draft-ietf-ldapbis-authmeth-00.txt   draft-ietf-ldapbis-authmeth-01.txt 
Internet Draft R. Harrison, Editor Individual Submission R. Harrison, Editor
Document: draft-ietf-ldapbis-authmeth-00.txt Novell, Inc. Internet Draft Novell, Inc.
Intended Category: Draft Standard February 20, 2001 Document: draft-ietf-ldapbis-authmeth-01.txt July 19, 2001
Obsoletes: RFC 2829 Intended Category: Draft Standard
Obsoletes: RFC 2829, RFC 2830
Authentication Methods for LDAPv3 Authentication Methods
and
Connection Level Security Mechanisms
for LDAPv3
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
This document is intended to be, after appropriate review and This document is intended to be, after appropriate review and
revision, submitted to the RFC Editor as a Standard Track document. revision, submitted to the RFC Editor as a Standard Track document.
Distribution of this memo is unlimited. Technical discussion of Distribution of this memo is unlimited. Technical discussion of
this document will take place on the IETF LDAP Extension Working this document will take place on the IETF LDAP Extension Working
skipping to change at line 38 skipping to change at page 1, line 43
as reference material or to cite them other than as "work in as reference material or to cite them other than as "work in
progress." progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet- http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-
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http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Abstract Abstract
This document specifies particular combinations of security This document describes LDAPv3 authentication methods and connection
mechanisms that are required and recommended in LDAPv3 [1] level security mechanisms that are required of all conforming LDAPv3
implementations. server implementations and makes recommendations for combinations of
these mechanisms to be used in various deployment circumstances.
1. Introduction Among the mechanisms described are
LDAPv3 is a powerful access protocol for directories. - the LDAPv3 Bind operation used for authenticating LDAP clients
It offers means of searching, fetching and manipulating directory to LDAP servers.
content, and ways to access a rich set of security functions.
In order to function for the best of the Internet, it is vital that - the Start TLS operation used to initiate Transport Layer
these security functions be interoperable; therefore there has to be Security on an established connection between an LDAP client and
server.
Authentication Methods for LDAPv3 July 19, 2001
- various forms of authentication including anonymous
authentication, password-based authentication, and certificate
based authentication.
1. Conventions Used in this Document
In this document, the term "user" represents any application which
is an LDAP client using the directory to retrieve or store
information.
Several terms and concepts relating to authentication and
authorization are presented in Appendix B of this document. While
the definition of these terms and concepts is outside the scope of
this document, an understanding of them is prerequisite to
understanding much of the material in this document. Readers who are
unfamiliar with security-related concepts are encouraged to review
Appendix B before reading the remainder of this document.
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 RFC 2119
[ReqsKeywords].
2. Introduction
LDAPv3 is a powerful access protocol for directories. It offers
means of searching, fetching and manipulating directory content, and
ways to access a rich set of security functions.
It is vital that these security functions be interoperable among all
LDAP clients and servers on the Internet; therefore there has to be
a minimum subset of security functions that is common to all a minimum subset of security functions that is common to all
implementations that claim LDAPv3 conformance. implementations that claim LDAPv3 conformance.
Basic threats to an LDAP directory service include: Basic threats to an LDAP directory service include:
Harrison Expires August 20, 2001 [Page 1] (1) Unauthorized access to directory data via data-fetching
Authentication Methods for LDAPv3 February 20, 2001 operations,
(1) Unauthorized access to data via data-fetching operations,
(2) Unauthorized access to reusable client authentication (2) Unauthorized access to reusable client authentication
information by monitoring others' access, information by monitoring others' access,
(3) Unauthorized access to data by monitoring others' access, (3) Unauthorized access to directory data by monitoring others'
access,
(4) Unauthorized modification of data, (4) Unauthorized modification of directory data,
(5) Unauthorized modification of configuration, (5) Unauthorized modification of configuration information,
(6) Unauthorized or excessive use of resources (denial of service), (6) Unauthorized or excessive use of resources (denial of service),
and and
Authentication Methods for LDAPv3 July 19, 2001
(7) Spoofing of directory: Tricking a client into believing that (7) Spoofing of directory: Tricking a client into believing that
information came from the directory when in fact it did not, information came from the directory when in fact it did not,
either by modifying data in transit or misdirecting the client's either by modifying data in transit or misdirecting the client's
connection. connection.
Threats (1), (4), (5) and (6) are due to hostile clients. Threats Threats (1), (4), (5) and (6) are due to hostile clients. Threats
(2), (3) and (7) are due to hostile agents on the path between (2), (3) and (7) are due to hostile agents on the path between
client and server, or posing as a server. client and server, or posing as a server.
The LDAP protocol suite can be protected with the following security The LDAP protocol suite can be protected with the following security
mechanisms: mechanisms:
(1) Client authentication by means of the SASL [2] mechanism set, (1) Client authentication by means of the SASL [SASL] mechanism set,
possibly backed by the TLS credentials exchange mechanism, possibly backed by the TLS [TLS] credentials exchange mechanism,
(2) Client authorization by means of access control based on the (2) Client authorization by means of access control based on the
requestor's authenticated identity, requestor's authenticated identity,
(3) Data integrity protection by means of the TLS protocol or data- (3) Data integrity protection by means of the TLS protocol or data-
integrity SASL mechanisms, integrity SASL mechanisms,
(4) Protection against snooping by means of the TLS protocol or (4) Protection against snooping by means of the TLS protocol or
data-encrypting SASL mechanisms, data-encrypting SASL mechanisms,
(5) Resource limitation by means of administrative limits on service (5) Resource usage limitation by means of administrative limits on
controls, and service controls, and
(6) Server authentication by means of the TLS protocol or SASL (6) Server authentication by means of the TLS protocol or SASL
mechanism. mechanism.
At the moment, imposition of access controls is done by means At the moment, imposition of access controls is done by means
outside the scope of the LDAP protocol. outside the scope of the LDAP protocol.
In this document, the term "user" represents any application which 3. Required Security Mechanisms
is an LDAP client using the directory to retrieve or store
information.
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Authentication Methods for LDAPv3 February 20, 2001
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 RFC 2119 [3].
2. Example deployment scenarios
The following scenarios are typical for LDAP directories on the
Internet, and have different security requirements. (In the
following, "sensitive" means data that will cause real damage to the
owner if revealed; there may be data that is protected but not
sensitive). This is not intended to be a comprehensive list, other
scenarios are possible, especially on physically protected networks.
(1) A read-only directory, containing no sensitive data, accessible
to "anyone", and TCP connection hijacking or IP spoofing is not
a problem. This directory requires no security functions except
administrative service limits.
(2) A read-only directory containing no sensitive data; read access
is granted based on identity. TCP connection hijacking is not
currently a problem. This scenario requires a secure
authentication function.
(3) A read-only directory containing no sensitive data; and the
client needs to ensure that the directory data is authenticated
by the server and not modified while being returned from the
server.
(4) A read-write directory, containing no sensitive data; read
access is available to "anyone", update access to properly
authorized persons. TCP connection hijacking is not currently a
problem. This scenario requires a secure authentication
function.
(5) A directory containing sensitive data. This scenario requires
session confidentiality protection AND secure authentication.
3. Authentication and Authorization: Definitions and Concepts
This section defines basic terms, concepts, and interrelationships
regarding authentication, authorization, credentials, and identity.
These concepts are used in describing how various security
approaches are utilized in client authentication and authorization.
3.1. Access Control Policy
An access control policy is a set of rules defining the protection
of resources, generally in terms of the capabilities of persons or
other entities accessing those resources. A common expression of an
access control policy is an access control list. Security objects
and mechanisms, such as those described here, enable the expression
of access control policies and their enforcement. Access control
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Authentication Methods for LDAPv3 February 20, 2001
policies are typically expressed in terms of access control
attributes as described below.
3.2. Access Control Factors
A request, when it is being processed by a server, may be associated
with a wide variety of security-related factors (section 4.2 of
[1]). The server uses these factors to determine whether and how to
process the request. These are called access control factors (ACFs).
They might include source IP address, encryption strength, the type
of operation being requested, time of day, etc. Some factors may be
specific to the request itself, others may be associated with the
connection via which the request is transmitted, others (e.g. time
of day) may be "environmental".
Access control policies are expressed in terms of access control
factors. E.g., a request having ACFs i,j,k can perform operation Y
on resource Z. The set of ACFs that a server makes available for
such expressions is implementation-specific.
3.3. Authentication, Credentials, Identity
Authentication credentials are the evidence supplied by one party to
another, asserting the identity of the supplying party (e.g. a user)
who is attempting to establish an association with the other party
(typically a server). Authentication is the process of generating,
transmitting, and verifying these credentials and thus the identity
they assert. An authentication identity is the name presented in a
credential.
There are many forms of authentication credentials -- the form used
depends upon the particular authentication mechanism negotiated by
the parties. For example: X.509 certificates, Kerberos tickets,
simple identity and password pairs. Note that an authentication
mechanism may constrain the form of authentication identities used
with it.
3.4. Authorization Identity
An authorization identity is one kind of access control factor. It
is the name of the user or other entity that requests that
operations be performed. Access control policies are often expressed
in terms of authorization identities; e.g., entity X can perform
operation Y on resource Z.
The authorization identity bound to an association is often exactly
the same as the authentication identity presented by the client, but
it may be different. SASL allows clients to specify an authorization
identity distinct from the authentication identity asserted by the
client's credentials. This permits agents such as proxy servers to
authenticate using their own credentials, yet request the access
privileges of the identity for which they are proxying [2]. Also,
the form of authentication identity supplied by a service like TLS
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Authentication Methods for LDAPv3 February 20, 2001
may not correspond to the authorization identities used to express a
server's access control policy, requiring a server-specific mapping
to be done. The method by which a server composes and validates an
authorization identity from the authentication credentials supplied
by a client is implementation-specific.
4. Required security mechanisms
It is clear that allowing any implementation, faced with the above It is clear that allowing any implementation, faced with the above
requirements, to pick and choose among the possible alternatives is requirements, to pick and choose among the possible alternatives is
not a strategy that is likely to lead to interoperability. In the not a strategy that is likely to lead to interoperability. In the
absence of mandates, clients will be written that do not support any absence of mandates, clients will be written that do not support any
security function supported by the server, or worse, support only security function supported by the server, or worse, support only
mechanisms like cleartext passwords that provide clearly inadequate mechanisms like cleartext passwords that provide clearly inadequate
security. security.
Active intermediary attacks are the most difficult for an attacker Active intermediary attacks are the most difficult for an attacker
to perform, and for an implementation to protect against. Methods to perform, and for an implementation to protect against. Methods
that protect only against hostile client and passive eavesdropping that protect only against hostile client and passive eavesdropping
attacks are useful in situations where the cost of protection attacks are useful in situations where the cost of protection
against active intermediary attacks is not justified based on the against active intermediary attacks is not justified based on the
perceived risk of active intermediary attacks. perceived risk of active intermediary attacks.
Given the presence of the Directory, there is a strong desire to see Given the presence of the Directory, there is a strong desire to see
mechanisms where identities take the form of an LDAP distinguished mechanisms where identities take the form of an LDAP distinguished
name and authentication data can be stored in the directory; this name and authentication data can be stored in the directory; this
Authentication Methods for LDAPv3 July 19, 2001
means that either this data is useless for faking authentication means that either this data is useless for faking authentication
(like the Unix "/etc/passwd" file format used to be), or its content (like the Unix "/etc/passwd" file format used to be), or its content
is never passed across the wire unprotected - that is, it's either is never passed across the wire unprotected - that is, it's either
updated outside the protocol or it is only updated in sessions well updated outside the protocol or it is only updated in sessions well
protected against snooping. It is also desirable to allow protected against snooping. It is also desirable to allow
authentication methods to carry authorization identities based on authentication methods to carry authorization identities based on
existing forms of user identities for backwards compatibility with existing forms of user identities for backwards compatibility with
non-LDAP-based authentication services. non-LDAP-based authentication services.
Therefore, the following implementation conformance requirements are Therefore, the following implementation conformance requirements are
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described in section 5, can be used. described in section 5, can be used.
(2) Implementations providing password-based authenticated access (2) Implementations providing password-based authenticated access
MUST support authentication using the DIGEST-MD5 SASL mechanism MUST support authentication using the DIGEST-MD5 SASL mechanism
[4], as described in section 6.2. This provides client [4], as described in section 6.2. This provides client
authentication with protection against passive eavesdropping authentication with protection against passive eavesdropping
attacks, but does not provide protection against active attacks, but does not provide protection against active
intermediary attacks. intermediary attacks.
(3) For a directory needing session protection and authentication, (3) For a directory needing session protection and authentication,
the Start TLS extended operation [5], and either the simple the Start TLS operation described in section 5, and either the
authentication choice or the SASL EXTERNAL mechanism, are to be simple authentication choice or the SASL EXTERNAL mechanism, are
used together. Implementations SHOULD support authentication to be used together. Implementations SHOULD support
with a password as described in section 6.2, and SHOULD support authentication with a password as described in section 7.2, and
SHOULD support authentication with a certificate as described in
Harrison Expires August 20, 2001 [Page 5] section 8.1. Together, these can provide integrity and
Authentication Methods for LDAPv3 February 20, 2001 disclosure protection of transmitted data, and authentication of
client and server, including protection against active
authentication with a certificate as described in section 7.1. intermediary attacks.
Together, these can provide integrity and disclosure protection
of transmitted data, and authentication of client and server,
including protection against active intermediary attacks.
If TLS is negotiated, the client MUST discard all information about If TLS is negotiated, the client MUST discard all information about
the server fetched prior to the TLS negotiation. In particular, the the server fetched prior to the TLS negotiation. In particular, the
value of supportedSASLMechanisms MAY be different after TLS has been value of supportedSASLMechanisms MAY be different after TLS has been
negotiated (specifically, the EXTERNAL mechanism or the proposed negotiated (specifically, the EXTERNAL mechanism or the proposed
PLAIN mechanism are likely to only be listed after a TLS negotiation PLAIN mechanism are likely to only be listed after a TLS negotiation
has been performed). has been performed).
If a SASL security layer is negotiated, the client MUST discard all If a SASL security layer is negotiated, the client MUST discard all
information about the server fetched prior to SASL. In particular, information about the server fetched prior to SASL. In particular,
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security layer is negotiated and verify that the value has not security layer is negotiated and verify that the value has not
changed after the SASL security layer was negotiated. This detects changed after the SASL security layer was negotiated. This detects
active attacks which remove supported SASL mechanisms from the active attacks which remove supported SASL mechanisms from the
supportedSASLMechanisms list, and allows the client to ensure that supportedSASLMechanisms list, and allows the client to ensure that
it is using the best mechanism supported by both client and server it is using the best mechanism supported by both client and server
(additionally, this is a SHOULD to allow for environments where the (additionally, this is a SHOULD to allow for environments where the
supported SASL mechanisms list is provided to the client through a supported SASL mechanisms list is provided to the client through a
different trusted source, e.g. as part of a digitally signed different trusted source, e.g. as part of a digitally signed
object). object).
5. Anonymous Authentication Authentication Methods for LDAPv3 July 19, 2001
Appendix A contains example deployment scenarios that list the
mechanisms that might be used to achieve a reasonable level of
security in various circumstances.
4. Bind Operation
The Bind operation allows authentication information to be exchanged
between the client and server.
4.1 Bind Request
The Bind Request is defined in section 4.2 of [LDAPv3] as follows:
BindRequest ::= [APPLICATION 0] SEQUENCE {
version INTEGER (1 .. 127),
name LDAPDN,
authentication AuthenticationChoice }
AuthenticationChoice ::= CHOICE {
simple [0] OCTET STRING,
-- 1 and 2 reserved
sasl [ReqsKeywords] SaslCredentials
}
SaslCredentials ::= SEQUENCE {
mechanism LDAPString,
credentials OCTET STRING OPTIONAL }
Parameters of the Bind Request are:
- version: A version number indicating the version of the protocol
to be used in this protocol session. This document describes
version 3 of the LDAP protocol. Note that there is no version
negotiation, and the client just sets this parameter to the
version it desires. If the client requests protocol version 2, a
server that supports the version 2 protocol as described in
[RFC1777] will not return any v3-specific protocol fields. (Note
that not all LDAP servers will support protocol version 2, since
they may be unable to generate the attribute syntaxes associated
with version 2.)
- name: The name of the directory object that the client wishes to
bind as. This field may take on a null value (a zero length
string) for the purposes of anonymous binds, when authentication
has been performed at a lower layer, or when using SASL
credentials with a mechanism that includes the name in the
credentials. Server behavior is undefined when the name is a
null value, simple authentication is used, and a password is
specified. Note that the server SHOULD NOT perform any alias
dereferencing in determining the object to bind as.
Authentication Methods for LDAPv3 July 19, 2001
- authentication: information used to authenticate the name, if
any, provided in the Bind Request.
Upon receipt of a Bind Request, a protocol server will authenticate
the requesting client, if necessary. The server will then return a
Bind Response to the client indicating the status of the
authentication.
Authorization is the use of this authentication information when
performing operations. Authorization MAY be affected by factors
outside of the LDAP Bind request, such as lower layer security
services.
4.2. Bind Response
The Bind Response is defined in section 4.2 of [LDAPv3] as follows.
BindResponse ::= [APPLICATION 1] SEQUENCE {
COMPONENTS OF LDAPResult,
serverSaslCreds [ABNF] OCTET STRING OPTIONAL }
BindResponse consists simply of an indication from the server of the
status of the client's request for authentication.
If the bind was successful, the resultCode will be success.
Otherwise it will be one of:
- operationsError: server encountered an internal error.
- protocolError: unrecognized version number or incorrect PDU
structure.
- authMethodNotSupported: unrecognized SASL mechanism name.
- strongAuthRequired: the server requires authentication be
performed with a SASL mechanism.
- referral: this server cannot accept this bind and the client
should try another.
- saslBindInProgress: the server requires the client to send a new
bind request, with the same sasl mechanism, to continue the
authentication process.
- inappropriateAuthentication: the server requires the client
which had attempted to bind anonymously or without supplying
credentials to provide some form of credentials.
- invalidCredentials: the wrong password was supplied or the SASL
credentials could not be processed.
- unavailable: the server is shutting down.
Authentication Methods for LDAPv3 July 19, 2001
If the server does not support the client's requested protocol
version it MUST set the resultCode to protocolError.
If the client receives a BindResponse response where the resultCode
was protocolError it MUST close the connection as the server will be
unwilling to accept further operations. (This is for compatibility
with earlier versions of LDAP, in which the bind was always the
first operation and there was no negotiation.)
The serverSaslCreds are used as part of a SASL-defined bind
mechanism to allow the client to authenticate the server to which it
is communicating, or to perform "challenge-response" authentication.
If the client bound with the password choice, or the SASL mechanism
does not require the server to return information to the client,
then this field is not to be included in the result.
4.3. Sequencing of the Bind Operation
4.3.1. Effect of Multiple Bind Requests
Subsequent to sending a bind request, A client MAY send a bind
request to change its identity. Such a bind request has the effect
of abandoning all operations outstanding on the connection. (This
simplifies server implementation.) Authentication from earlier binds
are subsequently ignored, and so if the bind fails, the connection
will be treated as anonymous (see section 4.3.3). If a SASL transfer
encryption or integrity mechanism has been negotiated, and that
mechanism does not support the changing of credentials from one
identity to another, then the client MUST instead establish a new
connection.
For some SASL authentication mechanisms, it may be necessary for the
client to invoke the BindRequest multiple times. If at any stage the
client wishes to abort the bind process it MAY unbind and then drop
the underlying connection. Clients MUST NOT invoke operations
between two Bind requests made as part of a multi-stage bind.
4.3.2. Aborting SASL Bind Negotiation
A client may abort a SASL bind negotiation by sending a BindRequest
with a different value in the mechanism field of SaslCredentials, or
an AuthenticationChoice other than sasl.
If the client sends a BindRequest with the sasl mechanism field as
an empty string, the server MUST return a BindResponse with
authMethodNotSupported as the resultCode. This will allow clients to
abort a negotiation if it wishes to try again with the same SASL
mechanism.
4.3.3. Unbound Connection Treated as Anonymous
Unlike LDAP v2, the client need not send a Bind Request in the first
PDU of the connection. The client may request any operations and the
Authentication Methods for LDAPv3 July 19, 2001
server MUST treat these as anonymous. If the server requires that
the client bind before browsing or modifying the directory, the
server MAY reject a request other than binding, unbinding or an
extended request with the "operationsError" result.
If the client did not bind before sending a request and receives an
operationsError, it may then send a Bind Request. If this also fails
or the client chooses not to bind on the existing connection, it
will close the connection, reopen it and begin again by first
sending a PDU with a Bind Request. This will aid in interoperating
with servers implementing other versions of LDAP.
4.4. Using SASL for Other Security Services
The simple authentication option provides minimal authentication
facilities, with the contents of the authentication field consisting
only of a cleartext password. Note that the use of cleartext
passwords is not recommended over open networks when the underlying
transport service cannot guarantee confidentiality; see the
"Security Considerations" section.
The sasl choice allows for any mechanism defined for use with SASL
[RFC2222]. The mechanism field contains the name of the mechanism.
The credentials field contains the arbitrary data used for
authentication, inside an OCTET STRING wrapper. Note that unlike
some Internet application protocols where SASL is used, LDAP is not
text-based, thus no base64 transformations are performed on the
credentials.
If any SASL-based integrity or confidentiality services are enabled,
they take effect following the transmission by the server and
reception by the client of the final BindResponse with resultCode
success.
The client can request that the server use authentication
information from a lower layer protocol by using the SASL EXTERNAL
mechanism.
4.4.1. Use of ANONYMOUS and PLAIN SASL Mechanisms
As LDAP includes native anonymous and plaintext authentication
methods, the "ANONYMOUS" and "PLAIN" SASL mechanisms are not used
with LDAP. If an authorization identity of a form different from a
DN is requested by the client, a mechanism that protects the
password in transit SHOULD be used.
4.4.2. Use of EXTERNAL SASL Mechanism
The "EXTERNAL" SASL mechanism can be used to request the LDAP server
make use of security credentials exchanged by a lower layer. If a
TLS session has not been established between the client and server
prior to making the SASL EXTERNAL Bind request and there is no other
external source of authentication credentials (e.g. IP-level
Authentication Methods for LDAPv3 July 19, 2001
security [RFC2401]), or if, during the process of establishing the
TLS session, the server did not request the client's authentication
credentials, the SASL EXTERNAL bind MUST fail with a result code of
inappropriateAuthentication. Any client authentication and
authorization state of the LDAP association is lost, so the LDAP
association is in an anonymous state after the failure.
4.4.3. SASL Mechanisms not Considered in this Document
The following SASL-based mechanisms are not considered in this
document: KERBEROS_V4, GSSAPI and SKEY.
4.5. SASL Authorization Identity
The authorization identity is carried as part of the SASL
credentials field in the LDAP Bind request and response.
When the "EXTERNAL" SASL mechanism is being negotiated, if the
credentials field is present, it contains an authorization identity
of the authzId form described below.
Other mechanisms define the location of the authorization identity
in the credentials field.
4.5.1. Authorization Identity Syntax
The authorization identity is a string in the UTF-8 character set,
corresponding to the following ABNF grammar [ABNF]:
; Specific predefined authorization (authz) id schemes are
; defined below -- new schemes may be defined in the future.
authzId = dnAuthzId / uAuthzId
; distinguished-name-based authz id.
dnAuthzId = "dn:" dn
dn = utf8string ; with syntax defined in RFC 2253
; unspecified authorization id, UTF-8 encoded.
uAuthzId = "u:" userid
userid = utf8string ; syntax unspecified
4.5.1.1. DN-based Authorization Identity
All servers that support the storage of authentication credentials,
such as passwords or certificates, in the directory MUST support the
dnAuthzId choice. The format for distinguishedName is defined in
Section 3 of draft-zeilenga-ldapbis-rfc2253-01.txt.
4.5.1.2. Unspecified Authorization Identity
Authentication Methods for LDAPv3 July 19, 2001
The uAuthzId choice allows for compatibility with client
applications that wish to authenticate to a local directory but do
not know their own distinguished name or that do not have a
directory entry. The format of utf8string is defined as only a
sequence of UTF-8 encoded ISO 10646 characters, and further
interpretation is subject to prior agreement between the client and
server.
For example, the userid could identify a user of a specific
directory service, or be a login name or the local-part of an RFC
822 email address. In general a uAuthzId MUST NOT be assumed to be
globally unique.
Additional authorization identity schemes MAY be defined in future
versions of this document.
4.6. SASL Service Name for LDAP
For use with SASL [SASL], a protocol must specify a service name to
be used with various SASL mechanisms, such as GSSAPI. For LDAP, the
service name is "ldap", which has been registered with the IANA as a
GSSAPI service name.
4.7. SASL Integrity and Privacy Protections
Any negotiated SASL integrity and privacy protections SHALL start on
the first octet of the first LDAP PDU following successful
completion of the SASL bind operation. If lower level security layer
is negotiated, such as TLS, any SASL security services SHALL be
layered on top of such security layers regardless of the order of
their negotiation.
5. Start TLS Operation
The Start Transport Layer Security (StartTLS) operation provides the
ability to establish Transport Layer Security [TLS] on an LDAP
association.
5.1. Start TLS Request
A client requests TLS establishment by transmitting a Start TLS
request PDU to the server. The Start TLS request is defined in terms
of the [LDAPv3] ExtendedRequest as follows:
ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
requestName [0] LDAPOID,
requestValue [LDAPv3] OCTET STRING OPTIONAL }
The requestName portion of the Start TLS request MUST be the OID
"1.3.6.1.4.1.1466.20037".
The requestValue field is absent.
Authentication Methods for LDAPv3 July 19, 2001
The client MUST NOT send any PDUs on this connection following this
request until it receives a Start TLS extended response.
5.2. Start TLS Response
When a Start TLS request is made, the server MUST return a Start TLS
response PDU to the requestor. The Start TLS response id defined in
terms of the [LDAPv3] ExtendedResponse as follows:
ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
COMPONENTS OF LDAPResult,
responseName [10] LDAPOID OPTIONAL,
response [11] OCTET STRING OPTIONAL }
The responseName portion of the Start TLS response MUST be the OID
"1.3.6.1.4.1.1466.20037". (Note that this OID is the same OID value
used in the requestName of the Start TLS request.)
The response field is absent.
The server MUST set the resultCode field to either success or one of
the other values outlined in section 5.2.2.
5.2.1. "Success" Response
If the ExtendedResponse contains a resultCode of success, this
indicates that the server is willing and able to negotiate TLS.
Refer to section 3, below, for details.
5.2.2. Response other than "success"
If the ExtendedResponse contains a resultCode other than success,
this indicates that the server is unwilling or unable to negotiate
TLS.
If the Start TLS extended request was not successful, the resultCode
will be one of:
operationsError (operations sequencing incorrect; e.g. TLS already
established)
protocolError (TLS not supported or incorrect PDU structure)
referral (this server doesn't do TLS, try this one)
unavailable (e.g. some major problem with TLS, or server is
shutting down)
The server MUST return operationsError if the client violates any of
the Start TLS extended operation sequencing requirements described
in section 5.3, below.
Authentication Methods for LDAPv3 July 19, 2001
If the server does not support TLS (whether by design or by current
configuration), it MUST set the resultCode to protocolError (see
section 4.1.1 of [LDAPv3]), or to referral. The server MUST include
an actual referral value in the LDAP Result if it returns a
resultCode of referral. The client's current session is unaffected
if the server does not support TLS. The client MAY proceed with any
LDAP operation, or it MAY close the connection.
The server MUST return unavailable if it supports TLS but cannot
establish a TLS connection for some reason, e.g. the certificate
server not responding, it cannot contact its TLS implementation, or
if the server is in process of shutting down. The client MAY retry
the StartTLS operation, or it MAY proceed with any other LDAP
operation, or it MAY close the connection.
5.3. Sequencing of the Start TLS Operation
This section describes the overall procedures clients and servers
MUST follow for TLS establishment. These procedures take into
consideration various aspects of the overall security of the LDAP
association including discovery of resultant security level and
assertion of the client's authorization identity.
Note that the precise effects, on a client's authorization identity,
of establishing TLS on an LDAP association are described in detail
in section 5.5.
5.3.1. Requesting to Start TLS on an LDAP Association
The client MAY send the Start TLS extended request at any time after
establishing an LDAP association, except that in the following cases
the client MUST NOT send a Start TLS extended request:
- if TLS is currently established on the connection, or
- during a multi-stage SASL negotiation, or
- if there are any LDAP operations outstanding on the
connection.
The result of violating any of these requirements is a resultCode of
operationsError, as described above in section 2.3.
The client MAY have already performed a Bind operation when it sends
a Start TLS request, or the client might have not yet bound.
If the client did not establish a TLS connection before sending any
other requests, and the server requires the client to establish a
TLS connection before performing a particular request, the server
MUST reject that request with a confidentialityRequired or
strongAuthRequired result. The client MAY send a Start TLS extended
request, or it MAY choose to close the connection.
5.3.2. Starting TLS
Authentication Methods for LDAPv3 July 19, 2001
The server will return an extended response with the resultCode of
success if it is willing and able to negotiate TLS. It will return
other resultCodes, documented above, if it is unable.
In the successful case, the client, which has ceased to transfer
LDAP requests on the connection, MUST either begin a TLS negotiation
or close the connection. The client will send PDUs in the TLS Record
Protocol directly over the underlying transport connection to the
server to initiate TLS negotiation [TLS].
5.3.3. TLS Version Negotiation
Negotiating the version of TLS or SSL to be used is a part of the
TLS Handshake Protocol, as documented in [TLS]. Please refer to that
document for details.
5.3.4. Discovery of Resultant Security Level
After a TLS connection is established on an LDAP association, both
parties MUST individually decide whether or not to continue based on
the privacy level achieved. Ascertaining the TLS connection's
privacy level is implementation dependent, and accomplished by
communicating with one's respective local TLS implementation.
If the client or server decides that the level of authentication or
privacy is not high enough for it to continue, it SHOULD gracefully
close the TLS connection immediately after the TLS negotiation has
completed (see sections 5.4.1 and 5.5.2 below). If the client
decides to continue, it MAY attempt to Start TLS again, it MAY send
an unbind request, or it MAY send any other LDAP request.
5.3.5. Assertion of Client's Authorization Identity
The client MAY, upon receipt of a Start TLS response indicating
success, assert that a specific authorization identity be utilized
in determining the client's authorization status. The client
accomplishes this via an LDAP Bind request specifying a SASL
mechanism of "EXTERNAL" [SASL] (see section 5.5.1.2 below).
5.3.6. Server Identity Check
The client MUST check its understanding of the server's hostname
against the server's identity as presented in the server's
Certificate message, in order to prevent man-in-the-middle attacks.
Matching is performed according to these rules:
- The client MUST use the server hostname it used to open the LDAP
connection as the value to compare against the server name as
expressed in the server's certificate. The client MUST NOT use
the server's canonical DNS name or any other derived form of
name.
Authentication Methods for LDAPv3 July 19, 2001
- If a subjectAltName extension of type dNSName is present in the
certificate, it SHOULD be used as the source of the server's
identity.
- Matching is case-insensitive.
- The "*" wildcard character is allowed. If present, it applies
only to the left-most name component.
E.g. *.bar.com would match a.bar.com, b.bar.com, etc. but not
bar.com. If more than one identity of a given type is present in
the certificate (e.g. more than one dNSName name), a match in any
one of the set is considered acceptable.
If the hostname does not match the dNSName-based identity in the
certificate per the above check, user-oriented clients SHOULD either
notify the user (clients MAY give the user the opportunity to
continue with the connection in any case) or terminate the
connection and indicate that the server's identity is suspect.
Automated clients SHOULD close the connection, returning and/or
logging an error indicating that the server's identity is suspect.
Beyond the server identity checks described in this section, clients
SHOULD be prepared to do further checking to ensure that the server
is authorized to provide the service it is observed to provide. The
client MAY need to make use of local policy information.
5.3.7. Refresh of Server Capabilities Information
The client MUST refresh any cached server capabilities information
(e.g. from the server's root DSE; see section 3.4 of [LDAPv3]) upon
TLS session establishment. This is necessary to protect against
active-intermediary attacks that may have altered any server
capabilities information retrieved prior to TLS establishment. The
server MAY advertise different capabilities after TLS establishment.
5.4. Closing a TLS Connection
Two forms of TLS connection closure--graceful and abrupt--are
supported.
5.4.1. Graceful Closure
Either the client or server MAY terminate the TLS connection on an
LDAP association by sending a TLS closure alert. This will leave the
LDAP association intact.
Before closing a TLS connection, the client MUST [RGH18]either wait
for any outstanding LDAP operations to complete, or explicitly
abandon them [LDAPv3].
After the initiator of a close has sent a TLS closure alert, it MUST
discard any TLS messages until it has received a TLS closure alert
Authentication Methods for LDAPv3 July 19, 2001
from the other party. It will cease to send TLS Record Protocol
PDUs, and following the receipt of the alert, MAY send and receive
LDAP PDUs.
The other party, if it receives a TLS closure alert, MUST
immediately transmit a TLS closure alert. It will subsequently
cease to send TLS Record Protocol PDUs, and MAY send and receive
LDAP PDUs.
5.4.2. Abrupt Closure
Either the client or server MAY abruptly close the entire LDAP
association and any TLS connection established on it by dropping the
underlying TCP connection. In this circumstance, a server MAY send
the client a Notice of Disconnection [LDAPv3] before dropping the
TCP connection.
5.5. Effects of TLS on a Client's Authorization Identity
This section describes the effects on a client's authorization
identity brought about by establishing TLS on an LDAP association.
The default effects are described first, and next the facilities for
client assertion of authorization identity are discussed including
error conditions. Lastly, the effects of closing the TLS connection
are described.
Authorization identities and related concepts are described in
Appendix B.
5.5.1. TLS Connection Establishment Effects
5.5.1.1. Default Effects
Upon establishment of the TLS connection onto the LDAP association,
any previously established authentication and authorization
identities MUST remain in force, including anonymous state. This
holds even in the case where the server requests client
authentication via TLS -- e.g. requests the client to supply its
certificate during TLS negotiation (see [TLS]).
5.5.1.2. Client Assertion of Authorization Identity
A client MAY either implicitly request that its LDAP authorization
identity be derived from its authenticated TLS credentials or it MAY
explicitly provide an authorization identity and assert that it be
used in combination with its authenticated TLS credentials. The
former is known as an implicit assertion, and the latter as an
explicit assertion.
5.5.1.2.1. Implicit Assertion
An implicit authorization identity assertion is accomplished after
TLS establishment by invoking a Bind request of the SASL form using
Authentication Methods for LDAPv3 July 19, 2001
the "EXTERNAL" mechanism name [SASL, LDAPv3] that SHALL NOT include
the optional credentials octet string (found within the
SaslCredentials sequence in the Bind Request). The server will
derive the client's authorization identity from the authentication
identity supplied in the client's TLS credentials (typically a
public key certificate) according to local policy. The underlying
mechanics of how this is accomplished are implementation specific.
5.5.1.2.2. Explicit Assertion
An explicit authorization identity assertion is accomplished after
TLS establishment by invoking a Bind request of the SASL form using
the "EXTERNAL" mechanism name [SASL, LDAPv3] that SHALL include the
credentials octet string. This string MUST be constructed as
documented in section 9 of [AuthMeth].
5.5.1.2.3. Error Conditions
For either form of assertion, the server MUST verify that the
client's authentication identity as supplied in its TLS credentials
is permitted to be mapped to the asserted authorization identity.
The server MUST reject the Bind operation with an invalidCredentials
resultCode in the Bind response if the client is not so authorized.
Additionally, with either form of assertion, if a TLS session has
not been established between the client and server prior to making
the SASL EXTERNAL Bind request and there is no other external source
of authentication credentials (e.g. IP-level security [IPSEC]), or
if, during the process of establishing the TLS session, the server
did not request the client's authentication credentials, the SASL
EXTERNAL bind MUST fail with a result code of
inappropriateAuthentication.
After the above Bind operation failures, any client authentication
and authorization state of the LDAP association is lost, so the LDAP
association is in an anonymous state after the failure. TLS
connection state is unaffected, though a server MAY end the TLS
connection, via a TLS close_notify message, based on the Bind
failure (as it MAY at any time).
5.5.2. TLS Connection Closure Effects
Closure of the TLS connection MUST cause the LDAP association to
move to an anonymous authentication and authorization state
regardless of the state established over TLS and regardless of the
authentication and authorization state prior to TLS connection
establishment.
6. Anonymous Authentication
Directory operations that modify entries or access protected Directory operations that modify entries or access protected
attributes or entries generally require client authentication. attributes or entries generally require client authentication.
Clients that do not intend to perform any of these operations Clients that do not intend to perform any of these operations
Authentication Methods for LDAPv3 July 19, 2001
typically use anonymous authentication. Servers SHOULD NOT allow typically use anonymous authentication. Servers SHOULD NOT allow
clients with anonymous authentication to modify directory entries or clients with anonymous authentication to modify directory entries or
access sensitive information in directory entries. access sensitive information in directory entries.
LDAP implementations MUST support anonymous authentication, as LDAP implementations MUST support anonymous authentication, as
defined in section 5.1. defined in section 6.1.
LDAP implementations MAY support anonymous authentication with TLS, LDAP implementations MAY support anonymous authentication with TLS,
as defined in section 5.2. as defined in section 6.2.
While there MAY be access control restrictions to prevent access to While there MAY be access control restrictions to prevent access to
directory entries, an LDAP server SHOULD allow an anonymously-bound directory entries, an LDAP server SHOULD allow an anonymously-bound
client to retrieve the supportedSASLMechanisms attribute of the root client to retrieve the supportedSASLMechanisms attribute of the root
DSE. DSE.
An LDAP server MAY use other information about the client provided An LDAP server MAY use other information about the client provided
by the lower layers or external means to grant or deny access even by the lower layers or external means to grant or deny access even
to anonymously authenticated clients. to anonymously authenticated clients.
5.1. Anonymous Authentication Procedure 6.1. Anonymous Authentication Procedure
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An LDAPv3 client that has not successfully completed a bind An LDAPv3 client that has not successfully completed a bind
operation on a connection is anonymously authenticated. operation on a connection is anonymously authenticated. See section
4.3.3.
An LDAP client MAY also bind anonymously using the procedure defined An LDAP client MAY also choose to explicitly bind anonymously. A
in section 4.2 of RFC 2251. client that wishes to do so MUST choose the simple authentication
option in the Bind Request (see section XXX) and set the password to
be of zero length. (This is often done by LDAPv2 clients.) Typically
the name is also of zero length.
5.2. Anonymous Authentication and TLS 6.2. Anonymous Authentication and TLS
An LDAP client MAY use the Start TLS operation [5] to negotiate the An LDAP client MAY use the Start TLS operation (section 4) to
use of TLS security [6]. If the client has not bound beforehand, negotiate the use of TLS security [TLS]. If the client has not bound
then until the client uses the EXTERNAL SASL mechanism to negotiate beforehand, then until the client uses the EXTERNAL SASL mechanism
the recognition of the client's certificate, the client is to negotiate the recognition of the client's certificate, the client
anonymously authenticated. is anonymously authenticated.
Recommendations on TLS ciphersuites are given in section 10. Recommendations on TLS ciphersuites are given in section 10.
An LDAP server which requests that clients provide their certificate An LDAP server which requests that clients provide their certificate
during TLS negotiation MAY use a local security policy to determine during TLS negotiation MAY use a local security policy to determine
whether to successfully complete TLS negotiation if the client did whether to successfully complete TLS negotiation if the client did
not present a certificate which could be validated. not present a certificate which could be validated.
6. Password-based authentication 7. Password-based authentication
6.1. Simple authentication 7.1. Simple authentication
The LDAP "simple" authentication choice is not suitable for The LDAP "simple" authentication choice is not suitable for
authentication in environments where there is no network or authentication in environments where there is no network or
transport layer confidentiality. LDAP implementations SHOULD support transport layer confidentiality. LDAP implementations SHOULD support
Authentication Methods for LDAPv3 July 19, 2001
authentication with the "simple" authentication choice when the authentication with the "simple" authentication choice when the
connection is protected against eavesdropping using TLS, as defined connection is protected against eavesdropping using TLS, as defined
in section 6.3. LDAP implementations SHOULD NOT support in section 6.3. LDAP implementations SHOULD NOT support
authentication with the "simple" authentication choice unless the authentication with the "simple" authentication choice unless the
data on the connection is protected using TLS or other privacy and data on the connection is protected using TLS or other privacy and
data-integrity protection. data-integrity protection.
6.2. Digest Authentication 7.2. Digest Authentication
LDAP implementations MUST support authentication with a password LDAP implementations MUST support authentication with a password
using the DIGEST-MD5 SASL mechanism for password protection, as using the DIGEST-MD5 SASL mechanism for password protection.
defined in section 6.1.
An LDAP client MAY determine whether the server supports this An LDAP client MAY determine whether the server supports this
mechanism by performing a search request on the root DSE, requesting mechanism by performing a search request on the root DSE, requesting
the supportedSASLMechanisms attribute, and checking whether the the supportedSASLMechanisms attribute, and checking whether the
string "DIGEST-MD5" is present as a value of this attribute. string "DIGEST-MD5" is present as a value of this attribute.
In the first stage of authentication, when the client is performing In the first stage of authentication, when the client is perfCorming
an "initial authentication" as defined in section 2.1 of [4], the an "initial authentication" as defined in section 2.1 of [RFC2831],
client sends a bind request in which the version number is 3, the the client sends a bind request in which the version number is 3,
authentication choice is sasl, the sasl mechanism name is "DIGEST- the authentication choice is sasl, the sasl mechanism name is
MD5", and the credentials are absent. The client then waits for a "DIGEST- MD5", and the credentials are absent. The client then waits
response from the server to this request. for a response from the server to this request.
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The server will respond with a bind response in which the resultCode The server will respond with a bind response in which the resultCode
is saslBindInProgress, and the serverSaslCreds field is present. The is saslBindInProgress, and the serverSaslCreds field is present. The
contents of this field is a string defined by "digest-challenge" in contents of this field is a string defined by "digest-challenge" in
section 2.1.1 of [4]. The server SHOULD include a realm indication section 2.1.1 of [RFC2831]. The server SHOULD include a realm
and MUST indicate support for UTF-8. indication and MUST indicate support for UTF-8.
The client will send a bind request with a distinct message id, in The client will send a bind request with a distinct message id, in
which the version number is 3, the authentication choice is sasl, which the version number is 3, the authentication choice is sasl,
the sasl mechanism name is "DIGEST-MD5", and the credentials contain the sasl mechanism name is "DIGEST-MD5", and the credentials contain
the string defined by "digest-response" in section 2.1.2 of [4]. The the string defined by "digest-response" in section 2.1.2 of
serv-type is "ldap". [RFC2831]. The serv-type is "ldap".
The server will respond with a bind response in which the resultCode The server will respond with a bind response in which the resultCode
is either success, or an error indication. If the authentication is is either success, or an error indication. If the authentication is
successful and the server does not support subsequent successful and the server does not support subsequent
authentication, then the credentials field is absent. If the authentication, then the credentials field is absent. If the
authentication is successful and the server supports subsequent authentication is successful and the server supports subsequent
authentication, then the credentials field contains the string authentication, then the credentials field contains the string
defined by "response-auth" in section 2.1.3 of [4]. Support for defined by "response-auth" in section 2.1.3 of [4]. Support for
subsequent authentication is OPTIONAL in clients and servers. subsequent authentication is OPTIONAL in clients and servers.
6.3. "simple" authentication choice under TLS encryption 7.3. "simple" authentication choice under TLS encryption
Following the negotiation of an appropriate TLS ciphersuite Following the negotiation of an appropriate TLS ciphersuite
providing connection confidentiality [6], a client MAY authenticate providing connection confidentiality [6], a client MAY authenticate
to a directory that supports the simple authentication choice by to a directory that supports the simple authentication choice by
performing a simple bind operation. performing a simple bind operation.
Authentication Methods for LDAPv3 July 19, 2001
The client will use the Start TLS operation [5] to negotiate the use The client will use the Start TLS operation [5] to negotiate the use
of TLS security [6] on the connection to the LDAP server. The client of TLS security [6] on the connection to the LDAP server. The client
need not have bound to the directory beforehand. need not have bound to the directory beforehand.
For this authentication procedure to be successful, the client and For this authentication procedure to be successful, the client and
server MUST negotiate a ciphersuite which contains a bulk encryption server MUST negotiate a ciphersuite which contains a bulk encryption
algorithm of appropriate strength. Recommendations on cipher suites algorithm of appropriate strength. Recommendations on cipher suites
are given in section 10. are given in section 10.
Following the successful completion of TLS negotiation, the client Following the successful completion of TLS negotiation, the client
MUST send an LDAP bind request with the version number of 3, the MUST send an LDAP bind request with the version number of 3, the
name field containing a DN , and the "simple" authentication choice, name field containing a DN , and the "simple" authentication choice,
containing a password. containing a password.
6.3.1 "simple" Authentication Choice 7.3.1 "simple" Authentication Choice
DSAs that map the DN sent in the bind request to a directory entry DSAs that map the DN sent in the bind request to a directory entry
with a userPassword attribute will, for each value of the with a userPassword attribute will, for each value of the
userPassword attribute in the named user's entry, compare these for userPassword attribute in the named user's entry, compare these for
case-sensitive equality with the client's presented password. If case-sensitive equality with the client's presented password. If
there is a match, then the server will respond with resultCode there is a match, then the server will respond with resultCode
success, otherwise the server will respond with resultCode success, otherwise the server will respond with resultCode
invalidCredentials. invalidCredentials.
6.4. Other authentication choices with TLS 7.4. Other authentication choices with TLS
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It is also possible, following the negotiation of TLS, to perform a It is also possible, following the negotiation of TLS, to perform a
SASL authentication that does not involve the exchange of plaintext SASL authentication that does not involve the exchange of plaintext
reusable passwords. In this case the client and server need not reusable passwords. In this case the client and server need not
negotiate a ciphersuite which provides confidentiality if the only negotiate a ciphersuite which provides confidentiality if the only
service required is data integrity. service required is data integrity.
7. Certificate-based authentication 8. Certificate-based authentication
LDAP implementations SHOULD support authentication via a client LDAP implementations SHOULD support authentication via a client
certificate in TLS, as defined in section 7.1. certificate in TLS, as defined in section 7.1.
7.1. Certificate-based authentication with TLS 8.1. Certificate-based authentication with TLS
A user who has a public/private key pair in which the public key has A user who has a public/private key pair in which the public key has
been signed by a Certification Authority may use this key pair to been signed by a Certification Authority may use this key pair to
authenticate to the directory server if the user's certificate is authenticate to the directory server if the user's certificate is
requested by the server. The user's certificate subject field SHOULD requested by the server. The user's certificate subject field SHOULD
be the name of the user's directory entry, and the Certification be the name of the user's directory entry, and the Certification
Authority that issued the userĘs certificate must be sufficiently Authority that issued the userĘs certificate must be sufficiently
trusted by the directory server in order for the server to process trusted by the directory server in order for the server to process
the certificate. The means by which servers validate certificate the certificate. The means by which servers validate certificate
paths is outside the scope of this document. paths is outside the scope of this document.
A server MAY support mappings for certificates in which the subject A server MAY support mappings for certificates in which the subject
field name is different from the name of the user's directory entry. field name is different from the name of the user's directory entry.
A server which supports mappings of names MUST be capable of being A server which supports mappings of names MUST be capable of being
configured to support certificates for which no mapping is required. configured to support certificates for which no mapping is required.
Authentication Methods for LDAPv3 July 19, 2001
The client will use the Start TLS operation [5] to negotiate the use The client will use the Start TLS operation [5] to negotiate the use
of TLS security [6] on the connection to the LDAP server. The client of TLS security [6] on the connection to the LDAP server. The client
need not have bound to the directory beforehand. need not have bound to the directory beforehand.
In the TLS negotiation, the server MUST request a certificate. The In the TLS negotiation, the server MUST request a certificate. The
client will provide its certificate to the server, and MUST perform client will provide its certificate to the server, and MUST perform
a private key-based encryption, proving it has the private key a private key-based encryption, proving it has the private key
associated with the certificate. associated with the certificate.
In deployments that require protection of sensitive data in transit, In deployments that require protection of sensitive data in transit,
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The server MUST verify that the client's certificate is valid. The The server MUST verify that the client's certificate is valid. The
server will normally check that the certificate is issued by a known server will normally check that the certificate is issued by a known
CA, and that none of the certificates on the client's certificate CA, and that none of the certificates on the client's certificate
chain are invalid or revoked. There are several procedures by which chain are invalid or revoked. There are several procedures by which
the server can perform these checks. the server can perform these checks.
Following the successful completion of TLS negotiation, the client Following the successful completion of TLS negotiation, the client
will send an LDAP bind request with the SASL "EXTERNAL" mechanism. will send an LDAP bind request with the SASL "EXTERNAL" mechanism.
8. Other mechanisms 9. TLS Ciphersuites
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8.1. Use of ANONYMOUS and PLAIN SASL Mechanisms
As LDAP includes native anonymous and plaintext authentication
methods, the "ANONYMOUS" and "PLAIN" SASL mechanisms are not used
with LDAP. If an authorization identity of a form different from a
DN is requested by the client, a mechanism that protects the
password in transit SHOULD be used.
8.2. SASL Mechanisms not Considered in this Document
The following SASL-based mechanisms are not considered in this
document: KERBEROS_V4, GSSAPI and SKEY.
8.3. Use of EXTERNAL SASL Mechanism
The "EXTERNAL" SASL mechanism can be used to request the LDAP server
make use of security credentials exchanged by a lower layer. If a
TLS session has not been established between the client and server
prior to making the SASL EXTERNAL Bind request and there is no other
external source of authentication credentials (e.g. IP-level
security [8]), or if, during the process of establishing the TLS
session, the server did not request the client's authentication
credentials, the SASL EXTERNAL bind MUST fail with a result code of
inappropriateAuthentication. Any client authentication and
authorization state of the LDAP association is lost, so the LDAP
association is in an anonymous state after the failure.
9. Authorization Identity
The authorization identity is carried as part of the SASL
credentials field in the LDAP Bind request and response.
When the "EXTERNAL" SASL mechanism is being negotiated, if the
credentials field is present, it contains an authorization identity
of the authzId form described below.
Other mechanisms define the location of the authorization identity
in the credentials field.
9.1. Authorization Identity Syntax
The authorization identity is a string in the UTF-8 character set,
corresponding to the following ABNF [7]:
; Specific predefined authorization (authz) id schemes are
; defined below -- new schemes may be defined in the future.
authzId = dnAuthzId / uAuthzId
; distinguished-name-based authz id.
dnAuthzId = "dn:" dn
dn = utf8string ; with syntax defined in RFC 2253
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; unspecified authorization id, UTF-8 encoded.
uAuthzId = "u:" userid
userid = utf8string ; syntax unspecified
9.1.1. DN-based Authorization Identity
All servers that support the storage of authentication credentials,
such as passwords or certificates, in the directory MUST support the
dnAuthzId choice. The format for distinguishedName is defined in
Section 3 of draft-zeilenga-ldapbis-rfc2253-01.txt.
9.1.2. Unspecified Authorization Identity
The uAuthzId choice allows for compatibility with client
applications that wish to authenticate to a local directory but do
not know their own distinguished name or that do not have a
directory entry. The format of utf8string is defined as only a
sequence of UTF-8 encoded ISO 10646 characters, and further
interpretation is subject to prior agreement between the client and
server.
For example, the userid could identify a user of a specific
directory service, or be a login name or the local-part of an RFC
822 email address. In general a uAuthzId MUST NOT be assumed to be
globally unique.
Additional authorization identity schemes MAY be defined in future
versions of this document.
10. TLS Ciphersuites
The following ciphersuites defined in [6] MUST NOT be used for The following ciphersuites defined in [6] MUST NOT be used for
confidentiality protection of passwords or data: confidentiality protection of passwords or data:
TLS_NULL_WITH_NULL_NULL TLS_NULL_WITH_NULL_NULL
TLS_RSA_WITH_NULL_MD5 TLS_RSA_WITH_NULL_MD5
TLS_RSA_WITH_NULL_SHA TLS_RSA_WITH_NULL_SHA
The following ciphersuites defined in [6] can be cracked easily The following ciphersuites defined in [6] can be cracked easily
(less than a day of CPU time on a standard CPU in 2000). These (less than a day of CPU time on a standard CPU in 2000). These
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protection of passwords or data. Client and server implementers protection of passwords or data. Client and server implementers
SHOULD carefully consider the value of the password or data being SHOULD carefully consider the value of the password or data being
protected before using these ciphersuites: protected before using these ciphersuites:
TLS_RSA_EXPORT_WITH_RC4_40_MD5 TLS_RSA_EXPORT_WITH_RC4_40_MD5
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA
Harrison Expires August 20, 2001 [Page 11]
Authentication Methods for LDAPv3 February 20, 2001
TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
The following ciphersuites are vulnerable to man-in-the-middle The following ciphersuites are vulnerable to man-in-the-middle
attacks, and SHOULD NOT be used to protect passwords or sensitive attacks, and SHOULD NOT be used to protect passwords or sensitive
Authentication Methods for LDAPv3 July 19, 2001
data, unless the network configuration is such that the danger of a data, unless the network configuration is such that the danger of a
man-in-the-middle attack is tolerable: man-in-the-middle attack is tolerable:
TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
TLS_DH_anon_WITH_RC4_128_MD5 TLS_DH_anon_WITH_RC4_128_MD5
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_anon_WITH_DES_CBC_SHA TLS_DH_anon_WITH_DES_CBC_SHA
TLS_DH_anon_WITH_3DES_EDE_CBC_SHA TLS_DH_anon_WITH_3DES_EDE_CBC_SHA
A client or server that supports TLS MUST support A client or server that supports TLS MUST support
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA and MAY support other ciphersuites TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA and MAY support other ciphersuites
offering equivalent or better protection. offering equivalent or better protection.
11. SASL service name for LDAP 10. Security Considerations
For use with SASL [2], a protocol must specify a service name to be
used with various SASL mechanisms, such as GSSAPI. For LDAP, the
service name is "ldap", which has been registered with the IANA as a
GSSAPI service name.
12. SASL Integrity and Privacy Protections
Any negotiated SASL integrity and privacy protections SHALL start on
the first octet of the first LDAP PDU following successful
completion of the SASL bind operation. If lower level security layer
is negotiated, such as TLS, any SASL security services SHALL be
layered on top of such security layers regardless of the order of
their negotiation.
13. Security Considerations
Security issues are discussed throughout this memo; the Security issues are discussed throughout this memo; the
(unsurprising) conclusion is that mandatory security is important, (unsurprising) conclusion is that mandatory security is important,
and that session encryption is required when snooping is a problem. and that session encryption is required when snooping is a problem.
Servers are encouraged to prevent modifications by anonymous users. Servers are encouraged to prevent modifications by anonymous users.
Servers may also wish to minimize denial of service attacks by Servers may also wish to minimize denial of service attacks by
timing out idle connections, and returning the unwillingToPerform timing out idle connections, and returning the unwillingToPerform
result code rather than performing computationally expensive result code rather than performing computationally expensive
operations requested by unauthorized clients. operations requested by unauthorized clients.
A connection on which the client has not performed the Start TLS A connection on which the client has not performed the Start TLS
operation or negotiated a suitable SASL mechanism for connection operation or negotiated a suitable SASL mechanism for connection
integrity and encryption services is subject to man-in-the-middle integrity and encryption services is subject to man-in-the-middle
attacks to view and modify information in transit. attacks to view and modify information in transit.
Harrison Expires August 20, 2001 [Page 12] 10.1. Start TLS Security Considerations
Authentication Methods for LDAPv3 February 20, 2001
The goals of using the TLS protocol with LDAP are to ensure
connection confidentiality and integrity, and to optionally provide
for authentication. TLS expressly provides these capabilities, as
described in [TLS].
All security gained via use of the Start TLS operation is gained by
the use of TLS itself. The Start TLS operation, on its own, does not
provide any additional security.
The use of TLS does not provide or ensure for confidentiality and/or
non-repudiation of the data housed by an LDAP-based directory
server. Nor does it secure the data from inspection by the server
administrators. Once established, TLS only provides for and ensures
confidentiality and integrity of the operations and data in transit
over the LDAP association, and only if the implementations on the
client and server support and negotiate it.
The level of security provided though the use of TLS depends
directly on both the quality of the TLS implementation used and the
style of usage of that implementation. Additionally, an active-
Authentication Methods for LDAPv3 July 19, 2001
intermediary attacker can remove the Start TLS extended operation
from the supportedExtension attribute of the root DSE. Therefore,
both parties SHOULD independently ascertain and consent to the
security level achieved once TLS is established and before beginning
use of the TLS connection. For example, the security level of the
TLS connection might have been negotiated down to plaintext.
Clients SHOULD either warn the user when the security level achieved
does not provide confidentiality and/or integrity protection, or be
configurable to refuse to proceed without an acceptable level of
security.
Client and server implementors SHOULD take measures to ensure proper
protection of credentials and other confidential data where such
measures are not otherwise provided by the TLS implementation.
Server implementors SHOULD allow for server administrators to elect
whether and when connection confidentiality and/or integrity is
required, as well as elect whether and when client authentication
via TLS is required.
Additional security considerations relating to the EXTERNAL Additional security considerations relating to the EXTERNAL
mechanism to negotiate TLS can be found in [2], [5] and [6]. mechanism to negotiate TLS can be found in [SASL] and [6].
14. Acknowledgements 11. Acknowledgements
The author acknowledges the work of Mark Wahl, Harald Tveit This document combines information originally contained in RFC 2829,
Alvestrand, Jeff Hodges, and RL "Bob" Morgan who authored RFC 2829, RFC 2830 and portions of RFC 2251. The author acknowledges the work
the document upon which this work is largely based. RFC 2829 was a of Harald Tveit Alvestrand, Jeff Hodges, Tim Howes, Steve Kille, RL
product of the IETF LDAPEXT Working Group. "Bob" Morgan , and Mark Wahl, each of whom authored one or more of
these documents. RFC 2829 and RFC 2830 were products of the IETF
LDAPEXT Working Group. RFC 2251 was a product of the ASID Working
Group.
This document is based upon input of the IETF LDAP Revision working This document is based upon input of the IETF LDAP Revision working
group. The contributions of its members is greatly appreciated. group. The contributions of its members is greatly appreciated.
15. Bibliography 12. Bibliography
[1] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory Access [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Protocol (v3)", RFC 2251, December 1997. Specifications: ABNF", RFC 2234, November 1997.
[2] Myers, J., "Simple Authentication and Security Layer (SASL)", [IPSEC] Kent, S. and R. Atkinson, "Security Architecture for the
RFC 2222, October 1997. Internet Protocol", RFC 2401, November 1998.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement [LDAPv3] Wahl, M., Kille S. and T. Howes, "Lightweight Directory
Levels", BCP 14, RFC 2119, March 1997. Access Protocol (v3)", RFC 2251, December 1997.
[4] Leach, P. and C. Newman, "Using Digest Authentication as a SASL [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Mechanism", RFC 2831, May 2000. Internet Protocol", RFC 2401, November 1998.
[5] Hodges, J., Morgan, R. and M. Wahl, "Lightweight Directory [RFC2831] Leach, P. and C. Newman, "Using Digest Authentication as a
Access Protocol (v3): Extension for Transport Layer Security", SASL Mechanism", RFC 2831, May 2000.
RFC 2830, May 2000.
[6] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC Authentication Methods for LDAPv3 July 19, 2001
2246, January 1999.
[7] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [ReqsKeywords] Bradner, S., "Key Words for use in RFCs to Indicate
Specifications: ABNF", RFC 2234, November 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[8] Kent, S. and R. Atkinson, "Security Architecture for the [SASL] Myers, J., "Simple Authentication and Security Layer (SASL)",
Internet Protocol", RFC 2401, November 1998. RFC 2222, October 1997.
15. Author's Address [TLS] Dierks, T. and C. Allen. "The TLS Protocol Version 1.0", RFC
2246, January 1999.
13. Author's Address
Roger Harrison Roger Harrison
Novell, Inc. Novell, Inc.
1800 S. Novell Place 1800 S. Novell Place
Provo, UT 84606 Provo, UT 84606
+1 801 861 2642 +1 801 861 2642
roger_harrison@novell.com roger_harrison@novell.com
16. Full Copyright Statement 14. Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved. Copyright (C) The Internet Society (2000). All Rights Reserved.
Harrison Expires August 20, 2001 [Page 13]
Authentication Methods for LDAPv3 February 20, 2001
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for developing Internet standards in which case the procedures for
skipping to change at line 752 skipping to change at page 23, line 53
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Appendix A - Change History Appendix A. Example Deployment Scenarios
The following scenarios are typical for LDAP directories on the
Internet, and have different security requirements. (In the
following, "sensitive" means data that will cause real damage to the
Authentication Methods for LDAPv3 July 19, 2001
owner if revealed; there may be data that is protected but not
sensitive). This is not intended to be a comprehensive list, other
scenarios are possible, especially on physically protected networks.
(1) A read-only directory, containing no sensitive data, accessible
to "anyone", and TCP connection hijacking or IP spoofing is not
a problem. This directory requires no security functions except
administrative service limits.
(2) A read-only directory containing no sensitive data; read access
is granted based on identity. TCP connection hijacking is not
currently a problem. This scenario requires a secure
authentication function.
(3) A read-only directory containing no sensitive data; and the
client needs to ensure that the directory data is authenticated
by the server and not modified while being returned from the
server.
(4) A read-write directory, containing no sensitive data; read
access is available to "anyone", update access to properly
authorized persons. TCP connection hijacking is not currently a
problem. This scenario requires a secure authentication
function.
(5) A directory containing sensitive data. This scenario requires
session confidentiality protection AND secure authentication.
Appendix B. Authentication and Authorization: Definitions and Concepts
This appendix defines basic terms, concepts, and interrelationships
regarding authentication, authorization, credentials, and identity.
These concepts are used in describing how various security
approaches are utilized in client authentication and authorization.
B.1. Access Control Policy
An access control policy is a set of rules defining the protection
of resources, generally in terms of the capabilities of persons or
other entities accessing those resources. A common expression of an
access control policy is an access control list. Security objects
and mechanisms, such as those described here, enable the expression
of access control policies and their enforcement. Access control
policies are typically expressed in terms of access control
attributes as described below.
B.2. Access Control Factors
A request, when it is being processed by a server, may be associated
with a wide variety of security-related factors (section 4.2 of
[LDAPv3]). The server uses these factors to determine whether and
how to process the request. These are called access control factors
(ACFs). They might include source IP address, encryption strength,
Authentication Methods for LDAPv3 July 19, 2001
the type of operation being requested, time of day, etc. Some
factors may be specific to the request itself, others may be
associated with the connection via which the request is transmitted,
others (e.g. time of day) may be "environmental".
Access control policies are expressed in terms of access control
factors. E.g., a request having ACFs i,j,k can perform operation Y
on resource Z. The set of ACFs that a server makes available for
such expressions is implementation-specific.
B.3. Authentication, Credentials, Identity
Authentication credentials are the evidence supplied by one party to
another, asserting the identity of the supplying party (e.g. a user)
who is attempting to establish an association with the other party
(typically a server). Authentication is the process of generating,
transmitting, and verifying these credentials and thus the identity
they assert. An authentication identity is the name presented in a
credential.
There are many forms of authentication credentials -- the form used
depends upon the particular authentication mechanism negotiated by
the parties. For example: X.509 certificates, Kerberos tickets,
simple identity and password pairs. Note that an authentication
mechanism may constrain the form of authentication identities used
with it.
B.4. Authorization Identity
An authorization identity is one kind of access control factor. It
is the name of the user or other entity that requests that
operations be performed. Access control policies are often expressed
in terms of authorization identities; e.g., entity X can perform
operation Y on resource Z.
The authorization identity bound to an association is often exactly
the same as the authentication identity presented by the client, but
it may be different. SASL allows clients to specify an authorization
identity distinct from the authentication identity asserted by the
client's credentials. This permits agents such as proxy servers to
authenticate using their own credentials, yet request the access
privileges of the identity for which they are proxying [SASL]. Also,
the form of authentication identity supplied by a service like TLS
may not correspond to the authorization identities used to express a
server's access control policy, requiring a server-specific mapping
to be done. The method by which a server composes and validates an
authorization identity from the authentication credentials supplied
by a client is implementation-specific.
Appendix C. RFC 2829 Change History
This appendix lists the changes made to the text of RFC 2829 in This appendix lists the changes made to the text of RFC 2829 in
preparing this document. preparing this document.
A.0. General Editorial Changes Authentication Methods for LDAPv3 July 19, 2001
Changed title: LDAP to LDAPv3 C.0. General Editorial Changes
Version -00
Changed other instances of the term LDAP to LDAPv3 where v3 of the - Changed other instances of the term LDAP to LDAPv3 where v3 of
protocol is implied. Also made all references to LDAPv3 use the same the protocol is implied. Also made all references to LDAPv3 use
wording. the same wording.
Made a small number of grammatical changes to improve readability.
Made capitalization in section headings consistent. - Miscellaneous grammatical changes to improve readability.
A.1. Changes to Section 1 - Made capitalization in section headings consistent.
None Version -01
A.2. Changes to Section 2 - Changed title to reflect inclusion of material from RFC 2830 and
2251.
None C.1. Changes to Section 1
A.3. Changes to Section 3 Version -01
None - Moved conventions used in document to a separate section.
A.4 Changes to Section 4 C.2. Changes to Section 2
Harrison Expires August 20, 2001 [Page 14] Version -01
Authentication Methods for LDAPv3 February 20, 2001
Changed "Distinguished Name" to "LDAP distinguished name". - Moved section to an appendix.
A.5. Changes to Section 5 C.3. Changes to Section 3
Added the following sentence: "Servers SHOULD NOT allow clients with Version -01
anonymous authentication to modify directory entries or access
sensitive information in directory entries."
A.5.1. Changes to Section 5.1 - Moved section to an appendix.
Replaced the text describing the procedure for performing an C.4 Changes to Section 4
Version -00
- Changed "Distinguished Name" to "LDAP distinguished name".
C.5. Changes to Section 5
Version -00
- Added the following sentence: "Servers SHOULD NOT allow clients
with anonymous authentication to modify directory entries or
access sensitive information in directory entries."
C.5.1. Changes to Section 5.1
Version -00
Authentication Methods for LDAPv3 July 19, 2001
- Replaced the text describing the procedure for performing an
anonymous bind (protocol) with a reference to section 4.2 of RFC anonymous bind (protocol) with a reference to section 4.2 of RFC
2251 (the protocol spec). 2251 (the protocol spec).
A.6. Changes to Section 6. Version -01
- Brought text describing procedure for performing an anonymous
bind from section 4.2 of RFC 2251 bis. This text will be
removed from the draft standard version of that document.
C.6. Changes to Section 6.
Version -00
Reorganized text in section 6.1 as follows: Reorganized text in section 6.1 as follows:
1. Added a new section (6.1) titled "Simple Authentication" and 1. Added a new section (6.1) titled "Simple Authentication" and
moved one of two introductory paragraphs for section 6 into section moved one of two introductory paragraphs for section 6 into
6.1. Added sentences to the paragraph indicating: section 6.1. Added sentences to the paragraph indicating:
a. simple authentication is not suitable for environments where a. simple authentication is not suitable for environments where
confidentiality is not available. confidentiality is not available.
b. LDAP implementations SHOULD NOT support simple b. LDAP implementations SHOULD NOT support simple
authentication unless confidentiality and data integrity authentication unless confidentiality and data integrity
mechanisms are in force. mechanisms are in force.
2. Moved first paragraph of section 6 (beginning with "LDAP 2. Moved first paragraph of section 6 (beginning with "LDAP
implementations MUST support authentication with a passwordą") to implementations MUST support authentication with a passwordą")
section on Digest Authentication (Now section 6.2). to section on Digest Authentication (Now section 6.2).
A.6.1. Changes to Section 6.1.
Renamed section to 6.2 C.6.1. Changes to Section 6.1.
Added sentence from original section 6 indicating that the DIGEST- Version -00 Renamed section to 6.2
MD5 SASL mechanism is required for all conforming LDAPv3
- Added sentence from original section 6 indicating that the
DIGEST-MD5 SASL mechanism is required for all conforming LDAPv3
implementations implementations
A.6.2 Changes to Section 6.2 C.6.2 Changes to Section 6.2
Renamed section to 6.3 Version -00
Reworded first paragraph to remove reference to user and the - Renamed section to 6.3
- Reworded first paragraph to remove reference to user and the
userPassword password attribute Made the first paragraph more userPassword password attribute Made the first paragraph more
general by simply saying that if a directory supports simple general by simply saying that if a directory supports simple
authentication that the simple bind operation MAY performed authentication that the simple bind operation MAY performed
following negotiation of a TLS ciphersuite that supports following negotiation of a TLS ciphersuite that supports
confidentiality. confidentiality.
Harrison Expires August 20, 2001 [Page 15] Authentication Methods for LDAPv3 July 19, 2001
Authentication Methods for LDAPv3 February 20, 2001
Replaced "the name of the user's entry" with "a DN" since not all - Replaced "the name of the user's entry" with "a DN" since not
bind operations are performed on behalf of a "user." all bind operations are performed on behalf of a "user."
Added Section 6.3.1 heading just prior to paragraph 5. - Added Section 6.3.1 heading just prior to paragraph 5.
Paragraph 5: replaced "The server" with "DSAs that map the DN sent - Paragraph 5: replaced "The server" with "DSAs that map the DN
in the bind request to a directory entry with a userPassword sent in the bind request to a directory entry with a
attribute." userPassword attribute."
A.6.3. Changes to section 6.3. C.6.3. Changes to section 6.3.
Renamed to section 6.4. Version -00
A.7. Changes to section 7. - Renamed to section 6.4.
C.7. Changes to section 7.
none none
A.7.1. Changes to section 7.1. C.7.1. Changes to section 7.1.
Clarified the entity issuing a certificate by moving the phrase "to Version -00
have issued the certificate" immediately after "Certification
Authority."
A.8. Changes to section 8. - Clarified the entity issuing a certificate by moving the phrase
"to have issued the certificate" immediately after
"Certification Authority."
Removed the first paragraph because simple authentication is covered C.8. Changes to section 8.
explicitly in section 6.
Added section 8.1. heading just prior to second paragraph. Version -00
Added section 8.2. heading just prior to third paragraph. - Removed the first paragraph because simple authentication is
covered explicitly in section 6.
Added section 8.3. heading just prior to fourth paragraph. - Added section 8.1. heading just prior to second paragraph.
A.9. Changes to section 9. - Added section 8.2. heading just prior to third paragraph.
Paragraph 2: changed "EXTERNAL mechanism" to "EXTERNAL SASL - Added section 8.3. heading just prior to fourth paragraph.
Version -01
- Moved entire section 8 of RFC 2829 into section 3.4 (Using SASL
for Other Security Services) to bring material on SASL
mechanisms together into one location.
C.9. Changes to section 9.
Version -00
- Paragraph 2: changed "EXTERNAL mechanism" to "EXTERNAL SASL
mechanism." mechanism."
Authentication Methods for LDAPv3 July 19, 2001
Added section 9.1. heading. - Added section 9.1. heading.
Modified a comment in the ABNF from "unspecified userid" to - Modified a comment in the ABNF from "unspecified userid" to
"unspecified authz id". "unspecified authz id".
Deleted sentence, "A utf8string is defined to be the UTF-8 encoding - Deleted sentence, "A utf8string is defined to be the UTF-8
of one or more ISO 10646 characters," because it is redundant. encoding of one or more ISO 10646 characters," because it is
redundant.
Added section 9.1.1. heading. - Added section 9.1.1. heading.
Added section 9.1.2. heading. - Added section 9.1.2. heading.
A.10. Changes to Section 10. Version -01
Harrison Expires August 20, 2001 [Page 16] - Moved entire section 9 to become section 3.5 so that it would be
Authentication Methods for LDAPv3 February 20, 2001 with other SASL material.
Updated reference to cracking from a week of CPU time in 1997 to be C.10. Changes to Section 10.
a day of CPU time in 2000.
Added text: "These ciphersuites are NOT RECOMMENDED for use... and Version -00
server implementers SHOULD" to sentence just prior the second list
of ciphersuites.
Added text: "and MAY support other ciphersuites offering equivalent - Updated reference to cracking from a week of CPU time in 1997 to
or better protection," to the last paragraph of the section. be a day of CPU time in 2000.
A.11. Changes to Section 11. - Added text: "These ciphersuites are NOT RECOMMENDED for use...
and server implementers SHOULD" to sentence just prior the
second list of ciphersuites.
None - Added text: "and MAY support other ciphersuites offering
equivalent or better protection," to the last paragraph of the
section.
A.12. Changes to Section 12. C.11. Changes to Section 11.
Inserted new section 12 that specifies when SASL protections begin Version -01
following SASL negotiation, etc.. The original section 12 is
renumbered to become section 13.
A.13 Changes to Section 13 (original section 12). - Moved to section 3.6 to be with other SASL material.
C.12. Changes to Section 12.
Version -00
- Inserted new section 12 that specifies when SASL protections
begin following SASL negotiation, etc. The original section 12
is renumbered to become section 13.
Version -01
- Moved to section 3.7 to be with other SASL material.
C.13 Changes to Section 13 (original section 12).
Authentication Methods for LDAPv3 July 19, 2001
None None
Appendix B Issues to be Resolved Appendix D. RFC 2830 Change History
This appendix lists the changes made to the text of RFC 2830 in
preparing this document.
D.0. General Editorial Changes
- Material showing the PDUs for the Start TLS response was broken
out into a new section.
- The wording of the definition of the Start TLS request and Start
TLS response was changed to make them parallel. NO changes were
made to the ASN.1 definition or the associated values of the
parameters.
- A separate section heading for graceful TLS closure was added
for parallelism with section on abrupt TLS closure.
Appendix E. RFC 2251 Change History
This appendix lists the changes made to the text of RFC 2251 in
preparing this document.
E.0. General Editorial Changes
- All material from section 4.2 of RFC 2251 was moved into this
document.
- A new section was created for the Bind Request
- Section 4.2.1 of RFC 2251 (Sequencing Bind Request) was moved
after the section on the Bind Response for parallelism with the
presentation of the Start TLS operations. The section was also
subdivided to explicitly call out the various effects being
described within it.
- All SASL profile information from RFC 2829 was brought within
the discussion of the Bind operation (primarily sections 4.4 -
4.7).
Appendix F. Issues to be Resolved
This appendix lists open questions and issues that need to be This appendix lists open questions and issues that need to be
resolved before work on this document is deemed complete. resolved before work on this document is deemed complete.
B.1. F.1.
Section 1 lists 6 security mechanisms that can be used by LADP Section 1 lists 6 security mechanisms that can be used by LDAP
servers. I'm not sure what mechanism 5, "Resource limitation by servers. I'm not sure what mechanism 5, "Resource limitation by
means of administrative limits on service controls" means. means of administrative limits on service controls" means.
B.2. Authentication Methods for LDAPv3 July 19, 2001
F.2.
Section 2 paragraph 1 defines the term, "sensitive." Do we want to Section 2 paragraph 1 defines the term, "sensitive." Do we want to
bring this term and other security-related terms in alignment with bring this term and other security-related terms in alignment with
usage with the IETF security glossary (RFC 2828)? usage with the IETF security glossary (RFC 2828)?
B.3. F.3.
Section 2, deployment scenario 2: What is meant by the term "secure Section 2, deployment scenario 2: What is meant by the term "secure
authentication function?" authentication function?"
B.4. F.4.
Section 3, deployment scenario 3: What is meant by the phrase, Section 3, deployment scenario 3: What is meant by the phrase,
"directory data is authenticated by the server?" "directory data is authenticated by the server?"
B.5. F.5.
Harrison Expires August 20, 2001 [Page 17]
Authentication Methods for LDAPv3 February 20, 2001
Section 4 paragraph 3: What is meatn by the phrase, "this means that Section 4 paragraph 3: What is meant by the phrase, "this means that
either this data is useless for faking authentication (like the Unix either this data is useless for faking authentication (like the Unix
"/etc/passwd" file format used to be)?" "/etc/passwd" file format used to be)?"
B.6. F.6.
Section 4 paragraph 7 begins: "For a directory needing session Section 4 paragraph 7 begins: "For a directory needing session
protection..." Is this referring to data confidentiality or data protection..." Is this referring to data confidentiality or data
integrity or both? integrity or both?
B.7. F.7.
Section 4 paragraph 8 indicates that "information about the server Section 4 paragraph 8 indicates that "information about the server
fetched fetched prior to the TLS negotiation" must be discarded. Do fetched fetched prior to the TLS negotiation" must be discarded. Do
we want to explicitly state that this applies to information fetched we want to explicitly state that this applies to information fetched
prior to the *completion* of the TLS negotiation or is this going prior to the *completion* of the TLS negotiation or is this going
too far? too far?
B.8. F.8.
Section 4 paragraph 9 indicates that clients SHOULD check the Section 4 paragraph 9 indicates that clients SHOULD check the
supportedSASLMechanisms list both before and after a SASL security supportedSASLMechanisms list both before and after a SASL security
layer is negotiated to ensure that they are using the best available layer is negotiated to ensure that they are using the best available
security mechanism supported mutually by the client and server. A security mechanism supported mutually by the client and server. A
note at the end of the paragraph indicates that this is a SHOULD note at the end of the paragraph indicates that this is a SHOULD
since there are environments where the client might get a list of since there are environments where the client might get a list of
supported SASL mechanisms from a different trusted source. supported SASL mechanisms from a different trusted source.
I wonder if the intent of this could be restated more plainly using I wonder if the intent of this could be restated more plainly using
one of these two approaches (I've paraphrased for the sake of one of these two approaches (I've paraphrased for the sake of
brevity): brevity):
Approach 1: Clients SHOULD check the supportedSASLMechanisms list Approach 1: Clients SHOULD check the supportedSASLMechanisms list
both before and after SASL negotiation or clients SHOULD use a both before and after SASL negotiation or clients SHOULD use a
Authentication Methods for LDAPv3 July 19, 2001
different trusted source to determine available supported SASL different trusted source to determine available supported SASL
mechanisms. mechanisms.
Approach 2: Clients MUST check the supportedSASLMechanisms list both Approach 2: Clients MUST check the supportedSASLMechanisms list both
before and after SASL negotiation UNLESS they use a different before and after SASL negotiation UNLESS they use a different
trusted source to determine available supported SASL mechanisms. trusted source to determine available supported SASL mechanisms.
B.9. F.9.
Section 6.3.1 states: "DSAs that map the DN sent in the bind request Section 6.3.1 states: "DSAs that map the DN sent in the bind request
to a directory entry with a userPassword attribute will... compare to a directory entry with a userPassword attribute will... compare
[each value in the named user's entry]... with the presented [each value in the named user's entry]... with the presented
password." This implies that this this applies only to user entries password." This implies that this this applies only to user entries
with userPassword attributes. What about other types of entries with userPassword attributes. What about other types of entries
that might allow passwords and might store in the password that might allow passwords and might store in the password
information in other attributes? Do we want to make this text more information in other attributes? Do we want to make this text more
general? general?
Harrison Expires August 20, 2001 [Page 18] F.10 userPassword and simple bind
We need to be sure that we don't require userPassword to be the only
attribute used for authenticating via simple bind. (See 2251 sec 4.2
and authmeth 6.3.1. Work with Jim Sermersheim on resolution to this.
On publication state something like: "This is the specific
implementation of what we discussed in our general reorg
conversation on the list." (Source: Kurt Zeilenga)
F.11 Meaning of LDAP Association
The original RFC 2830 uses the term "LDAP association" in describing
a connection between an LDAP client and server regardless of the
state of TLS on that connection. This term needs to be defined or
possibly changed.
F.12. Is DIGEST-MD5 mandatory for all implementations?
Reading 2829bis I think DIGEST-MD5 is mandatory ONLY IF your server
supports password based authentication...but the following makes it
sound mandatory to provide BOTH password authentication AND DIGEST-
MD5:
"6.2. Digest authentication
LDAP implementations MUST support authentication with a password
using the DIGEST-MD5 SASL mechanism for password protection, as
defined in section 6.1."
The thing is for acl it would be nice (though not critical) to be
able to default the required authentication level for a subject to a
single "fairly secure" mechanism--if there is no such mandatory
authentication scheme then you cannot do that. (Source: Rob Byrne)
Authentication Methods for LDAPv3 July 19, 2001
F.13. Ordering of authentication levels requested
Again on the subject of authentication level, is it possible to
define an ordering on authentication levels which defines their
relative "strengths" ? This would be useful in acl as you could say
things like"a given aci grants access to a given subject at this
authentication level AND ABOVE". David Chadwick raised this before
in the context of denying access to a subject at a given
authentication level, in which case he wanted to express "deny
access to this subject at this authentication level AND TO ALL
IDENTITIES AUTHENTICATED BELOW THAT LEVEL". (Source: Rob Byrne)
F.14. Document vulnerabilities of various mechanisms
While I'm here...in 2829, I think it would be good to have some
comments or explicit reference to a place where the security
properties of the particular mandatory authentication schemes are
outlined. When I say "security properties" I mean stuff like "This
scheme is vulnerable to such and such attacks, is only safe if the
key size is > 50, this hash is widely considered the best, etc...".
I think an LDAP implementor is likely to be interested in that
information, without having to wade through the security RFCs.
(Source: Rob Byrne)
F.15. Include a StartTLS state transition table
The pictoral representation it is nominally based on is here (URL
possibly folded):
http://www.stanford.edu/~hodges/doc/LDAPAssociationStateDiagram-
1999-12-14.html
(Source: Jeff Hodges)
F.16. Empty sasl credentials question
I spent some more time looking microscopically at ldap-auth-methods
and ldap-ext-tls drafts. The drafts say that the credential must
have the form dn:xxx or u:xxx or be absent, and although they don't
say what to do in the case of an empty octet string I would say that
we could send protocolError (claim it is a bad PDU).
There is still the question of what to do if the credential is 'dn:'
(or 'u:') followed by the empty string. (Source: ariel@columbia.edu
via Jeff Hodges)
F.17. Hostname check from MUST to SHOULD?
I am uneasy about the hostname check. My experience from PKI with
HTTP probably is a contributing factor; we have people using the
short hostname to get to a server which naturally has the FQDN in
the certificate, no end of problems. I have a certificate on my
laptop which has the FQDN for the casse when the system is on our
Authentication Methods for LDAPv3 July 19, 2001
Columbia network with a fixed IP; when I dial in however, I have
some horrible dialup name, and using the local https server becomes
annoying. Issuing a certificate in the name 'localhost' is not a
solution! Wildcard match does not solve this problem. For these
reasons I am inclined to argue for 'SHOULD' instead of
'MUST' in paragraph...
Also, The hostname check against the name in the certificate is a
very weak means of preventing man-in-the-middle attacks; the proper
solution is not here yet (SecureDNS or some equivalent). Faking out
DNS is not so hard, and we see this sort of thing in the press on a
pretty regular basis, where site A hijacks the DNS server for site B
and gets all their requests. Some mention of this should be made in
the draft. (Source: ariel@columbia.edu via Jeff Hodges)
F.18. Must SASL DN exist in the directory?
If the 'dn:' form of sasl creds is used, is it the intention of the
draft(ers) that this DN must exist in the directory and the client
will have the privileges associated with that entry, or can the
server map the sasl DN to perhaps some other DN in the directory,
in an implementation-dependent fashion?
We already know that if *no* sasl credentials are presented, the DN
or altname in the client certificate may be mapped to a DN in an
implementation-dependent fashion, or indeed to something not in the
directory at all. (Right?) (Source: ariel@columbia.edu via Jeff
Hodges)
 End of changes. 

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