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rfc:rfc4522

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.

Copyright Notice

 Copyright (C) The Internet Society (2006).

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

Legg Standards Track [Page 1] 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.

Legg Standards Track [Page 2] 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).

Legg Standards Track [Page 3] 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.

Legg Standards Track [Page 4] 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.

Legg Standards Track [Page 5] 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

Legg Standards Track [Page 6] 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

Legg Standards Track [Page 7] RFC 4522 LDAP: The Binary Encoding Option June 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 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.

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 Intellectual Property Rights or other rights that might be claimed to
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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Legg Standards Track [Page 8]

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