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✏️ Editing: rfc4522.txt

Network Working Group                                            S. Legg
Request for Comments: 4522                                       eB2Bcom
Category: Standards Track                                      June 2006

Lightweight Directory Access Protocol (LDAP):
                       The Binary Encoding Option

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

Each attribute stored in a Lightweight Directory Access Protocol
   (LDAP) directory has a defined syntax (i.e., data type).  A syntax
   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 defines an attribute option, the binary option, that can be
   used to specify that the associated attribute values are instead
   encoded according to the Basic Encoding Rules (BER) used by X.500
   directories.

Table of Contents

1. Introduction ....................................................2
   2. Conventions .....................................................2
   3. The Binary Option ...............................................2
   4. Syntaxes Requiring Binary Transfer ..............................3
   5. Attributes Returned in a Search .................................4
   6. All User Attributes .............................................4
   7. Conflicting Requests ............................................5
   8. Security Considerations .........................................5
   9. IANA Considerations .............................................5
   10. References .....................................................5
      10.1. Normative References ......................................5
      10.2. Informative References ....................................6

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RFC 4522            LDAP: The Binary Encoding Option           June 2006

1.  Introduction

Each attribute stored in a Lightweight Directory Access Protocol
   (LDAP) directory [RFC4510] has a defined syntax (i.e., data type)
   which constrains the structure and format of its values.

The description of each syntax [RFC4517] specifies how attribute or
   assertion values [RFC4512] conforming to the syntax are normally
   represented when transferred in LDAP operations [RFC4511].  This
   representation is referred to as the LDAP-specific encoding to
   distinguish it from other methods of encoding attribute values.

This document defines an attribute option, the binary option, which
   can be used in an attribute description [RFC4512] in an LDAP
   operation to specify that the associated attribute values or
   assertion values are, or are requested to be, encoded according to
   the Basic Encoding Rules (BER) [BER] as used by X.500 [X.500]
   directories, instead of the usual LDAP-specific encoding.

The binary option was originally defined in RFC 2251 [RFC2251].  The
   LDAP technical specification [RFC4510] has obsoleted the previously
   defined LDAP technical specification [RFC3377], which included RFC
   2251.  The binary option was not included in the revised LDAP
   technical specification for a variety of reasons including
   implementation inconsistencies.  No attempt is made here to resolve
   the known inconsistencies.

This document reintroduces the binary option for use with certain
   attribute syntaxes, such as certificate syntax [RFC4523], that
   specifically require it.  No attempt has been made to address use of
   the binary option with attributes of syntaxes that do not require its
   use.  Unless addressed in a future specification, this use is to be
   avoided.

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
   [BCP14].

3.  The Binary Option

The binary option is indicated with the attribute option string
   "binary" in an attribute description.  Note that, like all attribute
   options, the string representing the binary option is case
   insensitive.

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RFC 4522            LDAP: The Binary Encoding Option           June 2006

Where the binary option is present in an attribute description, the
   associated attribute values or assertion values MUST be BER encoded
   (otherwise the values are encoded according to the LDAP-specific
   encoding [RFC4517] for the attribute's syntax).  Note that it is
   possible for a syntax to be defined such that its LDAP-specific
   encoding is exactly the same as its BER encoding.

In terms of the protocol [RFC4511], the binary option specifies that
   the contents octets of the associated AttributeValue or
   AssertionValue OCTET STRING are a complete BER encoding of the
   relevant value.

The binary option is not a tagging option [RFC4512], so the presence
   of the binary option does not specify an attribute subtype.  An
   attribute description containing the binary option references exactly
   the same attribute as the attribute description without the binary
   option.  The supertype/subtype relationships of attributes with
   tagging options are not altered in any way by the presence or absence
   of the binary option.

An attribute description SHALL be treated as unrecognized if it
   contains the binary option and the syntax of the attribute does not
   have an associated ASN.1 type [RFC4517], or the BER encoding of
   values of that type is not supported.

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

4.  Syntaxes Requiring Binary Transfer

The attribute values of certain attribute syntaxes are defined
   without an LDAP-specific encoding and are required to be transferred
   in the BER-encoded form.  For the purposes of this document, these
   syntaxes are said to have a binary transfer requirement.  The
   certificate, certificate list, certificate pair, and supported
   algorithm syntaxes [RFC4523] 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.  In the absence of this requirement, LDAP clients
   would need to re-encode values using the Distinguished Encoding Rules
   (DER).

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RFC 4522            LDAP: The Binary Encoding Option           June 2006

5.  Attributes Returned in a Search

An LDAP search request [RFC4511] 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 [RFC4512].

The requested attributes list MAY contain attribute descriptions with
   the binary 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 the binary option).  The binary option in an
   attribute description in the requested attributes list implicitly
   applies to all the subtypes of the attribute type in the attribute
   description (however, see Section 7).

Attributes of a syntax with the binary transfer requirement, if
   returned, SHALL be returned in the binary form (i.e., with the binary
   option in the attribute description and the associated attribute
   values BER encoded) regardless of whether the binary option was
   present in the request (for the attribute or for one of its
   supertypes).

Attributes of a syntax without the binary transfer requirement, if
   returned, SHOULD be returned in the form explicitly requested.  That
   is, if the attribute description in the requested attributes list
   contains the binary option, then the corresponding attribute in the
   result SHOULD be in the binary form.  If the attribute description in
   the request does not contain the binary option, then the
   corresponding attribute in the result SHOULD NOT be in the binary
   form.  A server MAY omit an attribute from the result if it does not
   support the requested encoding.

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

6.  All User Attributes

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.

Attributes of a syntax with the binary transfer requirement, if
   returned, SHALL be returned in the binary form.

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RFC 4522            LDAP: The Binary Encoding Option           June 2006

Attributes of a syntax without the binary transfer requirement and
   having a defined LDAP-specific encoding SHOULD NOT be returned in the
   binary form.

Attributes of a syntax without the binary transfer requirement and
   without a defined LDAP-specific encoding may be returned in the
   binary form or omitted from the result.

7.  Conflicting Requests

A particular attribute could be explicitly requested by an attribute
   description and/or implicitly requested by the attribute descriptions
   of one or more of its supertypes, or by the special attribute
   description string "*".  If the binary option is present in at least
   one, but not all, of these attribute descriptions then the effect of
   the request with respect to binary transfer is implementation
   defined.

8.  Security Considerations

When interpreting security-sensitive fields, and in particular fields
   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.

9.  IANA Considerations

The Internet Assigned Numbers Authority (IANA) has updated the LDAP
   attribute description option registry [BCP64] as indicated by the
   following template:

Subject:
        Request for LDAP Attribute Description Option Registration
      Option Name: binary
      Family of Options: NO
      Person & email address to contact for further information:
        Steven Legg <steven.legg@eb2bcom.com>
      Specification: RFC 4522
      Author/Change Controller: IESG

10.  References

10.1.  Normative References

[BCP14]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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RFC 4522            LDAP: The Binary Encoding Option           June 2006

[BCP64]    Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
              Considerations for the Lightweight Directory Access
              Protocol (LDAP)", BCP 64, RFC 4520, June 2006.

[RFC4510]  Zeilenga, K., Ed., "Lightweight Directory Access Protocol
              (LDAP): Technical Specification Road Map", RFC RFC 4510,
              June 2006.

[RFC4511]  Sermersheim, J., "Lightweight Directory Access Protocol
              (LDAP): The Protocol", RFC 4511, June 2006.

[RFC4512]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Directory Information Models", RFC 4512, June
              2006.

[RFC4517]  Legg, S., Ed., "Lightweight Directory Access Protocol
              (LDAP):  Syntaxes and Matching Rules", RFC 4517, June
              2006.

[RFC4523]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP) Schema Definitions for X.509 Certificates", RFC
              4523, June 2006.

[BER]      ITU-T Recommendation X.690 (07/02) | ISO/IEC 8825-1,
              Information Technology - ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER).

10.2.  Informative References

[RFC2251]  Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
              Access Protocol (v3)", RFC 2251, December 1997.

[RFC3377]  Hodges, J. and R. Morgan, "Lightweight Directory Access
              Protocol (v3): Technical Specification", RFC 3377,
              September 2002.

[X.500]    ITU-T Recommendation X.500 (02/01) | ISO/IEC 9594-1:2001,
              Information technology - Open Systems Interconnection -
              The Directory:  Overview of concepts, models and services

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RFC 4522            LDAP: The Binary Encoding Option           June 2006

Author's Address

Dr. Steven Legg
   eB2Bcom
   Suite 3, Woodhouse Corporate Centre
   935 Station Street
   Box Hill North, Victoria 3129
   AUSTRALIA

Phone: +61 3 9896 7830
   Fax:   +61 3 9896 7801
   EMail: steven.legg@eb2bcom.com

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RFC 4522            LDAP: The Binary Encoding Option           June 2006

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