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Keywords: syntax data schema
Network Working Group S. Legg
Request for Comments: 3687 Adacel Technologies
Category: Standards Track February 2004
Lightweight Directory Access Protocol (LDAP)
and X.500 Component Matching Rules
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 (2004). All Rights Reserved.
Abstract
The syntaxes of attributes in a Lightweight Directory Access Protocol
(LDAP) or X.500 directory range from simple data types, such as text
string, integer, or boolean, to complex structured data types, such
as the syntaxes of the directory schema operational attributes.
Matching rules defined for the complex syntaxes usually only provide
the most immediately useful matching capability. This document
defines generic matching rules that can match any user selected
component parts in an attribute value of any arbitrarily complex
attribute syntax.
Legg Standards Track [Page 1]
RFC 3687 LDAP and X.500 Component Matching Rules February 2004
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. ComponentAssertion . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Component Reference. . . . . . . . . . . . . . . . . . . 6
3.1.1. Component Type Substitutions . . . . . . . . . . 7
3.1.2. Referencing SET, SEQUENCE and CHOICE Components. 8
3.1.3. Referencing SET OF and SEQUENCE OF Components. . 9
3.1.4. Referencing Components of Parameterized Types. . 10
3.1.5. Component Referencing Example. . . . . . . . . . 10
3.1.6. Referencing Components of Open Types . . . . . . 12
3.1.6.1. Open Type Referencing Example . . . . . 12
3.1.7. Referencing Contained Types. . . . . . . . . . . 14
3.1.7.1. Contained Type Referencing Example. . . 14
3.2. Matching of Components . . . . . . . . . . . . . . . . . 15
3.2.1. Applicability of Existing Matching Rules . . . . 17
3.2.1.1. String Matching . . . . . . . . . . . . 17
3.2.1.2. Telephone Number Matching . . . . . . . 17
3.2.1.3. Distinguished Name Matching . . . . . . 18
3.2.2. Additional Useful Matching Rules . . . . . . . . 18
3.2.2.1. The rdnMatch Matching Rule. . . . . . . 18
3.2.2.2. The presentMatch Matching Rule. . . . . 19
3.2.3. Summary of Useful Matching Rules . . . . . . . . 20
4. ComponentFilter. . . . . . . . . . . . . . . . . . . . . . . . 21
5. The componentFilterMatch Matching Rule . . . . . . . . . . . . 22
6. Equality Matching of Complex Components. . . . . . . . . . . . 24
6.1. The OpenAssertionType Syntax . . . . . . . . . . . . . . 24
6.2. The allComponentsMatch Matching Rule . . . . . . . . . . 25
6.3. Deriving Component Equality Matching Rules . . . . . . . 27
6.4. The directoryComponentsMatch Matching Rule . . . . . . . 28
7. Component Matching Examples. . . . . . . . . . . . . . . . . . 30
8. Security Considerations. . . . . . . . . . . . . . . . . . . . 37
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 37
10. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 37
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
11.1. Normative References. . . . . . . . . . . . . . . . . . 38
11.2. Informative References. . . . . . . . . . . . . . . . . 40
12. Intellectual Property Statement. . . . . . . . . . . . . . . . 40
13. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 41
14. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 42
Legg Standards Track [Page 2]
RFC 3687 LDAP and X.500 Component Matching Rules February 2004
1. Introduction
The structure or data type of data held in an attribute of a
Lightweight Directory Access Protocol (LDAP) [7] or X.500 [19]
directory is described by the attribute's syntax. Attribute syntaxes
range from simple data types, such as text string, integer, or
boolean, to complex data types, for example, the syntaxes of the
directory schema operational attributes.
In X.500, the attribute syntaxes are explicitly described by Abstract
Syntax Notation One (ASN.1) [13] type definitions. ASN.1 type
notation has a number of simple data types (e.g., PrintableString,
INTEGER, BOOLEAN), and combining types (i.e., SET, SEQUENCE, SET OF,
SEQUENCE OF, and CHOICE) for constructing arbitrarily complex data
types from simpler component types. In LDAP, the attribute syntaxes
are usually described in Augmented Backus-Naur Form (ABNF) [2],
though there is an implied association between the LDAP attribute
syntaxes and the X.500 ASN.1 types. To a large extent, the data
types of attribute values in either an LDAP or X.500 directory are
described by ASN.1 types. This formal description can be exploited
to identify component parts of an attribute value for a variety of
purposes. This document addresses attribute value matching.
With any complex attribute syntax there is normally a requirement to
partially match an attribute value of that syntax by matching only
selected components of the value. Typically, matching rules specific
to the attribute syntax are defined to fill this need. These highly
specific matching rules usually only provide the most immediately
useful matching capability. Some complex attribute syntaxes don't
even have an equality matching rule let alone any additional matching
rules for partial matching. This document defines a generic way of
matching user selected components in an attribute value of any
arbitrarily complex attribute syntax, where that syntax is described
using ASN.1 type notation. All of the type notations defined in
X.680 [13] are supported.
Section 3 describes the ComponentAssertion, a testable assertion
about the value of a component of an attribute value of any complex
syntax.
Section 4 introduces the ComponentFilter assertion, which is an
expression of ComponentAssertions. The ComponentFilter enables more
powerful filter matching of components in an attribute value.
Section 5 defines the componentFilterMatch matching rule, which
enables a ComponentFilter to be evaluated against attribute values.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
Section 6 defines matching rules for component-wise equality matching
of attribute values of any syntax described by an ASN.1 type
definition.
Examples showing the usage of componentFilterMatch are in Section 7.
For a new attribute syntax, the Generic String Encoding Rules [9] and
the specifications in sections 3 to 6 of this document make it
possible to fully and precisely define the LDAP-specific encoding,
the LDAP and X.500 binary encoding (and possibly other ASN.1
encodings in the future), a suitable equality matching rule, and a
comprehensive collection of component matching capabilities, by
simply writing down an ASN.1 type definition for the syntax. These
implicit definitions are also automatically extended if the ASN.1
type is later extended. The algorithmic relationship between the
ASN.1 type definition, the various encodings and the component
matching behaviour makes directory server implementation support for
the component matching rules amenable to automatic code generation
from ASN.1 type definitions.
Schema designers have the choice of storing related items of data as
a single attribute value of a complex syntax in some entry, or as a
subordinate entry where the related data items are stored as separate
attribute values of simpler syntaxes. The inability to search
component parts of a complex syntax has been used as an argument for
favouring the subordinate entries approach. The component matching
rules provide the analogous matching capability on an attribute value
of a complex syntax that a search filter has on a subordinate entry.
Most LDAP syntaxes have corresponding ASN.1 type definitions, though
they are usually not reproduced or referenced alongside the formal
definition of the LDAP syntax. Syntaxes defined with only a
character string encoding, i.e., without an explicit or implied
corresponding ASN.1 type definition, cannot use the component
matching capabilities described in this document unless and until a
semantically equivalent ASN.1 type definition is defined for them.
2. Conventions
Throughout this document "type" shall be taken to mean an ASN.1 type
unless explicitly qualified as an attribute type, and "value" shall
be taken to mean an ASN.1 value unless explicitly qualified as an
attribute value.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
Note that "ASN.1 value" does not mean a Basic Encoding Rules (BER)
[17] encoded value. The ASN.1 value is an abstract concept that is
independent of any particular encoding. BER is just one possible
encoding of an ASN.1 value. The component matching rules operate at
the abstract level without regard for the possible encodings of a
value.
Attribute type and matching rule definitions in this document are
provided in both the X.500 [10] and LDAP [4] description formats.
Note that the LDAP descriptions have been rendered with additional
white-space and line breaks for the sake of readability.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED" and "MAY" in this document are
to be interpreted as described in BCP 14, RFC 2119 [1]. The key word
"OPTIONAL" is exclusively used with its ASN.1 meaning.
3. ComponentAssertion
A ComponentAssertion is an assertion about the presence, or values
of, components within an ASN.1 value, i.e., an instance of an ASN.1
type. The ASN.1 value is typically an attribute value, where the
ASN.1 type is the syntax of the attribute. However, a
ComponentAssertion may also be applied to a component part of an
attribute value. The assertion evaluates to either TRUE, FALSE or
Undefined for each tested ASN.1 value.
A ComponentAssertion is described by the following ASN.1 type
(assumed to be defined with "EXPLICIT TAGS" in force):
ComponentAssertion ::= SEQUENCE {
component ComponentReference (SIZE(1..MAX)) OPTIONAL,
useDefaultValues BOOLEAN DEFAULT TRUE,
rule MATCHING-RULE.&id,
value MATCHING-RULE.&AssertionType }
ComponentReference ::= UTF8String
MATCHING-RULE.&id equates to the OBJECT IDENTIFIER of a matching
rule. MATCHING-RULE.&AssertionType is an open type (formerly known
as the ANY type).
The "component" field of a ComponentAssertion identifies which
component part of a value of some ASN.1 type is to be tested, the
"useDefaultValues" field indicates whether DEFAULT values are to be
substituted for absent component values, the "rule" field indicates
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
how the component is to be tested, and the "value" field is an
asserted ASN.1 value against which the component is tested. The
ASN.1 type of the asserted value is determined by the chosen rule.
The fields of a ComponentAssertion are described in detail in the
following sections.
3.1. Component Reference
The component field in a ComponentAssertion is a UTF-8 character
string [6] whose textual content is a component reference,
identifying a component part of some ASN.1 type or value. A
component reference conforms to the following ABNF [2], which extends
the notation defined in Clause 14 of X.680 [13]:
component-reference = ComponentId *( "." ComponentId )
ComponentId = identifier /
from-beginning /
count /
from-end / ; extends Clause 14
content / ; extends Clause 14
select / ; extends Clause 14
all
identifier = lowercase *alphanumeric
*(hyphen 1*alphanumeric)
alphanumeric = uppercase / lowercase / decimal-digit
uppercase = %x41-5A ; "A" to "Z"
lowercase = %x61-7A ; "a" to "z"
hyphen = "-"
from-beginning = positive-number
count = "0"
from-end = "-" positive-number
content = %x63.6F.6E.74.65.6E.74 ; "content"
select = "(" Value *( "," Value ) ")"
all = "*"
positive-number = non-zero-digit *decimal-digit
decimal-digit = %x30-39 ; "0" to "9"
non-zero-digit = %x31-39 ; "1" to "9"
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
An <identifier> conforms to the definition of an identifier in ASN.1
notation (Clause 11.3 of X.680 [13]). It begins with a lowercase
letter and is followed by zero or more letters, digits, and hyphens.
A hyphen is not permitted to be the last character and a hyphen is
not permitted to be followed by another hyphen.
The <Value> rule is described by the Generic String Encoding Rules
(GSER) [9].
A component reference is a sequence of one or more ComponentIds where
each successive ComponentId identifies either an inner component at
the next level of nesting of an ASN.1 combining type, i.e., SET,
SEQUENCE, SET OF, SEQUENCE OF, or CHOICE, or a specific type within
an ASN.1 open type.
A component reference is always considered in the context of a
particular complex ASN.1 type. When applied to the ASN.1 type the
component reference identifies a specific component type. When
applied to a value of the ASN.1 type a component reference identifies
zero, one or more component values of that component type. The
component values are potentially in a DEFAULT value if
useDefaultValues is TRUE. The specific component type identified by
the component reference determines what matching rules are capable of
being used to match the component values.
The component field in a ComponentAssertion may also be absent, in
which case the identified component type is the ASN.1 type to which
the ComponentAssertion is applied, and the identified component value
is the whole ASN.1 value.
A valid component reference for a particular complex ASN.1 type is
constructed by starting with the outermost combining type and
repeatedly selecting one of the permissible forms of ComponentId to
identify successively deeper nested components. A component
reference MAY identify a component with a complex ASN.1 type, i.e.,
it is not required that the component type identified by a component
reference be a simple ASN.1 type.
3.1.1. Component Type Substitutions
ASN.1 type notation has a number of constructs for referencing other
defined types, and constructs that are irrelevant for matching
purposes. These constructs are not represented in a component
reference in any way and substitutions of the component type are
performed to eliminate them from further consideration. These
substitutions automatically occur prior to each ComponentId, whether
constructing or interpreting a component reference, but do not occur
after the last ComponentId, except as allowed by Section 3.2.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
If the ASN.1 type is an ASN.1 type reference then the component type
is taken to be the actual definition on the right hand side of the
type assignment for the referenced type.
If the ASN.1 type is a tagged type then the component type is taken
to be the type without the tag.
If the ASN.1 type is a constrained type (see X.680 [13] and X.682
[15] for the details of ASN.1 constraint notation) then the component
type is taken to be the type without the constraint.
If the ASN.1 type is an ObjectClassFieldType (Clause 14 of X.681
[14]) that denotes a specific ASN.1 type (e.g., MATCHING-RULE.&id
denotes the OBJECT IDENTIFIER type) then the component type is taken
to be the denoted type. Section 3.1.6 describes the case where the
ObjectClassFieldType denotes an open type.
If the ASN.1 type is a selection type other than one used in the list
of components for a SET or SEQUENCE type then the component type is
taken to be the selected alternative type from the named CHOICE.
If the ASN.1 type is a TypeFromObject (Clause 15 of X.681 [14]) then
the component type is taken to be the denoted type.
If the ASN.1 type is a ValueSetFromObjects (Clause 15 of X.681 [14])
then the component type is taken to be the governing type of the
denoted values.
3.1.2. Referencing SET, SEQUENCE and CHOICE Components
If the ASN.1 type is a SET or SEQUENCE type then the <identifier>
form of ComponentId may be used to identify the component type within
that SET or SEQUENCE having that identifier. If <identifier>
references an OPTIONAL component type and that component is not
present in a particular value then there are no corresponding
component values. If <identifier> references a DEFAULT component
type and useDefaultValues is TRUE (the default setting for
useDefaultValues) and that component is not present in a particular
value then the component value is taken to be the default value. If
<identifier> references a DEFAULT component type and useDefaultValues
is FALSE and that component is not present in a particular value then
there are no corresponding component values.
If the ASN.1 type is a CHOICE type then the <identifier> form of
ComponentId may be used to identify the alternative type within that
CHOICE having that identifier. If <identifier> references an
alternative other than the one used in a particular value then there
are no corresponding component values.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
The COMPONENTS OF notation in Clause 24 of X.680 [13] augments the
defined list of components in a SET or SEQUENCE type by including all
the components of another defined SET or SEQUENCE type respectively.
These included components are referenced directly by identifier as
though they were defined in-line in the SET or SEQUENCE type
containing the COMPONENTS OF notation.
The SelectionType (Clause 29 of X.680 [13]), when used in the list of
components for a SET or SEQUENCE type, includes a single component
from a defined CHOICE type. This included component is referenced
directly by identifier as though it was defined in-line in the SET or
SEQUENCE type.
The REAL type is treated as though it is the SEQUENCE type defined in
Clause 20.5 of X.680 [13].
The EMBEDDED PDV type is treated as though it is the SEQUENCE type
defined in Clause 33.5 of X.680 [13].
The EXTERNAL type is treated as though it is the SEQUENCE type
defined in Clause 8.18.1 of X.690 [17].
The unrestricted CHARACTER STRING type is treated as though it is the
SEQUENCE type defined in Clause 40.5 of X.680 [13].
The INSTANCE OF type is treated as though it is the SEQUENCE type
defined in Annex C of X.681 [14].
The <identifier> form MUST NOT be used on any other ASN.1 type.
3.1.3. Referencing SET OF and SEQUENCE OF Components
If the ASN.1 type is a SET OF or SEQUENCE OF type then the
<from-beginning>, <from-end>, <count> and <all> forms of ComponentId
may be used.
The <from-beginning> form of ComponentId may be used to identify one
instance (i.e., value) of the component type of the SET OF or
SEQUENCE OF type (e.g., if Foo ::= SET OF Bar, then Bar is the
component type), where the instances are numbered from one upwards.
If <from-beginning> references a higher numbered instance than the
last instance in a particular value of the SET OF or SEQUENCE OF type
then there is no corresponding component value.
The <from-end> form of ComponentId may be used to identify one
instance of the component type of the SET OF or SEQUENCE OF type,
where "-1" is the last instance, "-2" is the second last instance,
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
and so on. If <from-end> references a lower numbered instance than
the first instance in a particular value of the SET OF or SEQUENCE OF
type then there is no corresponding component value.
The <count> form of ComponentId identifies a notional count of the
number of instances of the component type in a value of the SET OF or
SEQUENCE OF type. This count is not explicitly represented but for
matching purposes it has an assumed ASN.1 type of INTEGER (0..MAX).
A ComponentId of the <count> form, if used, MUST be the last
ComponentId in a component reference.
The <all> form of ComponentId may be used to simultaneously identify
all instances of the component type of the SET OF or SEQUENCE OF
type. It is through the <all> form that a component reference can
identify more than one component value. However, if a particular
value of the SET OF or SEQUENCE OF type is an empty list, then there
are no corresponding component values.
Where multiple component values are identified, the remaining
ComponentIds in the component reference, if any, can identify zero,
one or more subcomponent values for each of the higher level
component values.
The corresponding ASN.1 type for the <from-beginning>, <from-end>,
and <all> forms of ComponentId is the component type of the SET OF or
SEQUENCE OF type.
The <from-beginning>, <count>, <from-end> and <all> forms MUST NOT be
used on ASN.1 types other than SET OF or SEQUENCE OF.
3.1.4. Referencing Components of Parameterized Types
A component reference cannot be formed for a parameterized type
unless the type has been used with actual parameters, in which case
the type is treated as though the DummyReferences [16] have been
substituted with the actual parameters.
3.1.5. Component Referencing Example
Consider the following ASN.1 type definitions.
ExampleType ::= SEQUENCE {
part1 [0] INTEGER,
part2 [1] ExampleSet,
part3 [2] SET OF OBJECT IDENTIFIER,
part4 [3] ExampleChoice }
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
ExampleSet ::= SET {
option PrintableString,
setting BOOLEAN }
ExampleChoice ::= CHOICE {
eeny-meeny BIT STRING,
miney-mo OCTET STRING }
Following are component references constructed with respect to the
type ExampleType.
The component reference "part1" identifies a component of a value of
ExampleType having the ASN.1 tagged type [0] INTEGER.
The component reference "part2" identifies a component of a value of
ExampleType having the ASN.1 type of [1] ExampleSet
The component reference "part2.option" identifies a component of a
value of ExampleType having the ASN.1 type of PrintableString. A
ComponentAssertion could also be applied to a value of ASN.1 type
ExampleSet, in which case the component reference "option" would
identify the same kind of information.
The component reference "part3" identifies a component of a value of
ExampleType having the ASN.1 type of [2] SET OF OBJECT IDENTIFIER.
The component reference "part3.2" identifies the second instance of
the part3 SET OF. The instance has the ASN.1 type of OBJECT
IDENTIFIER.
The component reference "part3.0" identifies the count of the number
of instances in the part3 SET OF. The count has the corresponding
ASN.1 type of INTEGER (0..MAX).
The component reference "part3.*" identifies all the instances in the
part3 SET OF. Each instance has the ASN.1 type of OBJECT IDENTIFIER.
The component reference "part4" identifies a component of a value of
ExampleType having the ASN.1 type of [3] ExampleChoice.
The component reference "part4.miney-mo" identifies a component of a
value of ExampleType having the ASN.1 type of OCTET STRING.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
3.1.6. Referencing Components of Open Types
If a sequence of ComponentIds identifies an ObjectClassFieldType
denoting an open type (e.g., ATTRIBUTE.&Type denotes an open type)
then the ASN.1 type of the component varies. An open type is
typically constrained by some other component(s) in an outer
enclosing type, either formally through the use of a component
relation constraint [15], or informally in the accompanying text, so
the actual ASN.1 type of a value of the open type will generally be
known. The constraint will also limit the range of permissible
types. The <select> form of ComponentId may be used to identify one
of these permissible types in an open type. Subcomponents of that
type can then be identified with further ComponentIds.
The other components constraining the open type are termed the
referenced components [15]. The <select> form contains a list of one
or more values which take the place of the value(s) of the referenced
component(s) to uniquely identify one of the permissible types of the
open type.
Where the open type is constrained by a component relation
constraint, there is a <Value> in the <select> form for each of the
referenced components in the component relation constraint, appearing
in the same order. The ASN.1 type of each of these values is the
same as the ASN.1 type of the corresponding referenced component.
The type of a referenced component is potentially any ASN.1 type
however it is typically an OBJECT IDENTIFIER or INTEGER, which means
that the <Value> in the <select> form of ComponentId will nearly
always be an <ObjectIdentifierValue> or <IntegerValue> [9].
Furthermore, component relation constraints typically have only one
referenced component.
Where the open type is not constrained by a component relation
constraint, the specification introducing the syntax containing the
open type should explicitly nominate the referenced components and
their order, so that the <select> form can be used.
If an instance of <select> contains a value other than the value of
the referenced component used in a particular value of the outer
enclosing type then there are no corresponding component values for
the open type.
3.1.6.1. Open Type Referencing Example
The ASN.1 type AttributeTypeAndValue [10] describes a single
attribute value of a nominated attribute type.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
AttributeTypeAndValue ::= SEQUENCE {
type ATTRIBUTE.&id ({SupportedAttributes}),
value ATTRIBUTE.&Type ({SupportedAttributes}{@type}) }
ATTRIBUTE.&id denotes an OBJECT IDENTIFIER and
({SupportedAttributes}) constrains the OBJECT IDENTIFIER to be a
supported attribute type.
ATTRIBUTE.&Type denotes an open type, in this case an attribute
value, and ({SupportedAttributes}{@type}) is a component relation
constraint that constrains the open type to be of the attribute
syntax for the attribute type. The component relation constraint
references only the "type" component, which has the ASN.1 type of
OBJECT IDENTIFIER, thus if the <select> form of ComponentId is used
to identify attribute values of specific attribute types it will
contain a single OBJECT IDENTIFIER value.
The component reference "value" on AttributeTypeAndValue refers to
the open type.
One of the X.500 standard attributes is facsimileTelephoneNumber
[12], which is identified with the OBJECT IDENTIFIER 2.5.4.23, and is
defined to have the following syntax.
FacsimileTelephoneNumber ::= SEQUENCE {
telephoneNumber PrintableString(SIZE(1..ub-telephone-number)),
parameters G3FacsimileNonBasicParameters OPTIONAL }
The component reference "value.(2.5.4.23)" on AttributeTypeAndValue
specifies an attribute value with the FacsimileTelephoneNumber
syntax.
The component reference "value.(2.5.4.23).telephoneNumber" on
AttributeTypeAndValue identifies the telephoneNumber component of a
facsimileTelephoneNumber attribute value. The component reference
"value.(facsimileTelephoneNumber)" is equivalent to
"value.(2.5.4.23)".
If the AttributeTypeAndValue ASN.1 value contains an attribute type
other than facsimileTelephoneNumber then there are no corresponding
component values for the component references "value.(2.5.4.23)" and
"value.(2.5.4.23).telephoneNumber".
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
3.1.7. Referencing Contained Types
Sometimes the contents of a BIT STRING or OCTET STRING value are
required to be the encodings of other ASN.1 values of specific ASN.1
types. For example, the extnValue component of the Extension type
component in the Certificate type [11] is an OCTET STRING that is
required to contain a Distinguished Encoding Rules (DER) [17]
encoding of a certificate extension value. It is useful to be able
to refer to the embedded encoded value and its components. An
embedded encoded value is here referred to as a contained value and
its associated type as the contained type.
If the ASN.1 type is a BIT STRING or OCTET STRING type containing
encodings of other ASN.1 values then the <content> form of
ComponentId may be used to identify the contained type.
Subcomponents of that type can then be identified with further
ComponentIds.
The contained type may be (effectively) an open type, constrained by
some other component in an outer enclosing type (e.g., in a
certificate Extension, extnValue is constrained by the chosen
extnId). In these cases the next ComponentId, if any, MUST be of the
<select> form.
For the purpose of building component references, the content of the
extnValue OCTET STRING in the Extension type is assumed to be an open
type having a notional component relation constraint with the extnId
component as the single referenced component, i.e.,
EXTENSION.&ExtnType ({ExtensionSet}{@extnId})
The data-value component of the associated types for the EMBEDDED PDV
and CHARACTER STRING types is an OCTET STRING containing the encoding
of a data value described by the identification component. For the
purpose of building component references, the content of the
data-value OCTET STRING in these types is assumed to be an open type
having a notional component relation constraint with the
identification component as the single referenced component.
3.1.7.1. Contained Type Referencing Example
The Extension ASN.1 type [11] describes a single certificate
extension value of a nominated extension type.
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Extension ::= SEQUENCE {
extnId EXTENSION.&id ({ExtensionSet}),
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING
-- contains a DER encoding of a value of type &ExtnType
-- for the extension object identified by extnId -- }
EXTENSION.&id denotes an OBJECT IDENTIFIER and ({ExtensionSet})
constrains the OBJECT IDENTIFIER to be the identifier of a supported
certificate extension.
The component reference "extnValue" on Extension refers to a
component type of OCTET STRING. The corresponding component values
will be OCTET STRING values. The component reference
"extnValue.content" on Extension refers to the type of the contained
type, which in this case is an open type.
One of the X.509 [11] standard extensions is basicConstraints, which
is identified with the OBJECT IDENTIFIER 2.5.29.19 and is defined to
have the following syntax.
BasicConstraintsSyntax ::= SEQUENCE {
cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER (0..MAX) OPTIONAL }
The component reference "extnValue.content.(2.5.29.19)" on Extension
specifies a BasicConstraintsSyntax extension value and the component
reference "extnValue.content.(2.5.29.19).cA" identifies the cA
component of a BasicConstraintsSyntax extension value.
3.2. Matching of Components
The rule in a ComponentAssertion specifies how the zero, one or more
component values identified by the component reference are tested by
the assertion. Attribute matching rules are used to specify the
semantics of the test.
Each matching rule has a notional set of attribute syntaxes
(typically one), defined as ASN.1 types, to which it may be applied.
When used in a ComponentAssertion these matching rules apply to the
same ASN.1 types, only in this context the corresponding ASN.1 values
are not necessarily complete attribute values.
Note that the referenced component type may be a tagged and/or
constrained version of the expected attribute syntax (e.g.,
[0] INTEGER, whereas integerMatch would expect simply INTEGER), or an
open type. Additional type substitutions of the kind described in
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Section 3.1.1 are performed as required to reduce the component type
to the same type as the attribute syntax expected by the matching
rule.
If a matching rule applies to more than one attribute syntax (e.g.,
objectIdentifierFirstComponentMatch [12]) then the minimum number of
substitutions required to conform to any one of those syntaxes is
performed. If a matching rule can apply to any attribute syntax
(e.g., the allComponentsMatch rule defined in Section 6.2) then the
referenced component type is used as is, with no additional
substitutions.
The value in a ComponentAssertion will be of the assertion syntax
(i.e., ASN.1 type) required by the chosen matching rule. Note that
the assertion syntax of a matching rule is not necessarily the same
as the attribute syntax(es) to which the rule may be applied.
Some matching rules do not have a fixed assertion syntax (e.g.,
allComponentsMatch). The required assertion syntax is determined in
each instance of use by the syntax of the attribute type to which the
matching rule is applied. For these rules the ASN.1 type of the
referenced component is used in place of an attribute syntax to
decide the required assertion syntax.
The ComponentAssertion is Undefined if:
a) the matching rule in the ComponentAssertion is not known to the
evaluating procedure,
b) the matching rule is not applicable to the referenced component
type, even with the additional type substitutions,
c) the value in the ComponentAssertion does not conform to the
assertion syntax defined for the matching rule,
d) some part of the component reference identifies an open type in
the tested value that cannot be decoded, or
e) the implementation does not support the particular combination of
component reference and matching rule.
If the ComponentAssertion is not Undefined then the
ComponentAssertion evaluates to TRUE if there is at least one
component value for which the matching rule applied to that component
value returns TRUE, and evaluates to FALSE otherwise (which includes
the case where there are no component values).
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3.2.1. Applicability of Existing Matching Rules
3.2.1.1. String Matching
ASN.1 has a number of built in restricted character string types with
different character sets and/or different character encodings. A
directory user generally has little interest in the particular
character set or encoding used to represent a character string
component value, and some directory server implementations make no
distinction between the different string types in their internal
representation of values. So rather than define string matching
rules for each of the restricted character string types, the existing
case ignore and case exact string matching rules are extended to
apply to component values of any of the restricted character string
types and any ChoiceOfStrings type [9], in addition to component
values of the DirectoryString type. This extension is only for the
purposes of component matching described in this document.
The relevant string matching rules are: caseIgnoreMatch,
caseIgnoreOrderingMatch, caseIgnoreSubstringsMatch, caseExactMatch,
caseExactOrderingMatch and caseExactSubstringsMatch. The relevant
restricted character string types are: NumericString,
PrintableString, VisibleString, IA5String, UTF8String, BMPString,
UniversalString, TeletexString, VideotexString, GraphicString and
GeneralString. A ChoiceOfStrings type is a purely syntactic CHOICE
of these ASN.1 string types. Note that GSER [9] declares each and
every use of the DirectoryString{} parameterized type to be a
ChoiceOfStrings type.
The assertion syntax of the string matching rules is still
DirectoryString regardless of the string syntax of the component
being matched. Thus an implementation will be called upon to compare
a DirectoryString value to a value of one of the restricted character
string types, or a ChoiceOfStrings type. As is the case when
comparing two DirectoryStrings where the chosen alternatives are of
different string types, the comparison proceeds so long as the
corresponding characters are representable in both character sets.
Otherwise matching returns FALSE.
3.2.1.2. Telephone Number Matching
Early editions of X.520 [12] gave the syntax of the telephoneNumber
attribute as a constrained PrintableString. The fourth edition of
X.520 equates the ASN.1 type name TelephoneNumber to the constrained
PrintableString and uses TelephoneNumber as the attribute and
assertion syntax. For the purposes of component matching,
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
telephoneNumberMatch and telephoneNumberSubstringsMatch are permitted
to be applied to any PrintableString value, as well as to
TelephoneNumber values.
3.2.1.3. Distinguished Name Matching
The DistinguishedName type is defined by assignment to be the same as
the RDNSequence type, however RDNSequence is sometimes directly used
in other type definitions. For the purposes of component matching,
distinguishedNameMatch is also permitted to be applied to values of
the RDNSequence type.
3.2.2. Additional Useful Matching Rules
This section defines additional matching rules that may prove useful
in ComponentAssertions. These rules may also be used in
extensibleMatch search filters [3].
3.2.2.1. The rdnMatch Matching Rule
The distinguishedNameMatch matching rule can match whole
distinguished names but it is sometimes useful to be able to match
specific Relative Distinguished Names (RDNs) in a Distinguished Name
(DN) without regard for the other RDNs in the DN. The rdnMatch
matching rule allows component RDNs of a DN to be tested.
The LDAP-style definitions for rdnMatch and its assertion syntax are:
( 1.2.36.79672281.1.13.3 NAME 'rdnMatch'
SYNTAX 1.2.36.79672281.1.5.0 )
( 1.2.36.79672281.1.5.0 DESC 'RDN' )
The LDAP-specific encoding for a value of the RDN syntax is given by
the <RelativeDistinguishedNameValue> rule [9].
The X.500-style definition for rdnMatch is:
rdnMatch MATCHING-RULE ::= {
SYNTAX RelativeDistinguishedName
ID { 1 2 36 79672281 1 13 3 } }
The rdnMatch rule evaluates to true if the component value and
assertion value are the same RDN, using the same RDN comparison
method as distinguishedNameMatch.
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When using rdnMatch to match components of DNs it is important to
note that the LDAP-specific encoding of a DN [5] reverses the order
of the RDNs. So for the DN represented in LDAP as
"cn=Steven Legg,o=Adacel,c=AU", the RDN "cn=Steven Legg" corresponds
to the component reference "3", or alternatively, "-1".
3.2.2.2. The presentMatch Matching Rule
At times it would be useful to test not if a specific value of a
particular component is present, but whether any value of a
particular component is present. The presentMatch matching rule
allows the presence of a particular component value to be tested.
The LDAP-style definitions for presentMatch and its assertion syntax
are:
( 1.2.36.79672281.1.13.5 NAME 'presentMatch'
SYNTAX 1.2.36.79672281.1.5.1 )
( 1.2.36.79672281.1.5.1 DESC 'NULL' )
The LDAP-specific encoding for a value of the NULL syntax is given by
the <NullValue> rule [9].
The X.500-style definition for presentMatch is:
presentMatch MATCHING-RULE ::= {
SYNTAX NULL
ID { 1 2 36 79672281 1 13 5 } }
When used in a extensible match filter item, presentMatch behaves
like the "present" case of a regular search filter. In a
ComponentAssertion, presentMatch evaluates to TRUE if and only if the
component reference identifies one or more component values,
regardless of the actual component value contents. Note that if
useDefaultValues is TRUE then the identified component values may be
(part of) a DEFAULT value.
The notional count referenced by the <count> form of ComponentId is
taken to be present if the SET OF value is present, and absent
otherwise. Note that in ASN.1 notation an absent SET OF value is
distinctly different from a SET OF value that is present but empty.
It is up to the specification using the ASN.1 notation to decide
whether the distinction matters. Often an empty SET OF component and
an absent SET OF component are treated as semantically equivalent.
If a SET OF value is present, but empty, a presentMatch on the SET OF
component SHALL return TRUE and the notional count SHALL be regarded
as present and equal to zero.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
3.2.3. Summary of Useful Matching Rules
The following is a non-exhaustive list of useful matching rules and
the ASN.1 types to which they can be applied, taking account of all
the extensions described in Section 3.2.1, and the new matching rules
defined in Section 3.2.2.
+================================+==============================+
| Matching Rule | ASN.1 Type |
+================================+==============================+
| bitStringMatch | BIT STRING |
+--------------------------------+------------------------------+
| booleanMatch | BOOLEAN |
+--------------------------------+------------------------------+
| caseIgnoreMatch | NumericString |
| caseIgnoreOrderingMatch | PrintableString |
| caseIgnoreSubstringsMatch | VisibleString (ISO646String) |
| caseExactMatch | IA5String |
| caseExactOrderingMatch | UTF8String |
| caseExactSubstringsMatch | BMPString (UCS-2, UNICODE) |
| | UniversalString (UCS-4) |
| | TeletexString (T61String) |
| | VideotexString |
| | GraphicString |
| | GeneralString |
| | any ChoiceOfStrings type |
+--------------------------------+------------------------------+
| caseIgnoreIA5Match | IA5String |
| caseExactIA5Match | |
+--------------------------------+------------------------------+
| distinguishedNameMatch | DistinguishedName |
| | RDNSequence |
+--------------------------------+------------------------------+
| generalizedTimeMatch | GeneralizedTime |
| generalizedTimeOrderingMatch | |
+--------------------------------+------------------------------+
| integerMatch | INTEGER |
| integerOrderingMatch | |
+--------------------------------+------------------------------+
| numericStringMatch | NumericString |
| numericStringOrderingMatch | |
| numericStringSubstringsMatch | |
+--------------------------------+------------------------------+
| objectIdentifierMatch | OBJECT IDENTIFIER |
+--------------------------------+------------------------------+
| octetStringMatch | OCTET STRING |
| octetStringOrderingMatch | |
| octetStringSubstringsMatch | |
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
+--------------------------------+------------------------------+
| presentMatch | any ASN.1 type |
+--------------------------------+------------------------------+
| rdnMatch | RelativeDistinguishedName |
+--------------------------------+------------------------------+
| telephoneNumberMatch | PrintableString |
| telephoneNumberSubstringsMatch | TelephoneNumber |
+--------------------------------+------------------------------+
| uTCTimeMatch | UTCTime |
| uTCTimeOrderingMatch | |
+--------------------------------+------------------------------+
Note that the allComponentsMatch matching rule defined in Section 6.2
can be used for equality matching of values of the ENUMERATED, NULL,
REAL and RELATIVE-OID ASN.1 types, among other things.
4. ComponentFilter
The ComponentAssertion allows the value(s) of any one component type
in a complex ASN.1 type to be matched, but there is often a desire to
match the values of more than one component type. A ComponentFilter
is an assertion about the presence, or values of, multiple components
within an ASN.1 value.
The ComponentFilter assertion, an expression of ComponentAssertions,
evaluates to either TRUE, FALSE or Undefined for each tested ASN.1
value.
A ComponentFilter is described by the following ASN.1 type (assumed
to be defined with "EXPLICIT TAGS" in force):
ComponentFilter ::= CHOICE {
item [0] ComponentAssertion,
and [1] SEQUENCE OF ComponentFilter,
or [2] SEQUENCE OF ComponentFilter,
not [3] ComponentFilter }
Note: despite the use of SEQUENCE OF instead of SET OF for the "and"
and "or" alternatives in ComponentFilter, the order of the component
filters is not significant.
A ComponentFilter that is a ComponentAssertion evaluates to TRUE if
the ComponentAssertion is TRUE, evaluates to FALSE if the
ComponentAssertion is FALSE, and evaluates to Undefined otherwise.
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The "and" of a sequence of component filters evaluates to TRUE if the
sequence is empty or if each component filter evaluates to TRUE,
evaluates to FALSE if at least one component filter is FALSE, and
evaluates to Undefined otherwise.
The "or" of a sequence of component filters evaluates to FALSE if the
sequence is empty or if each component filter evaluates to FALSE,
evaluates to TRUE if at least one component filter is TRUE, and
evaluates to Undefined otherwise.
The "not" of a component filter evaluates to TRUE if the component
filter is FALSE, evaluates to FALSE if the component filter is TRUE,
and evaluates to Undefined otherwise.
5. The componentFilterMatch Matching Rule
The componentFilterMatch matching rule allows a ComponentFilter to be
applied to an attribute value. The result of the matching rule is
the result of applying the ComponentFilter to the attribute value.
The LDAP-style definitions for componentFilterMatch and its assertion
syntax are:
( 1.2.36.79672281.1.13.2 NAME 'componentFilterMatch'
SYNTAX 1.2.36.79672281.1.5.2 )
( 1.2.36.79672281.1.5.2 DESC 'ComponentFilter' )
The LDAP-specific encoding for the ComponentFilter assertion syntax
is specified by GSER [9].
As a convenience to implementors, an equivalent ABNF description of
the GSER encoding for ComponentFilter is provided here. In the event
that there is a discrepancy between this ABNF and the encoding
determined by GSER, GSER is to be taken as definitive. The GSER
encoding of a ComponentFilter is described by the following
equivalent ABNF:
ComponentFilter = filter-item /
and-filter /
or-filter /
not-filter
filter-item = item-chosen ComponentAssertion
and-filter = and-chosen SequenceOfComponentFilter
or-filter = or-chosen SequenceOfComponentFilter
not-filter = not-chosen ComponentFilter
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item-chosen = %x69.74.65.6D.3A ; "item:"
and-chosen = %x61.6E.64.3A ; "and:"
or-chosen = %x6F.72.3A ; "or:"
not-chosen = %x6E.6F.74.3A ; "not:"
SequenceOfComponentFilter = "{" [ sp ComponentFilter
*( "," sp ComponentFilter) ] sp "}"
ComponentAssertion = "{" [ sp component "," ]
[ sp useDefaultValues "," ]
sp rule ","
sp assertion-value sp "}"
component = component-label msp StringValue
useDefaultValues = use-defaults-label msp BooleanValue
rule = rule-label msp ObjectIdentifierValue
assertion-value = value-label msp Value
component-label = %x63.6F.6D.70.6F.6E.65.6E.74 ; "component"
use-defaults-label = %x75.73.65.44.65.66.61.75.6C.74.56.61.6C.75
%x65.73 ; "useDefaultValues"
rule-label = %x72.75.6C.65 ; "rule"
value-label = %x76.61.6C.75.65 ; "value"
sp = *%x20 ; zero, one or more space characters
msp = 1*%x20 ; one or more space characters
The ABNF for <Value>, <StringValue>, <ObjectIdentifierValue> and
<BooleanValue> is defined by GSER [9].
The ABNF descriptions of LDAP-specific encodings for attribute
syntaxes typically do not clearly or consistently delineate the
component parts of an attribute value. A regular and uniform
character string encoding for arbitrary component data types is
needed to encode the assertion value in a ComponentAssertion. The
<Value> rule from GSER provides a human readable text encoding for a
component value of any arbitrary ASN.1 type.
The X.500-style definition [10] for componentFilterMatch is:
componentFilterMatch MATCHING-RULE ::= {
SYNTAX ComponentFilter
ID { 1 2 36 79672281 1 13 2 } }
A ComponentAssertion can potentially use any matching rule, including
componentFilterMatch, so componentFilterMatch may be nested. The
component references in a nested componentFilterMatch are relative to
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
the component corresponding to the containing ComponentAssertion. In
Section 7, an example search on the seeAlso attribute shows this
usage.
6. Equality Matching of Complex Components
It is possible to test if an attribute value of a complex ASN.1
syntax is the same as some purported (i.e., assertion) value by using
a complicated ComponentFilter that tests if corresponding components
are the same. However, it would be more convenient to be able to
present a whole assertion value to a matching rule that could do the
component-wise comparison of an attribute value with the assertion
value for any arbitrary attribute syntax. Similarly, the ability to
do a straightforward equality comparison of a component value that is
itself of a complex ASN.1 type would also be convenient.
It would be difficult to define a single matching rule that
simultaneously satisfies all notions of what the equality matching
semantics should be. For example, in some instances a case sensitive
comparison of string components may be preferable to a case
insensitive comparison. Therefore a basic equality matching rule,
allComponentsMatch, is defined in Section 6.2, and the means to
derive new matching rules from it with slightly different equality
matching semantics are described in Section 6.3.
The directoryComponentsMatch defined in Section 6.4 is a derivation
of allComponentsMatch that suits typical uses of the directory.
Other specifications are free to derive new rules from
allComponentsMatch or directoryComponentsMatch, that suit their usage
of the directory.
The allComponentsMatch rule, the directoryComponentsMatch rule and
any matching rules derived from them are collectively called
component equality matching rules.
6.1. The OpenAssertionType Syntax
The component equality matching rules have a variable assertion
syntax. In X.500 this is indicated by omitting the optional SYNTAX
field in the MATCHING-RULE information object. The assertion syntax
then defaults to the target attribute's syntax in actual usage,
unless the description of the matching rule says otherwise. The
SYNTAX field in the LDAP-specific encoding of a
MatchingRuleDescription is mandatory, so the OpenAssertionType syntax
is defined to fill the same role. That is, the OpenAssertionType
syntax is semantically equivalent to an omitted SYNTAX field in an
X.500 MATCHING-RULE information object. OpenAssertionType MUST NOT
be used as the attribute syntax in an attribute type definition.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
Unless explicitly varied by the description of a particular matching
rule, if an OpenAssertionType assertion value appears in a
ComponentAssertion its LDAP-specific encoding is described by the
<Value> rule in GSER [9], otherwise its LDAP-specific encoding is the
encoding defined for the syntax of the attribute type to which the
matching rule with the OpenAssertionType assertion syntax is applied.
The LDAP definition for the OpenAssertionType syntax is:
( 1.2.36.79672281.1.5.3 DESC 'OpenAssertionType' )
6.2. The allComponentsMatch Matching Rule
The LDAP-style definition for allComponentsMatch is:
( 1.2.36.79672281.1.13.6 NAME 'allComponentsMatch'
SYNTAX 1.2.36.79672281.1.5.3 )
The X.500-style definition for allComponentsMatch is:
allComponentsMatch MATCHING-RULE ::= {
ID { 1 2 36 79672281 1 13 6 } }
When allComponentsMatch is used in a ComponentAssertion the assertion
syntax is the same as the ASN.1 type of the identified component.
Otherwise, the assertion syntax of allComponentsMatch is the same as
the attribute syntax of the attribute to which the matching rule is
applied.
Broadly speaking, this matching rule evaluates to true if and only if
corresponding components of the assertion value and the attribute or
component value are the same.
In detail, equality is determined by the following cases applied
recursively.
a) Two values of a SET or SEQUENCE type are the same if and only if,
for each component type, the corresponding component values are
either,
1) both absent,
2) both present and the same, or
3) absent or the same as the DEFAULT value for the component, if a
DEFAULT value is defined.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
Values of an EMBEDDED PDV, EXTERNAL, unrestricted CHARACTER
STRING, or INSTANCE OF type are compared according to their
respective associated SEQUENCE type (see Section 3.1.2).
b) Two values of a SEQUENCE OF type are the same if and only if, the
values have the same number of (possibly duplicated) instances and
corresponding instances are the same.
c) Two values of a SET OF type are the same if and only if, the
values have the same number of instances and each distinct
instance occurs in both values the same number of times, i.e.,
both values have the same instances, including duplicates, but in
any order.
d) Two values of a CHOICE type are the same if and only if, both
values are of the same chosen alternative and the component values
are the same.
e) Two BIT STRING values are the same if and only if the values have
the same number of bits and corresponding bits are the same. If
the BIT STRING type is defined with a named bit list then trailing
zero bits in the values are treated as absent for the purposes of
this comparison.
f) Two BOOLEAN values are the same if and only if both are TRUE or
both are FALSE.
g) Two values of a string type are the same if and only if the values
have the same number of characters and corresponding characters
are the same. Letter case is significant. For the purposes of
allComponentsMatch, the string types are NumericString,
PrintableString, TeletexString (T61String), VideotexString,
IA5String, GraphicString, VisibleString (ISO646String),
GeneralString, UniversalString, BMPString, UTF8String,
GeneralizedTime, UTCTime and ObjectDescriptor.
h) Two INTEGER values are the same if and only if the integers are
equal.
i) Two ENUMERATED values are the same if and only if the enumeration
item identifiers are the same (equivalently, if the integer values
associated with the identifiers are equal).
j) Two NULL values are always the same, unconditionally.
k) Two OBJECT IDENTIFIER values are the same if and only if the
values have the same number of arcs and corresponding arcs are the
same.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
l) Two OCTET STRING values are the same if and only if the values
have the same number of octets and corresponding octets are the
same.
m) Two REAL values are the same if and only if they are both the same
special value, or neither is a special value and they have the
same base and represent the same real number. The special values
for REAL are zero, PLUS-INFINITY and MINUS-INFINITY.
n) Two RELATIVE-OID values are the same if and only if the values
have the same number of arcs and corresponding arcs are the same.
The respective starting nodes for the RELATIVE-OID values are
disregarded in the comparison, i.e., they are assumed to be the
same.
o) Two values of an open type are the same if and only if both are of
the same ASN.1 type and are the same according to that type. If
the actual ASN.1 type of the values is unknown then the
allComponentsMatch rule evaluates to Undefined.
Tags and constraints, being part of the type definition and not part
of the abstract values, are ignored for matching purposes.
The allComponentsMatch rule may be used as the defined equality
matching rule for an attribute.
6.3. Deriving Component Equality Matching Rules
A new component equality matching rule with more refined matching
semantics may be derived from allComponentsMatch, or any other
component equality matching rule, using the convention described in
this section.
The matching behaviour of a derived component equality matching rule
is specified by nominating, for each of one or more identified
components, a commutative equality matching rule that will be used to
match values of that component. This overrides the matching that
would otherwise occur for values of that component using the base
rule for the derivation. These overrides can be conveniently
represented as rows in a table of the following form.
Component | Matching Rule
============+===============
|
|
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
Usually, all component values of a particular ASN.1 type are to be
matched the same way. An ASN.1 type reference (e.g.,
DistinguishedName) or an ASN.1 built-in type name (e.g., INTEGER) in
the Component column of the table specifies that the nominated
equality matching rule is to be applied to all values of the named
type, regardless of context.
An ASN.1 type reference with a component reference appended
(separated by a ".") specifies that the nominated matching rule
applies only to the identified components of values of the named
type. Other component values that happen to be of the same ASN.1
type are not selected.
Additional type substitutions as described in Section 3.2 are assumed
to be performed to align the component type with the matching rule
assertion syntax.
Conceptually, the rows in a table for the base rule are appended to
the rows in the table for a derived rule for the purpose of deciding
the matching semantics of the derived rule. Notionally,
allComponentsMatch has an empty table.
A row specifying values of an outer containing type (e.g.,
DistinguishedName) takes precedence over a row specifying values of
an inner component type (e.g., RelativeDistinguishedName), regardless
of their order in the table. Specifying a row for component values
of an inner type is only useful if a value of the type can also
appear on its own, or as a component of values of a different outer
type. For example, if there is a row for DistinguishedName then a
row for RelativeDistinguishedName can only ever apply to
RelativeDistinguishedName component values that are not part of a
DistinguishedName. A row for values of an outer type in the table
for the base rule takes precedence over a row for values of an inner
type in the table for the derived rule.
Where more than one row applies to a particular component value the
earlier row takes precedence over the later row. Thus rows in the
table for the derived rule take precedence over any rows for the same
component in the table for the base rule.
6.4. The directoryComponentsMatch Matching Rule
The directoryComponentsMatch matching rule is derived from the
allComponentsMatch matching rule.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
The LDAP-style definition for directoryComponentsMatch is:
( 1.2.36.79672281.1.13.7 NAME 'directoryComponentsMatch'
SYNTAX 1.2.36.79672281.1.5.3 )
The X.500-style definition for directoryComponentsMatch is:
directoryComponentsMatch MATCHING-RULE ::= {
ID { 1 2 36 79672281 1 13 7 } }
The matching semantics of directoryComponentsMatch are described by
the following table, using the convention described in Section 6.3.
ASN.1 Type | Matching Rule
=========================================+========================
RDNSequence | distinguishedNameMatch
RelativeDistinguishedName | rdnMatch
TelephoneNumber | telephoneNumberMatch
FacsimileTelephoneNumber.telephoneNumber | telephoneNumberMatch
NumericString | numericStringMatch
GeneralizedTime | generalizedTimeMatch
UTCTime | uTCTimeMatch
DirectoryString{} | caseIgnoreMatch
BMPString | caseIgnoreMatch
GeneralString | caseIgnoreMatch
GraphicString | caseIgnoreMatch
IA5String | caseIgnoreMatch
PrintableString | caseIgnoreMatch
TeletexString | caseIgnoreMatch
UniversalString | caseIgnoreMatch
UTF8String | caseIgnoreMatch
VideotexString | caseIgnoreMatch
VisibleString | caseIgnoreMatch
Notes:
1) The DistinguishedName type is defined by assignment to be the same
as the RDNSequence type. Some types (e.g., Name and LocalName)
directly reference RDNSequence rather than DistinguishedName.
Specifying RDNSequence captures all these DN-like types.
2) A RelativeDistinguishedName value is only matched by rdnMatch if
it is not part of an RDNSequence value.
3) The telephone number component of the FacsimileTelephoneNumber
ASN.1 type [12] is defined as a constrained PrintableString.
PrintableString component values that are part of a
FacsimileTelephoneNumber value can be identified separately from
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other components of PrintableString type by the specifier
FacsimileTelephoneNumber.telephoneNumber, so that
telephoneNumberMatch can be selectively applied. The fourth
edition of X.520 defines the telephoneNumber component of
FacsimileTelephoneNumber to be of the type TelephoneNumber, making
the row for FacsimileTelephoneNumber.telephoneNumber components
redundant.
The directoryComponentsMatch rule may be used as the defined equality
matching rule for an attribute.
7. Component Matching Examples
This section contains examples of search filters using the
componentFilterMatch matching rule. The filters are described using
the string representation of LDAP search filters [18]. Note that
this representation requires asterisks to be escaped in assertion
values (in these examples the assertion values are all
<ComponentAssertion> encodings). The asterisks have not been escaped
in these examples for the sake of clarity, and to avoid confusing the
protocol representation of LDAP search filter assertion values, where
such escaping does not apply. Line breaks and indenting have been
added only as an aid to readability.
The example search filters using componentFilterMatch are all single
extensible match filter items, though there is no reason why
componentFilterMatch can't be used in more complicated search
filters.
The first examples describe searches over the objectClasses schema
operational attribute, which has an attribute syntax described by the
ASN.1 type ObjectClassDescription [10], and holds the definitions of
the object classes known to a directory server. The definition of
ObjectClassDescription is as follows:
ObjectClassDescription ::= SEQUENCE {
identifier OBJECT-CLASS.&id,
name SET OF DirectoryString {ub-schema} OPTIONAL,
description DirectoryString {ub-schema} OPTIONAL,
obsolete BOOLEAN DEFAULT FALSE,
information [0] ObjectClassInformation }
ObjectClassInformation ::= SEQUENCE {
subclassOf SET OF OBJECT-CLASS.&id OPTIONAL,
kind ObjectClassKind DEFAULT structural,
mandatories [3] SET OF ATTRIBUTE.&id OPTIONAL,
optionals [4] SET OF ATTRIBUTE.&id OPTIONAL }
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ObjectClassKind ::= ENUMERATED {
abstract (0),
structural (1),
auxiliary (2) }
OBJECT-CLASS.&id and ATTRIBUTE.&id are equivalent to the OBJECT
IDENTIFIER ASN.1 type. A value of OBJECT-CLASS.&id is an OBJECT
IDENTIFIER for an object class. A value of ATTRIBUTE.&id is an
OBJECT IDENTIFIER for an attribute type.
The following search filter finds the object class definition for the
object class identified by the OBJECT IDENTIFIER 2.5.6.18:
(objectClasses:componentFilterMatch:=
item:{ component "identifier",
rule objectIdentifierMatch, value 2.5.6.18 })
A match on the "identifier" component of objectClasses values is
equivalent to the objectIdentifierFirstComponentMatch matching rule
applied to attribute values of the objectClasses attribute type. The
componentFilterMatch matching rule subsumes the functionality of the
objectIdentifierFirstComponentMatch, integerFirstComponentMatch and
directoryStringFirstComponentMatch matching rules.
The following search filter finds the object class definition for the
object class called foobar:
(objectClasses:componentFilterMatch:=
item:{ component "name.*",
rule caseIgnoreMatch, value "foobar" })
An object class definition can have multiple names and the above
filter will match an objectClasses value if any one of the names is
"foobar".
The component reference "name.0" identifies the notional count of the
number of names in an object class definition. The following search
filter finds object class definitions with exactly one name:
(objectClasses:componentFilterMatch:=
item:{ component "name.0", rule integerMatch, value 1 })
The "description" component of an ObjectClassDescription is defined
to be an OPTIONAL DirectoryString. The following search filter finds
object class definitions that have descriptions, regardless of the
contents of the description string:
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
(objectClasses:componentFilterMatch:=
item:{ component "description",
rule presentMatch, value NULL })
The presentMatch returns TRUE if the description component is present
and FALSE otherwise.
The following search filter finds object class definitions that don't
have descriptions:
(objectClasses:componentFilterMatch:=
not:item:{ component "description",
rule presentMatch, value NULL })
The following search filter finds object class definitions with the
word "bogus" in the description:
(objectClasses:componentFilterMatch:=
item:{ component "description",
rule caseIgnoreSubstringsMatch,
value { any:"bogus" } })
The assertion value is of the SubstringAssertion syntax, i.e.,
SubstringAssertion ::= SEQUENCE OF CHOICE {
initial [0] DirectoryString {ub-match},
any [1] DirectoryString {ub-match},
final [2] DirectoryString {ub-match} }
The "obsolete" component of an ObjectClassDescription is defined to
be DEFAULT FALSE. An object class is obsolete if the "obsolete"
component is present and set to TRUE. The following search filter
finds all obsolete object classes:
(objectClasses:componentFilterMatch:=
item:{ component "obsolete", rule booleanMatch, value TRUE })
An object class is not obsolete if the "obsolete" component is not
present, in which case it defaults to FALSE, or is present but is
explicitly set to FALSE. The following search filter finds all non-
obsolete object classes:
(objectClasses:componentFilterMatch:=
item:{ component "obsolete", rule booleanMatch, value FALSE })
The useDefaultValues flag in the ComponentAssertion defaults to TRUE
so the componentFilterMatch rule treats an absent "obsolete"
component as being present and set to FALSE. The following search
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
filter finds only object class definitions where the "obsolete"
component has been explicitly set to FALSE, rather than implicitly
defaulting to FALSE:
(objectClasses:componentFilterMatch:=
item:{ component "obsolete", useDefaultValues FALSE,
rule booleanMatch, value FALSE })
With the useDefaultValues flag set to FALSE, if the "obsolete"
component is absent the component reference identifies no component
value and the matching rule will return FALSE. The matching rule can
only return TRUE if the component is present and set to FALSE.
The "information.kind" component of the ObjectClassDescription is an
ENUMERATED type. The allComponentsMatch matching rule can be used to
match values of an ENUMERATED type. The following search filter
finds object class definitions for auxiliary object classes:
(objectClasses:componentFilterMatch:=
item:{ component "information.kind",
rule allComponentsMatch, value auxiliary })
The following search filter finds auxiliary object classes with
commonName (cn or 2.5.4.3) as a mandatory attribute:
(objectClasses:componentFilterMatch:=and:{
item:{ component "information.kind",
rule allComponentsMatch, value auxiliary },
item:{ component "information.mandatories.*",
rule objectIdentifierMatch, value cn } })
The following search filter finds auxiliary object classes with
commonName as a mandatory or optional attribute:
(objectClasses:componentFilterMatch:=and:{
item:{ component "information.kind",
rule allComponentsMatch, value auxiliary },
or:{
item:{ component "information.mandatories.*",
rule objectIdentifierMatch, value cn },
item:{ component "information.optionals.*",
rule objectIdentifierMatch, value cn } } })
Extra care is required when matching optional SEQUENCE OF or SET OF
components because of the distinction between an absent list of
instances and a present, but empty, list of instances. The following
search filter finds object class definitions with less than three
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
names, including object class definitions with a present but empty
list of names, but does not find object class definitions with an
absent list of names:
(objectClasses:componentFilterMatch:=
item:{ component "name.0",
rule integerOrderingMatch, value 3 })
If the "name" component is absent the "name.0" component is also
considered to be absent and the ComponentAssertion evaluates to
FALSE. If the "name" component is present, but empty, the "name.0"
component is also present and equal to zero, so the
ComponentAssertion evaluates to TRUE. To also find the object class
definitions with an absent list of names the following search filter
would be used:
(objectClasses:componentFilterMatch:=or:{
not:item:{ component "name", rule presentMatch, value NULL },
item:{ component "name.0",
rule integerOrderingMatch, value 3 } })
Distinguished names embedded in other syntaxes can be matched with a
componentFilterMatch. The uniqueMember attribute type has an
attribute syntax described by the ASN.1 type NameAndOptionalUID.
NameAndOptionalUID ::= SEQUENCE {
dn DistinguishedName,
uid UniqueIdentifier OPTIONAL }
The following search filter finds values of the uniqueMember
attribute containing the author's DN:
(uniqueMember:componentFilterMatch:=
item:{ component "dn",
rule distinguishedNameMatch,
value "cn=Steven Legg,o=Adacel,c=AU" })
The DistinguishedName and RelativeDistinguishedName ASN.1 types are
also complex ASN.1 types so the component matching rules can be
applied to their inner components.
DistinguishedName ::= RDNSequence
RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
RelativeDistinguishedName ::= SET SIZE (1..MAX) OF
AttributeTypeAndValue
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
AttributeTypeAndValue ::= SEQUENCE {
type AttributeType ({SupportedAttributes}),
value AttributeValue ({SupportedAttributes}{@type}) }
AttributeType ::= ATTRIBUTE.&id
AttributeValue ::= ATTRIBUTE.&Type
ATTRIBUTE.&Type is an open type. A value of ATTRIBUTE.&Type is
constrained by the type component of AttributeTypeAndValue to be of
the attribute syntax of the nominated attribute type. Note: the
fourth edition of X.500 extends and renames the AttributeTypeAndValue
SEQUENCE type.
The seeAlso attribute has the DistinguishedName syntax. The
following search filter finds seeAlso attribute values containing the
RDN, "o=Adacel", anywhere in the DN:
(seeAlso:componentFilterMatch:=
item:{ component "*", rule rdnMatch, value "o=Adacel" })
The following search filter finds all seeAlso attribute values with
"cn=Steven Legg" as the RDN of the named entry (i.e., the "first" RDN
in an LDAPDN or the "last" RDN in an X.500 DN):
(seeAlso:componentFilterMatch:=
item:{ component "-1",
rule rdnMatch, value "cn=Steven Legg" })
The following search filter finds all seeAlso attribute values naming
entries in the DIT subtree of "o=Adacel,c=AU":
(seeAlso:componentFilterMatch:=and:{
item:{ component "1", rule rdnMatch, value "c=AU" },
item:{ component "2", rule rdnMatch, value "o=Adacel" } })
The following search filter finds all seeAlso attribute values
containing the naming attribute types commonName (cn) and
telephoneNumber in the same RDN:
(seeAlso:componentFilterMatch:=
item:{ component "*", rule componentFilterMatch,
value and:{
item:{ component "*.type",
rule objectIdentifierMatch, value cn },
item:{ component "*.type",
rule objectIdentifierMatch,
value telephoneNumber } } })
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
The following search filter would find all seeAlso attribute values
containing the attribute types commonName and telephoneNumber, but
not necessarily in the same RDN:
(seeAlso:componentFilterMatch:=and:{
item:{ component "*.*.type",
rule objectIdentifierMatch, value cn },
item:{ component "*.*.type",
rule objectIdentifierMatch, value telephoneNumber } })
The following search filter finds all seeAlso attribute values
containing the word "Adacel" in any organizationalUnitName (ou)
attribute value in any AttributeTypeAndValue of any RDN:
(seeAlso:componentFilterMatch:=
item:{ component "*.*.value.(2.5.4.11)",
rule caseIgnoreSubstringsMatch,
value { any:"Adacel" } })
The component reference "*.*.value" identifies an open type, in this
case an attribute value. In a particular AttributeTypeAndValue, if
the attribute type is not organizationalUnitName then the
ComponentAssertion evaluates to FALSE. Otherwise the substring
assertion is evaluated against the attribute value.
Absent component references in ComponentAssertions can be exploited
to avoid false positive matches on multi-valued attributes. For
example, suppose there is a multi-valued attribute named
productCodes, defined to have the Integer syntax
(1.3.6.1.4.1.1466.115.121.1.27). Consider the following search
filter:
(&(!(productCodes:integerOrderingMatch:=3))
(productCodes:integerOrderingMatch:=8))
An entry whose productCodes attribute contains only the values 1 and
10 will match the above filter. The first subfilter is satisfied by
the value 10 (10 is not less than 3), and the second subfilter is
satisfied by the value 1 (1 is less than 8). The following search
filter can be used instead to only match entries that have a
productCodes value in the range 3 to 7, because the ComponentFilter
is evaluated against each productCodes value in isolation:
(productCodes:componentFilterMatch:= and:{
not:item:{ rule integerOrderingMatch, value 3 },
item:{ rule integerOrderingMatch, value 8 } })
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
An entry whose productCodes attribute contains only the values 1 and
10 will not match the above filter.
8. Security Considerations
The component matching rules described in this document allow for a
compact specification of matching capabilities that could otherwise
have been defined by a plethora of specific matching rules, i.e.,
despite their expressiveness and flexibility the component matching
rules do not behave in a way uncharacteristic of other matching
rules, so the security issues for component matching rules are no
different than for any other matching rule. However, because the
component matching rules are applicable to any attribute syntax,
support for them in a directory server may allow searching of
attributes that were previously unsearchable by virtue of there not
being a suitable matching rule. Such attribute types ought to be
properly protected with appropriate access controls. A generic,
interoperable access control mechanism has not yet been developed,
however, and implementors should be aware of the interaction of that
lack with the increased risk of exposure described above.
9. Acknowledgements
The author would like to thank Tom Gindin for private email
discussions that clarified and refined the ideas presented in this
document.
10. IANA Considerations
The Internet Assigned Numbers Authority (IANA) has updated the LDAP
descriptors registry [8] as indicated by the following templates:
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): componentFilterMatch
Object Identifier: 1.2.36.79672281.1.13.2
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: other (matching rule)
Specification: RFC 3687
Author/Change Controller: IESG
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): rdnMatch
Object Identifier: 1.2.36.79672281.1.13.3
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: other (matching rule)
Specification: RFC 3687
Author/Change Controller: IESG
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): presentMatch
Object Identifier: 1.2.36.79672281.1.13.5
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: other (matching rule)
Specification: RFC 3687
Author/Change Controller: IESG
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): allComponentsMatch
Object Identifier: 1.2.36.79672281.1.13.6
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: other (matching rule)
Specification: RFC 3687
Author/Change Controller: IESG
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): directoryComponentsMatch
Object Identifier: 1.2.36.79672281.1.13.7
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: other (matching rule)
Specification: RFC 3687
Author/Change Controller: IESG
The object identifiers have been assigned for use in this
specification by Adacel Technologies, under an arc assigned to Adacel
by Standards Australia.
11. References
11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
[2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[3] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[4] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight
Directory Access Protocol (v3): Attribute Syntax Definitions",
RFC 2252, December 1997.
[5] Wahl, M., Kille S. and T. Howes. "Lightweight Directory Access
Protocol (v3): UTF-8 String Representation of Distinguished
Names", RFC 2253, December 1997.
[6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
63, RFC 3629, November 2003.
[7] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377, September
2002.
[8] Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
Considerations for the Lightweight Directory Access Protocol
(LDAP)", BCP 64, RFC 3383, September 2002.
[9] Legg, S., "Generic String Encoding Rules (GSER) for ASN.1
Types", RFC 3641, October 2003.
[10] ITU-T Recommendation X.501 (1993) | ISO/IEC 9594-2:1994,
Information Technology - Open Systems Interconnection - The
Directory: Models
[11] ITU-T Recommendation X.509 (1997) | ISO/IEC 9594-8:1998,
Information Technology - Open Systems Interconnection - The
Directory: Authentication Framework
[12] ITU-T Recommendation X.520 (1993) | ISO/IEC 9594-6:1994,
Information technology - Open Systems Interconnection - The
Directory: Selected attribute types
[13] ITU-T Recommendation X.680 (07/02) | ISO/IEC 8824-1:2002,
Information technology - Abstract Syntax Notation One (ASN.1):
Specification of basic notation
[14] ITU-T Recommendation X.681 (07/02) | ISO/IEC 8824-2:2002,
Information technology - Abstract Syntax Notation One (ASN.1):
Information object specification
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
[15] ITU-T Recommendation X.682 (07/02) | ISO/IEC 8824-3:2002,
Information technology - Abstract Syntax Notation One (ASN.1):
Constraint specification
[16] ITU-T Recommendation X.683 (07/02) | ISO/IEC 8824-4:2002,
Information technology - Abstract Syntax Notation One (ASN.1):
Parameterization of ASN.1 specifications
[17] 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)
12.2. Informative References
[18] Howes, T., "The String Representation of LDAP Search Filters",
RFC 2254, December 1997.
[19] ITU-T Recommendation X.500 (1993) | ISO/IEC 9594-1:1994,
Information Technology - Open Systems Interconnection - The
Directory: Overview of concepts, models and services
12. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Legg Standards Track [Page 40]
RFC 3687 LDAP and X.500 Component Matching Rules February 2004
13. 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
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RFC 3687 LDAP and X.500 Component Matching Rules February 2004
14. Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Legg Standards Track [Page 42]