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INTERNET-DRAFT Editor: R. Harrison
draft-ietf-ldapbis-authmeth-13.txt Novell, Inc.
Obsoletes: 2829, 2830 October, 2004
Intended Category: Draft Standard
LDAP: Authentication Methods
and
Connection Level Security Mechanisms
Status of this Memo
By submitting this Internet-Draft, I accept the provisions of
Section 4 of RFC 3667. By submitting this Internet-Draft, I certify
that any applicable patent or other IPR claims of which I am aware
have been disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
This document is intended to be, after appropriate review and
revision, submitted to the RFC Editor as a Standard Track document.
Distribution of this memo is unlimited. Technical discussion of
this document will take place on the IETF LDAP Revision Working
Group mailing list <ietf-ldapbis@OpenLDAP.org>. Please send
editorial comments directly to the author
<roger_harrison@novell.com>.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
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This document describes authentication methods and connection level
security mechanisms of the Lightweight Directory Access Protocol
(LDAP).
This document details establishment of TLS (Transport Layer
Security) using the StartTLS operation.
This document details the simple Bind authentication method
including anonymous, unauthenticated, and plain-text password
mechanisms and the SASL (Simple Authentication and Security Layer)
Bind authentication method including DIGEST-MD5 and EXTERNAL
mechanisms.
This document discusses various authentication and authorization
states through which a connection to an LDAP server may pass and the
actions that trigger these state changes.
Table of Contents
1. Introduction.....................................................3
1.1. Relationship to Other Documents................................5
1.2. Conventions Used in this Document..............................6
1.2.1. Glossary of Terms............................................6
1.2.2. Security Terms and Concepts..................................6
1.2.3. Keywords.....................................................6
2. Implementation Requirements......................................6
3. StartTLS Operation...............................................7
3.1. Sequencing of the StartTLS Operation...........................7
3.1.1. StartTLS Request ............................................7
3.1.2. StartTLS Response............................................8
3.1.3. TLS Version Negotiation......................................8
3.1.4. Client Certificate...........................................8
3.1.5. Discovery of Resultant Security Level........................9
3.1.6. Server Identity Check........................................9
3.1.7. Refresh of Server Capabilities Information..................10
3.2. Effects of TLS on a Client's Authorization Identity...........10
3.2.1. TLS Connection Establishment Effects........................10
3.2.2. Client Assertion of Authorization Identity..................10
3.2.3. TLS Connection Closure Effects..............................10
3.3. TLS Ciphersuites..............................................11
3.3.1. TLS Ciphersuites Recommendations............................11
4. Associations....................................................12
4.1. Anonymous Association on Unbound Connections..................12
4.2. Anonymous Association After Failed Bind.......................12
4.3. Invalidated Associations......................................12
5. Bind Operation..................................................13
5.1. Simple Authentication Choice..................................13
5.2. SASL Authentication Choice....................................13
6. Anonymous Authentication Mechanism of Simple Bind...............13
7. Unauthenticated Authentication Mechanism of Simple Bind.........13
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8. Simple Authentication Mechanism of Simple Bind .................14
9. SASL Protocol Profile...........................................15
9.1. SASL Service Name for LDAP....................................15
9.2. SASL Authentication Initiation and Protocol Exchange..........15
9.3. Octet Where Negotiated Security Mechanisms Take Effect........16
9.4. Determination of Supported SASL Mechanisms....................16
9.5. Rules for Using SASL Security Layers..........................17
9.6 Support for Multiple Authentications...........................17
10. SASL EXTERNAL Authentication Mechanism.........................17
10.1. Implicit Assertion...........................................17
10.2. Explicit Assertion...........................................18
10.3. SASL Authorization Identity..................................18
10.4. SASL Authorization Identity Syntax...........................18
11. SASL DIGEST-MD5 Authentication Mechanism.......................19
12. Security Considerations........................................19
12.1. General LDAP Security Considerations.........................19
12.1.1. Password-related Security Considerations...................20
12.2. StartTLS Security Considerations.............................20
12.3. Unauthenticated Mechanism Security Considerations............21
12.4. Simple Mechanism Security Considerations.....................21
12.5. SASL DIGEST-MD5 Mechanism Security Considerations............21
12.6. Related Security Considerations..............................22
13. IANA Considerations............................................22
Acknowledgments....................................................22
Normative References...............................................22
Informative References.............................................23
Author's Address...................................................24
Appendix A. Association State Transition Tables....................24
A.1. Association States............................................24
A.2. Actions that Affect Association State.........................25
A.3. Decisions Used in Making Association State Changes............25
A.4. Association State Transition Table............................25
Appendix B. Authentication and Authorization Concepts..............26
B.1. Access Control Policy.........................................26
B.2. Access Control Factors........................................26
B.3. Authentication, Credentials, Identity.........................27
B.4. Authorization Identity........................................27
Appendix C. RFC 2829 Change History................................27
Appendix D. RFC 2830 Change History................................31
Appendix E. RFC 2251 Change History................................32
Appendix F. Change History to Combined Document....................32
Added implementation requirement that server implementations ......45
Intellectual Property Rights.......................................45
1. Introduction
The Lightweight Directory Access Protocol (LDAP) [Roadmap] is a
powerful protocol for accessing directories. It offers means of
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searching, retrieving 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
implementations that claim LDAP conformance.
Basic threats to an LDAP directory service include:
(1) Unauthorized access to directory data via data-retrieval
operations,
(2) Unauthorized access to directory data by monitoring others'
access,
(3) Unauthorized access to reusable client authentication
information by monitoring others' access,
(4) Unauthorized modification of directory data,
(5) Unauthorized modification of configuration information,
(6) Denial of Service: Use of resources (commonly in excess) in a
manner intended to deny service to others,
(7) Spoofing: Tricking a user or client into believing that
information came from the directory when in fact it did not,
either by modifying data in transit or misdirecting the client's
connection. Tricking a user or client into sending privileged
information to a hostile entity that appears to be the directory
server but is not. Tricking a directory server into believing
that information came from a particular client when in fact it
came from a hostile entity, and
(8) Hijacking: An attacker seizes control of an established protocol
session.
Threats (1), (4), (5), (6), (7) are (8) are active attacks. Threats
(2) and (3) are passive attacks.
Threats (1), (4), (5) and (6) are due to hostile clients. Threats
(2), (3), (7) and (8) are due to hostile agents on the path between
client and server or hostile agents posing as a server, e.g. IP
spoofing.
LDAP offers the following security mechanisms:
(1) Authentication by means of the Bind operation. The Bind
operation provides a simple method which supports anonymous,
unauthenticated, and authenticated with password mechanisms, and
the Secure Authentication and Security Layer (SASL) method which
supports a wide variety of authentication mechanisms,
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(2) Mechanisms to support vendor-specific access control facilities
(LDAP does not offer a standard access control facility)
(3) Data integrity protection by means of security layers in TLS or
SASL mechanisms,
(4) Data confidentiality protection by means of security layers in
TLS or SASL mechanisms,
(5) Server resource usage limitation by means of administrative
limits configured on the server, and
(6) Server authentication by means of the TLS protocol or SASL
mechanism.
LDAP may also be protected by means outside the LDAP protocol, e.g.
with IP-level security [RFC2401].
At the moment, imposition of access controls is done by means
outside the scope of LDAP.
Considering the above requirements, experience has shown that simply
allowing implementations to pick and choose among the possible
alternatives is not a strategy that leads to interoperability. In
the absence of mandates, clients will continue to be written that do
not support any security function supported by the server, or worse,
they will support only clear text passwords that provide inadequate
security for most circumstances.
It is desirable to allow clients to authenticate using a variety of
mechanisms including mechanisms where identities are represented as
distinguished names [X.501] [Models] in string form [LDAPDN] or are
used in different systems (e.g. user name in string form). Because
some authentication mechanisms transmit credentials in plain text
form and/or do not provide data security services, it is necessary
to ensure secure interoperability by identifying a mandatory-to-
implement mechanism for establishing transport-layer security
services.
The set of security mechanisms provided in LDAP and described in
this document is intended to meet the security needs for a wide
range of deployment scenarios and still provide a high degree of
interoperability among various LDAP implementations and deployments.
Appendix B contains example deployment scenarios that list the
mechanisms that might be used to achieve a reasonable level of
security in various circumstances.
1.1. Relationship to Other Documents
This document is an integral part of the LDAP Technical
Specification [Roadmap].
This document obsoletes RFC 2829.
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Sections 2 and 4 of RFC 2830 are obsoleted by [Protocol]. The
remainder of RFC 2830 is obsoleted by this document.
1.2. Conventions Used in this Document
1.2.1. Glossary of Terms
The following terms are used in this document. To aid the reader,
these terms are defined here.
- "user" represents any human or application entity which is
accessing the directory using a directory client. A directory
client (or client) is also known as a directory user agent (DUA).
- "connection" refers to the underlying transport protocol
connection used to carry the protocol exchange.
- "TLS connection" refers to an LDAP connection with TLS
protection [TLS].
- "association" refers to the association that exists between the
connection to its current authorization state. As a shorthand,
an association with an authorization state of <state> can be
referred to as a "<state> association", e.g. an association with
an anonymous authorization state is an anonymous association.
1.2.2. Security Terms and Concepts
In general, security terms in this document are used consistently
with the definitions provided in [RFC2828]. In addition, several
terms and concepts relating to security, authentication, and
authorization are presented in Appendix C of this document. While
the formal 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 C before reading the remainder of this document.
1.2.3. Keywords
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 [RFC2119].
2. Implementation Requirements
LDAP server implementations MUST support the anonymous
authentication mechanism of simple bind (as discussed in Section 6).
LDAP implementations that support any authentication mechanism other
than the anonymous authentication mechanism of simple bind MUST
support the DIGEST-MD5 [DIGEST-MD5] mechanism of SASL bind (as
detailed in section 11). DIGEST-MD5 is a reasonably strong
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authentication mechanism that provides (mandatory-to-implement) data
security (data integrity and data confidentiality) services.
LDAP impementations SHOULD support the simple (DN and password)
authentication mechanism of simple bind (as detailed in section 8).
Implementations that support this mechanism MUST be capable of
protecting it by establishment of TLS (as discussed in section 3) or
other suitable suitable data confidentiality and data integrity
protection (e.g. IPSec).
Implementations MAY support additional authentication mechanisms.
Some of these mechanisms are discussed below.
LDAP server implementations SHOULD support client assertion of
authorization identity via the SASL EXTERNAL mechanism (sections
3.2.2 and 9).
LDAP server implementations SHOULD support the StartTLS operation,
and server implementations that do support the StartTLS operation
MUST support the TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA ciphersuite.
3. StartTLS Operation
The Start Transport Layer Security (StartTLS) operation defined in
section 4.14 of [Protocol] provides the ability to establish TLS
[TLS] on an LDAP connection.
The goals of using the TLS [TLS] protocol with LDAP are to ensure
data confidentiality and integrity, and to optionally provide for
authentication. TLS expressly provides these capabilities, although
the authentication services of TLS are available to LDAP only in
combination with the SASL EXTERNAL authentication method (see
section 10), and then only if the SASL EXTERNAL implementation
chooses to make use of the TLS credentials.
3.1. Sequencing of the StartTLS Operation
This section describes the overall procedures clients and servers
must follow for TLS establishment. These procedures take into
consideration various aspects of the association including discovery
of resultant security level and assertion of the client's
authorization identity.
3.1.1. StartTLS Request
A client may send the StartTLS extended request at any time after
establishing an LDAP connection, except:
- when TLS is currently established on the connection,
- when a multi-stage SASL negotiation is in progress on the
connection, or
- when it has not yet received responses for all operation
requests previously issued on the connection.
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As described in [Protocol] Section 4.14.2.2, a (detected) violation
of any of these requirements results in a return of the
operationsError resultCode.
Client implementers should ensure that they strictly follow these
operation sequencing requirements to prevent interoperability
issues. Operational experience has shown that violating these
requirements causes interoperability issues because there are race
conditions that prevent servers from detecting some violations of
these requirements due to server hardware speed, network latencies,
etc.
There is no general requirement that the client have or have not
already performed a Bind operation (section 4) before sending a
StartTLS operation request.
If the client did not establish a TLS connection before sending a
request and the server requires the client to establish a TLS
connection before performing that request, the server MUST reject
that request by sending a resultCode of confidentialityRequired.
3.1.2. StartTLS Response
The server will return an extended response with the resultCode of
success if it is willing and able to negotiate TLS.
It will return a resultCode other than success (documented in
[Protocol] section 4.13.2.2) if it is unwilling or unable to do so.
The state of the association is unaffected if a non-success
resultCode is returned.
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.
3.1.3. TLS Version Negotiation
Negotiating the version of TLS to be used is a part of the TLS
Handshake Protocol [TLS]. Please refer to that document for details.
3.1.4. Client Certificate
If an LDAP server requests a client to provide its certificate
during TLS negotiation and the client does not present a suitable
certificate (e.g. one that can be validated), the server may use a
local security policy to determine whether to successfully complete
TLS negotiation.
If the client provides a certificate that can be validated,
information in the certificate may be used by the server in
establishing the client's authorization identity by use of the SASL
EXTERNAL mechanism as discussed in Section 9.
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3.1.5. Discovery of Resultant Security Level
After a TLS connection is established on an LDAP connection, both
parties are to individually decide whether or not to continue based
on the security level achieved. The procedure for ascertaining the
TLS connection's security level is implementation dependent.
If the client or server decides that the security level is not high
enough for it to continue, it SHOULD gracefully close the TLS
connection immediately after the TLS negotiation has completed (see
[Protocol] section 4.13.3.1 and section 3.2.3 below). The client
may then close the connection, attempt to StartTLS again, send an
unbind request, or send any other LDAP request.
3.1.6. 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 name provided by the user (or
other trusted entity) as the value to compare against the server
name as expressed in the server's certificate. A hostname
derived from user input is to be considered provided by the user
only if derived in a secure fashion (e.g., DNSSEC).
- If a subjectAltName extension of type dNSName is present in the
certificate, it SHOULD be used as the source of the server's
identity.
- The string values to be compared MUST be prepared according to
the rules described in [Matching].
- The "*" wildcard character is allowed. If present, it applies
only to the left-most name component.
For example, *.bar.com would match a.bar.com and b.bar.com, but
it would not match a.x.bar.com nor would it match 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.
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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 in making
this determination.
3.1.7. Refresh of Server Capabilities Information
Upon TLS session establishment, the client SHOULD discard or refresh
all information about the server it obtained prior to the initiation
of the TLS negotiation and not obtained through secure mechanisms.
This protects against man-in-the-middle attacks that may have
altered any server capabilities information retrieved prior to TLS
establishment.
The server may advertise different capabilities after TLS
establishment. In particular, the value of supportedSASLMechanisms
may be different after TLS has been negotiated (specifically, the
EXTERNAL and PLAIN [PLAIN] mechanisms are likely to be listed only
after a TLS negotiation has been performed).
3.2. 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 connection.
The default effects are described first, and next the facilities for
client assertion of authorization identity are discussed including
error conditions. Finally, the effects of closing the TLS connection
are described.
Authorization identities and related concepts are described in
Appendix B.
3.2.1. TLS Connection Establishment Effects
The decision to keep or invalidate the established state of the
association (section 4.3) after TLS connection establishment is a
matter of local server policy.
3.2.2. Client Assertion of Authorization Identity
After successfully establishing a TLS session, a client may request
that its certificate exchanged during the TLS establishment be
utilized to determine the authorization identity of the association.
The client accomplishes this via an LDAP Bind request specifying a
SASL mechanism of EXTERNAL [SASL] (section 10).
3.2.3. TLS Connection Closure Effects
The decision to keep or invalidate the established state of the
association after TLS closure is a matter of local server policy.
3.3. TLS Ciphersuites
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Several issues should be considered when selecting TLS ciphersuites
that are appropriate for use in a given circumstance. These issues
include the following:
- The ciphersuite's ability to provide adequate confidentiality
protection for passwords and other data sent over the LDAP
connection. Client and server implementers should recognize that
some TLS ciphersuites provide no confidentiality protection
while other ciphersuites that do provide confidentiality
protection may be vulnerable to being cracked using brute force
methods, especially in light of ever-increasing CPU speeds that
reduce the time needed to successfully mount such attacks.
Client and server implementers should carefully consider the
value of the password or data being protected versus the level
of confidentially protection provided by the ciphersuite to
ensure that the level of protection afforded by the ciphersuite
is appropriate.
- The ciphersuite's vulnerability (or lack thereof) to man-in-the-
middle attacks. Ciphersuites vulnerable to man-in-the-middle
attacks SHOULD NOT be used to protect passwords or sensitive
data, unless the network configuration is such that the danger
of a man-in-the-middle attack is tolerable.
3.3.1. TLS Ciphersuites Recommendations
[[TODO: Kurt will have someone from security to look at this and
will propose how to handle discussion of specific TLS ciphersuites
in this draft.]]
As of the writing of this document, the following recommendations
regarding TLS ciphersuites are applicable. Because circumstances are
constantly changing, this list must not be considered exhaustive,
but is hoped that it will serve as a useful starting point for
implementers.
The following ciphersuites defined in [TLS] MUST NOT be used for
confidentiality protection of passwords or data:
TLS_NULL_WITH_NULL_NULL
TLS_RSA_WITH_NULL_MD5
TLS_RSA_WITH_NULL_SHA
The following ciphersuites defined in [TLS] can be cracked easily
(less than a day of CPU time on a standard CPU in 2000) and are NOT
RECOMMENDED for use in confidentiality protection of passwords or
data:
TLS_RSA_EXPORT_WITH_RC4_40_MD5
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA
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TLS_DHE_DSS_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_DES40_CBC_SHA
The following ciphersuites are vulnerable to man-in-the-middle
attacks:
TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
TLS_DH_anon_WITH_RC4_128_MD5
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_anon_WITH_DES_CBC_SHA
TLS_DH_anon_WITH_3DES_EDE_CBC_SHA
4. Associations
Every LDAP connection has an associated authorization state referred
to as the "association". The Bind operation defined in section 4.2
of [Protocol] and discussed further in section 5 below allows
information to be exchanged between the client and server to change
the authorization state of the association.
4.1. Anonymous Association on Unbound Connections
Prior to the successful completion of a Bind operation and during
any subsequent authentication exchange, the association has an
anonymous authorization state. Among other things this implies that
the client need not send a Bind Request in the first PDU of the
connection. The client may send any operation request prior to
binding, and the server MUST treat it as if it had been performed
after an anonymous bind operation (section 6). This association
state is sometimes referred to as an implied anonymous bind.
4.2. Anonymous Association After Failed Bind
Upon receipt of a Bind request, the association is moved to an
anonymous state and only upon successful completion of the
authentication exchange (and the Bind operation) is the association
moved to an authenticated state. Thus, a failed Bind operation
produces an anonymous association.
4.3. Invalidated Associations
The server may move the association to an invalidated state at any
time, e.g. if an established security layer between the client and
server has unexpectedly failed or been compromised. While the
connection has an invalid association, the server may reject any
operation request other than Bind, Unbind, and StartTLS by
responding with a resultCode of strongAuthRequired to indicate that
the server requires stronger authentication before it will attempt
to perform the requested operation. In practice, this means that the
client needs to bind to(re)establish a suitably strong authorization
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state on the association before the server will attempt to perform
the requested operation.
5. Bind Operation
The Bind operation ([Protocol] section 4.2) allows authentication
information to be exchanged between the client and server to
establish a new authorization state on the association.
The Bind request typically specifies the desired authentication
identity. Some Bind mechanisms also allow the client to specify the
authorization identity. If the authorization identity is not
specified, the server derives it from the authentication identity in
an implementation-specific manner.
If the authorization identity is specified the server MUST verify
that the client's authentication identity is permitted to assume
(e.g. proxy for) 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.
5.1. Simple Authentication Choice
The simple authentication choice of the Bind Operation provides
three authentication mechanisms:
1. an anonymous authentication mechanism (section 6),
2. an unauthenticated authentication mechanism (section 7), and
3. a simple authentication mechanism using credentials consisting
of a name (in the form of an LDAP distinguished name [LDAPDN])
and a password (section 8).
5.2. SASL Authentication Choice
The sasl authentication choice of the Bind Operation provides
facilities for using any SASL mechanism (sections 9-11) including
authentication mechanisms and other services (e.g. data security
services).
6. Anonymous Authentication Mechanism of Simple Bind
An LDAP client may use the anonymous authentication mechanism of the
simple Bind choice to explicitly establish an anonymous association
by sending a Bind request with a name value of zero length and with
the simple authentication choice containing a password value of zero
length.
7. Unauthenticated Authentication Mechanism of Simple Bind
An LDAP client may use the unauthenticated authentication mechanism
of the simple Bind choice to establish an anonymous association by
sending a Bind request with a name value, a distinguished name in
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LDAP string form [LDAPDN], of non-zero length, and specifying the
the simple authentication choice containing a password value of zero
length.
Unauthenticated binds can have significant security issues (see
section 12.3). Servers SHOULD by default reject unauthenticated bind
requests with a resultCode of invalidCredentials, and clients may
need to actively detect situations where they would unintentionally
make an unauthenticated bind request.
8. Simple Authentication Mechanism of Simple Bind
An LDAP client may use the simple authentication mechanism of the
simple Bind choice to establish an authenticated association by
sending a Bind request with a name value, a distinguished name in
LDAP string form [LDAPDN], and specifying the simple authentication
choice containing an OCTET STRING password value of non-zero length.
Servers that map the DN sent in the bind request to a directory
entry with an associated set of one or more passwords used with this
mechanism, will compare the presented password to that set of
passwords. The presented password is considered valid if it matches
any member of this set.
If the DN is syntactically invalid, the server returns the
invalidDNSyntax result code. If the DN is syntactically correct but
not valid for purposes of authentication, or the password is not
valid for the DN, or the server otherwise considers the credentials
to be invalid, the server returns the invalidCredentials result
code. The server is only to return the success result code when the
credentials are valid and the server is willing to provide service
to the entity these credentials identify.
Server behavior is undefined for bind requests specifying the simple
authentication mechanism with a zero-length name value and a
password value of non-zero length.
The simple authentication mechanism of simple bind is not suitable
for authentication in environments where there is no network or
transport layer confidentiality. LDAP implementations SHALL NOT
support this mechanism unless they are capable of protecting it by
establishment of TLS (as discussed in section 3) or other suitable
data confidentiality and data integrity protection(e.g. IPSec). LDAP
implementations SHOULD support authentication with the "simple"
authentication choice when the connection is protected against
eavesdropping using TLS, as defined in section 3. LDAP
implementations SHOULD NOT support authentication with the "simple"
authentication choice unless the data on the connection is protected
using TLS or other data confidentiality and data integrity
protection.
9. SASL Protocol Profile
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LDAP allows authentication via any SASL mechanism [SASL]. As LDAP
includes native anonymous and simple (plain text) authentication
methods, the ANONYMOUS [ANONYMOUS] and PLAIN [PLAIN] SASL mechanisms
are typically not used with LDAP.
Each protocol that utilizes SASL services is required to supply
certain information profiling the way they are exposed through the
protocol ([SASL] section 5). This section explains how each of these
profiling requirements are met by LDAP.
9.1. SASL Service Name for LDAP
The SASL service name for LDAP is "ldap", which has been registered
with the IANA as a SASL service name.
9.2. SASL Authentication Initiation and Protocol Exchange
SASL authentication is initiated via an LDAP bind request
([Protocol] section 4.2) with the following parameters:
- The version is 3.
- The AuthenticationChoice is sasl.
- The mechanism element of the SaslCredentials sequence contains
the value of the desired SASL mechanism.
- The optional credentials field of the SaslCredentials sequence
may be used to provide an initial client response for
mechanisms that are defined to have the client send data first
(see [SASL] sections 5 and 5.1).
In general, a SASL authentication protocol exchange consists of a
series of server challenges and client responses, the contents of
which are specific to and defined by the SASL mechanism. Thus for
some SASL authentication mechanisms, it may be necessary for the
client to respond to one or more server challenges by invoking the
BindRequest multiple times. A challenge is indicated by the server
sending a BindResponse with the resultCode set to
saslBindInProgress. This indicates that the server requires the
client to send a new bind request with the same sasl mechanism to
continue the authentication process.
To the LDAP protocol, these challenges and responses are opaque
binary tokens of arbitrary length. LDAP servers use the
serverSaslCreds field, an OCTET STRING, in a bind response message
to transmit each challenge. LDAP clients use the credentials field,
an OCTET STRING, in the SaslCredentials sequence of a bind request
message to transmit each response. Note that unlike some Internet
protocols where SASL is used, LDAP is not text-based, thus no Base64
transformations are performed on these challenge and response values.
Clients sending a bind request with the sasl choice selected SHOULD
send an zero-length value in the name field. Servers receiving a
bind request with the sasl choice selected SHALL ignore any value in
the name field.
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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.
The server indicates completion of the SASL challenge-response
exchange by responding with a bind response in which the resultCode
is either success, or an error indication.
The serverSaslCreds field in the BindResponse can be used to include
an optional challenge with a success notification for mechanisms
which are defined to have the server send additional data along with
the indication of successful completion. If a server does not intend
to send a challenge value in a BindResponse message, the server
SHALL omit the serverSaslCreds field (rather than including the
field with a zero-length value).
9.3. Octet Where Negotiated Security Mechanisms Take Effect
SASL security layers take effect following the transmission by the
server and reception by the client of the final successful
BindResponse in the exchange.
Once a SASL security layer providing data integrity or
confidentiality services takes effect, the layer remains in effect
until a new layer is installed (i.e. at the first octet following
the final BindResponse of the bind operation that caused the new
layer to take effect). Thus, an established SASL security layer is
not affected by a failed or non-SASL Bind.
9.4. Determination of Supported SASL Mechanisms
Clients may determine the SASL mechanisms a server supports by
reading the supportedSASLMechanisms attribute from the root DSE
(DSA-Specific Entry) ([Models] section 5.1). The values of this
attribute, if any, list the mechanisms the server supports in the
current LDAP session state. LDAP servers SHOULD allow an
anonymously-bound client to retrieve the supportedSASLMechanisms
attribute of the root DSE.
Because SASL mechanisms provide critical security functions, clients
and servers should be configurable to specify what mechanisms are
acceptable and allow only those mechanisms to be used. Both clients
and servers must confirm that the negotiated security level meets
their requirements before proceeding to use the connection.
9.5. Rules for Using SASL Security Layers
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If a SASL security layer is negotiated, the client SHOULD discard
information about the server it obtained prior to the initiation of
the SASL negotiation and not obtained through secure mechanisms.
If a lower level security layer (such as TLS) is negotiated, any
SASL security services SHALL be layered on top of such security
layers regardless of the order of their negotiation. In all other
respects, SASL security services and other security layers act
independently, e.g. if both TLS and SASL security service are in
effect then removing the SASL security service does not affect the
continuing service of TLS and vice versa.
9.6 Support for Multiple Authentications
LDAP supports multiple SASL authentications as defined in [SASL]
section 6.3.
10. SASL EXTERNAL Authentication Mechanism
A client can use the SASL EXTERNAL [SASL] mechanism to request the
LDAP server to authenticate and establish a resulting authorization
identity using security credentials exchanged by a lower security
layer (such as by TLS authentication or IP-level security
[RFC2401]).
The authorization identity used to determine the state of the
association is derived from the security credentials in an
implementation-specific manner. If the client's authentication
credentials have not been established at a lower security layer, the
SASL EXTERNAL bind MUST fail with a resultCode of
inappropriateAuthentication. Although this situation has the effect
of leaving the association in an anonymous state (section 5), the
state of any established security layer is unaffected.
A client may either implicitly request that its authorization
identity be derived from its authentication credentials exchanged at
a lower security layer or it may explicitly provide an authorization
identity and assert that it be used in combination with those
authentication credentials. The former is known as an implicit
assertion, and the latter as an explicit assertion.
10.1. Implicit Assertion
An implicit authorization identity assertion is performed by
invoking a Bind request of the SASL form using the EXTERNAL
mechanism name that does 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 by the security layer
(e.g., a public key certificate used during TLS establishment)
according to local policy. The underlying mechanics of how this is
accomplished are implementation specific.
10.2. Explicit Assertion
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An explicit authorization identity assertion is performed by
invoking a Bind request of the SASL form using the EXTERNAL
mechanism name that includes the credentials octet string. This
string MUST be constructed as documented in section 10.4.
10.3. SASL Authorization Identity
When the EXTERNAL SASL mechanism is being negotiated, if the
SaslCredentials credentials field is present, it contains an
authorization identity. Other mechanisms define the location of the
authorization identity in the credentials field. In either case, the
authorization identity is represented in the authzId form described
below.
10.4. SASL Authorization Identity Syntax
The authorization identity is a string of UTF-8 [RFC3629] encoded
[Unicode] characters corresponding to the following ABNF [RFC2234]
grammar:
authzId ::= dnAuthzId / uAuthzId
DNCOLON ::= %x64 %x6e %x3a ; "dn:"
UCOLON ::= %x75 %x3a ; "u:"
; distinguished-name-based authz id.
dnAuthzId ::= DNCOLON distinguishedName
; unspecified authorization id, UTF-8 encoded.
uAuthzId ::= UCOLON userid
userid ::= *UTF8 ; syntax unspecified
where the <distinguishedName> production is defined in section 3 of
[LDAPDN] and <UTF8> production is defined in section 1.3 of [Models].
In order to support additional specific authorization identity
forms, future updates to this specification may add new choices
supporting other forms of the authzId production.
The dnAuthzId choice is used to assert authorization identities in
the form of a distinguished name to be matched in accordance with
the distinguishedNameMatch matching rule [Syntaxes]. The decision to
allow or disallow an authentication identity to have access to the
requested authorization identity is a matter of local policy ([SASL]
section 4.2). For this reason there is no requirement that the
asserted dn be that of an entry in the directory.
The uAuthzId choice allows clients to assert an authorization
identity that is not in distinguished name form. The format of
userid is defined as only a sequence of UTF-8 [RFC3629] encoded
[Unicode] characters, and any further interpretation is a local
matter. To compare uAuthzID values, each uAuthzID value MUST be
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prepared using [SASLPrep] and then the two values are compared
octet-wise.
For example, the userid could identify a user of a specific
directory service, be a login name, or be an email address. A
uAuthzId SHOULD NOT be assumed to be globally unique.
11. SASL DIGEST-MD5 Authentication Mechanism
LDAP servers that implement any authentication method or mechanism
other than simple anonymous bind MUST implement the SASL
DIGEST-MD5 mechanism [DIGEST-MD5]. This provides client
authentication with protection against passive eavesdropping attacks
but does not provide protection against man-in-the-middle attacks.
DIGEST-MD5 also provides data integrity and data confidentiality
capabilities.
Support for subsequent authentication ([DIGEST-MD5] section 2.2) is
OPTIONAL in clients and servers.
Implementers must take care to ensure that they maintain the
semantics of the DIGEST-MD5 specification even when handling data
that has different semantics in the LDAP protocol.
For example, the SASL DIGEST-MD5 authentication mechanism utilizes
realm and username values ([DIGEST-MD5] section 2.1) which are
syntactically simple strings and semantically simple realm and
username values. These values are not LDAP DNs, and there is no
requirement that they be represented or treated as such. Username
and realm values that look like LDAP DNs in form, e.g. <cn=bob,
dc=example,dc=com>, are syntactically allowed, however DIGEST-MD5
treats them as simple strings for comparison purposes. To illustrate
further, the two DNs <cn=Bob,dc=example,dc=com> (upper case "B") and
<cn=bob,dc=example,dc=com> (lower case "b") are equivalent when
being compared semantically as LDAP DNs because the cn attribute is
defined to be case insensitive, however the two values are not
equivalent if they represent username values in DIGEST-MD5 because
[SASLPrep] semantics are used by DIGEST-MD5.
12. Security Considerations
Security issues are discussed throughout this document. The
unsurprising conclusion is that security is an integral and
necessary part of LDAP. This section discusses a number of LDAP-
related security considerations.
12.1. General LDAP Security Considerations
LDAP itself provides no security or protection from accessing or
updating the directory by other means than through the LDAP
protocol, e.g. from inspection by database administrators. Access
control SHOULD always be applied when reading sensitive information
or updating directory information.
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Servers can minimize denial of service attacks by providing the
ability to configure and enforce administrative limits on
operations, timing out idle connections and returning the
unwillingToPerform resultCode rather than performing computationally
expensive operations requested by unauthorized clients.
A connection on which the client has not established connection
integrity and privacy services (e.g via StartTLS, IPSec or a
suitable SASL mechanism) is subject to man-in-the-middle attacks to
view and modify information in transit. Client and server
implementors SHOULD take measures to protect confidential data from
these attacks by using data protection services as discussed in this
document.
12.1.1. Password-related Security Considerations
LDAP allows multi-valued password attributes. In systems where
entries are expected to have one and only one password,
administrative controls should be provided to enforce this behavior.
The use of clear text passwords and other unprotected authentication
credentials is strongly discouraged over open networks when the
underlying transport service cannot guarantee confidentiality.
The transmission of passwords in the clear--typically for
authentication or modification--poses a significant security risk.
This risk can be avoided by using SASL authentication [SASL]
mechanisms that do not transmit passwords in the clear or by
negotiating transport or session layer data confidentiality services
before transmitting password values.
To mitigate the security risks associated with the transfer of
passwords, a server implementation that supports any password-based
authentication mechanism that transmits passwords in the clear MUST
support a policy mechanism that at the time of authentication or
password modification, requires:
A StartTLS encryption layer has been successfully negotiated.
OR
Some other data confidentiality mechanism that protects the
password value from snooping has been provided.
OR
The server returns a resultCode of confidentialityRequired for
the operation (i.e. simple bind with password value, SASL bind
transmitting a password value in the clear, add or modify
including a userPassword value, etc.), even if the password
value is correct.
12.2. StartTLS Security Considerations
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All security gained via use of the StartTLS operation is gained by
the use of TLS itself. The StartTLS operation, on its own, does not
provide any additional security.
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, a man-in-the-
middle attacker can remove the StartTLS extended operation from the
supportedExtension attribute of the root DSE. 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 by default either warn the user when the security
level achieved does not provide an acceptable level of data
confidentiality and/or data integrity protection, or be configured
to refuse to proceed without an acceptable level of security.
Server implementors SHOULD allow server administrators to elect
whether and when data confidentiality and integrity are required, as
well as elect whether authentication of the client during the TLS
handshake is required.
Implementers should be aware of and understand TLS security
considerations as discussed in the TLS specification [TLS].
12.3. Unauthenticated Mechanism Security Considerations
Operational experience shows that clients can (and frequently do)
misuse the unauthenticated authentication mechanism of simple bind
(see section 7). For example, a client program might make a
decision to grant access to non-directory information on the basis
of completing a successful bind operation. LDAP server
implementations may return a success response to an unauthenticated
bind request thus leaving the client with the impression that the
server has successfully authenticated the identity represented by
the user name, when in effect, an anonymous association has been
established. Clients that use the results from a simple bind
operation to make authorization decisions should actively detect
unauthenticated bind requests (by verifying that the supplied
password is not empty) and react appropriately.
12.4. Simple Mechanism Security Considerations
The simple authentication mechanism of simple bind discloses the
password to the server, which is an inherent security risk. There
are other mechanisms such as DIGEST-MD5 that do not disclose
password to server.
12.5. SASL DIGEST-MD5 Mechanism Security Considerations
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The SASL DIGEST-MD5 mechanism is prone to the qop substitution
attack, as discussed in 3.6 of [DIGEST-MD5]. The qop substitution
attack can be mitigated (as discussed in 3.6 of [DIGEST-MD5]).
The SASL DIGEST-MD5 mechanism [DIGEST-MD5] provides client
authentication with protection against passive eavesdropping attacks
but does not provide protection against man-in-the-middle attacks.
Implementers should be aware of and understand DIGEST-MD5 security
considerations as discussed in the DIGEST-MD5 specification [DIGEST-
MD5].
12.6. Related Security Considerations
Additional security considerations relating to the various
authentication methods and mechanisms discussed in this document
apply and can be found in [SASL], [SASLPrep], [StringPrep] and
[RFC3629].
13. IANA Considerations
The following IANA considerations apply to this document:
It is requested that the IANA update the LDAP Protocol Mechanism
registry to indicate that this document and [Protocol] provide the
definitive technical specification for the StartTLS
(1.3.6.1.4.1.1466.20037) extended operation.
[[TODO: add any missing IANA Considerations.]]
Acknowledgments
This document combines information originally contained in RFC 2829
and RFC 2830. The editor acknowledges the work of Harald Tveit
Alvestrand, Jeff Hodges, Tim Howes, Steve Kille, RL "Bob" Morgan ,
and Mark Wahl, each of whom authored one or more of these documents.
This document is based upon input of the IETF LDAP Revision working
group. The contributions and suggestions made by its members in
shaping the contents and technical accuracy of this document is
greatly appreciated.
Normative References
[[Note to the RFC Editor: please replace the citation tags used in
referencing Internet-Drafts with tags of the form RFCnnnn.]]
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, November 1997.
[DIGEST-MD5] Leach, P. C. Newman, and A. Melnikov, "Using Digest
Authentication as a SASL Mechanism", draft-ietf-sasl-
rfc2831bis-xx.txt, a work in progress.
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[RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[LDAPDN] Zeilenga, Kurt D. (editor), "LDAP: String
Representation of Distinguished Names", draft-ietf-
ldapbis-dn-xx.txt, a work in progress.
[Matching] Hoffman, Paul and Steve Hanna, "Matching Text Strings
in PKIX Certificates", draft-hoffman-pkix-stringmatch-
xx.txt, a work in progress.
[Models] Zeilenga, Kurt D. (editor), "LDAP: Directory
Information Models", draft-ietf-ldapbis-models-xx.txt,
a work in progress.
[Protocol] Sermersheim, J., "LDAP: The Protocol", draft-ietf-
ldapbis-protocol-xx.txt, a work in progress.
[Roadmap] K. Zeilenga, "LDAP: Technical Specification Road Map",
draft-ietf-ldapbis-roadmap-xx.txt, a work in progress.
[SASL] Melnikov, A. (editor), "Simple Authentication and
Security Layer (SASL)", draft-ietf-sasl-rfc2222bis-
xx.txt, a work in progress.
[SASLPrep] Zeilenga, K., "Stringprep profile for user names and
passwords", draft-ietf-sasl-saslprep-xx.txt, (a work in
progress).
[StringPrep] M. Blanchet, "Preparation of Internationalized Strings
('stringprep')", draft-hoffman-rfc3454bis-xx.txt, a
work in progress.
[Syntaxes] Legg, S. (editor), "LDAP: Syntaxes and Matching Rules",
draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress.
[TLS] Dierks, T. and C. Allen. "The TLS Protocol Version
1.1", draft-ietf-tls-rfc2246-bis-xx.txt, a work in
progress.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 3629, STD 63, November 2003.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
3.2.0" is defined by "The Unicode Standard, Version
3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-
61633-5), as amended by the "Unicode Standard Annex
#27: Unicode 3.1"
(http://www.unicode.org/reports/tr27/) and by the
"Unicode Standard Annex #28: Unicode 3.2"
(http://www.unicode.org/reports/tr28/).
Informative References
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[ANONYMOUS] Zeilenga, K.,"Anonymous SASL Mechanism", draft-
zeilenga-sasl-anon-xx.txt, a work in progress.
[RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828, May
2000.
[PLAIN] Zeilenga, K.,"Plain SASL Mechanism", draft-zeilenga-
sasl-plain-xx.txt, a work in progress.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for
the Internet Protocol", RFC 2401, November 1998.
Author's Address
Roger Harrison
Novell, Inc.
1800 S. Novell Place
Provo, UT 84606
USA
+1 801 861 2642
roger_harrison@novell.com
Appendix A. Association State Transition Tables
This section provides a state transition table to represent a state
diagram for the various authentication states through which an
association may pass during the course of its existence and the
actions that cause these changes in state.
This section is based entirely on information found in this document
and other documents that are part of the LDAP Technical
Specification [Roadmap]. As such, it is strictly informational in
nature.
A.1. Association States
The following table lists the valid association states and provides
a description of each state. The ID for each state is used in the
state transition table in section A.4.
ID State Description
-- --------------------------------------------------------------
S1 Anonymous
no Authentication ID is associated with the LDAP connection
no Authorization ID is in force
S2 Authenticated
Authentication ID = I
Authorization ID = X
S3 Authenticated SASL EXTERNAL, implicit authorization ID
Authentication ID = J
Authorization ID = Y
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S4 Authenticated SASL EXTERNAL, explicit authorization ID Z
Authentication ID = J
Authorization ID = Z
S5 Invalidated
A.2. Actions that Affect Association State
The following table lists the actions that can affect the
authentication and authorization state of an association. The ID for
each action is used in the state transition table in section A.4.
ID Action
-- --------------------------------------------------------------
A1 Client bind request fails
A2 Client successfully performs anonymous simple bind or
unauthenticated simple bind
A3 Client successfully performs simple bind with name and password
OR SASL bind with any mechanism except EXTERNAL using an
authentication ID = I that maps to authorization ID X
A4 Client Binds SASL EXTERNAL with implicit assertion of
authorization ID (section 9.1). The current authentication ID
maps to authorization ID = Y.
A5 Client Binds SASL EXTERNAL with explicit assertion of
authorization ID = Z (section 9.2).
A6 Client StartTLS request fails
A7 Client StartTLS request succeeds
A8 Client or Server: graceful TLS removal
A9 Server decides to invalidate current association state
A.3. Decisions Used in Making Association State Changes
Certain changes in the authentication and authorization state of an
association are only allowed if the server can affirmatively answer
a question. These questions are applied as part of the criteria for
allowing or disallowing a state transition in the state transition
table in section A.4.
ID Decision Question
-- --------------------------------------------------------------
D1 Are lower-layer credentials available?
D2 Can lower-layer credentials for Auth ID "K" be mapped to
asserted AuthZID "L"?
A.4. Association State Transition Table
The Association table below lists the the actions that could affect
the authorization state of an association and the resulting state of
an association after a given action occurs.
S1, the initial state for the state machine described in this table,
is the association state when an LDAP connection is initially
established.
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Next State
Action Comment
------------------ ----------- --------------------------------
A1 S1 Section 4
A2 S1 Sections 6 & 7
A3 S2 Sections 8, 9
A4, S1 Failed bind, section 10.1
D1=no
A4, S3
D1=yes
A5, S1 Failed bind, section 10.2
D1=no
A5, S1 Failed bind, section 10.2
D1=yes,
D2=no
A5, S4
D1=yes, D2=yes
A6 no change* [Protocol] section 4.14.2.2
A7 no change* [Protocol] section 4.14.2.1
A8 S1 [Protocol] section 4.14.3.1
A9 S5
* The server may invalidate the association after TLS
establishment or closure (section 3.2).
Appendix B. Authentication and Authorization 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. Security objects and
mechanisms, such as those described here, enable the expression of
access control policies and their enforcement.
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
[Protocol]). 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
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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 a new association state 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 performed in an implementation-specific manner.
Appendix C. RFC 2829 Change History
This appendix lists the changes made to the text of RFC 2829 in
preparing this document.
C.0. General Editorial Changes
Version -00
- Changed other instances of the term LDAP to LDAP where v3 of the
protocol is implied. Also made all references to LDAP use the
same wording.
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- Miscellaneous grammatical changes to improve readability.
- Made capitalization in section headings consistent.
Version -01
- Changed title to reflect inclusion of material from RFC 2830 and
2251.
C.1. Changes to Section 1
Version -01
- Moved conventions used in document to a separate section.
C.2. Changes to Section 2
Version -01
- Moved section to an appendix.
C.3. Changes to Section 3
Version -01
- Moved section to an appendix.
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
- Replaced the text describing the procedure for performing an
anonymous bind (protocol) with a reference to section 4.2 of RFC
2251 (the protocol spec).
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.
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C.6. Changes to Section 6.
Version -00
Reorganized text in section 6.1 as follows:
1. Added a new section (6.1) titled "Simple Authentication" and
moved one of two introductory paragraphs for section 6 into
section 6.1. Added sentences to the paragraph indicating:
a. simple authentication is not suitable for environments where
confidentiality is not available.
b. LDAP implementations SHOULD NOT support simple
authentication unless confidentiality and data integrity
mechanisms are in force.
2. Moved first paragraph of section 6 (beginning with "LDAP
implementations MUST support authentication with a password...")
to section on Digest Authentication (Now section 6.2).
C.6.1. Changes to Section 6.1.
Version -00 Renamed section to 6.2
- Added sentence from original section 6 indicating that the
DIGEST-MD5 SASL mechanism is required for all conforming LDAP
implementations
C.6.2. Changes to Section 6.2
Version -00
- Renamed section to 6.3
- Reworded first paragraph to remove reference to user and the
userPassword password attribute Made the first paragraph more
general by simply saying that if a directory supports simple
authentication that the simple bind operation MAY performed
following negotiation of a TLS ciphersuite that supports
confidentiality.
- Replaced "the name of the user's entry" with "a DN" since not
all bind operations are performed on behalf of a "user."
- Added Section 6.3.1 heading just prior to paragraph 5.
- Paragraph 5: replaced "The server" with "DSAs that map the DN
sent in the bind request to a directory entry with a
userPassword attribute."
C.6.3. Changes to section 6.3.
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Version -00
- Renamed to section 6.4.
C.7. Changes to section 7.
none
C.7.1. Changes to section 7.1.
Version -00
- Clarified the entity issuing a certificate by moving the phrase
"to have issued the certificate" immediately after
"Certification Authority."
C.8. Changes to section 8.
Version -00
- Removed the first paragraph because simple authentication is
covered explicitly in section 6.
- Added section 8.1. heading just prior to second paragraph.
- Added section 8.2. heading just prior to third paragraph.
- 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."
- Added section 9.1. heading.
- Modified a comment in the ABNF from "unspecified userid" to
"unspecified authz id".
- Deleted sentence, "A utf8string is defined to be the UTF-8
encoding of one or more ISO 10646 characters," because it is
redundant.
- Added section 9.1.1. heading.
- Added section 9.1.2. heading.
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Version -01
- Moved entire section 9 to become section 3.5 so that it would be
with other SASL material.
C.10. Changes to Section 10.
Version -00
- Updated reference to cracking from a week of CPU time in 1997 to
be a day of CPU time in 2000.
- Added text: "These ciphersuites are NOT RECOMMENDED for use...
and server implementers SHOULD" to sentence just prior the
second list of ciphersuites.
- Added text: "and MAY support other ciphersuites offering
equivalent or better protection," to the last paragraph of the
section.
C.11. Changes to Section 11.
Version -01
- 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).
None
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 StartTLS response was broken
out into a new section.
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- The wording of the definition of the StartTLS request and
StartTLS 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 StartTLS 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. Change History to Combined Document
F.1. Changes for draft-ldap-bis-authmeth-02
General
- Added references to other LDAP standard documents, to sections
within the document, and fixed broken references.
- General editorial changes--punctuation, spelling, formatting,
etc.
Section 1.
- Added glossary of terms and added sub-section headings
Section 2.
- Clarified security mechanisms 3, 4, & 5 and brought language in
line with IETF security glossary.
Section 3.
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- Brought language in requirement (3) in line with security
glossary.
- Clarified that information fetched prior to initiation of TLS
negotiation must be discarded
-Clarified that information fetched prior to initiation of SASL
negotiation must be discarded
- Rewrote paragraph on SASL negotiation requirements to clarify
intent
Section 4.4.
- Added stipulation that sasl choice allows for any SASL mechanism
not prohibited by this document. (Resolved conflict between this
statement and one that prohibited use of ANONYMOUS and PLAIN
SASL mechanisms.)
Section 5.3.6
- Added a.x.bar.com to wildcard matching example on hostname check.
Section 6
- Added Association State Transition Tables to show the various
states through which an association may pass along with the
actions and decisions required to traverse from state to state.
Appendix A
- Brought security terminology in line with IETF security glossary
throughout the appendix.
F.2. Changes for draft-ldapbis-authmeth-03
General
- Added introductory notes and changed title of document and
references to conform to WG chair suggestions for the overall
technical specification.
- Several issues--H.13, H.14, H.16, H.17--were resolved without
requiring changes to the document.
Section 3
- Removed reference to /etc/passwd file and associated text.
Section 4
- Removed sections 4.1, 4.2 and parts of section 4.3. This
information was being duplicated in the protocol specification
and will now reside there permanently.
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Section 4.2
- changed words, "not recommended" to "strongly discouraged"
Section 4.3
- Based on ldapbis WG discussion at IETF52 two sentences were
added indicating that clients SHOULD NOT send a DN value when
binding with the sasl choice and servers SHALL ignore any value
received in this circumstance.
-
Section 8.3.1
- Generalized the language of this section to not refer to any
specific password attribute or to refer to the directory entry
as a "user" entry.
Section 11
- Added security consideration regarding misuse of unauthenticated
access.
- Added security consideration requiring access control to be
applied only to authenticated users and recommending it be
applied when reading sensitive information or updating directory
information.
F.3. Changes for draft-ldapbis-authmeth-04
General
- Changed references to use [RFCnnnn] format wherever possible.
(References to works in progress still use [name] format.)
- Various edits to correct typos and bring field names, etc. in
line with specification in [Protocol] draft.
- Several issues--H.13, H.14, H.16, H.17--were resolved without
requiring changes to the document.
Section 4.4.1.
- Changed ABNF grammar to use productions that are like those in
the model draft.
Section 5
- Removed sections 5.1, 5.2, and 5.4 that will be added to
[Protocol]. Renumbered sections to accommodate this change.
-
Section 6
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- Reviewed Association State table for completeness and accuracy.
Renumbered actions A3, , and A5 to be A5, A3, and A4
respectively. Re-ordered several lines in the table to ensure
that actions are in ascending order (makes analyzing the table
much more logical). Added action A2 to several states where it
was missing and valid. Added actions A7 and A8 placeholders to
states S1, S2, S4 and S5 pending resolution of issue H.28.
Section 11
- Modified security consideration (originally added in -03)
requiring access control to be applied only to authenticated
users. This seems nonsensical because anonymous users may have
access control applied to limit permissible actions.
-
Section 13
- Verified all normative references and moved informative
references to a new section 14.
F.4. Changes for draft-ldapbis-authmeth-05
General
- General editory changes to fix punctuation, spelling, line
length issues, etc.
- Verified and updated intra- and inter-document references
throughout.
- Document-wide review for proper usage of RFC 2119 keywords with
several changes to correct improper usage.
Abstract
- Updated to match current contents of documents. This was needed
due to movement of material on Bind and StartTLS operations to
[Protocol] in this revision.
Section 3.
- Renamed section to "Rationale for LDAP Security Mechanisms" and
removed text that did not support this theme. Part of the
motivation for this change was to remove the implication of the
previous section title, "Required Security Mechanisms", and
other text found in the section that everything in the section
was a requirement
- Information from several removed paragraphs that describe
deployment scenarios will be added Appendix A in the next
revision of the draft.
- Paragraph beginning, " If TLS is negotiated, the client MUST
discard all information..." was moved to section 5.1.7 and
integrated with related material there.
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- Paragraph beginning, "If a SASL security layer is negotiated..."
was moved to section 4.2
Section 4.l.
- Changed wording of first paragraph to clarify meaning.
Section 4.2.
- Added paragraph from section 3 of -04 beginning, "If a SASL
security layer is negotiated..."
Section 4.3.3.
- Renamed to "Other SASL Mechanisms" and completely rewrote the
section (one sentence) to generalize the treatment of SASL
mechanisms not explicitly mentioned in this document.
Section 4.4.1.
- Added paragraph beginning, "The dnAuthzID choice allows client
applications..." to clarify whether DN form authorization
identities have to also have a corresponding directory entry.
This change was based on editor's perception of WG consensus.
- Made minor clarifying edits in the paragraph beginning, "The
uAuthzID choice allows for compatibility..."
Section 5.1.1.
- Made minor clarifying edits in the last paragraph of the
section.
Section 5.1.7.
- Wording from section 3 paragraph beginning " If TLS is
negotiated, the client MUST discard all information..." was
moved to this section and integrated with existing text.
Section 5.2.
- Changed usage of "TLS connection" to "TLS session" throughout.
- Removed empty section 5.2.1 and renumbered sections it had
previously contained.
Section 8.
- Added introductory paragraph at beginning of section.
Section 8.1.
- Changed term "data privacy" to "data confidentiality" to be
consistent with usage in rest of document.
Section 8.2.
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- Changed first paragraph to require implementations that
implement *password-based* authentication to implement and
support DIGEST-MD5 SASL authentication.
Section 11.
- First paragraph: changed "session encryption" to "session
confidentiality protection" to be consistent with usage in rest
of document.
Appendix B.
- Began changes to incorporate information on deployment scenarios
removed from section 3.
F.5. Changes for draft-ldapbis-authmeth-06
General
- Combined Section 2 (Introduction) and Section 3 (Motivation) and
moved Introduction to section 1. All following sections numbers
were decremented by one as result.
- Edits to fix typos, I-D nits, etc.
- Opened several new issues in Appendix G based on feedback from
WG. Some of these have been resolved. Others require further
discussion.
Section 1
- Added additional example of spoofing under threat (7).
Section 2.1
- Changed definition of "association" and added terms,
"connection" and "TLS connection" to bring usage in line with
[Protocol].
Section 4.1.6
- Clarified sentence stating that the client MUST NOT use derived
forms of DNS names.
Section 5.1
- Began edits to association state table to clarify meaning of
various states and actions.
- Added action A9 to cover abandoned bind operation and added
appropriate transitions to the state transition table to
accommodate it.
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Section 7.2
- Replaced first paragraph to clarify that the "DIGEST-MD5" SASL
mechanism is required to implement.
Section 9
- Rewrote the section to make the advice more applicable over the
long term, i.e. more "timeless." The intent of content in the
original section was preserved.
Section 10
- Added a clarifying example to the consideration regarding misuse
of unauthenticated access.
F.6. Changes for draft-ldapbis-authmeth-07
General
- Updated external and internal references to accommodate changes
in recent drafts.
- Opened several new issues in Appendix G based on feedback from
WG. Some of these have been resolved. Others require further
discussion.
Section 3
- Rewrote much of section 3.3 to meet the SASL profile
requirements of draft-ietf-sasl-rfc2222bis-xx.txt section 5.
- Changed treatement of SASL ANONYMOUS and PLAIN mechanisms to
bring in line with WG consensus.
Section 4
- Note to implementers in section 4.1.1 based on operational
experience.
- Clarification on client continuing by performing a StartTLS with
TLS already established in section 4.1.4.
- Moved verification of mapping of client's authentication ID to
asserted authorization ID to apply only to explicit assertion.
The local policy in place for implicit assertion is adequate.
Section 7
- Removed most of section 7.2 as the information is now covered
adequately via the new SASL profile in section 3.3. Added note
to implementors regarding the treatment of username and realm
values in DIGEST-MD5.
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- Section 7.3. Minor clarifications in wording.
- Section 7.3.1. Clarification that a match of the presented value
to any member of the set of stored passwords constitutes a
successful authentication.
F.7. Changes for draft-ldapbis-authmeth-08
General
- Changed usage from LDAPv3 to LDAP for usage consistency across
LDAP technical specification.
- Fixed a number of usage nits for consistency and to bring doc in
conformance with publication guidelines.
Abstract
- Significant cleanup and rewording of abstract based on WG
feedback.
Section 2.1
- New definition of user.
Section 3
- Added 1.5 sentences at end of introductory paragraph indicating
the effect of the Bind op on the association.
Section 3.1
- Retitled section and clarified wording
Section 3.2
- Clarified that simple authentication choice provides three types
of authentication: anonymous, unauthenticated, and simple
password.
Section 3.3.3
- New wording clarifying when negotiated security mechanisms take
effect.
Section 3.3.5
- Changed requirement to discard information about server fetched
prior to SASL negotiation from MUST to SHOULD to allow for
information obtained through secure mechanisms.
Section 3.3.6
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- Simplified wording of first paragraph based on suggestion from
WG.
Section 3.4
- Minor clarifications in wording.
Section 3.4.1
- Minor clarifications in wording in first sentence.
- Explicitly called out that the DN value in the dnAuthzID form is
to be matched using DN matching rules.
- Called out that the uAuthzID MUST be prepared using SASLprep
rules before being compared.
- Clarified requirement on assuming global uniqueness by changing
a "generally... MUST" wording to "SHOULD".
Section 4.1.1
- Simplified wording describing conditions when StartTLS cannot be
sent.
- Simplified wording in note to implementers regarding race
condition with outstanding LDAP operations on connection.
Section 4.1.5
- Removed section and moved relevant text to section 4.2.2.
Section 4.1.6
- Renumbered to 4.1.5.
- Updated server identity check rules for server's name based on
WG list discussion.
Section 4.1.7
- Renumbered to 4.1.6
- Changed requirement to discard information about server fetched
prior to TLS negotion from MUST to SHOULD to allow for
information obtained through secure mechanisms.
Section 6.1
- Clarified wording.
- Added definition of anonymous and unauthenticated binds.
Section 10
- Added security consideration (moved from elsewhere) discouraging
use of cleartext passwords on unprotected communication
channels.
Section 11
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- Added an IANA consideration to update GSSAPI service name
registry to point to [Roadmap] and [Authmeth]
F.8. Changes for draft-ldapbis-authmeth-09
General
- Updated section references within document
- Changed reference tags to match other docs in LDAP TS
- Used non-quoted names for all SASL mechanisms
Abstract
- Inspected keyword usage and removed several improper usages.
- Removed sentence saying DIGEST-MD5 is LDAP's mandatory-to-
implement mechanism. This is covered elsewhere in document.
- Moved section 5, authentication state table, of -08 draft to
section 8 of -09 and completely rewrote it.
Section 1
- Reworded sentence beginning, "It is also desirable to allow
authentication methods to carry identities based on existing,
non-LDAP DN-forms..."
- Clarified relationship of this document to other documents in
the LDAP TS.
Section 3.3.5
- Removed paragraph beginning,"If the client is configured to
support multiple SASL mechanisms..." because the actions
specified in the paragraph do not provide the protections
indicated. Added a new paragraph indicating that clients and
server should allow specification of acceptable mechanisms and
only allow those mechanisms to be used.
- Clarified independent behavior when TLS and SASL security layers
are both in force (e.g. one being removed doesn't affect the
other).
Section 3.3.6
- Moved most of section 4.2.2, Client Assertion of Authorization
Identity, to sections 3.3.6, 3.3.6.1, and 3.3.6.2.
Section 3.3.6.4
- Moved some normative comments into text body.
Section 4.1.2
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- Non success resultCode values are valid if server is *unwilling*
or unable to negotiate TLS.
Section 4.2.1
- Rewrote entire section based on WG feedback.
Section 4.2.2
- Moved most of this section to 3.3.6 for better document flow.
Section 4.2.3
- Rewrote entire section based on WG feedback.
Section 5.1
- Moved imperative language regarding unauthenticated access from
security considerations to here.
Section 6
- Added several paragraphs regarding the risks of transmitting
passwords in the clear and requiring server implementations to
provide a specific configuration that reduces these risks.
Section 6.2
- Added sentence describing protections provided by DIGEST-MD5
method.
- Changed DNs in exmple to be dc=example,dc=com.
Section 10
- Updated consideration on use of cleartext passwords to include
other unprotected authentication credentials
- Substantial rework of consideration on misuse of unauthenticated
bind.
F.9. Changes for draft-ldapbis-authmeth-10
- Reorganized content of sections 3-9 to improve document flow and
reduce redundancy.
- Resolved issue of effect of Start TLS and TLS closure on
association state.
- Made numerous minor wording changes based on WG feedback.
- Updated list of threats for Section 1.
- Recommendation that servers should not support weaker TLS
ciphersuites unless other protection is in place.
- Moved authentication state table to appendix and relettered
appendices.
F.10. Changes for draft-ldapbis-authmeth-11
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General
- Many editorial changes throughout to clarify wording and better
express intent, primarily based on suggestions from WG mail
list.
- More standard naming of authentication mechanisms throughout
document, e.g. "Anonymous Authentication Mechanism of the Simple
Bind Choice".
Section 1
- Editorial changes to add clarity.
- Moved section 2 of authmeth -09 into section 1
Section 2
- New section outlining implementation requirements.
Section 3.1.1
- Editorial clarification on need for following operation
sequencing requirements.
Section 3.1.4
- New section added to describe use of client certificates with
StartTLS. Incorporates material moved from other sections of
authmeth -09.
Section 4
- New section added to discuss associations. Related material was
moved from various other sections of authmeth -09 and
incorporated into this new section.
Section 5
- Added several paragraphs regarding transmission and derivation
of authentication and authorization identities using the Bind
operation.
Section 8
- Clarified rules for determining valid credentials and situations
where invalidCredentials result is to be returned.
Section 14
- Added three security considerations based on WG feedback.
Appendix A
- Simplfied state tables by removing two unnecessary actions from
the actions table, and removing the current state column of the
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state transition table. Updated references to authmeth and
[Protocol].
F.11. Changes for draft-ldapbis-authmeth-12
General
- Changed refererences from Start TLS to StartTLS.
- Removed Appendix B: Example Deployment Scenarios
- Removed Appendix H as all issues listed in the appendix are now
resolved.
Section 2
- Added implementation requirement that server implementations
that SUPPORT StartTLS MUST support the
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA ciphersuite.
Section 3.1.2
- Added wording clarifying that a client's association is
unaffected if a non-success resultCode is returned in the
StartTLS response.
Section 9.2
- Final paragraph of this section details requirements for
serverSaslCreds field when no challenge value is sent.
Section 10
- Clarified language on uAuthzID usage.
Section 12
- Moved entire section into security considerations. New section
number is 12.1.1.
- Reorganized security considerations by topic.
- Added several security considerations based on WG feedback.
Section 13
- Moved section to become section 3.3.
F.12. Changes for draft-ldapbis-authmeth-13
General
- General edits for clarity and to remove errors.
- Reworded definition of association (section 1.2) and reworked
usage of association throughout document. Current semantics:
every connection has an association with the same lifetime as
the connection, and that association passes through various
authorization states.
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- Made usage of data confidentiality consistent throughout
document.
Section 1
- Reworded mechanisms 3 and 4 for more parallelism.
- Changed language on rationale for required mechansisms from
future to past tense.
Section 2
- Clarified that implementations may support any additional
authentication mechanism, not just mechanisms associated with
simple and SASL bind choices.
Section 3
- Moved paragraph explaining goals for using TLS with LDAP from
security considerations to here.
Section 4.3
- Reworked text to better explain meaning of strongAuthRequired
result code when for invalidated associations.
Section 8
- Clarified action when simple bind request has a DN with invalid
syntax.
Section 12.1
- Added ability to configure and enforce administrative service
limits as a way to protect against denial of service attacks.
Section 12.2
- Clarified that this security consideration relates to performing
client authentication during the TLS handshake and not to
subsequent SASL EXTERNAL authentication.
Appendix A
- Updated tables by collapsing identical states and actions. Also
added an invalidated association state and accompanying actions.
Added implementation requirement that server implementations
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