Internet-Draft E. Stokes
LDAP Extensions WG D. Byrne
Intended Category: Standards Track IBM
Expires: 5 April 2000 B. Blakley
Dascom
5 October 1999
Access Control Model for LDAP
<draft-ietf-ldapext-acl-model-04.txt>
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
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COPYRIGHT NOTICE
Copyright (C) The Internet Society (1997). All Rights
Reserved.
ABSTRACT
This document describes the access control model for the
Lightweight Directory Application Protocol (LDAP)
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directory service. It includes a description of the
model, the LDAP controls, and the extended operations to
the LDAP protocol. The current LDAP APIs are sufficient
for most access control operations. An API (in a
separate document) is needed for the extended operation
getEffectiveAccess and specifyCredentials. RFC2219
[Bradner97] terminology is used.
1. Introduction
The ability to securely access (replicate and distribute)
directory information throughout the network is necessary
for successful deployment. LDAP's acceptance as an
access protocol for directory information is driving the
need to provide an access control model definition for
LDAP directory content among servers within an enterprise
and the Internet. Currently LDAP does not define an
access control model, but one is needed to ensure
consistent secure access across heterogeneous LDAP
implementations. The major objective is to provide a
simple, but secure, highly efficient access control model
for LDAP while also providing the appropriate flexibility
to meet the needs of both the Internet and enterprise
environments and policies. This document defines the
model and the protocol extensions (controls and extended
operations).
2. Overview
Access Control mechanisms evaluate requests for access to
protected resources and make decisions about whether
those requests should be granted or denied. In order to
make a grant/deny decision about a request for access to
a protected resource, an access control mechanism needs
to evaluate policy data. This policy data describes
security-relevant characteristics of the requesting
subject and the rules which govern the use of the target
object.
The access control model defines
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- A wire protocol for interoperability: The existing
LDAP protocol flows for add, delete, modify, and
search are used to manipulate access control
information. There are additional LDAP controls and
extended protocol operations defined to further help
management of access control information:
getEffectiveRights and specifyCredentials.
- A set of access control information (ACI) attributes
for application portability: These attributes are
used as input to the LDAP APIs so access control
information can be addressed uniformly independent
of how that information is addressed and stored at
the server. These same attributes appear in LDIF
output for interchange of access control
information.
- A set of attributes to identity the access control
mechanisms supported by a server and a given part of
the namespace.
Encoding of access control information on the wire is per
the LDAPv3 specifications.
The instantiation of an access control model at the
directory server is not defined in this document.
No mechanisms are defined in this document to control
access to access control information or for storage of
access control information at the server; this is vendor
dependent.
A separate requirements document for access control
exists. The access control model used the requirements
documents as a guideline for the development of this
specification and are reflected in this specification to
the extent that the working group could agree on an
access control model.
3. Terminology
An "access control list" contains the access control
policy information controlling access to an object or
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collection of objects. An access control list consists
of a set of access control list entries.
An "access control list entry" defines a single subject
security attribute's granted rights for the objects
governed by the access control list to which it belongs.
The "access control information" (aci) for an object or a
collection of objects defines which subject security
attributes entitle a subject to which granted rights.
The access control information for an object may be
stored in an access control list.
An "access decision" is a boolean-valued function which
answers the question: "can the subject with these subject
security attributes perform this operation on this
object?"
An "access decision function" is an algorithm which makes
an access decision based on subject security attributes,
access control information, an object identifier, and an
operation name (possibly augmented by additional
contextual information).
An "access decision function interface" is a programmatic
interface through which applications can request an
access decision.
An "access identity" is an identity which is used by an
access decision function to make an access decision.
An "audit identity" is an identity which does not, in the
absence of additional information, enable a party
receiving and examining it to determine which subject it
belongs to.
A "credential" is a collection of subject security
attributes.
"effective rights" are the complete set of rights a
subject is entitled to based on all access control lists
which apply to a specific object and based on all of the
subject's security attributes.
"granted rights" are the complete set of rights an access
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control list entitles a subject to based on a specific
subject security attribute.
A "group" is a privilege attribute asserting a subject's
membership in the collection of subjects whose name is
that of the group.
An "identity" is a subject security attribute which is
unique to a single subject.
A "privilege attribute" is a subject security attribute
which may be shared by several subjects.
"required rights" are the complete set of rights needed
to authorize a requester to perform a specific operation
on an object of a specific type.
A "right" is the basic unit of access control
administration. For each object type in an information
system, a security administrator defines a set of
required rights for each operation. For each object in
the system, a security administrator defines a set of
granted rights for each subject security attribute. When
an access decision is required, an access decision
function checks to make sure that the requester's subject
security attributes have been granted all required rights
needed to perform the requested operation on the
specified target object.
A "role" is a privilege attribute asserting a subject's
organizational position and entitlement to perform the
operations appropriate to that organizational position.
A "subject' is an entity which initiate actions in an
information system.
A "subject security attribute" is a defined property
which is used by a security policy evaluation system to
make policy decisions.
4. The Model
The access control mechanism described in this draft
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addresses these activities:
- Definition of subject security attributes
information
- Definition of access control policy
- Retrieval of subject security attributes
- Retrieval of effective access rights
- Externalization of access control policy information
4.1 Access Control Information Model
This document does not define formats for storage of
access control information; it does define the
operational semantics of access control operations.
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The diagram below illustrates the componentry of a LDAP
system and the placement of the function specified in
this draft.
+-------------+
| Application |<--attrs to address ACI
+-------------+ - aCI
+--------+ - vendorACI
| LDAP | - policyOwner
| Client |
+--------+
|
| <-- LDAP controls
| - getEffectiveAccess
| - specifyCredentials
| <-- LDAP extended operations
| - getEffectiveAccess
v
+-----------------------------+
| LDAP Server (e.g. SLAPD) |
+-----------------------------+
. |
. |
. |
. |
v v
+----------+ +-----------+
| Access | | |<-attrs to define
| Control |<--| Datastore | access control mechanisms
| Manager | | | - supportedACIMechanisms
+----------+ +-----------+ - aCIMechanism
LDAP clients use the controls and extended operations
specified in this document to administer access control
policy enforced by LDAP servers. Servers may store
access control information in any way they choose. In
particular, servers may use the access control mechanisms
of their datastores to store and enforce LDAP access
control, or they may implement access control managers
external to their datastores. Datastores and external
access control managers may implement any access control
rule syntax and semantics they choose, as long as the
semantics are compatible with that defined in the section
titled "Operational Semantics of Access Control
Operations".
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The access control administration mechanisms specified in
this document are neutral with respect to policy
inheritance mechanisms, explicit vs. implicit denial,
and group nesting.
4.2 Bind and Credentials
A bind authenticates a principal to the directory. A
principal is represented by a DN. A principal has a set
of credentials that are used to determine access to
resources specified in ldap operations. These
credentials may be pushed to the server by the client by
using the specifyCredentials control (see section on the
specifyCredentials control) or may be pulled by the
server from the directory data, i.e. access control
information associated with a directory entry using
normal LDAP operations. Credentials may be local with
respect to the server. If the credentials are not local
to the server, i.e. owned by another server or
administrative scope, then the server may decide to
define a trust model that states how to evaluate the
trust of a credential at bind time. The definition of
such a trust model is outside the scope of this document.
5. Access Control Mechanism Attributes
There are several attributes defined associated with
access control. Two attributes are defined to identity
which access control mechanisms are supported by a given
server and by a given subtree: supportedACIMechanisms
and aCIMechanism.
5.1 Root DSE Attribute for Access Control Mechanism
The server advertises which access control mechanisms it
supports by inclusion of the 'supportedACIMechanisms'
attribute in the root DSE. This attribute is a list of
OIDs, each of which identify an access control mechanism
supported by the server.
(<OID to be assigned>
NAME 'supportedACIMechanisms'
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DESC list of access control mechanisms supported
by this directory server
SYNTAX LDAPOID
USAGE dSAOperation
)
The access control mechanism defined is:
LDAPv3 <OID to be assigned>
Other vendor access control mechanisms can be defined (by
OID) and are the responsibility of those vendors to
provide the definition and OID.
5.2 Subschema Attribute for Access Control Mechanism
A given naming context must provide information about
which access control mechanism is in effect for that
portion of the namespace. The following attribute must
be in each subschema entry associated with a naming
context whose access control mechanism is different from
adjacent naming contexts supported by that directory
server.
aCIMechanism lists the value (an OID) that defines the
access control mechanism in effect for the scope of that
subschema entry.
(<OID to be assigned>
NAME 'aCIMechanism'
DESC list of access control mechanism supported
in this subtree
SYNTAX LDAPOID
USAGE dSAOperation
)
6. Access Control Information Attributes
The intent of the following attribute definitions is to
design a common interchange format. Any given LDAP
server should be able to translate the below defined
attributes into a meaningful operation requests. Each
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server should be able to understand the attributes; there
should not be any ambiguity into what any part of the
syntax means.
While the end goal is to have a common behavior model
between different LDAP server implementations, the
attribute definition alone will not ensure identical ACL
processing behavior between servers. The semantics of
how a server interprets the ACI syntax are defined in the
"Operational Semantics of Access Control' section of this
document. Additionally, while the server must recognize
and act on the attribute when received over the wire,
there are no requirements for the server to physically
store this attribute.
The attribute definition maintains an assumption that the
receiving server supports inheritance within the security
model. If the server does not support inheritance, the
receiving server must expand any inherited information
based on the scope flag.
Three attributes are defined so access control
information (ACI) can be addressed in a server
independent of server implementation. These attributes
are used in typical LDAP APIs and in LDIF output of ACI.
There are three attributes which may be queried or set on
all directory objects: aci, vendorAci and policyOwner.
Their BNF and definitions are defined below.
6.1 The BNF
< aci > ::= < acl entry syntax >
+ [ '#' <acl entry syntax > ]*
< vendorAci > ::= <oid> + '#' + < printable string >
< acl entry syntax > ::= <familyOID> + '#' + <scope > + '#'
+ < rights > + '#' + < dnType >
+ '#' + < subjectDn >
< policyOwner > ::= < familyOid > + '#' + <scope >
+ '#' +< dnType > + '#' + < subjectDn >
< subjectDn > ::= < printable string > | "public" | "this"
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< familyOid > ::= < oid >
<scope > ::= "entry" | "subtree" | <level>
< level > ::= numericstring
< dnType > ::= "access-id" | "role" | "group"
< rights > ::= [ ] | [ < right > + [ '$'
+ <right> ] * ]
< rightsList > ::= <permissions> + ';' + <attrs>
< right > ::= <action > + ';' + <rightsList>
< action > ::= "grant" | "deny"
< permissions > ::= [ ] | [ < permission >
+ [ ',' + <permission> ] ] *
< attrs > ::= [ < attributeString>
+ [ ',' + < attributeString > ] * ]
< attributeString > ::= "[all]" | "[entry]"
| <printableString >
< permission > ::= "a" | "d" | "r" | "s" | "w" |
"c" | "g" | "s" | "m" | "u" | "e"
These are the permissions defined for the IETF family OID.
"a" corresponds to add
"d" corresponds to delete
"r" corresponds to read
"w" corresponds to write
"c" corresponds to compare
"g" corresponds to get
"s" corresponds to set
"m" corresponds to manage
"u" corresponds to use
"e" corresponds to editDn
6.2 Other Defined Parameters
This section defines additional parameters that are used
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in the three (3) attributes that address access control
information.
6.2.1 Rights Families and Rights
The rightsFamilyOID tells what permission set etc. will
follow in the string. The idea was to allow a different
permission set, scope etc. but with the same syntax.
So, for a single aCIMechanism ( the IETF one ) there
could be multiple rights families; one which IETF
defines, and MUST be recognized by servers claiming
support for this ACI mechanism, and other rights families
for models which can use the defined syntax, but need a
different permission set etc.
The following rights families are defined:
LDAPv3 <OID to be assigned>
Other rights families can be defined (by OID). It is the
responsibility of those parties to provide the definition
and OID.
6.2.1.1 LDAPv3 Rights Family
Access rights can apply to an entire object or to
attributes of the object. Each of the LDAP access rights
are discrete. One permission does not imply another
permission. The rights may be ORed together to provide
the desired rights list. The rights which apply to
attributes and the entry parallel the type of ldap
operations that can be performed.
Rights which apply to attributes:
1 Read Read attribute values
2 Write Write attribute values
4 Search Search entries with specified attributes
8 Compare Compare attributes
Rights that apply to an entire entry:
16 Add Add an entry below this entry
32 Delete Delete this entry
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64 EditDN Edit an entry's DN
Rights that apply to the object to which the directory
entry points:
128 Manage Perform a privileged operation; used to
restrict access to operations which
read or write especially sensitive data
256 Use Execute; useful in controlling access to
the objects referred to by directory
entries rather than in controlling
access
to the directory entries themselves
512 Get Get retrieves the attribute values
1024 Set Set writes the attribute values
The rights that apply to the object to which the
directory entry points (manage/use/get/set) are best
described by example. Suppose the object to which the
directory entry points is a pointer.
Manage addresses the right to perform a privileged
operation such as administrative operations on the
printer. It can be used to restrict access to operations
which read/write especially sensitive data. Examples of
these operations are start queue, stop queue, and flush
queue.
Use addresses the right to execute and is useful to
control access to the objects referred to by the
directory entry. This right is not applicable to the
printer example; however, some objects support access to
user functions as well as data and administrative
functions to which this right could apply.
Get in this printer example addresses the right to send
data access commands to the print that retrieve data. An
example is list jobs in the queue.
Set in this printer example addresses the right to send
data modification commands to the printer that affect
printer operations. Examples are send job to print queue
and flush job from queue.
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6.2.2 DN Types
The following DN Types strings are defined and MUST be
supported:
- access-id
- group
- role
An access-id is a non-collection (non-group and non-role
objects) DN that can be authenticated.
Other parties can (and will) define other DN Types. It
is the responsibility of those parties to provide the
definition and OID.
6.3 Basic ACI Attribute (aCI)
( aciOID NAME 'aCI' DESC 'Access control information'
EQUALITY caseIgnoreMatch SYNTAX directoryString )
Within the access control syntax, the family OID
describes the permissions, dnType, subjectDn and scope
that will be found in the following string. If the OID
within the ACI attribute is listed as other than the IETF
family oid, the syntax is the same as listed below, but
one or more of the scope, dnType, subjectDn or
permissions may vary from the IETF defined syntax.
Within the access control syntax, there is a string which
describes the rights. This is a composite of the
permissions and resources to which the subject is being
granted or denied access. The set of permissions is
fixed. Either of the actions "grant" | "deny" may be
used when creating or updating ACI.
The attributeString is an attribute Name (defined to be a
printable string). If the string refers to an attribute
not defined in the given server's schema, the server
SHOULD report an error. Another option for the
attributeString is "[entry]". This is provided to
describe permissions which apply to an entire object.
This could mean actions such as delete the object, or add
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a child object. The third option for attributeString is
"[all]" which means the permission set should apply to
all attributes.
If the keyword "[all]" and another attribute are both
specified within an aci, the more specific permission set
for the attribute overrides the less specific permission
set for "[all]".
If two ACIs contain identical familyOID, scope, DnTypes
and DNs, the permission given DN is specified in two
distinct acis on any given entry, the rights lists can be
combined into one list. For example,
aci: 1.2.3.4#subtree#grant;r,w;[all]#group#cn=Dept XYZ
aci: 1.2.3.4#subtree#grant;r;attribute1#group#cn=Dept
XYZ
is the equivalent of
aci: 1.2.3.4#subtree#grant;r,w;[all];
r,attribute1#group#cn=Dept XYZ
Using the defined BNF it is possible for the permission
string to be empty. The ACI
aci: 1.2.3.4#subtree#grant;;attribute1$grant;r,s;
[all]#group#cn=Dept XYZ,c=US
means that this group is granted permission to read and
search all attributes except attribute1.
Similarly, the ACI
aci: 1.2.3.4#subtree##group#cn=Dept XYZ, c=US
simply means that no permissions have been defined for
this group. It is up to the server implementation as to
whether the group does or does not receive permission to
attributes on an entry with an empty rights list.
Multiple attributeStrings can be listed after any given
permission set; for instance, "r,w ; attribute1,
attribute2". This means that if the server supports a
attribute aggregation mechanism, attribute1 and
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attribute2 should be considered to be part of the same
group. If the server does not support a grouping
mechanism, the permission set applies independently to
attribute1 and attribute2. For servers that do not
support attribute grouping, "grant ; r,w ; attribute1,
attribute2" results in the same operations as "grant ;
r,w; attribute1$grant; r,w; attribute2"
6.3.1 LDAP Operations
The attributes which are defined for access control
interchange may be used in all LDAP operations.
Within the ldapmodify-delete operation, the entire acl may
be deleted by specifying
dn: cn = some Entry
changetype: modify
delete: aci
In this case, the entry would then inherit its ACI from some
other node in the tree depending on the server inheritance
model.
Deleting the last ACI value from an entry is not the same as
deleting the ACI from the entry. It is possible for an entry
to contain an ACI with no values. In this case, nothing is
returned to the client when querying the aci. It is server
dependent whether access is granted or denied in the absence
of any ACI information. Deleting an ACI value which does
not exist will result in an unchanged ACI and a return code
specifying that the attribute value does not exist.
6.4 ACI Examples
6.4.1 Attribute Definition
Pretend IETFFamilyOID = 1.2.3.4
The following two examples show an administrative
subdomain being established. The first example shows a
single user being assigned the policyOwner for the entire
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domain. The second example shows a group of ids assigned
to the policy Owner.
policyOwner: 1.2.3.4#subtree#access-id#cn=Hoyt
policyOwner: 1.2.3.4#subtree#group#cn=System Owners,
o=Company
The next example shows an aci attribute where a group
"cn=Dept XYZ, c=US" is being given permissions to read,
search and compare attribute1. The permission should
apply to the entire subtree below the node containing
this ACI.
aci:1.2.3.4#subtree#grant;r,s,c;
attribute1#group#cn=Dept XYZ,c=US
The next example shows an ACI attribute where a role
"cn=SysAdmins,o=Company" is being given permissions to
add objects below this node, and read, search and compare
attributes 2 and 3. The permission should apply to the
entire subtree below the node containing this ACI.
aci: 1.2.3.4#subtree#grant;a;[entry]$grant;
r,s,c;attribute2, attribute3#role#
cn=SysAdmins,o=Company
6.4.2 Modifying the ACI Values
Replace works similarly to all other attributes. If the
attribute value does not exist, create the value. If the
attribute does exist, replace the value. If the ACI value
is replaced, all ACI values are replaced.
A given aci for an entry:
aci: 1.2.3.4#subtree#deny;r,w;[all]$grant;r,s,c;
attribute2#group#cn=Dept ABC
aci: 1.2.3.4#subtree#grant;r;[all]$grant;r,s,c;
attribute1#group#cn=Dept XYZ
perform the following change:
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dn: cn=someEntry
changetype: modify
replace: aci
aci: 1.2.3.4#subtree#grant;r,w;[all];#group#cn=Dept LMN
The resulting acl is:
aci: 1.2.3.4#subtree#grant;r,w;[all];#group#cn=Dept LMN
( aci values for Dept XYZ and ABC are lost through the
replace )
During an ldapmodify-add, if the ACI does not exist, the
create the ACI with the specific aci value(s). If the ACI
does exist, then add the specified values to the given ACI.
For example a given ACI:
aci: 1.2.3.4#subtree#grant;r,w;[all]#group#cn=Dept XYZ
with a modification:
dn: cn=someEntry
changetype: modify
add: aci
aci: 1.2.3.4#subtree#grant;r;attribute1#group#cn=Dept XYZ
would yield an multi-valued aci of:
aci: 1.2.3.4#subtree#grant;r,w;[all]#group#cn=Dept XYZ
aci: 1.2.3.4#subtree#grant;r;attribute1#group#cn=Dept XYZ
To delete a particular aci value, use the regular ldapmodify
- delete syntax
Given an ACI of:
aci: 1.2.3.4#subtree#grant;r,w;[all]#group#cn=Dept XYZ
aci: 1.2.3.4#subtree#grant;r;attribute1#group#cn=Dept XYZ
dn: cn = some Entry
changetype: modify
delete: aci
aci: 1.2.3.4#subtree#grant;r;attribute1#group#cn=Dept XYZ
would yield a remaining ACI on the server of
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aci: 1.2.3.4#subtree#grant;r,w;[all]#group#cn=Dept XYZ
6.5 Vendor ACI Attribute (vendorAci)
( vendorAciOID NAME 'vendorACI' DESC 'Vendor specific
Access control information' EQUALITY caseIgnoreMatch SYNTAX
directoryString )
The Vendor specific ACI information is listed in its own
attribute. This may be used by vendors to provide vendor
specific access control related information which can not be
expressed in defined ACISyntax. Within the vendorACI, the
oid determines the format or the printable string to follow.
6.6 Policy Owner Attribute (policyOwner)
( policyOwnerOID NAME 'policyOwner' DESC 'Policy Owner
Access Control Information' EQUALITY caseIgnoreMatch
SYNTAX directoryString )
Policy ownership controls administrative subdomains. It
can also control who has permission to set / change acls
for implementations that do not have ACI controlling
access to itself. If there are multiple policy owners
it is implementation specific as to the behavior of
whether policy owner #1 can override policy owner # 2.
The syntax for policyOwner includes the 'scope' flag.
Servers which do not support inheritance must expand the
policyOwner inheritance similar to the expansion of the
ACI. The scope and any inheritance hierarchy for policy
ownership is distinct from any inheritance hierarchy
defined for ACI values.
If the policy owner is not specified for any object in
the tree, behavior is implementation defined. For
instance, if no object anywhere in the tree has a
policy owner, then the server could simply assert that
the 'root DN' is considered the policy owner for all
objects. An alternate approach might be that the
implementation defines the entryDN to be the policy
owner.
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7. Operational Semantics of Access Control Operations
The semantics of access control operations described in
this document are defined operationally in terms of
"histories". A history is a sequence of actions (x1, x2,
..., xN).
7.1 Types of actions
We consider five types of actions:
- LDAP Access Control Policy Update actions:
invocations of ldap modify when used to add, delete,
or replace the aci attribute; invocations of ldap
add when used to add an entry with an aci attribute.
A LDAP Access Control Policy Update action may
replace the policy (by completely replacing the aci
attribute with new policy information) or it may
grant or deny specific rights while leaving others
unaffected.
- LDAP Access Control Policy Query operations:
invocations of ldap search when used to retrieve the
aci attribute; invocations of ldap search with the
getEffectiveRightsRequest control; invocations of
the ldapGetEffectiveRightsRequest extended
operation.
- Datastore Access Control Policy Update Actions: any
operation implemented by the server which LDAP is
using as its datastore which changes the access
policy enforced with respect to attempts to access
LDAP directory entries and their attributes.
- LDAP Access Request operations: invocations of LDAP
entry or attribute access operations (Read, Update,
Search, Compare, etc...).
- Other operations: anything else, including Datastore
operations which do not change the access policy
enforced by the server.
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7.2 Semantics of Histories
The semantics of histories are defined as follows:
- LDAP Update (Replace), LDAP Query
The Query will show that the subject has all rights
granted by the Update operation, and no rights not
granted by the Update operation.
- LDAP Update (Grant), LDAP Query
The Query will show that the subject has all rights
granted by the Update operation. The Query may show
that the subject also has other rights not granted
by the Update operation, depending on the policy in
force before the Update operation.
- LDAP Update (Deny), LDAP Query
The Query will show that the subject does not have
any right denied by the Update operation. The Query
may show that the subject has rights not denied by
the Update operation, depending on the policy in
force before the Update operation.
- LDAP Update (Replace), LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request will fail with an access-
denied exception if it requires any right not
granted by the Update operation.
- LDAP Update (Grant), LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request may succeed if it requires
rights not granted by the Update operation,
depending on the policy in force before the Update
operation.
- LDAP Update (Deny), LDAP Access Request
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The Request will fail with an access-denied
exception if it requires any right denied to the
requesting subject by the Update operation. If the
Request requires only rights which were not denied
by the Update operation, it may succeed, depending
on the policy in force before the Update operation.
- LDAP Update (Replace), Other, LDAP Query
The Query will show that the subject has all rights
granted by the Update operation, and no rights not
granted by the Update operation.
- LDAP Update (Grant), Other, LDAP Query
The Query will show that the subject has all rights
granted by the Update operation. The Query may show
that the subject also has other rights not granted
by the Update operation, depending on the policy in
force before the Update operation.
- LDAP Update (Deny), Other, LDAP Query
The Query will show that the subject does not have
any right denied by the Update operation. The Query
may show that the subject has rights not denied by
the Update operation, depending on the policy in
force before the Update operation.
- LDAP Update (Replace), Other, LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request will fail with an access-
denied exception if it requires any right not
granted by the Update operation.
- LDAP Update (Grant), Other, LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request may succeed if it requires
rights not granted by the Update operation,
depending on the policy in force before the Update
operation.
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- LDAP Update (Deny), Other, LDAP Access Request
The Request will fail with an access-denied
exception if it requires any right denied to the
requesting subject by the Update operation. If the
Request requires only rights which were not denied
by the Update operation, it may succeed, depending
on the policy in force before the Update operation.
- LDAP Update (Replace), Datastore Policy Update, LDAP
Query
The result of the Query is not defined.
- LDAP Update (Grant), Datastore Policy Update, LDAP
Query
The result of the Query is not defined.
- LDAP Update (Deny), Datastore Policy Update, LDAP
Query
The result of the Query is not defined.
- LDAP Update (Replace), Datastore Policy Update, LDAP
Access Request
The result of the Access Request is not defined.
- LDAP Update (Grant), Datastore Policy Update, LDAP
Access Request
The result of the Access Request is not defined.
- LDAP Update (Deny), Datastore Policy Update, LDAP
Access Request
The result of the Access Request is not defined.
8. Access Control Parameters for LDAP Controls & Extended
Operations
This section defines the parameters used in the access
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control LDAP controls and extended operations in this
document.
targetDN specifies the initial directory entry in DN
syntax on which the control or extended operation is
performed.
whichObject specifies whether the access control
information (in the get effective rights control) which
is retrieved is for the target directory entry (ENTRY) or
the target directory entry and its subtree (SUBTREE).
rightsFamily specifies the family of rights that will be
retrieved for the get effective rights control or
extended operation performed. A rights family has a
defined set of rights.
rightsList in the get effective rights control or
extended operations response is of the form specified in
the BNF for <rightsList>.
dnType speficies the type of subject security attribute.
Defined types are access-id, group, and role.
subjectDN is a LDAP string that defines the subject or
value of the dnType. The subjectDN may be a DN or
another string such as IPAddress (dotted-decimal string
representation) on which access control is get/set. If
the subject is an entry in the directory, then the syntax
of the LDAP string is DN. Two well-known subjectDNs
strings are defined
- public - meaning public access for all users
- this - meaning the user whose name matches the entry
being accessed
9. Access Control Information (ACI) Controls
The access control information controls provide a way to
manipulate access control information in conjunction with
a LDAP operation. Two LDAP controls are defined. These
controls allow access control information to be get/set
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while manipulating other directory information for that
entry. The controls are:
- getEffectiveRights to obtain the effective rights
for a given directory entry(s) for a given subject
during a ldap_search operation
- specifyCredentials to specify a set of credentials
for the bind identity (DN) during a ldap_bind
operation
9.1 getEffectiveRights Control
9.1.1 Request Control
This control may only be included in the ldap_search
message as part of the controls field of the
LDAPMessage, as defined in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE) at the client's option. The
controlValue is an OCTET STRING, whose value is the BER
encoding of a value of the following SEQUENCE:
getEffectiveRightsRequest ::= SEQUENCE {
effectiveRightsRequest SEQUENCE OF SEQUENCE {
rightsFamily LDAPOID | "*",
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
dnType "access-id"|"group"|"role"|"*",
subjectDN LDAPString,
}
}
The effectiveRightsRequest is a set of sequences that
state the whichObject (entry or entry plus subtree) and
specifics of the control request to be performed. One or
more rightsFamily can be be obtained for a given
subjectDN ad dnType. A "*" in the rightsFamily field
indicates that the rights for all rights families defined
for the subjectDN / dnType are to be returned. A "*" in
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the dnType field specifies that all DN types are to be
used in returning the effective rights. This control is
applied to the filter and scope set by the ldap_search
operation, i.e. base, one-level, subtree.
9.1.2 Response Control
This control is included in the ldap_search_response
message as part of the controls field of the LDAPMessage,
as defined in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE). The controlValue is an OCTET
STRING, whose value is the BER encoding of a value of the
following SEQUENCE:
getEffectiveRightsResponse ::= {
result ENUMERATED {
success (0),
operationsError (1),
unavailableCriticalExtension (12),
noSuchAttribute (16),
undefinedAttributeType (17),
invalidAttributeSyntax (21),
insufficientRights (50),
unavailable (52),
unwillingToPerform (53),
other (80)
}
}
The effective rights returned are returned with each
entry returned by the search result. The control
response for ldap_search is:
PartialEffectiveRightsList ::= SEQUENCE OF SEQUENCE {
rightFamily LDAPOID,
rightsList LDAPString,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
}
dnType LDAPString
subjectDN LDAPString
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}
Although this extends the search operation, there are no
incompatibilities between versions. LDAPv2 cannot send a
control, hence the above structure cannot be returned to
a LDAPv2 client. A LDAPv3 client cannot send this
request to a LDAPv2 server. A LDAPv3 server not
supporting this control cannot return the additional
data.
9.1.3 Client-Server Interaction
The getEffectiveRightsRequest control requests the rights
that MUST be in effect for requested directory
entry/attribute based on the subject DN. The server that
consumes the search operation looks up the rights for the
returned directory information based on the subject DN
and returns that rights information.
There are six possible scenarios that may occur as a
result of the getEffectiveRights control being included
on the search request:
1. If the server does not support this control and the
client specified TRUE for the control's criticality
field, then the server MUST return
unavailableCriticalExtension as a return code in
the searchResponse message and not send back any
other results. This behavior is specified in
section 4.1.12 of [LDAPv3].
2. If the server does not support this control and the
client specified FALSE for the control's
criticality field, then the server MUST ignore the
control and process the request as if it were not
present. This behavior is specified in section
4.1.12 of [LDAPv3].
3. If the server supports this control but for some
reason such as cannot process specified
rightsFamily and the client specified TRUE for the
control's criticality field, then the server SHOULD
do the following: return
unavailableCriticalExtension as a return code in
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the searchResult message.
4. If the server supports this control but for some
reason such as cannot process specified
rightsFamily and the client specified FALSE for the
control's criticality field, then the server should
process as 'no rights returned for that family' and
include the result Unavailable in the
getEffectiveRightsResponse control in the
searchResult message.
5. If the server supports this control and can return
the rights per the rightsFamily information, then
it should include the getEffectiveRightsResponse
control in the searchResult message with a result
of success.
6. If the search request failed for any other reason,
then the server SHOULD omit the
getEffectiveRightsResponse control from the
searchResult message.
The client application is assured that the correct rights
are returned for scope of the search operation if and
only if the getEffectiveRightsResponse control returns
the rights. If the server omits the
getEffectiveRightsResponse control from the searchResult
message, the client SHOULD assume that the control was
ignored by the server.
The getEffectiveRightsResponse control, if included by
the server in the searchResponse message, should have the
getEffectiveRightsResult set to either success if the
rights are returned or set to the appropriate error code
as to why the rights could not be returned.
The server may not be able to return a right because it
may not exist in that directory object's attribute; in
this case, the rights request is ignored with success.
9.2 specifyCredentials Control
This control is used with the ldap_bind() operation to
push credentials from the client to the server. A
privilege attribute certificate is an example of a
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credential that could be pushed from the client to the
server.
9.2.1 Request Control
This control is included in the ldap_bind message as
part of the controls field of the LDAPMessage, as
defined in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE) at the client's option. The
controlValue is an OCTET STRING, whose value is the BER
encoding of a value of the following SEQUENCE:
specifyCredentialRequest ::= SEQUENCE {
credential LDAPString
}
}
The credential specifies the credential (e.g. groups,
roles, etc) that the client is requesting be associated
with the bind DN for access control determination in
subsequent ldap operations. This provides a 'push' model
for credentials where the client attempts to 'push' the
credential to the server. The server may process at bind
time as follows:
- server may unconditionally ignore
- server may unconditionally accept
- server may define trust model and evaluate of the
trust of each credential
If this control is not used, it is assumed that the
server determines (pulls) the credentials associated with
the bind DN when needed in subsequent ldap operations to
provide access control.
9.2.2 Response Control
This control is included in the ldap_bind message as part
of the controls field of the LDAPMessage, as defined in
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Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE). The controlValue is an OCTET
STRING, whose value is the BER encoding of a value of the
following SEQUENCE:
specifyCredentialsResponse ::= {
result ENUMERATED {
success (0),
operationsError (1),
unavailableCriticalExtension (12),
unavailable (52),
unwillingToPerform (53),
other (80)
}
}
No data is returned; just the result is returned.
Although this extends the bind operation, there are no
incompatibilities between versions. LDAPv2 cannot send a
control. A LDAPv3 client cannot send this request to a
LDAPv2 server. A LDAPv3 server not supporting this
control cannot return the additional data.
9.2.3 Client-Server Interaction
The specifyCredentialsRequest control specifies the
credentials that the client wants the server to use for
access control in subsequent ldap operations. The server
that consumes the bind operation may unconditionally
accept, ignore, or evaluate the trust of the specified
credentials at bind time and returns only a success or
failure response (no data returned).
There are six possible scenarios that may occur as a
result of the specifyCredential control being included on
the bind request:
1. If the server does not support this control and the
client specified TRUE for the control's criticality
field, then the server MUST return
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unavailableCriticalExtension as a return code in
the bindResponse message. This behavior is
specified in section 4.1.12 of [LDAPv3].
2. If the server does not support this control and the
client specified FALSE for the control's
criticality field, then the server MUST ignore the
control and process the request as if it were not
present. This behavior is specified in section
4.1.12 of [LDAPv3].
3. If the server supports this control but for some
reason such as cannot process specified credential
(e.g. server decided to evaluate the trust of that
credential and the result is the server not
trusting all the credentials or unconditionally
ignores the credential) and the client specified
TRUE for the control's criticality field, then the
server SHOULD do the following: return
unavailableCriticalExtension as a return code in
the bindResult message and omit the
specifyCredentialResponse control in the bindResult
message.
4. If the server supports this control but for some
reason such as cannot process specified credential
(e.g. server decided to evaluate the trust of that
credential and the result is the server not
trusting all the credentials or unconditionally
ignores the credential) and the client specified
FALSE for the control's criticality field, then the
server should process as 'credential ignored' and
include the result Unavailable in the
specifyCredentialResponse control in the bindResult
message.
5. If the server supports this control and evaulates
the trust of that credential and the result is the
server trusting all the credentials, then it should
include the specifyCredentialResponse control in
the bindResult message with a result of success.
6. If the bind request failed for any other reason,
then the server SHOULD omit the
specifyCredentialResponse control from the
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bindResult message.
The client application is assured that the correct
credentials are used by the server when specified by the
client for subsequent ldap operations if and only if the
specifyCredentialResponse is successful. If the server
omits the specifyCredentialResponse control from the
bindResponse message, the client SHOULD assume that the
control was ignored by the server.
The specifyCredentialResponse control, if included by the
server in the bindResponse message, should have the
bindResult set to either success if the credentials were
accepted by the server or set to the appropriate error
code as to why the credentials were not accepted.
10. Access Control Extended Operation
An extended operation, get effective rights, is defined
to obtain the effective rights for a given directory
entry for a given subject. This operation may help with
the management of access control information independent
of manipulating other directory information.
10.1 LDAP Get Effective Rights Operation
ldapGetEffectiveRightsRequest ::= [APPLICATION 23]
SEQUENCE {
requestName [0] <OID to be assigned>,
requestValue [1] OCTET STRING OPTIONAL }
where
requestValue ::= SEQUENCE {
targetDN LDAPDN,
updates SEQUENCE OF SEQUENCE {
rightsFamily LDAPOID | "*",
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
dnType LDAPOID | "*",
subjectDN LDAPString,
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}
}
The requestName is a dotted-decimal representation of the
OBJECT IDENTIFIER corresponding to the request. The
requestValue is information in a form defined by that
request, encapsulated inside an OCTET STRING.
The server will respond to this with an LDAPMessage
containing the ExtendedResponse which is a rights list.
ldapGetEffectiveRightsResponse ::= [APPLICATION 24]
SEQUENCE {
COMPONENTS OF LDAPResult,
responseName [10] <OID to be assigned> OPTIONAL,
effectiveRights [11] OCTET STRING OPTIONAL }
where
effectiveRights ::= SEQUENCE OF SEQUENCE {
rightFamily LDAPOID,
rightsList ENUMERATED,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
subjectDnType LDAPOID,
subjectDN LDAPSTRING
}
If the server does not recognize the request name, it
MUST return only the response fields from LDAPResult,
containing the protocolError result code.
11. Security Considerations
This document proposes protocol elements for transmission
of security policy information. Security considerations
are discussed throughout this draft. Because subject
security attribute information is used to evaluate
decision requests, it is security-sensitive information
and must be protected against unauthorized modification
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whenever it is stored or transmitted.
12. References
[LDAPv3] M. Wahl, T. Howes, S. Kille, "Lightweight
Directory Access Protocol (v3)", RFC 2251, December 1997.
[ECMA] ECMA, "Security in Open Systems: A Security
Framework" ECMA TR/46, July 1988
[REQTS] Stokes, Byrne, Blakley, "Access Control
Requirements for LDAP, INTERNET-DRAFT <draft-ietf-
ldapext-acl-reqts-02.txt>, August 1998.
[ATTR] M.Wahl, A, Coulbeck, T. Howes, S. Kille,
"Lightweight Directory Access Protocol (v3)": Attribute
Syntax Definitions, RFC 2252, December 1997.
[UTF] M. Wahl, S. Kille, "Lightweight Directory Access
Protocol (v3)": A UTF-8 String Representation of
Distinguished Names", RFC 2253, December 1997.
[Bradner97] Bradner, Scott, "Key Words for use in RFCs to
Indicate Requirement Levels", RFC 2119.
AUTHOR(S) ADDRESS
Ellen Stokes Bob Blakley
IBM Dascom
11400 Burnet Rd 5515 Balcones Drive
Austin, TX 78758 Austin, TX 78731
USA USA
mail-to: stokes@austin.ibm.com mail-to: blakley@dascom.com
phone: +1 512 838 3725 phone: +1 512 458 4037 ext 5012
fax: +1 512 838 8597 fax: +1 512 458 237
Debbie Byrne
IBM
11400 Burnet Rd
Austin, TX 78758
USA
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mail-to: djbyrne@us.ibm.com
phone: +1 512 838 1960
fax: +1 512 838 8597
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CONTENTS
1. Introduction....................................... 2
2. Overview........................................... 2
3. Terminology........................................ 3
4. The Model.......................................... 5
4.1 Access Control Information Model............. 6
4.2 Bind and Credentials......................... 8
5. Access Control Mechanism Attributes................ 8
5.1 Root DSE Attribute for Access Control
Mechanism.................................... 8
5.2 Subschema Attribute for Access Control
Mechanism.................................... 9
6. Access Control Information Attributes.............. 9
6.1 The BNF...................................... 10
6.2 Other Defined Parameters..................... 11
6.2.1 Rights Families and Rights 12
6.2.2 DN Types 14
6.3 Basic ACI Attribute (aCI).................... 14
6.3.1 LDAP Operations 16
6.4 ACI Examples................................. 16
6.4.1 Attribute Definition 16
6.4.2 Modifying the ACI Values 17
6.5 Vendor ACI Attribute (vendorAci)............. 19
6.6 Policy Owner Attribute (policyOwner)......... 19
7. Operational Semantics of Access Control
Operations......................................... 20
7.1 Types of actions............................. 20
7.2 Semantics of Histories....................... 21
8. Access Control Parameters for LDAP Controls &
Extended Operations................................ 23
9. Access Control Information (ACI) Controls.......... 24
9.1 getEffectiveRights Control................... 25
9.1.1 Request Control 25
9.1.2 Response Control 26
9.1.3 Client-Server Interaction 27
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9.2 specifyCredentials Control................... 28
9.2.1 Request Control 29
9.2.2 Response Control 29
9.2.3 Client-Server Interaction 30
10. Access Control Extended Operation.................. 32
10.1 LDAP Get Effective Rights Operation.......... 32
11. Security Considerations............................ 33
12. References......................................... 34
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Full Copyright Statement
Copyright (C) The Internet Society (1999).á All Rights
Reserved.
This document and translations of it may be copied and
furnished to others, and derivative works that comment on or
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prepared, copied, published and distributed, in whole or in
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above copyright notice and this paragraph are included on
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