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INTERNET-DRAFT S. Legg
draft-legg-ldap-acm-bac-03.txt Adacel Technologies
Intended Category: Standards Track June 16, 2004
Updates: RFC 2252
Lightweight Directory Access Protocol (LDAP):
Basic and Simplified Access Control
Copyright (C) The Internet Society (2004). All Rights Reserved.
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Distribution of this document is unlimited. Comments should be sent
to the author.
This Internet-Draft expires on 16 December 2004.
Abstract
An access control scheme describes the means by which access to
directory information and potentially to access rights themselves may
be controlled. This document adapts the X.500 directory Basic Access
Control and Simplied Access Control schemes for use by the
Lightweight Directory Access Protocol.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions. . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Basic Access Control . . . . . . . . . . . . . . . . . . . . . 4
3.1. Permissions. . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Read . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Compare. . . . . . . . . . . . . . . . . . . . . 6
3.1.3. Browse . . . . . . . . . . . . . . . . . . . . . 6
3.1.4. ReturnDN . . . . . . . . . . . . . . . . . . . . 6
3.1.5. FilterMatch. . . . . . . . . . . . . . . . . . . 6
3.1.6. Modify . . . . . . . . . . . . . . . . . . . . . 6
3.1.7. Add. . . . . . . . . . . . . . . . . . . . . . . 6
3.1.8. Remove . . . . . . . . . . . . . . . . . . . . . 7
3.1.9. DiscloseOnError. . . . . . . . . . . . . . . . . 7
3.1.10. Rename . . . . . . . . . . . . . . . . . . . . . 7
3.1.11. Export . . . . . . . . . . . . . . . . . . . . . 7
3.1.12. Import . . . . . . . . . . . . . . . . . . . . . 8
3.1.13. Invoke . . . . . . . . . . . . . . . . . . . . . 8
3.2. Representation of Access Control Information . . . . . . 8
3.2.1. Identification Tag . . . . . . . . . . . . . . . 11
3.2.2. Precedence . . . . . . . . . . . . . . . . . . . 11
3.2.3. Authentication Level . . . . . . . . . . . . . . 11
3.2.4. itemFirst and userFirst Components . . . . . . . 12
3.2.5. Determining Group Membership . . . . . . . . . . 16
3.3. ACI Operational Attributes . . . . . . . . . . . . . . . 17
3.3.1. Prescriptive ACI . . . . . . . . . . . . . . . . 17
3.3.2. Entry ACI. . . . . . . . . . . . . . . . . . . . 17
3.3.3. Subentry ACI . . . . . . . . . . . . . . . . . . 18
3.3.4. Protecting the ACI . . . . . . . . . . . . . . . 18
3.4. Access Control Decision Points for LDAP Operations . . . 18
3.4.1. Common Elements of Procedure . . . . . . . . . . 19
3.4.1.1. Alias Dereferencing. . . . . . . . . . 19
3.4.1.2. Return of Names in Errors. . . . . . . 19
3.4.1.3. Non-disclosure of Entry Existence. . . 20
3.4.2. Compare Operation Decision Points. . . . . . . . 20
3.4.3. Search Operation Decision Points . . . . . . . . 20
3.4.4. Add Operation Decision Points. . . . . . . . . . 23
3.4.5. Delete Operation Decision Points . . . . . . . . 24
3.4.6. Modify Operation Decision Points . . . . . . . . 24
3.4.7. Modify DN Operation Decision Points. . . . . . . 25
3.5. Access Control Decision Function . . . . . . . . . . . . 26
3.5.1. Inputs . . . . . . . . . . . . . . . . . . . . . 26
3.5.2. Tuples . . . . . . . . . . . . . . . . . . . . . 26
3.5.3. Discarding Irrelevant Tuples . . . . . . . . . . 27
3.5.4. Highest Precedence and Specificity . . . . . . . 28
4. Simplified Access Control. . . . . . . . . . . . . . . . . . . 28
5. Security Considerations. . . . . . . . . . . . . . . . . . . . 29
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6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
7. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 29
Appendix A. LDAP Specific Encoding for the ACI Item Syntax . . . . 30
Normative References . . . . . . . . . . . . . . . . . . . . . . . 39
Informative References . . . . . . . . . . . . . . . . . . . . . . 40
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 40
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 40
1. Introduction
An access control scheme describes the means by which access to
directory information and potentially to access rights themselves may
be controlled. Control of access to information means the prevention
of unauthorized detection, disclosure, or modification of that
information. The definition of an access control scheme in the
context of a Lightweight Directory Access Protocol (LDAP) [RFC3371]
directory includes methods to specify Access Control Information
(ACI), and to enforce access rights defined by that ACI.
This document adapts the X.500 Basic Access Control and Simplied
Access Control schemes [X501] for use in LDAP. Both schemes conform
to, and make use of, the access control administrative framework for
LDAP [ACA].
Section 3 describes the Basic Access Control scheme and defines how
it applies to LDAP operations [RFC2251].
Simplified Access Control is a functional subset of the Basic Access
Control scheme. This subset is described in Section 4.
As a matter of security policy, an implementation supporting Basic
Access Control or Simplified Access Control is permitted to grant or
deny any form of access to particular attributes (e.g., password
attributes) irrespective of access controls which may otherwise
apply. However, since such security policy has no standardized
representation, it cannot be propagated in replicated information.
This document is derived from, and duplicates substantial portions
of, Section 8 of X.501 [X501], and selected extracts from X.511
[X511].
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
[RFC2119].
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Schema definitions are provided using LDAP description formats
[RFC2252]. Note that the LDAP descriptions have been rendered with
additional white-space and line breaks for the sake of readability.
3. Basic Access Control
This section describes the functionality of the Basic Access Control
scheme.
When Basic Access Control is used, the accessControlScheme
operational attribute [ACA] SHALL have the value basic-access-control
(2.5.28.1).
This LDAP profile for Basic Access Control defines, for every LDAP
operation, one or more points at which access control decisions take
place. An access control decision will involve a requestor,
protected items, and permissions.
A requestor is the user requesting the operation. Basic Access
Control requires a user's authorization identity to be represented as
a distinguished name (with an optional unique identifier). The
mapping of the authentication identity to an authorization identity,
and the mapping of the authorization identity to a distinguished name
and optional unique identifier, are outside the scope of this
document.
A protected item is the element of directory information being
accessed. The protected items are entries, attributes, attribute
values and distinguished names. Access to each protected item can be
separately controlled through ACI.
A permission is a particular right necessary to complete a portion of
the operation.
The Access Control Information, which is used to make access control
decisions, associates protected items and user classes with
permissions. ACI is represented in the directory as values of
operational attributes with the ACI Item syntax [RFC2252]. Each such
value is referred to as an ACI item.
The scope of access controls can be a single entry or a collection of
entries that are logically related by being within the scope of an
access control subentry of an administrative point (see [ACA]).
The Access Control Decision Function (ACDF) (Section 3.5) is used to
decide whether a particular requestor has a particular access right
by virtue of applicable ACI items.
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Access to DSEs and operational attributes is controlled in the same
way as for entries and user attributes.
For query purposes, collective attributes [COLLECT] that are
associated with an entry are protected precisely as if they were
attributes actually stored in that entry.
For the purposes of modification, collective attributes are
associated with the subentry that holds them, not with entries within
the scope of the subentry. Modify-related access controls are
therefore not relevant to collective attributes, except when they
apply to the collective attribute and its values within the subentry.
3.1. Permissions
Access is controlled by granting or denying permissions. Access is
allowed only when there is an explicitly provided grant present in
the ACI used to make the access control decision. The only default
access decision provided in the model is to deny access in the
absence of explicit ACI that grants access. All other factors being
equal, a denial specified in ACI always overrides a grant.
Certain combinations of grants or denials are illogical, but it is
the responsibility of directory clients, rather than the directory
server, to ensure that such combinations are absent.
The decision whether or not to permit access to an entry or its
contents is strictly determined by the position of the entry in the
Directory Information Tree (DIT), in terms of its distinguished name,
and is independent of how the directory server locates that entry.
The following sections introduce the permissions by indicating the
intent associated with the granting of each. The actual influence of
a particular granted permission on access control decisions are,
however, determined by the ACDF and the access control decision
points for each LDAP operation, described in detail in Section 3.4.
3.1.1. Read
If granted for an entry, Read permits the entry to be accessed using
LDAP Compare and baseObject Search operations, but does not imply
access to all the attributes and values.
If granted for an attribute type, Read permits the attribute type to
be returned as entry information in a Search result. Read or Browse
permission for the entry is a prerequisite.
If granted for an attribute value, Read permits the attribute value
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to be returned as entry information in a Search result. Read or
Browse permission for the entry and Read permission for the attribute
type are prerequisites.
3.1.2. Compare
If granted for an attribute type, Compare permits the attribute type
to be tested by the assertion in an LDAP Compare operation. Read
permission for the entry is a prerequisite.
If granted for an attribute value, Compare permits the value to be
tested by the assertion in an LDAP Compare operation. Read
permission for the entry and Compare permission for the attribute
type are prerequisites.
3.1.3. Browse
If granted for an entry, Browse permits the entry to be accessed by
the LDAP Search operation, including baseObject searches, but does
not imply access to all the attributes and values.
3.1.4. ReturnDN
If granted for an entry, ReturnDN allows the distinguished name of
the entry to be disclosed in a search result.
3.1.5. FilterMatch
If granted for an attribute type, Filtermatch permits the attribute
type to satisfy a Filter item.
If granted for an attribute value, Filtermatch permits the attribute
value to satisfy a Filter item. FilterMatch permission for the
attribute type is a prerequisite.
3.1.6. Modify
If granted for an entry, Modify permits the information contained
within an entry to be modified by the LDAP Modify operation, subject
to controls on the attribute types and values.
3.1.7. Add
If granted for an entry, Add permits creation of an entry in the DIT,
subject to being able to add all specified attributes and attribute
values. Add permission granted for an entry is ineffective if Add
permission is not also granted for at least the mandatory attributes
and their values. There is no specific "add subordinate permission".
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Permission to add an entry is controlled using prescriptive ACI.
If granted for an attribute type, Add permits adding a new attribute,
subject to being able to add all specified attribute values. Add or
Modify permission for the entry is a prerequisite.
If granted for an attribute value, Add permits adding that value to
an existing attribute. Add or Modify permission for the entry is a
prerequisite.
3.1.8. Remove
If granted for an entry, Remove permits the entry to be removed from
the DIT regardless of controls on attributes or attribute values
within the entry.
If granted for an attribute, Remove permits removing an attribute,
subject to being able to remove any explicitly specified attribute
values. Remove permission for values not explicitly specified is not
required.
If granted for an attribute value, Remove permits the attribute value
to be removed from an existing attribute.
3.1.9. DiscloseOnError
If granted for an entry, DiscloseOnError permits the name of an entry
to be disclosed in an error result.
If granted for an attribute, DiscloseOnError permits the presence of
the attribute to be disclosed by an error.
If granted for an attribute value, DiscloseOnError permits the
presence of the attribute value to be disclosed by an error.
3.1.10. Rename
If granted for an entry, Rename permits an entry to be renamed with a
new RDN. No permissions are required for the attributes and values
altered by the operation, even if they are added or removed as a
result of the changes to the RDN.
3.1.11. Export
If granted for an entry, Export permits the entry and its
subordinates, if any, to be removed from the current location and
placed in a new location, subject to the granting of Import
permission at the destination.
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If the last RDN is changed, Rename permission at the current location
is also required
3.1.12. Import
If granted for an entry, Import permits an entry and its
subordinates, if any, to be placed at the location to which the
permission applies, subject to the granting of Export permission at
the source location.
3.1.13. Invoke
Invoke, if granted for an operational attribute, or value thereof,
permits the directory server to carry out some function associated
with the operational attribute on behalf of the user. The specific
function carried out by invocation depends on the attribute. No
other permissions are required by user for the operational attribute,
or on the entry/subentry that holds it, in order for it to be
"invoked".
3.2. Representation of Access Control Information
Access Control Information is represented as a set of ACI items,
where each ACI item grants or denies permissions in regard to certain
specified users and protected items.
An ACI item is represented as a value of an operational attribute
with the ACI Item syntax (1.3.6.1.4.1.1466.115.121.1.1) [RFC2252].
This document updates [RFC2252] by specifying a human-readable
LDAP-specific encoding for ACI items. The LDAP-specific encoding of
values of the ACI Item syntax is defined by the Generic String
Encoding Rules [GSER]. Appendix A provides an equivalent ABNF for
this syntax.
For convenience in specifying access control policies, the ACI Item
syntax provides the means to identify collections of related items,
such as attributes in an entry or all attribute values of a given
attribute, and to specify a common protection for them.
The ACI Item syntax corresponds to the ACIItem ASN.1 [ASN1] type
defined in X.501 [X501]. It is reproduced here for convenience:
ACIItem ::= SEQUENCE {
identificationTag DirectoryString { ub-tag },
precedence Precedence,
authenticationLevel AuthenticationLevel,
itemOrUserFirst CHOICE {
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itemFirst [0] SEQUENCE {
protectedItems ProtectedItems,
itemPermissions SET OF ItemPermission },
userFirst [1] SEQUENCE {
userClasses UserClasses,
userPermissions SET OF UserPermission } } }
Precedence ::= INTEGER (0..255)
ProtectedItems ::= SEQUENCE {
entry [0] NULL OPTIONAL,
allUserAttributeTypes [1] NULL OPTIONAL,
attributeType [2] SET SIZE (1..MAX) OF
AttributeType OPTIONAL,
allAttributeValues [3] SET SIZE (1..MAX) OF
AttributeType OPTIONAL,
allUserAttributeTypesAndValues [4] NULL OPTIONAL,
attributeValue [5] SET SIZE (1..MAX) OF
AttributeTypeAndValue OPTIONAL,
selfValue [6] SET SIZE (1..MAX) OF
AttributeType OPTIONAL,
rangeOfValues [7] Filter OPTIONAL,
maxValueCount [8] SET SIZE (1..MAX) OF
MaxValueCount OPTIONAL,
maxImmSub [9] INTEGER OPTIONAL,
restrictedBy [10] SET SIZE (1..MAX) OF
RestrictedValue OPTIONAL,
contexts [11] SET SIZE (1..MAX) OF
ContextAssertion OPTIONAL,
classes [12] Refinement OPTIONAL }
MaxValueCount ::= SEQUENCE {
type AttributeType,
maxCount INTEGER }
RestrictedValue ::= SEQUENCE {
type AttributeType,
valuesIn AttributeType }
UserClasses ::= SEQUENCE {
allUsers [0] NULL OPTIONAL,
thisEntry [1] NULL OPTIONAL,
name [2] SET SIZE (1..MAX) OF NameAndOptionalUID OPTIONAL,
userGroup [3] SET SIZE (1..MAX) OF NameAndOptionalUID OPTIONAL,
-- dn component shall be the name of an
-- entry of GroupOfUniqueNames
subtree [4] SET SIZE (1..MAX) OF
SubtreeSpecification OPTIONAL }
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NameAndOptionalUID ::= SEQUENCE {
dn DistinguishedName,
uid UniqueIdentifier OPTIONAL }
UniqueIdentifier ::= BIT STRING
ItemPermission ::= SEQUENCE {
precedence Precedence OPTIONAL,
-- defaults to precedence in ACIItem
userClasses UserClasses,
grantsAndDenials GrantsAndDenials }
UserPermission ::= SEQUENCE {
precedence Precedence OPTIONAL,
-- defaults to precedence in ACIItem
protectedItems ProtectedItems,
grantsAndDenials GrantsAndDenials }
AuthenticationLevel ::= CHOICE {
basicLevels SEQUENCE {
level ENUMERATED { none(0), simple(1), strong(2) },
localQualifier INTEGER OPTIONAL,
signed BOOLEAN DEFAULT FALSE },
other EXTERNAL }
GrantsAndDenials ::= BIT STRING {
-- permissions that may be used in conjunction
-- with any component of ProtectedItems
grantAdd (0),
denyAdd (1),
grantDiscloseOnError (2),
denyDiscloseOnError (3),
grantRead (4),
denyRead (5),
grantRemove (6),
denyRemove (7),
-- permissions that may be used only in conjunction
-- with the entry component
grantBrowse (8),
denyBrowse (9),
grantExport (10),
denyExport (11),
grantImport (12),
denyImport (13),
grantModify (14),
denyModify (15),
grantRename (16),
denyRename (17),
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grantReturnDN (18),
denyReturnDN (19),
-- permissions that may be used in conjunction
-- with any component, except entry, of ProtectedItems
grantCompare (20),
denyCompare (21),
grantFilterMatch (22),
denyFilterMatch (23),
grantInvoke (24),
denyInvoke (25) }
AttributeTypeAndValue ::= SEQUENCE {
type ATTRIBUTE.&id ({SupportedAttributes}),
value ATTRIBUTE.&Type ({SupportedAttributes}{@type}) }
The SubtreeSpecification and Refinement ASN.1 types are defined in
X.501 [X501], and separately described for LDAP [SUBENTRY].
The following sections describe the components of ACIItem.
3.2.1. Identification Tag
identificationTag is used to identify a particular ACI item. This is
used to discriminate among individual ACI items for the purposes of
protection and administration.
3.2.2. Precedence
Precedence is used to control the relative order in which ACI items
are considered during the course of making an access control decision
using the ACDF. ACI items having higher precedence values prevail
over others with lower precedence values, other factors being equal.
Precedence values are integers and are compared as such.
3.2.3. Authentication Level
AuthenticationLevel defines the minimum requestor authentication
level required for this ACI item. It has two forms:
1) basicLevels: which indicates the level of authentication,
optionally qualified by positive or negative integer
localQualifier.
2) other: an externally defined measure.
When basicLevels is used, an AuthenticationLevel consisting of a
level and optional localQualifier SHALL be assigned to the requestor
by the directory server according to local policy. For a requestor's
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authentication level to meet or exceed the minimum requirement, the
requestor's level must meet or exceed that specified in the ACI item,
and in addition the requestor's localQualifier must be arithmetically
greater than or equal to that of the ACI item. Strong authentication
of the requestor is considered to exceed a requirement for simple or
no authentication, and simple authentication exceeds a requirement
for no authentication. For access control purposes, the "simple"
authentication level requires at least a password; the case of
identification only, with no password supplied, is considered "none".
If a localQualifier is not specified in the ACI item, then the
requestor need not have a corresponding value (if such a value is
present it is ignored).
The signed component of basicLevels is ignored for LDAP.
When other is used, an appropriate AuthenticationLevel shall be
assigned to the requestor by the directory server according to local
policy. The form of this AuthenticationLevel and the method by which
it is compared with the AuthenticationLevel in the ACI is a local
matter.
An authentication level associated with an explicit grant indicates
the minimum level to which a requestor shall be authenticated in
order to be granted access.
An authentication level associated with an explicit deny indicates
the minimum level to which a requestor shall be authenticated in
order not to be denied access. For example, an ACI item that denies
access to a particular user class and requires strong authentication
will deny access to all requestors who cannot prove, by means of a
strongly authenticated identity, that they are not in that user
class.
The directory server may base authentication level on factors other
than values received in protocol exchanges.
3.2.4. itemFirst and userFirst Components
Each ACI item contains a choice of itemFirst or userFirst. The
choice allows grouping of permissions depending on whether they are
most conveniently grouped by user classes or by protected items. The
itemFirst and userFirst components are equivalent in the sense that
they capture the same access control information; however, they
organize that information differently. The choice between them is
based on administrative convenience. The subcomponents of itemFirst
and userFirst are described below.
a) ProtectedItems defines the items to which the specified access
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controls apply. It is defined as a set selected from the
following:
- entry means the entry contents as a whole. It does not
necessarily include the information in these entries. This
element SHALL be ignored if the classes component is present,
since this latter element selects protected entries on the basis
of their object class.
- allUserAttributeTypes means all user attribute type information
associated with the entry, but not values associated with those
attributes.
- allUserAttributeTypesAndValues means all user attribute
information associated with the entry, including all values of
all user attributes.
The allUserAttributeTypes and allUserAttributeTypesAndValues
components do not include operational attributes, which MUST be
specified on a per attribute basis, using attributeType,
allAttributeValues or attributeValue.
- attributeType means attribute type information pertaining to
specific attributes but not values associated with the type.
- allAttributeValues means all attribute value information
pertaining to specific attributes.
- attributeValue means specific values of specific attribute
types.
- selfValue means the attribute values of the specified attribute
types that match the distinguished name (and unique identifier)
of the requestor. It can only apply in the specific case where
the attribute specified is of DN syntax
(1.3.6.1.4.1.1466.115.121.1.12) or Name And Optional UID syntax
(1.3.6.1.4.1.1466.115.121.1.34) [RFC2252].
- rangeOfValues means any attribute value which matches the
specified filter, i.e., for which the specified filter evaluated
on that attribute value would return TRUE. The filter is not
evaluated on any entries in the DIB, rather it is evaluated
using the semantics defined in 7.8 of [X511], operating on a
fictitious entry that contains only the single attribute value
which is the protected item. Note that the filter is an X.500
search Filter. It has a different syntax from the LDAP search
Filter, but the same semantics.
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The following items provide constraints that may disable the
granting of certain permissions to protected items in the same
value of ProtectedItems:
- maxValueCount restricts the maximum number of attribute values
allowed for a specified attribute type. It is examined if the
protected item is an attribute value of the specified type and
the permission sought is Add. Values of that attribute in the
entry are counted, without regard to attribute options and
access control, as though the operation which is attempting to
add the values is successful. If the number of values in the
attribute exceeds maxCount, the ACI item is treated as not
granting Add permission.
- maxImmSub restricts the maximum number of immediate subordinates
of the superior entry to an entry being added or imported. It
is examined if the protected item is an entry, the permission
sought is Add or Import, and the immediate superior entry is in
the same server as the entry being added or imported. Immediate
subordinates of the superior entry are counted, without regard
to access control, as though the entry addition or importing is
successful. If the number of subordinates exceeds maxImmSub,
the ACI item is treated as not granting Add or Import
permission.
- restrictedBy restricts values added to the attribute type to
being values that are already present in the same entry as
values of the attribute identified by the valuesIn component.
It is examined if the protected item is an attribute value of
the specified type and the permission sought is Add. Values of
the valuesIn attribute are checked, without regard to attribute
options and access control, as though the operation which adds
the values is successful. If the value to be added is not
present in valuesIn the ACI item is treated as not granting Add
permission.
- contexts is not used in this version of the LDAP profile for
Basic Access Control.
- classes means the contents of entries that have object class
values that satisfy the predicate defined by Refinement (see
[SUBENTRY]).
b) UserClasses defines a set of zero or more users the permissions
apply to. The set of users is selected from the following:
- allUsers means every directory user (with possible requirements
for AuthenticationLevel).
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- thisEntry means the user with the same distinguished name as the
entry being accessed.
- name is the set of users with the specified distinguished names
(each with an optional unique identifier).
- userGroup is the set of users who are members of the groups
(i.e., groupOfNames or groupOfUniqueNames entries [RFC2256])
identified by the specified distinguished names (each with an
optional unique identifier). Members of a group of unique names
are treated as individual user distinguished names, and not as
the names of other groups of unique names. How group membership
is determined is described in 5.2.5.
- subtree is the set of users whose distinguished names fall
within the scope of the unrefined subtrees (specificationFilter
components SHOULD NOT be used - they SHALL be ignored if
present).
c) SubtreeSpecification is used to specify a subtree relative to the
root DSE, and is not constrained by administrative areas. The
specificationFilter component SHOULD NOT be used. It SHALL be
ignored if present.
A subtree refinement is not allowed because membership in a
subtree whose specification includes only base and/or a
ChopSpecification can be evaluated in isolation, whereas
membership in a subtree definition using specificationFilter can
only be evaluated by obtaining information from the user's entry,
which is potentially in another directory server. Basic Access
Control is designed to avoid remote operations in the course of
making an access control decision.
d) ItemPermission contains a collection of users and their
permissions with respect to ProtectedItems within an itemFirst
specification. The permissions are specified in grantsAndDenials
as discussed in item f). Each of the permissions specified in
grantsAndDenials is considered to have the precedence level
specified in precedence for the purpose of the ACDF. If
precedence is omitted within ItemPermission, then precedence is
taken from the precedence specified for ACIItem.
e) UserPermission contains a collection of protected items and the
associated permissions with respect to userClasses within a
userFirst specification. The associated permissions are specified
in grantsAndDenials as discussed in item f). Each of the
permissions specified in grantsAndDenials is considered to have
the precedence level specified in precedence for the purpose of
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the ACDF. If precedence is omitted within UserPermission, the
precedence is taken from the precedence specified for ACIItem.
f) GrantsAndDenials specify the access rights that are granted or
denied by the ACI item.
g) UniqueIdentifier may be used by the authentication mechanism to
distinguish between instances of distinguished name reuse. If
this component is present, then for a requestor's name to match
the UserClasses of an ACIItem that grants permissions, in addition
to the requirement that the requestor's distinguished name match
the specified distinguished name, the authentication of the
requestor shall yield an associated unique identifier, and that
value shall match for equality with the specified value.
3.2.5. Determining Group Membership
Determining whether a given requestor is a group member requires
checking two criteria. The determination may also be constrained if
the group definition is not known locally. The criteria for
membership and the treatment of non-local groups are discussed below.
a) A directory server is not required to perform a remote operation
to determine whether the requestor belongs to a particular group
for the purposes of Basic Access Control. If membership in the
group cannot be evaluated, the server shall assume that the
requestor does not belong to the group if the ACI item grants the
permission sought, and does belong to the group if it denies the
permission sought.
Access control administrators should beware of basing access
controls on membership of non-locally available groups or groups
which are available only through replication (and which may,
therefore, be out of date).
b) In order to determine whether the requestor is a member of a
userGroup user class, the following criteria apply:
- The entry named by the userGroup specification is an instance of
the object class groupOfNames or groupOfUniqueNames.
- The name of the requestor is a value of the member or
uniqueMember attribute of that entry.
Values of the member or uniqueMember attribute that do not match
the name of the requestor are ignored, even if they represent the
names of groups of which the originator could be found to be a
member. Hence, nested groups are not supported when evaluating
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access controls.
3.3. ACI Operational Attributes
ACI is stored as values of operational attributes of entries and
subentries. The operational attributes are multi-valued, which
allows ACI to be represented as a set of ACI items.
3.3.1. Prescriptive ACI
The prescriptiveACI attribute is defined as an operational attribute
of an access control subentry. It contains prescriptive ACI
applicable to entries within that subentry's scope.
The LDAP description [RFC2252] for the prescriptiveACI operational
attribute is:
( 2.5.24.4 NAME 'prescriptiveACI'
EQUALITY directoryStringFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.1
USAGE directoryOperation )
The directoryStringFirstComponentMatch matching rule is described in
[SCHEMA].
Prescriptive ACI within the subentries of a particular administrative
point never applies to the same or any other subentry of that
administrative point, but can be applicable to the subentries of
subordinate administrative points.
Note that prescriptiveACI attributes are not collective attributes.
Although the values of a prescriptiveACI attribute contribute to
access control decisions for each entry within the scope of the
subentry that holds the attribute, the prescriptiveACI attribute does
not appear as part of those entries.
3.3.2. Entry ACI
The entryACI attribute is defined as an operational attribute of an
entry or subentry (not just access control subentries). It contains
entry ACI applicable to the entry or subentry in which it appears,
and that (sub)entry's contents.
The LDAP description [RFC2252] for the entryACI operational attribute
is:
( 2.5.24.5 NAME 'entryACI'
EQUALITY directoryStringFirstComponentMatch
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SYNTAX 1.3.6.1.4.1.1466.115.121.1.1
USAGE directoryOperation )
3.3.3. Subentry ACI
The subentryACI attribute is defined as an operational attribute of
administrative entries [ADMIN] (for any aspect of administration).
It contains subentry ACI that applies to each of the subentries of
the administrative entry in which it appears. Only administrative
entries are permitted to contain a subentryACI attribute.
The LDAP description [RFC2252] for the subentryACI operational
attribute is:
( 2.5.24.6 NAME 'subentryACI'
EQUALITY directoryStringFirstComponentMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.1
USAGE directoryOperation )
3.3.4. Protecting the ACI
ACI operational attributes are subject to the same protection
mechanisms as other attributes.
The identificationTag provides an identifier for each ACI item. This
tag can be used to remove a specific ACI item value, or to protect it
by prescriptive ACI, entry ACI or subentry ACI. Directory rules
ensure that only one ACI item per access control operational
attribute possesses any specific identificationTag value.
The creation of subentries for an administrative entry may be
controlled by means of the subentryACI operational attribute in the
administrative entry. The right to create prescriptive access
controls may also be governed directly by security policy; this
provision is required to create access controls in new autonomous
administrative areas [ADMIN].
3.4. Access Control Decision Points for LDAP Operations
Each LDAP operation involves making a series of access control
decisions on the various protected items that the operation accesses.
For some operations (e.g., the Modify operation), each such access
control decision must grant access for the operation to succeed; if
access is denied to any protected item, the whole operation fails.
For other operations (e.g., the Search operation), protected items to
which access is denied are simply omitted from the operation result
and processing continues.
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If the requested access is denied, further access control decisions
may be needed to determine if the user has DiscloseOnError
permissions to the protected item. Only if DiscloseOnError
permission is granted may the server respond with an error that
reveals the existence of the protected item. In all other cases, the
server MUST act so as to conceal the existence of the protected item.
The permissions required to access each protected item, are specified
for each operation in the following sections. The algorithm by which
a permission is determined to be granted or not granted is specified
in Section 3.5.
3.4.1. Common Elements of Procedure
This section defines the elements of procedure that are common to all
LDAP operations when Basic Access Control is in effect.
3.4.1.1. Alias Dereferencing
If, in the process of locating a target object entry (nominated in an
LDAP request), alias dereferencing is required, no specific
permissions are necessary for alias dereferencing to take place.
However, if alias dereferencing would result in a referral being
returned, the following sequence of access controls applies.
1) Read permission is required to the alias entry. If permission is
not granted, the operation fails in accordance to the procedure
described in 5.4.1.3.
2) Read permission is required to the aliasedEntryName attribute and
to the single value that it contains. If permission is not
granted, the operation fails and the resultCode
aliasDereferencingProblem SHALL be returned. The matchedDN field
of the LDAPResult SHALL contain the name of the alias entry.
In addition to the access controls described above, security policy
may prevent the disclosure of knowledge of other servers which would
otherwise be conveyed in a referral. If such a policy is in effect
the resultCode insufficientAccessRights SHALL be returned.
3.4.1.2. Return of Names in Errors
Certain LDAP result codes, i.e., noSuchObject, aliasProblem,
invalidDNSyntax and aliasDereferencingProblem, provide the name of an
entry in the matchedDN field of an LDAPResult. The DN of an entry
SHALL only be provided in the matchedDN field if DiscloseOnError
permission is granted to that entry, otherwise, the matchedDN field
of the LDAPResult SHALL either contain the name of the next superior
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entry to which DiscloseOnError permission is granted, or, if
DiscloseOnError permission is not granted to any superior entry, the
name of the root DSE (i.e., a zero-length LDAPDN).
3.4.1.3. Non-disclosure of Entry Existence
If, while performing an LDAP operation, the necessary entry level
permission is not granted to the specified target object entry -
e.g., the entry to be modified - the operation fails; if
DiscloseOnError permission is granted to the target entry, the
resultCode insufficientAccessRights SHALL be returned, otherwise, the
resultCode noSuchObject SHALL be returned. The matchedDN field of
the LDAPResult SHALL either contain the name of the next superior
entry to which DiscloseOnError permission is granted, or, if
DiscloseOnError permission is not granted to any superior entry, the
name of the root DSE (i.e., a zero-length LDAPDN).
Additionally, whenever the server detects an operational error
(including a referral resultCode), it shall ensure that in returning
that error it does not compromise the existence of the named target
entry and any of its superiors. For example, before returning a
resultCode of timeLimitExceeded or notAllowedOnNonLeaf, the server
verifies that DiscloseOnError permission is granted to the target
entry. If it is not, the procedure described in the paragraph above
SHALL be followed.
3.4.2. Compare Operation Decision Points
The following sequence of access controls applies for an entry being
compared.
1) Read permission for the entry to be compared is required. If
permission is not granted, the operation fails in accordance with
5.4.1.3.
2) Compare permission for the attribute to be compared is required.
If permission is not granted, the operation fails: if
DiscloseOnError permission is granted to the attribute being
compared, a resultCode of insufficientAccessRight SHALL be
returned, otherwise, the resultCode noSuchAttribute SHALL be
returned.
3) If there exists a value within the attribute being compared that
matches the purported argument and for which Compare permission is
granted, the operation returns the resultCode compareTrue,
otherwise the operation returns the resultCode compareFalse.
3.4.3. Search Operation Decision Points
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The following sequence of access controls applies for a portion of
the DIT being searched.
1) No specific permission is required to the entry identified by the
baseObject argument in order to initiate a search. However, if
the baseObject is within the scope of the SearchArgument (i.e.,
when the subset argument specifies baseObject or wholeSubtree) the
access controls specified in 2) through 5) will apply.
2) Browse or Read permission is required for the single entry within
the scope of a baseObject search. An entry for which neither of
these permissions is granted is ignored.
This differs from the X.500 DAP Search operation where the Browse
permission alone is required. An entry with Read permission but
not Browse permission cannot be searched but can still be examined
with an X.500 DAP Read operation. LDAP relies on baseObject
search operations to provide the functionality of the DAP Read
operation. Accepting Read permission for the target entry in a
baseObject search gives an LDAP baseObject search the same access
rights to the entry as the DAP Read operation.
3) Browse permission is required for an entry within the scope of a
singleLevel or wholeSubtree search to be a candidate for
consideration. Entries for which this permission is not granted
are ignored.
4) The filter argument is applied to each entry left to be considered
after taking 2) and 3) into account, in accordance with the
following:
a) For a present Filter item, if there exists an attribute value
such that the attribute type of the value (possibly a subtype
of the attribute type in the FilterItem) satisfies the Filter
item and FilterMatch permission is granted for the value and
for the attribute type then the FilterItem evaluates to TRUE,
otherwise, it evaluates to FALSE.
If a directory server does not support True/False filters
[FILTER] on LDAP searches, or if directory clients do not
exploit this capability, then access control administrators
SHOULD grant FilterMatch permission for the objectClass
attribute over entries where Read permission is also granted so
that an LDAP baseObject search with a filter testing for the
presence of the objectClass attribute will have the same access
rights to the target entry as the DAP Read operation. An LDAP
baseObject search with a True filter does not require
FilterMatch permission for any particular attribute type.
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b) For an equalityMatch, substrings, greaterOrEqual, lessOrEqual,
approxMatch or extensibleMatch Filter item, if there exists an
attribute value such that the value satisfies the Filter item
and FilterMatch permission is granted for the value and for its
attribute type (possibly a subtype of the attribute type in the
FilterItem) then the FilterItem evaluates to TRUE, otherwise,
it evaluates to FALSE.
Once the access controls defined in 2) through 4) have been applied,
an entry is either selected or discarded.
5) For each selected entry the information returned is as follows:
a) ReturnDN permission for an entry is required in order to return
its distinguished name in a SearchResultEntry response. If
this permission is not granted, the server SHALL either, return
the name of a valid alias to the entry, or, omit the entry from
the search result.
If the base entry of the search was located using an alias,
then that alias is known to be a valid alias. Otherwise, how
it is ensured that the alias is valid is outside the scope of
this specification.
Where a server has a choice of alias names available to it for
return, it is RECOMMENDED that where possible it choose the
same alias name for repeated requests by the same client, in
order to provide a consistent service.
b) If the typesOnly field of the SearchRequest is TRUE then, for
each attribute type that is to be returned, Read permission for
the attribute type and Read permission for at least one value
of the attribute is required. If permission is not granted,
the attribute type is omitted from the attribute list in the
SearchResultEntry. If as a consequence of applying these
controls no attribute type information is selected, the
SearchResultEntry is returned but no attribute type information
is conveyed with it (i.e., the attribute list is empty).
c) If the typesOnly field of the SearchRequest is FALSE then Read
permission is required for each attribute type and for each
attribute value that is to be returned. If permission to an
attribute type is not granted, the attribute is omitted from
the SearchResultEntry. If permission to an attribute value is
not granted, the value is omitted from its corresponding
attribute. If all values of an attribute are omitted then the
attribute type is omitted from the attribute list in the
SearchResultEntry. If as a consequence of applying these
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controls no attribute information is selected, the
SearchResultEntry is returned but no attribute information is
conveyed with it (i.e., the attribute list is empty).
6) If as a consequence of applying the above controls to the entire
scoped subtree the search result contains no entries (excluding
any SearchResultReferences) and if DiscloseOnError permission is
not granted to the entry identified by the baseObject argument,
the operation fails and the resultCode noSuchObject SHALL be
returned. The matchedDN field of the LDAPResult SHALL either
contain the name of the next superior entry to which
DiscloseOnError permission is granted, or the name of the root DSE
(i.e., a zero-length LDAPDN). Otherwise, the operation succeeds
but no subordinate information is conveyed with it.
Security policy may prevent the disclosure of knowledge of other
servers which would otherwise be conveyed as SearchResultReferences.
If such a policy is in effect SearchResultReferences are omitted from
the search result.
No specific permissions are necessary to allow alias dereferencing to
take place in the course of a search operation. However, for each
alias entry encountered, if alias dereferencing would result in a
SearchResultReference being returned, the following access controls
apply: Read permission is required to the alias entry, the
aliasedEntryName attribute and to the single value that it contains.
If any of these permissions is not granted, the SearchResultReference
SHALL be omitted from the search result.
3.4.4. Add Operation Decision Points
The following sequence of access controls apply for an entry being
added.
1) No specific permission is required for the immediate superior of
the entry identified by the entry field of the AddRequest.
2) If an entry already exists with a distinguished name equal to the
entry field the operation fails; if DiscloseOnError or Add
permission is granted to the existing entry, the resultCode
entryAlreadyExists SHALL be returned, otherwise, the procedure
described in 5.4.1.3 is followed with respect to the entry being
added.
3) Add permission is required for the new entry being added. If this
permission is not granted, the operation fails; the procedure
described in 5.4.1.3 is followed with respect to the entry being
added.
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The Add permission is provided as prescriptive ACI when attempting
to add an entry and as prescriptive ACI or subentry ACI when
attempting to add a subentry. Any values of the entryACI
attribute in the entry being added SHALL be ignored.
4) Add permission is required for each attribute type and for each
value that is to be added. If any permission is absent, the
operation fails and the resultCode insufficientAccessRights SHALL
be returned.
3.4.5. Delete Operation Decision Points
The following sequence of access controls apply for an entry being
removed.
1) Remove permission is required for the entry being removed. If
this permission is not granted, the operation fails in accordance
with 5.4.1.3.
2) No specific permissions are required for any of the attributes and
attribute values present within the entry being removed.
3.4.6. Modify Operation Decision Points
The following sequence of access controls apply for an entry being
modified.
1) Modify permission is required for the entry being modified. If
this permission is not granted, the operation fails in accordance
with 5.4.1.3.
2) For each of the specified modification arguments applied in
sequence, the following permissions are required:
a) Add permission is required for each of the attribute values
specified in an add modification. If the attribute does not
currently exist then Add permission for the attribute type is
also required. If these permissions are not granted, or any of
the attribute values already exist, the operation fails; if an
attribute value already exists and DiscloseOnError or Add is
granted to that attribute value, the resultCode
attributeOrValueExists SHALL be returned, otherwise, the
resultCode insufficientAccessRights SHALL be returned.
b) Remove permission is required for the attribute type specified
in a delete modification with no listed attribute values. If
this permission is not granted, the operation fails; if
DiscloseOnError permission is granted to the attribute being
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removed and the attribute exists, the resultCode
insufficientAccessRights SHALL be returned, otherwise, the
resultCode noSuchAttribute SHALL be returned.
No specific permissions are required for any of the attribute
values present within the attribute being removed.
c) Remove permission is required for each of the values in a
delete modification with listed attribute values. If all
current values of the attribute are specified to be removed
(which causes the attribute itself to be removed), then Remove
permission for the attribute type is also required. If these
permissions are not granted, the operation fails; if
DiscloseOnError permission is granted to any of the attribute
values being removed, the resultCode insufficientAccessRights
SHALL be returned, otherwise, the resultCode noSuchAttribute
SHALL be returned.
d) Remove and Add permission is required for the attribute type,
and Add permission is required for each of the specified
attribute values, in a replace modification. If these
permissions are not granted the operation fails and the
resultCode insufficientAccessRights SHALL be returned.
No specific permissions are required to remove any existing
attribute values of the attribute being replaced.
3.4.7. Modify DN Operation Decision Points
The following sequence of access controls apply for an entry having
its DN modified.
1) If the effect of the operation is to change the RDN of the entry
then Rename permission (determined with respect to its original
name) is required for the entry. If this permission is not
granted, the operation fails; the procedure described in 5.4.1.3
is followed with respect to the entry being renamed (considered
with its original name).
No additional permissions are required even if, as a result of
modifying the RDN of the entry, a new distinguished value needs to
be added, or an old one removed. No specific permissions are
required for the subordinates of the renamed entry.
2) If the effect of the operation is to move an entry to a new
superior in the DIT then Export permission (determined with
respect to its original name) and Import permission (determined
with respect to its new name) are required for the entry. If
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either of these permissions is not granted, the operation fails;
the procedure described in 5.4.1.3 is followed with respect to the
entry being moved (considered with its original name).
The Import permission is provided as prescriptive ACI when
attempting to move an entry and as prescriptive ACI or subentry
ACI when attempting to move a subentry. Any values of the
entryACI attribute in the entry or subentry being moved SHALL be
ignored.
No specific permissions are required for the subordinates of the
moved entry.
Note that a single Modify DN Operation may simultaneously rename and
move an entry.
3.5. Access Control Decision Function
This section describes how ACI items are processed in order to decide
whether to grant or deny a particular requestor a specified
permission to a given protected item.
Section 3.5.1 describes the inputs to the ACDF. Sections 3.5.2
through 3.5.4 describe the steps in the ACDF. The output is a
decision to grant or deny access to the protected item.
3.5.1. Inputs
For each invocation of the ACDF, the inputs are:
a) the requestor's Distinguished Name, unique identifier, and
authentication level, or as many of these as are available;
b) the protected item (an entry, an attribute, or an attribute value)
being considered at the current decision point for which the ACDF
was invoked;
c) the requested permission specified for the current decision point;
d) the ACI items applicable to the entry containing (or which is) the
protected item.
In addition, if the ACI items include any of the protected item
constraints described in 5.2.1.4, the whole entry and the number of
immediate subordinates of its superior entry may also be required as
inputs.
3.5.2. Tuples
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For each ACI item, expand the item into a set of tuples, one tuple
for each element of the itemPermissions and userPermissions sets,
containing the following elements:
( userClasses, authenticationLevel, protectedItems,
grantsAndDenials, precedence )
Collect all tuples from all ACI items into a single set.
For any tuple whose grantsAndDenials specify both grants and denials,
replace the tuple with two tuples - one specifying only grants and
the other specifying only denials.
3.5.3. Discarding Irrelevant Tuples
Perform the following steps to discard all irrelevant tuples:
1) Discard all tuples that do not include the requestor in the
tuple's userClasses as follows:
a) For tuples that grant access, discard all tuples that do not
include the requestor's identity in the tuples's userClasses
element, taking into account UniqueIdentifier elements if
relevant. Where a tuple's userClasses specifies a
UniqueIdentifier, a matching value shall be present in the
requestor's identity if the tuple is not to be discarded.
Discard tuples that specify an authentication level higher than
that associated with the requestor.
b) For tuples that deny access, retain all tuples that include the
requestor in the tuple's userClasses element, taking into
account uniqueIdentifier elements if relevant. Also retain all
tuples that deny access and which specify an authentication
level higher than that associated with the requestor. This
reflects the fact that the requestor has not adequately proved
non-membership in the user class for which the denial is
specified. All other tuples that deny access are discarded.
2) Discard all tuples that do not include the protected item in
protectedItems.
3) Examine all tuples that include maxValueCount, maxImmSub or
restrictedBy. Discard all such tuples which grant access and
which do not satisfy any of these constraints.
4) Discard all tuples that do not include the requested permission as
one of the set bits in grantsAndDenials.
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The order in which tuples are discarded does not change the output of
the ACDF.
3.5.4. Highest Precedence and Specificity
Perform the following steps to select those tuples of highest
precedence and specificity:
1) Discard all tuples having a precedence less than the highest
precedence among the remaining tuples.
2) If more than one tuple remains, choose the tuples with the most
specific user class. If there are any tuples matching the
requestor with UserClasses element name or thisEntry, discard all
other tuples. Otherwise if there are any tuples matching
UserGroup, discard all other tuples. Otherwise if there are any
tuples matching subtree, discard all other tuples.
3) If more than one tuple remains, choose the tuples with the most
specific protected item. If the protected item is an attribute
and there are tuples that specify the attribute type explicitly,
discard all other tuples. If the protected item is an attribute
value, and there are tuples that specify the attribute value
explicitly, discard all other tuples. A protected item which is a
rangeOfValues is to be treated as specifying an attribute value
explicitly.
Grant access if and only if one or more tuples remain and all grant
access. Otherwise deny access.
4. Simplified Access Control
This section describes the functionality of the Simplified Access
Control scheme. It provides a subset of the functionality found in
Basic Access Control.
When Simplified Access Control is used, the accessControlScheme
operational attribute [ACA] SHALL have the value
simplified-access-control (2.5.28.2).
The functionality of Simplified Access Control is the same as Basic
Access Control except that:
1) Access control decisions shall be made only on the basis of values
of prescriptiveACI and subentryACI operational attributes. Values
of the entryACI attribute, if present, SHALL NOT be used to make
access control decisions.
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2) Access Control Inner Areas are not used. Values of
prescriptiveACI attributes appearing in subentries of ACIPs SHALL
NOT be used to make access control decisions.
All other provisions SHALL be as defined for Basic Access Control.
5. Security Considerations
Access control administrators should beware of basing access controls
on membership of non-locally available groups or groups which are
available only through replication (and which may, therefore, be out
of date).
A particular DSA might not have the ACI governing any data that it
caches. Administrators should be aware that a directory server with
the capability of caching may pose a significant security risk to
other directory servers, in that it may reveal information to
unauthorized users.
6. Acknowledgements
This document is derived from, and duplicates substantial portions
of, Section 8 of X.501 [X501], and selected extracts from X.511
[X511].
7. IANA Considerations
The Internet Assigned Numbers Authority (IANA) is requested to update
the LDAP descriptors registry [BCP64] as indicated by the following
templates:
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): basic-access-control
Object Identifier: 2.5.28.1
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: other (access control scheme)
Specification: RFC XXXX
Author/Change Controller: IESG
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): simplified-access-control
Object Identifier: 2.5.28.2
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: other (access control scheme)
Specification: RFC XXXX
Author/Change Controller: IESG
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Subject: Request for LDAP Descriptor Registration
Descriptor (short name): prescriptiveACI
Object Identifier: 2.5.24.4
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: attribute type
Specification: RFC XXXX
Author/Change Controller: IESG
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): entryACI
Object Identifier: 2.5.24.5
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: attribute type
Specification: RFC XXXX
Author/Change Controller: IESG
Subject: Request for LDAP Descriptor Registration
Descriptor (short name): subentryACI
Object Identifier: 2.5.24.6
Person & email address to contact for further information:
Steven Legg <steven.legg@adacel.com.au>
Usage: attribute type
Specification: RFC XXXX
Author/Change Controller: IESG
Appendix A. LDAP Specific Encoding for the ACI Item Syntax
This appendix is non-normative.
The LDAP-specific encoding for the ACI Item syntax is specified by
the Generic String Encoding Rules [GSER]. The ABNF [RFC2234] in this
appendix for this syntax is provided only as a convenience and is
equivalent to the encoding specified by the application of GSER.
Since the ACI Item ASN.1 type may be extended in future editions of
X.501 [X501], the provided ABNF should be regarded as a snapshot in
time. The LDAP-specific encoding for any extension to the ACI Item
ASN.1 type can be determined from the rules of GSER.
In the event that there is a discrepancy between this ABNF and the
encoding determined by GSER, then GSER is to be taken as definitive.
ACIItem = "{" sp aci-identificationTag ","
sp aci-precedence ","
sp aci-authenticationLevel ","
sp aci-itemOrUserFirst
sp "}"
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aci-identificationTag = id-identificationTag msp
DirectoryString
aci-precedence = id-precedence msp Precedence
aci-authenticationLevel = id-authenticationLevel msp
AuthenticationLevel
aci-itemOrUserFirst = id-itemOrUserFirst msp
ItemOrUserFirst
id-identificationTag = %x69.64.65.6E.74.69.66.69.63.61.74.69.6F
%x6E.54.61.67 ; "identificationTag"
id-precedence = %x70.72.65.63.65.64.65.6E.63.65
; "precedence"
id-authenticationLevel = %x61.75.74.68.65.6E.74.69.63.61.74.69.6F
%x6E.4C.65.76.65.6C
; "authenticationLevel"
id-itemOrUserFirst = %x69.74.65.6D.4F.72.55.73.65.72.46.69.72
%x73.74 ; "itemOrUserFirst"
Precedence = INTEGER-0-MAX ; MUST be less than 256
AuthenticationLevel = al-basicLevels / al-other
al-basicLevels = id-basicLevels ":" BasicLevels
al-other = id-other ":" EXTERNAL
id-basicLevels = %x62.61.73.69.63.4C.65.76.65.6C.73
; "basicLevels"
id-other = %x6F.74.68.65.72 ; "other"
BasicLevels = "{" sp bl-level
[ "," sp bl-localQualifier ]
[ "," sp bl-signed ]
sp "}"
bl-level = id-level msp Level
bl-localQualifier = id-localQualifier msp INTEGER
bl-signed = id-signed msp BOOLEAN
Level = id-none / id-simple / id-strong
id-level = %x6C.65.76.65.6C ; "level"
id-localQualifier = %x6C.6F.63.61.6C.51.75.61.6C.69.66.69.65.72
; "localQualifier"
id-signed = %x73.69.67.6E.65.64 ; "signed"
id-none = %x6E.6F.6E.65 ; "none"
id-simple = %x73.69.6D.70.6C.65 ; "simple"
id-strong = %x73.74.72.6F.6E.67 ; "strong"
ItemOrUserFirst = ( id-itemFirst ":" ItemFirst ) /
( id-userFirst ":" UserFirst )
id-itemFirst = %x69.74.65.6D.46.69.72.73.74 ; "itemFirst"
id-userFirst = %x75.73.65.72.46.69.72.73.74 ; "userFirst"
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ItemFirst = "{" sp if-protectedItems ","
sp if-itemPermissions
sp "}"
if-protectedItems = id-protectedItems msp ProtectedItems
if-itemPermissions = id-itemPermissions msp ItemPermissions
id-protectedItems = %x70.72.6F.74.65.63.74.65.64.49.74.65.6D.73
; "protectedItems"
id-itemPermissions = %x69.74.65.6D.50.65.72.6D.69.73.73.69.6F.6E
%x73 ; "itemPermissions"
UserFirst = "{" sp uf-userClasses ","
sp uf-userPermissions
sp "}"
uf-userClasses = id-userClasses msp UserClasses
uf-userPermissions = id-userPermissions msp UserPermissions
id-userClasses = %x75.73.65.72.43.6C.61.73.73.65.73
; "userClasses"
id-userPermissions = %x75.73.65.72.50.65.72.6D.69.73.73.69.6F.6E
%x73 ; "userPermissions"
ItemPermissions = "{" [ sp ItemPermission
*( "," sp ItemPermission ) ] sp "}"
ItemPermission = "{" [ sp ip-precedence "," ]
sp ip-userClasses ","
sp ip-grantsAndDenials
sp "}"
ip-precedence = id-precedence msp Precedence
ip-userClasses = id-userClasses msp UserClasses
ip-grantsAndDenials = id-grantsAndDenials msp GrantsAndDenials
id-grantsAndDenials = %x67.72.61.6E.74.73.41.6E.64.44.65.6E.69.61
%x6C.73 ; "grantsAndDenials"
UserClasses = "{" [ sp uc-allUsers ]
[ sep sp uc-thisEntry ]
[ sep sp uc-name ]
[ sep sp uc-userGroup ]
[ sep sp uc-subtree ]
sp "}"
uc-allUsers = id-allUsers msp NULL
uc-thisEntry = id-thisEntry msp NULL
uc-name = id-name msp NameAndOptionalUIDs
uc-userGroup = id-userGroup msp NameAndOptionalUIDs
uc-subtree = id-subtree msp SubtreeSpecifications
id-allUsers = %x61.6C.6C.55.73.65.72.73 ; "allUsers"
id-thisEntry = %x74.68.69.73.45.6E.74.72.79 ; "thisEntry"
id-name = %x6E.61.6D.65 ; "name"
id-userGroup = %x75.73.65.72.47.72.6F.75.70 ; "userGroup"
id-subtree = %x73.75.62.74.72.65.65 ; "subtree"
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NameAndOptionalUIDs = "{" sp NameAndOptionalUID
*( "," sp NameAndOptionalUID ) sp "}"
NameAndOptionalUID = "{" sp nu-dn
[ "," sp nu-uid ]
sp "}"
nu-dn = id-dn msp DistinguishedName
nu-uid = id-uid msp UniqueIdentifier
UniqueIdentifier = BIT-STRING
id-dn = %x64.6E ; "dn"
id-uid = %x75.69.64 ; "uid"
SubtreeSpecifications = "{" sp SubtreeSpecification
*( "," sp SubtreeSpecification ) sp "}"
UserPermissions = "{" [ sp UserPermission
*( "," sp UserPermission ) ] sp "}"
UserPermission = "{" [ sp up-precedence "," ]
sp up-protectedItems ","
sp up-grantsAndDenials
sp "}"
up-precedence = id-precedence msp Precedence
up-protectedItems = id-protectedItems msp ProtectedItems
up-grantsAndDenials = id-grantsAndDenials msp GrantsAndDenials
ProtectedItems = "{" [ sp pi-entry ]
[ sep sp pi-allUserAttributeTypes ]
[ sep sp pi-attributeType ]
[ sep sp pi-allAttributeValues ]
[ sep sp pi-allUserTypesAndValues ]
[ sep sp pi-attributeValue ]
[ sep sp pi-selfValue ]
[ sep sp pi-rangeOfValues ]
[ sep sp pi-maxValueCount ]
[ sep sp pi-maxImmSub ]
[ sep sp pi-restrictedBy ]
; contexts omitted
[ sep sp pi-classes ]
sp "}"
pi-entry = id-entry msp NULL
pi-allUserAttributeTypes = id-allUserAttributeTypes msp NULL
pi-attributeType = id-attributeType msp AttributeTypes
pi-allAttributeValues = id-allAttributeValues msp
AttributeTypes
pi-allUserTypesAndValues = id-allUserAttributeTypesAndValues msp
NULL
pi-attributeValue = id-attributeValue msp
AttributeTypeAndValues
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pi-selfValue = id-selfValue msp AttributeTypes
pi-rangeOfValues = id-rangeOfValues msp Filter
pi-maxValueCount = id-maxValueCount msp MaxValueCounts
pi-maxImmSub = id-maxImmSub msp INTEGER
pi-restrictedBy = id-restrictedBy msp RestrictedValues
pi-classes = id-classes msp Refinement
id-entry = %x65.6E.74.72.79 ; "entry"
id-allUserAttributeTypes = %x61.6C.6C.55.73.65.72.41.74.74.72.69
%x62.75.74.65.54.79.70.65.73
; "allUserAttributeTypes"
id-attributeType = %x61.74.74.72.69.62.75.74.65.54.79.70
%x65 ; "attributeType"
id-allAttributeValues = %x61.6C.6C.41.74.74.72.69.62.75.74.65
%x56.61.6C.75.65.73
; "allAttributeValues"
id-attributeValue = %x61.74.74.72.69.62.75.74.65.56.61.6C
%x75.65 ; "attributeValue"
id-selfValue = %x73.65.6C.66.56.61.6C.75.65
; "selfValue"
id-rangeOfValues = %x72.61.6E.67.65.4F.66.56.61.6C.75.65
%x73 ; "rangeOfValues"
id-maxValueCount = %x6D.61.78.56.61.6C.75.65.43.6F.75.6E
%x74 ; "maxValueCount"
id-maxImmSub = %x6D.61.78.49.6D.6D.53.75.62
; "maxImmSub"
id-restrictedBy = %x72.65.73.74.72.69.63.74.65.64.42.79
; "restrictedBy"
id-classes = %x63.6C.61.73.73.65.73 ; "classes"
id-allUserAttributeTypesAndValues = %x61.6C.6C.55.73.65.72.41.74
%x74.72.69.62.75.74.65.54.79.70.65.73
%x41.6E.64.56.61.6C.75.65.73
; "allUserAttributeTypesAndValues"
AttributeTypes = "{" sp AttributeType
*( "," sp AttributeType ) sp "}"
AttributeTypeAndValues = "{" sp AttributeTypeAndValue
*( "," sp AttributeTypeAndValue )
sp "}"
AttributeTypeAndValue = "{" sp atav-type ","
sp atav-value
sp "}"
atav-type = id-type msp AttributeType
atav-value = id-value msp Value
id-type = %x74.79.70.65 ; "type"
id-value = %x76.61.6C.75.65 ; "value"
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MaxValueCounts = "{" sp MaxValueCount
*( "," sp MaxValueCount ) sp "}"
MaxValueCount = "{" sp mvc-type ","
sp mvc-maxCount
sp "}"
mvc-type = id-type msp AttributeType
mvc-maxCount = id-maxCount msp INTEGER
id-maxCount = %x6D.61.78.43.6F.75.6E.74 ; "maxCount"
RestrictedValues = "{" sp RestrictedValue
*( "," sp RestrictedValue ) sp "}"
RestrictedValue = "{" sp rv-type ","
sp rv-valuesin
sp "}"
rv-type = id-type msp AttributeType
rv-valuesin = id-valuesin msp AttributeType
id-valuesin = %x76.61.6C.75.65.73.69.6E ; "valuesin"
GrantsAndDenials = "{" [ sp grantOrDeny
*( "," sp grantOrDeny ) ] sp "}"
grantOrDeny = id-grantAdd
/ id-denyAdd
/ id-grantDiscloseOnError
/ id-denyDiscloseOnError
/ id-grantRead
/ id-denyRead
/ id-grantRemove
/ id-denyRemove
/ id-grantBrowse
/ id-denyBrowse
/ id-grantExport
/ id-denyExport
/ id-grantImport
/ id-denyImport
/ id-grantModify
/ id-denyModify
/ id-grantRename
/ id-denyRename
/ id-grantReturnDN
/ id-denyReturnDN
/ id-grantCompare
/ id-denyCompare
/ id-grantFilterMatch
/ id-denyFilterMatch
; grantInvoke omitted
; denyInvoke omitted
id-grantAdd = %x67.72.61.6E.74.41.64.64 ; "grantAdd"
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id-denyAdd = %x64.65.6E.79.41.64.64 ; "denyAdd"
id-grantBrowse = %x67.72.61.6E.74.42.72.6F.77.73.65
; "grantBrowse"
id-denyBrowse = %x64.65.6E.79.42.72.6F.77.73.65 ; "denyBrowse"
id-grantCompare = %x67.72.61.6E.74.43.6F.6D.70.61.72.65
; "grantCompare"
id-denyCompare = %x64.65.6E.79.43.6F.6D.70.61.72.65
; "denyCompare"
id-grantDiscloseOnError = %x67.72.61.6E.74.44.69.73.63.6C.6F.73.65
%x4F.6E.45.72.72.6F.72
; "grantDiscloseOnError"
id-denyDiscloseOnError = %x64.65.6E.79.44.69.73.63.6C.6F.73.65.4F
%x6E.45.72.72.6F.72
; "denyDiscloseOnError"
id-grantExport = %x67.72.61.6E.74.45.78.70.6F.72.74
; "grantExport"
id-denyExport = %x64.65.6E.79.45.78.70.6F.72.74
; "denyExport"
id-grantFilterMatch = %x67.72.61.6E.74.46.69.6C.74.65.72.4D.61.74
%x63.68 ; "grantFilterMatch"
id-denyFilterMatch = %x64.65.6E.79.46.69.6C.74.65.72.4D.61.74.63
%x68 ; "denyFilterMatch"
id-grantImport = %x67.72.61.6E.74.49.6D.70.6F.72.74
; "grantImport"
id-denyImport = %x64.65.6E.79.49.6D.70.6F.72.74
; "denyImport"
id-grantModify = %x67.72.61.6E.74.4D.6F.64.69.66.79
; "grantModify"
id-denyModify = %x64.65.6E.79.4D.6F.64.69.66.79
; "denyModify"
id-grantRead = %x67.72.61.6E.74.52.65.61.64 ; "grantRead"
id-denyRead = %x64.65.6E.79.52.65.61.64 ; "denyRead"
id-grantRemove = %x67.72.61.6E.74.52.65.6D.6F.76.65
; "grantRemove"
id-denyRemove = %x64.65.6E.79.52.65.6D.6F.76.65
; "denyRemove"
id-grantRename = %x67.72.61.6E.74.52.65.6E.61.6D.65
; "grantRename"
id-denyRename = %x64.65.6E.79.52.65.6E.61.6D.65
; "denyRename"
id-grantReturnDN = %x67.72.61.6E.74.52.65.74.75.72.6E.44.4E
; "grantReturnDN"
id-denyReturnDN = %x64.65.6E.79.52.65.74.75.72.6E.44.4E
; "denyReturnDN"
The <sp>, <msp>, <sep>, <AttributeType>, <BIT-STRING>, <BOOLEAN>,
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<DirectoryString>, <DistinguishedName>, <EXTERNAL>, <INTEGER>,
<INTEGER-0-MAX> and <NULL> rules are described in [GCE].
The <SubtreeSpecification> and <Refinement> rules are described in
[SUBENTRY].
The <Value> rule is described in [GSER].
Filter = filter-item / filter-and / filter-or / filter-not
filter-item = id-item ":" FilterItem
filter-and = id-and ":" SetOfFilter
filter-or = id-or ":" SetOfFilter
filter-not = id-not ":" Filter
id-and = %x61.6E.64 ; "and"
id-item = %x69.74.65.6D ; "item"
id-not = %x6E.6F.74 ; "not"
id-or = %x6F.72 ; "or"
SetOfFilter = "{" [ sp Filter *( "," sp Filter ) ] sp "}"
FilterItem = fi-equality
/ fi-substrings
/ fi-greaterOrEqual
/ fi-lessOrEqual
/ fi-present
/ fi-approximateMatch
/ fi-extensibleMatch
; contextPresent omitted
fi-equality = id-equality ":" AttributeValueAssertion
fi-substrings = id-substrings ":" SubstringsAssertion
fi-greaterOrEqual = id-greaterOrEqual ":"
AttributeValueAssertion
fi-lessOrEqual = id-lessOrEqual ":" AttributeValueAssertion
fi-present = id-present ":" AttributeType
fi-approximateMatch = id-approximateMatch ":"
AttributeValueAssertion
fi-extensibleMatch = id-extensibleMatch ":" MatchingRuleAssertion
id-equality = %x65.71.75.61.6C.69.74.79 ; "equality"
id-substrings = %x73.75.62.73.74.72.69.6E.67.73
; "substrings"
id-greaterOrEqual = %x67.72.65.61.74.65.72.4F.72.45.71.75.61.6C
; "greaterOrEqual"
id-lessOrEqual = %x6C.65.73.73.4F.72.45.71.75.61.6C
; "lessOrEqual"
id-present = %x70.72.65.73.65.6E.74 ; "present"
id-approximateMatch = %x61.70.70.72.6F.78.69.6D.61.74.65.4D.61.74
%x63.68 ; "approximateMatch"
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id-extensibleMatch = %x65.78.74.65.6E.73.69.62.6C.65.4D.61.74.63
%x68 ; "extensibleMatch"
AttributeValueAssertion = "{" sp ava-type ","
sp ava-assertion
; assertedContexts omitted
sp "}"
ava-type = id-type msp AttributeType
ava-assertion = id-assertion msp Value
id-assertion = %x61.73.73.65.72.74.69.6F.6E ; "assertion"
SubstringsAssertion = "{" sp sa-type ","
sp sa-strings
sp "}"
sa-type = id-type msp AttributeType
sa-strings = id-strings msp Substrings
id-strings = %x73.74.72.69.6E.67.73 ; "strings"
Substrings = "{" [ sp Substring *( "," sp Substring ) ] sp "}"
Substring = ss-initial
/ ss-any
/ ss-final
; control omitted
ss-initial = id-initial ":" Value
ss-any = id-any ":" Value
ss-final = id-final ":" Value
id-initial = %x69.6E.69.74.69.61.6C ; "initial"
id-any = %x61.6E.79 ; "any"
id-final = %x66.69.6E.61.6C ; "final"
MatchingRuleAssertion = "{" sp mra-matchingRule
[ "," sp mra-type ]
"," sp mra-matchValue
[ "," sp mra-dnAttributes ]
sp "}"
mra-matchingRule = id-matchingRule msp MatchingRuleIds
mra-type = id-type msp AttributeType
mra-matchValue = id-matchValue msp Value
mra-dnAttributes = id-dnAttributes msp BOOLEAN
id-matchingRule = %x6D.61.74.63.68.69.6E.67.52.75.6C.65
; "matchingRule"
id-matchValue = %x6D.61.74.63.68.56.61.6C.75.65 ; "matchValue"
id-dnAttributes = %x64.6E.41.74.74.72.69.62.75.74.65.73
; "dnAttributes"
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MatchingRuleIds = "{" sp MatchingRuleId *( "," sp MatchingRuleId ) sp "}"
MatchingRuleId = OBJECT-IDENTIFIER
The <OBJECT-IDENTIFIER> rule is described in [GCE].
Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2251] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory
Access Protocol (v3)", RFC 2251, December 1997.
[RFC2252] Wahl, M., Coulbeck, A., Howes, T. and S. Kille,
"Lightweight Directory Access Protocol (v3): Attribute
Syntax Definitions", RFC 2252, December 1997.
[RFC2256] Wahl, M., "A Summary of the X.500(96) User Schema for use
with LDAPv3", RFC 2256, December 1997.
[RFC3377] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377,
September 2002.
[BCP64] Zeilenga, K., "Internet Assigned Numbers
Authority (IANA) Considerations for the Lightweight
Directory Access Protcol (LDAP)", BCP 64, RFC 3383,
September 2002.
[GSER] Legg, S., "Generic String Encoding Rules for ASN.1 Types",
RFC 3641, October 2003.
[COLLECT] Zeilenga, K., "Collective Attributes in the Lightweight
Directory Access Protocol (LDAP)", RFC 3671, December
2003.
[SUBENTRY] Zeilenga, K. and S. Legg, "Subentries in the Lightweight
Directory Access Protocol (LDAP)", RFC 3672, December
2003.
[SCHEMA] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Additional Matching Rules", RFC 3698, February
2004.
[ADMIN] Legg, S., "Lightweight Directory Access Protocol (LDAP):
Directory Administrative Model",
draft-legg-ldap-admin-xx.txt, a work in progress, June
2004.
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[ACA] Legg, S., "Lightweight Directory Access Protocol (LDAP):
Access Control Administration",
draft-legg-ldap-acm-admin-xx.txt, a work in progress, June
2004.
[FILTER] Zeilenga, K., "LDAP Absolute True and False Filters",
draft-zeilenga-ldap-t-f-xx.txt, a work in progress,
February 2004.
[ASN1] ITU-T Recommendation X.680 (07/02) | ISO/IEC 8824-1,
Information technology - Abstract Syntax Notation One
(ASN.1): Specification of basic notation
Informative References
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[GCE] Legg, S., "Common Elements of Generic String Encoding
Rules (GSER) Encodings", RFC 3642, October 2003.
[X501] ITU-T Recommendation X.501 (02/01) | ISO/IEC 9594-2:2001,
Information technology - Open Systems Interconnection -
The Directory: Models
[X511] ITU-T Recommendation X.511 (02/01) | ISO/IEC 9594-3:2001,
Information technology - Open Systems Interconnection -
The Directory: Abstract service definition
Author's Address
Steven Legg
Adacel Technologies Ltd.
250 Bay Street
Brighton, Victoria 3186
AUSTRALIA
Phone: +61 3 8530 7710
Fax: +61 3 8530 7888
EMail: steven.legg@adacel.com.au
Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
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"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights 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; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Changes in Draft 01
The Internet draft draft-legg-ldap-acm-admin-00.txt has been split
into two drafts, draft-legg-ldap-admin-00.txt and
draft-legg-ldap-acm-admin-01.txt. Section 8 of
draft-legg-ldapext-component-matching-06.txt has been extracted to
become a separate Internet draft, draft-legg-ldap-gser-xx.txt. The
references in this document have been updated accordingly.
The term "native LDAP encoding" has been replaced by the term
"LDAP-specific encoding" to align with terminology anticipated to be
used in the revision of RFC 2252.
Changes have been made to the Search Operation Decision Points
(Section 3.4.3):
In 4) a), the assumed FilterMatch permission for a present match of
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INTERNET-DRAFT Basic and Simplified Access Control June 16, 2004
the objectClass attribute has been removed. An LDAP search with a
True filter [FILTER] is the best analogue of the DAP read operation.
A True filter does not filter any attribute type and therefore does
not require FilterMatch permissions to succeed.
In 5) b) and c), there is an additional requirement for Read
permission for at least one attribute value before an attribute type
can be returned in a search result. Without this change a search
result could, in some circumstances, disclose the existence of
particular hidden attribute values.
Changes in Draft 02
RFC 3377 replaces RFC 2251 as the reference for LDAP.
An IANA Considerations section has been added.
Changes in Draft 03
The document has been reformatted in line with current practice.
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