predictability in the results returned to clients who request
   "transfer-ber".

The attribute option string "transfer-der" specifies that the
   associated attribute values or assertion value are (to be) encoded
   according to the Distinguished Encoding Rules [X690] of ASN.1.

The attribute option string "transfer-gser" specifies that the
   associated attribute values or assertion value are (to be) encoded
   according to the Generic String Encoding Rules (GSER) [RFC3641].

The attribute option string "transfer-rxer" specifies that the
   associated attribute values or assertion value are (to be) encoded as
   an XML document [XML].  The [local name] of the [document element] of
   the document information item representing the associated value SHALL
   be the identifier of the NamedType [X680] in the LDAP ASN.1
   specification [PROT] defining the associated attribute value or
   assertion value, or "item" if the associated value isn't in a
   NamedType.  This means:

- for an AttributeValue the identifier is "value" in every case,

- for an AssertionValue in an AttributeValueAssertion the identifier
      is "assertionValue",

- for an AssertionValue in a SubstringFilter the identifier is
      "initial", "any" or "final", as appropriate,

- for an AssertionValue in a MatchingRuleAssertion the identifier is
      "matchValue".

The [namespace name] of the [document element] SHALL have no value.
   The content of the [document element] is the Robust XML Encoding
   Rules (RXER) [RXER] encoding of the associated attribute or assertion

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value.  Note that the enclosing element for the RXER encoding has the
   form it would take in an XLDAP operation [XLDAP].

Note that, like all attribute options, the strings representing
   transfer encoding options are case insensitive.

All future registrations of option strings for transfer encoding
   options should use the "transfer-" prefix so that LDAP clients and
   servers can recognize that an option is a transfer encoding option
   even though the particular encoding rules may be unrecognized.

5.  Attributes Returned in a Search

An LDAP search request [PROT] contains a list of the attributes (the
   requested attributes list) to be returned from each entry matching
   the search filter.  An attribute description in the requested
   attributes list also implicitly requests all subtypes of the
   attribute type in the attribute description, whether through
   attribute subtyping or attribute tagging option subtyping [MODELS].

The requested attributes list MAY contain attribute descriptions with
   a transfer encoding option, but MUST NOT contain two attribute
   descriptions with the same attribute type and the same tagging
   options (even if only one of them has a transfer encoding option).  A
   transfer encoding option in an attribute description in the requested
   attributes list implicitly applies to the subtypes of the attribute
   type in the attribute description.

If the list of attributes in a search request is empty, or contains
   the special attribute description string "*", then all user
   attributes are requested to be returned.

In general, it is possible for a particular attribute to be
   explicitly requested by an attribute description and/or implicitly
   requested by the attribute descriptions of one or more of its
   supertypes.  In such cases the effective transfer encoding being
   requested for a particular attribute is determined by the transfer
   encoding option (or lack thereof) in the most specific attribute
   description in the requested attributes list that applies to the
   attribute.

An applicable attribute description with an actual attribute type is
   more specific than the special attribute description string "*".

If the attribute type of one applicable attribute description is a
   direct or indirect subtype of the attribute type in another
   applicable attribute description then the former attribute
   description is more specific than the latter attribute description.

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If two applicable attribute descriptions have the same attribute type
   and the tagging options of one attribute description are a superset
   of the tagging options of the other attribute description then the
   former attribute description is more specific than the latter
   attribute description.

Attributes MUST either be returned in the effective transfer encoding
   requested, be returned with no attribute values, or be omitted from
   the results.  An attribute SHALL NOT be returned using an encoding
   other than the effective transfer encoding requested.

Regardless of the encoding chosen, a particular attribute value is
   returned at most once.

6.  Syntaxes Requiring Binary Transfer

Certain syntaxes are required to be transferred in the BER encoded
   form.  These syntaxes are said to have a binary transfer requirement.
   The Certificate, Certificate List, Certificate Pair and Supported
   Algorithm syntaxes [PKI] are examples of syntaxes with a binary
   transfer requirement.  These syntaxes also have an additional
   requirement that the exact BER encoding must be preserved.  Note that
   this is a property of the syntaxes themselves, and not a property of
   the binary option or any of the transfer encoding options.

Transfer encoding options SHALL take precedence over the requirement
   for binary transfer.  For example, if the effective transfer encoding
   requested is say "transfer-gser", then attribute values of a syntax
   with a binary transfer requirement will be GSER encoded.  In the
   absence of a transfer encoding option the normal rules on binary
   transfer and the use of the binary option SHALL apply.

7.  Security Considerations

There is a requirement on some attribute syntaxes that the exact BER
   encoding of values of that syntax be preserved.  In general, a
   transformation from the BER encoding into some other encoding (e.g.,
   GSER) and back into the BER encoding will not necessarily reproduce
   exactly the octets of the original BER encoding.

Applications needing the original BER encoding to be preserved, e.g.,
   for the verification of digital signatures, MUST NOT request
   attributes with such a requirement using a transfer encoding option.
   These attributes MUST be requested explicitly or implicitly with the
   binary option, or implicitly without the binary option (or any
   transfer encoding option).

When interpreting security-sensitive fields, and in particular fields

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used to grant or deny access, implementations MUST ensure that any
   matching rule comparisons are done on the underlying abstract value,
   regardless of the particular encoding used.

8.  IANA Considerations

The Internet Assigned Numbers Authority (IANA) is requested to update
   the LDAP attribute description option registry [BCP64] as indicated
   by the following templates:

Subject: Request for
        LDAP Attribute Description Option Registration
      Option Name: transfer-ber
      Family of Options: NO
      Person & email address to contact for further information:
        Steven Legg <steven.legg@adacel.com.au>
      Specification: RFC XXXX
      Author/Change Controller: IESG
      Comments:

Subject: Request for
        LDAP Attribute Description Option Registration
      Option Name: transfer-der
      Family of Options: NO
      Person & email address to contact for further information:
        Steven Legg <steven.legg@adacel.com.au>
      Specification: RFC XXXX
      Author/Change Controller: IESG
      Comments:

Subject: Request for
        LDAP Attribute Description Option Registration
      Option Name: transfer-gser
      Family of Options: NO
      Person & email address to contact for further information:
        Steven Legg <steven.legg@adacel.com.au>
      Specification: RFC XXXX
      Author/Change Controller: IESG
      Comments:

Subject: Request for
        LDAP Attribute Description Option Registration
      Option Name: transfer-rxer
      Family of Options: NO
      Person & email address to contact for further information:
        Steven Legg <steven.legg@adacel.com.au>
      Specification: RFC XXXX
      Author/Change Controller: IESG

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Comments:

9.  References

9.1.  Normative References

[KEYWORD]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

[BCP64]    Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
              Considerations for the Lightweight Directory Access
              Protcol (LDAP)", BCP 64, RFC 3383, September 2002.

[ROADMAP]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Technical Specification Road Map",
              draft-ietf-ldapbis-roadmap-xx.txt, a work in progress,
              June 2004.

[MODELS]   Zeilenga, K., "LDAP: Directory Information Models",
              draft-ietf-ldapbis-models-xx.txt, a work in progress, June
              2004.

[PROT]     Sermersheim, J., "LDAP: The Protocol",
              draft-ietf-ldapbis-protocol-xx.txt, a work in progress,
              May 2004.

[SYNTAX]   Legg, S. and K. Dally, "Lightweight Directory Access
              Protocol (LDAP): Syntaxes and Matching Rules",
              draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress,
              May 2004.

[RFC3641]  Legg, S., "Generic String Encoding Rules (GSER) for ASN.1
              Types", RFC 3641, October 2003.

[BINARY]   Legg, S., "Lightweight Directory Access Protocol (LDAP):
              The Binary Encoding Option",
              draft-legg-ldap-binary-xx.txt, a work in progress, June
              2004.

[RXER]     Legg, S. and D. Prager, "Robust XML Encoding Rules for
              ASN.1 Types", draft-legg-xed-rxer-00.txt, a work in
              progress, June 2004.

[X680]     ITU-T Recommendation X.680 (07/02) | ISO/IEC 8824-1,
              Information technology - Abstract Syntax Notation One
              (ASN.1): Specification of basic notation.

[X690]     ITU-T Recommendation X.690 (07/02) | ISO/IEC 8825-1,

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Information Technology - ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER).

[XML]      Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E. and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Third
              Edition)", W3C Recommendation,
              http://www.w3.org/TR/2004/REC-xml-20040204, February 2004.

[ISET]     Cowan, J. and R. Tobin, "XML Information Set",
              http://www.w3.org/TR/2001/REC-xml-infoset-20011024,
              October 2001.

9.2.  Informative References

[XLDAP]    Legg, S. and D. Prager, "The XML Enabled Directory:
              Protocols", draft-legg-xed-protocols-xx.txt, a work in
              progress, May 2004.

Author's Address

Steven Legg
   Adacel Technologies Ltd.
   250 Bay Street
   Brighton, Victoria 3186
   AUSTRALIA

Phone: +61 3 8530 7710
     Fax: +61 3 8530 7888
   Email: steven.legg@adacel.com.au

Full Copyright Statement

Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

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The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
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Changes in Draft 01

A transfer encoding option for RXER has been added.

Changes in Draft 02

The local name of the root element of the XML document representing
   an attribute value encoded according to the transfer-rxer encoding
   option has been changed from "item" to "value" to align with
   revisions to the LDAP protocol specification [PROT].

The Directory XML Encoding Rules (DXER) have been renamed to the
   Robust XML Encoding Rules (RXER).

Changes in Draft 03

The special attribute description strings that consist of the
   asterisk character followed by a transfer encoding option, e.g.,
   "*;transfer-ber", "*;transfer-gser", have been removed from this
   specification.  An LDAP control will be defined in a separate
   document to provide equivalent functionality.

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