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+Network Working Group                                   R. Harrison, Ed.
+Request for Comments: 4513                                  Novell, Inc.
+Obsoletes: 2251, 2829, 2830                                    June 2006
+Category: Standards Track
+
+
+             Lightweight Directory Access Protocol (LDAP):
+             Authentication Methods and Security Mechanisms
+
+Status of This Memo
+
+   This document specifies an Internet standards track protocol for the
+   Internet community, and requests discussion and suggestions for
+   improvements.  Please refer to the current edition of the "Internet
+   Official Protocol Standards" (STD 1) for the standardization state
+   and status of this protocol.  Distribution of this memo is unlimited.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2006).
+
+Abstract
+
+   This document describes authentication methods and security
+   mechanisms of the Lightweight Directory Access Protocol (LDAP).  This
+   document details establishment of Transport Layer Security (TLS)
+   using the StartTLS operation.
+
+   This document details the simple Bind authentication method including
+   anonymous, unauthenticated, and name/password mechanisms and the
+   Simple Authentication and Security Layer (SASL) Bind authentication
+   method including the EXTERNAL mechanism.
+
+   This document discusses various authentication and authorization
+   states through which a session to an LDAP server may pass and the
+   actions that trigger these state changes.
+
+   This document, together with other documents in the LDAP Technical
+   Specification (see Section 1 of the specification's road map),
+   obsoletes RFC 2251, RFC 2829, and RFC 2830.
+
+
+
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                     [Page 1]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+Table of Contents
+
+   1. Introduction ....................................................4
+      1.1. Relationship to Other Documents ............................6
+      1.2. Conventions ................................................6
+   2. Implementation Requirements .....................................7
+   3. StartTLS Operation ..............................................8
+      3.1.  TLS Establishment Procedures ..............................8
+           3.1.1. StartTLS Request Sequencing .........................8
+           3.1.2. Client Certificate ..................................9
+           3.1.3. Server Identity Check ...............................9
+                  3.1.3.1. Comparison of DNS Names ...................10
+                  3.1.3.2. Comparison of IP Addresses ................11
+                  3.1.3.3. Comparison of Other subjectName Types .....11
+           3.1.4. Discovery of Resultant Security Level ..............11
+           3.1.5. Refresh of Server Capabilities Information .........11
+      3.2.  Effect of TLS on Authorization State .....................12
+      3.3. TLS Ciphersuites ..........................................12
+   4. Authorization State ............................................13
+   5. Bind Operation .................................................14
+      5.1. Simple Authentication Method ..............................14
+           5.1.1. Anonymous Authentication Mechanism of Simple Bind ..14
+           5.1.2. Unauthenticated Authentication Mechanism of
+                  Simple Bind ........................................14
+           5.1.3. Name/Password Authentication Mechanism of
+                  Simple Bind ........................................15
+      5.2. SASL Authentication Method ................................16
+           5.2.1. SASL Protocol Profile ..............................16
+                  5.2.1.1. SASL Service Name for LDAP ................16
+                  5.2.1.2. SASL Authentication Initiation and
+                           Protocol Exchange .........................16
+                  5.2.1.3. Optional Fields ...........................17
+                  5.2.1.4. Octet Where Negotiated Security
+                           Layers Take Effect ........................18
+                  5.2.1.5. Determination of Supported SASL
+                           Mechanisms ................................18
+                  5.2.1.6. Rules for Using SASL Layers ...............19
+                  5.2.1.7. Support for Multiple Authentications ......19
+                  5.2.1.8. SASL Authorization Identities .............19
+           5.2.2. SASL Semantics within LDAP .........................20
+           5.2.3. SASL EXTERNAL Authentication Mechanism .............20
+                  5.2.3.1. Implicit Assertion ........................21
+                  5.2.3.2. Explicit Assertion ........................21
+   6. Security Considerations ........................................21
+      6.1. General LDAP Security Considerations ......................21
+      6.2. StartTLS Security Considerations ..........................22
+      6.3. Bind Operation Security Considerations ....................23
+           6.3.1. Unauthenticated Mechanism Security Considerations ..23
+
+
+
+Harrison                    Standards Track                     [Page 2]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+           6.3.2. Name/Password Mechanism Security Considerations ....23
+           6.3.3. Password-Related Security Considerations ...........23
+           6.3.4. Hashed Password Security Considerations ............24
+      6.4. SASL Security Considerations ..............................24
+      6.5. Related Security Considerations ...........................25
+   7. IANA Considerations ............................................25
+   8. Acknowledgements ...............................................25
+   9. Normative References ...........................................26
+   10. Informative References ........................................27
+   Appendix A. Authentication and Authorization Concepts .............28
+      A.1. Access Control Policy .....................................28
+      A.2. Access Control Factors ....................................28
+      A.3. Authentication, Credentials, Identity .....................28
+      A.4. Authorization Identity ....................................29
+   Appendix B. Summary of Changes ....................................29
+      B.1. Changes Made to RFC 2251 ..................................30
+           B.1.1. Section 4.2.1 ("Sequencing of the Bind Request") ...30
+           B.1.2. Section 4.2.2 ("Authentication and Other Security
+                  Services") .........................................30
+      B.2. Changes Made to RFC 2829 ..................................30
+           B.2.1. Section 4 ("Required security mechanisms") .........30
+           B.2.2. Section 5.1 ("Anonymous authentication
+                  procedure") ........................................31
+           B.2.3. Section 6 ("Password-based authentication") ........31
+           B.2.4. Section 6.1 ("Digest authentication") ..............31
+           B.2.5. Section 6.2 ("'simple' authentication choice under
+                  TLS encryption") ...................................31
+           B.2.6. Section 6.3 ("Other authentication choices with
+                  TLS") ..............................................31
+           B.2.7. Section 7.1 ("Certificate-based authentication
+                  with TLS") .........................................31
+           B.2.8. Section 8 ("Other mechanisms") .....................32
+           B.2.9. Section 9 ("Authorization Identity") ...............32
+           B.2.10. Section 10 ("TLS Ciphersuites") ...................32
+      B.3. Changes Made to RFC 2830 ..................................32
+           B.3.1. Section 3.6 ("Server Identity Check") ..............32
+           B.3.2. Section 3.7 ("Refresh of Server Capabilities
+                  Information") ......................................33
+           B.3.3. Section 5 ("Effects of TLS on a Client's
+                  Authorization Identity") ...........................33
+           B.3.4. Section 5.2 ("TLS Connection Closure Effects") .....33
+
+
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                     [Page 3]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+1.  Introduction
+
+   The Lightweight Directory Access Protocol (LDAP) [RFC4510] is a
+   powerful protocol for accessing directories.  It offers means of
+   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 (but are not
+   limited to):
+
+   (1) Unauthorized access to directory data via data-retrieval
+       operations.
+
+   (2) Unauthorized access to directory data by monitoring access of
+       others.
+
+   (3) Unauthorized access to reusable client authentication information
+       by monitoring access of others.
+
+   (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
+       transport 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.
+
+   (8) Hijacking: An attacker seizes control of an established protocol
+       session.
+
+   Threats (1), (4), (5), (6), (7), and (8) are active attacks.  Threats
+   (2) and (3) are passive attacks.
+
+
+
+
+
+
+Harrison                    Standards Track                     [Page 4]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   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 that supports anonymous,
+       unauthenticated, and name/password mechanisms, and the Simple
+       Authentication and Security Layer (SASL) method, which supports a
+       wide variety of authentication mechanisms.
+
+   (2) Mechanisms to support vendor-specific access control facilities
+       (LDAP does not offer a standard access control facility).
+
+   (3) Data integrity service by means of security layers in Transport
+       Layer Security (TLS) or SASL mechanisms.
+
+   (4) Data confidentiality service by means of security layers in TLS
+       or SASL mechanisms.
+
+   (5) Server resource usage limitation by means of administrative
+       limits configured on the server.
+
+   (6) Server authentication by means of the TLS protocol or SASL
+       mechanisms.
+
+   LDAP may also be protected by means outside the LDAP protocol, e.g.,
+   with IP layer security [RFC4301].
+
+   Experience has shown that simply allowing implementations to pick and
+   choose the security mechanisms that will be implemented 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 only support
+   mechanisms 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][RFC4512], in string form [RFC4514], or as
+   used in different systems (e.g., simple user names [RFC4013]).
+   Because some authentication mechanisms transmit credentials in plain
+   text form, and/or do not provide data security services and/or are
+   subject to passive attacks, it is necessary to ensure secure
+   interoperability by identifying a mandatory-to-implement mechanism
+   for establishing transport-layer security services.
+
+
+
+
+Harrison                    Standards Track                     [Page 5]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   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.
+
+1.1.  Relationship to Other Documents
+
+   This document is an integral part of the LDAP Technical Specification
+   [RFC4510].
+
+   This document, together with [RFC4510], [RFC4511], and [RFC4512],
+   obsoletes RFC 2251 in its entirety.  Sections 4.2.1 (portions) and
+   4.2.2 of RFC 2251 are obsoleted by this document.  Appendix B.1
+   summarizes the substantive changes made to RFC 2251 by this document.
+
+   This document obsoletes RFC 2829 in its entirety.  Appendix B.2
+   summarizes the substantive changes made to RFC 2829 by this document.
+
+   Sections 2 and 4 of RFC 2830 are obsoleted by [RFC4511].  The
+   remainder of RFC 2830 is obsoleted by this document.  Appendix B.3
+   summarizes the substantive changes made to RFC 2830 by this document.
+
+1.2.  Conventions
+
+   The key words "MUST", "MUST NOT", "SHALL", "SHOULD", "SHOULD NOT",
+   "MAY", and "OPTIONAL" in this document are to be interpreted as
+   described in RFC 2119 [RFC2119].
+
+   The term "user" represents any human or application entity that is
+   accessing the directory using a directory client.  A directory client
+   (or client) is also known as a directory user agent (DUA).
+
+   The term "transport connection" refers to the underlying transport
+   services used to carry the protocol exchange, as well as associations
+   established by these services.
+
+   The term "TLS layer" refers to TLS services used in providing
+   security services, as well as associations established by these
+   services.
+
+   The term "SASL layer" refers to SASL services used in providing
+   security services, as well as associations established by these
+   services.
+
+   The term "LDAP message layer" refers to the LDAP Message (PDU)
+   services used in providing directory services, as well as
+   associations established by these services.
+
+
+
+
+Harrison                    Standards Track                     [Page 6]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   The term "LDAP session" refers to combined services (transport
+   connection, TLS layer, SASL layer, LDAP message layer) and their
+   associations.
+
+   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 A 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 A before reading the remainder of this document.
+
+2.  Implementation Requirements
+
+   LDAP server implementations MUST support the anonymous authentication
+   mechanism of the simple Bind method (Section 5.1.1).
+
+   LDAP implementations that support any authentication mechanism other
+   than the anonymous authentication mechanism of the simple Bind method
+   MUST support the name/password authentication mechanism of the simple
+   Bind method (Section 5.1.3) and MUST be capable of protecting this
+   name/password authentication using TLS as established by the StartTLS
+   operation (Section 3).
+
+   Implementations SHOULD disallow the use of the name/password
+   authentication mechanism by default when suitable data security
+   services are not in place, and they MAY provide other suitable data
+   security services for use with this authentication mechanism.
+
+   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 (Section
+   5.2.3).
+
+   LDAP server implementations that support no authentication mechanism
+   other than the anonymous mechanism of the simple bind method SHOULD
+   support use of TLS as established by the StartTLS operation (Section
+   3).  (Other servers MUST support TLS per the second paragraph of this
+   section.)
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                     [Page 7]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   Implementations supporting TLS MUST support the
+   TLS_RSA_WITH_3DES_EDE_CBC_SHA ciphersuite and SHOULD support the
+   TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA ciphersuite.  Support for the
+   latter ciphersuite is recommended to encourage interoperability with
+   implementations conforming to earlier LDAP StartTLS specifications.
+
+3.  StartTLS Operation
+
+   The Start Transport Layer Security (StartTLS) operation defined in
+   Section 4.14 of [RFC4511] provides the ability to establish TLS
+   [RFC4346] in an LDAP session.
+
+   The goals of using the 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
+   5.2.3), and then only if the SASL EXTERNAL implementation chooses to
+   make use of the TLS credentials.
+
+3.1.  TLS Establishment Procedures
+
+   This section describes the overall procedures clients and servers
+   must follow for TLS establishment.  These procedures take into
+   consideration various aspects of the TLS layer including discovery of
+   resultant security level and assertion of the client's authorization
+   identity.
+
+3.1.1.  StartTLS Request Sequencing
+
+   A client may send the StartTLS extended request at any time after
+   establishing an LDAP session, except:
+
+      - when TLS is currently established on the session,
+      - when a multi-stage SASL negotiation is in progress on the
+        session, or
+      - when there are outstanding responses for operation requests
+        previously issued on the session.
+
+   As described in [RFC4511], Section 4.14.1, 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
+
+
+
+
+
+Harrison                    Standards Track                     [Page 8]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   causes interoperability issues because there are race conditions that
+   prevent servers from detecting some violations of these requirements
+   due to factors such as server hardware speed and network latencies.
+
+   There is no general requirement that the client have or have not
+   already performed a Bind operation (Section 5) before sending a
+   StartTLS operation request; however, where a client intends to
+   perform both a Bind operation and a StartTLS operation, it SHOULD
+   first perform the StartTLS operation so that the Bind request and
+   response messages are protected by the data security services
+   established by the StartTLS operation.
+
+3.1.2.  Client Certificate
+
+   If an LDAP server requests or demands that a client provide a user
+   certificate during TLS negotiation and the client does not present a
+   suitable user 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 a client that has provided a suitable certificate subsequently
+   performs a Bind operation using the SASL EXTERNAL authentication
+   mechanism (Section 5.2.3), information in the certificate may be used
+   by the server to identify and authenticate the client.
+
+3.1.3.  Server Identity Check
+
+   In order to prevent man-in-the-middle attacks, the client MUST verify
+   the server's identity (as presented in the server's Certificate
+   message).  In this section, the client's understanding of the
+   server's identity (typically the identity used to establish the
+   transport connection) is called the "reference identity".
+
+   The client determines the type (e.g., DNS name or IP address) of the
+   reference identity and performs a comparison between the reference
+   identity and each subjectAltName value of the corresponding type
+   until a match is produced.  Once a match is produced, the server's
+   identity has been verified, and the server identity check is
+   complete.  Different subjectAltName types are matched in different
+   ways.  Sections 3.1.3.1 - 3.1.3.3 explain how to compare values of
+   various subjectAltName types.
+
+   The client may map the reference identity to a different type prior
+   to performing a comparison.  Mappings may be performed for all
+   available subjectAltName types to which the reference identity can be
+   mapped; however, the reference identity should only be mapped to
+   types for which the mapping is either inherently secure (e.g.,
+   extracting the DNS name from a URI to compare with a subjectAltName
+
+
+
+Harrison                    Standards Track                     [Page 9]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   of type dNSName) or for which the mapping is performed in a secure
+   manner (e.g., using DNSSEC, or using user- or admin-configured host-
+   to-address/address-to-host lookup tables).
+
+   The server's identity may also be verified by comparing the reference
+   identity to the Common Name (CN) [RFC4519] value in the leaf Relative
+   Distinguished Name (RDN) of the subjectName field of the server's
+   certificate.  This comparison is performed using the rules for
+   comparison of DNS names in Section 3.1.3.1, below, with the exception
+   that no wildcard matching is allowed.  Although the use of the Common
+   Name value is existing practice, it is deprecated, and Certification
+   Authorities are encouraged to provide subjectAltName values instead.
+   Note that the TLS implementation may represent DNs in certificates
+   according to X.500 or other conventions.  For example, some X.500
+   implementations order the RDNs in a DN using a left-to-right (most
+   significant to least significant) convention instead of LDAP's
+   right-to-left convention.
+
+   If the server identity check fails, user-oriented clients SHOULD
+   either notify the user (clients may give the user the opportunity to
+   continue with the LDAP session in this case) or close the transport
+   connection and indicate that the server's identity is suspect.
+   Automated clients SHOULD close the transport connection and then
+   return or log an error indicating that the server's identity is
+   suspect or both.
+
+   Beyond the server identity check 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 requested to provide.  The
+   client may need to make use of local policy information in making
+   this determination.
+
+3.1.3.1.  Comparison of DNS Names
+
+   If the reference identity is an internationalized domain name,
+   conforming implementations MUST convert it to the ASCII Compatible
+   Encoding (ACE) format as specified in Section 4 of RFC 3490 [RFC3490]
+   before comparison with subjectAltName values of type dNSName.
+   Specifically, conforming implementations MUST perform the conversion
+   operation specified in Section 4 of RFC 3490 as follows:
+
+      * in step 1, the domain name SHALL be considered a "stored
+        string";
+      * in step 3, set the flag called "UseSTD3ASCIIRules";
+      * in step 4, process each label with the "ToASCII" operation; and
+      * in step 5, change all label separators to U+002E (full stop).
+
+
+
+
+
+Harrison                    Standards Track                    [Page 10]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   After performing the "to-ASCII" conversion, the DNS labels and names
+   MUST be compared for equality according to the rules specified in
+   Section 3 of RFC3490.
+
+   The '*' (ASCII 42) wildcard character is allowed in subjectAltName
+   values of type dNSName, and then only as the left-most (least
+   significant) DNS label in that value.  This wildcard matches any
+   left-most DNS label in the server name.  That is, the subject
+   *.example.com matches the server names a.example.com and
+   b.example.com, but does not match example.com or a.b.example.com.
+
+3.1.3.2.  Comparison of IP Addresses
+
+   When the reference identity is an IP address, the identity MUST be
+   converted to the "network byte order" octet string representation
+   [RFC791][RFC2460].  For IP Version 4, as specified in RFC 791, the
+   octet string will contain exactly four octets.  For IP Version 6, as
+   specified in RFC 2460, the octet string will contain exactly sixteen
+   octets.  This octet string is then compared against subjectAltName
+   values of type iPAddress.  A match occurs if the reference identity
+   octet string and value octet strings are identical.
+
+3.1.3.3.  Comparison of Other subjectName Types
+
+   Client implementations MAY support matching against subjectAltName
+   values of other types as described in other documents.
+
+3.1.4.  Discovery of Resultant Security Level
+
+   After a TLS layer is established in an LDAP session, both parties are
+   to each independently decide whether or not to continue based on
+   local policy and the security level achieved.  If either party
+   decides that the security level is inadequate for it to continue, it
+   SHOULD remove the TLS layer immediately after the TLS (re)negotiation
+   has completed (see [RFC4511], Section 4.14.3, and Section 3.2 below).
+   Implementations may reevaluate the security level at any time and,
+   upon finding it inadequate, should remove the TLS layer.
+
+3.1.5.  Refresh of Server Capabilities Information
+
+   After a TLS layer is established in an LDAP session, the client
+   SHOULD discard or refresh all information about the server that it
+   obtained prior to the initiation of the TLS negotiation and that it
+   did not obtain through secure mechanisms.  This protects against
+   man-in-the-middle attacks that may have altered any server
+   capabilities information retrieved prior to TLS layer installation.
+
+
+
+
+
+Harrison                    Standards Track                    [Page 11]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   The server may advertise different capabilities after installing a
+   TLS layer.  In particular, the value of 'supportedSASLMechanisms' may
+   be different after a TLS layer has been installed (specifically, the
+   EXTERNAL and PLAIN [PLAIN] mechanisms are likely to be listed only
+   after a TLS layer has been installed).
+
+3.2.  Effect of TLS on Authorization State
+
+   The establishment, change, and/or closure of TLS may cause the
+   authorization state to move to a new state.  This is discussed
+   further in Section 4.
+
+3.3.  TLS Ciphersuites
+
+   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 transport
+        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 confidentiality 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 negligible.
+
+      - After a TLS negotiation (either initial or subsequent) is
+        completed, both protocol peers should independently verify that
+        the security services provided by the negotiated ciphersuite are
+        adequate for the intended use of the LDAP session.  If they are
+        not, the TLS layer should be closed.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 12]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+4.  Authorization State
+
+   Every LDAP session has an associated authorization state.  This state
+   is comprised of numerous factors such as what (if any) authentication
+   state has been established, how it was established, and what security
+   services are in place.  Some factors may be determined and/or
+   affected by protocol events (e.g., Bind, StartTLS, or TLS closure),
+   and some factors may be determined by external events (e.g., time of
+   day or server load).
+
+   While it is often convenient to view authorization state in
+   simplistic terms (as we often do in this technical specification)
+   such as "an anonymous state", it is noted that authorization systems
+   in LDAP implementations commonly involve many factors that
+   interrelate in complex manners.
+
+   Authorization in LDAP is a local matter.  One of the key factors in
+   making authorization decisions is authorization identity.  The Bind
+   operation (defined in Section 4.2 of [RFC4511] and discussed further
+   in Section 5 below) allows information to be exchanged between the
+   client and server to establish an authorization identity for the LDAP
+   session.  The Bind operation may also be used to move the LDAP
+   session to an anonymous authorization state (see Section 5.1.1).
+
+   Upon initial establishment of the LDAP session, the session has an
+   anonymous authorization identity.  Among other things this implies
+   that the client need not send a BindRequest in the first PDU of the
+   LDAP message layer.  The client may send any operation request prior
+   to performing a Bind operation, and the server MUST treat it as if it
+   had been performed after an anonymous Bind operation (Section 5.1.1).
+
+   Upon receipt of a Bind request, the server immediately moves the
+   session to an anonymous authorization state.  If the Bind request is
+   successful, the session is moved to the requested authentication
+   state with its associated authorization state.  Otherwise, the
+   session remains in an anonymous state.
+
+   It is noted that other events both internal and external to LDAP may
+   result in the authentication and authorization states being moved to
+   an anonymous one.  For instance, the establishment, change, or
+   closure of data security services may result in a move to an
+   anonymous state, or the user's credential information (e.g.,
+   certificate) may have expired.  The former is an example of an event
+   internal to LDAP, whereas the latter is an example of an event
+   external to LDAP.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 13]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+5.  Bind Operation
+
+   The Bind operation ([RFC4511], Section 4.2) allows authentication
+   information to be exchanged between the client and server to
+   establish a new authorization state.
+
+   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 Method
+
+   The simple authentication method of the Bind Operation provides three
+   authentication mechanisms:
+
+      - An anonymous authentication mechanism (Section 5.1.1).
+
+      - An unauthenticated authentication mechanism (Section 5.1.2).
+
+      - A name/password authentication mechanism using credentials
+        consisting of a name (in the form of an LDAP distinguished name
+        [RFC4514]) and a password (Section 5.1.3).
+
+5.1.1.  Anonymous Authentication Mechanism of Simple Bind
+
+   An LDAP client may use the anonymous authentication mechanism of the
+   simple Bind method to explicitly establish an anonymous authorization
+   state by sending a Bind request with a name value of zero length and
+   specifying the simple authentication choice containing a password
+   value of zero length.
+
+5.1.2.  Unauthenticated Authentication Mechanism of Simple Bind
+
+   An LDAP client may use the unauthenticated authentication mechanism
+   of the simple Bind method to establish an anonymous authorization
+   state by sending a Bind request with a name value (a distinguished
+   name in LDAP string form [RFC4514] of non-zero length) and specifying
+   the simple authentication choice containing a password value of zero
+   length.
+
+
+
+
+Harrison                    Standards Track                    [Page 14]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   The distinguished name value provided by the client is intended to be
+   used for trace (e.g., logging) purposes only.  The value is not to be
+   authenticated or otherwise validated (including verification that the
+   DN refers to an existing directory object).  The value is not to be
+   used (directly or indirectly) for authorization purposes.
+
+   Unauthenticated Bind operations can have significant security issues
+   (see Section 6.3.1).  In particular, users intending to perform
+   Name/Password Authentication may inadvertently provide an empty
+   password and thus cause poorly implemented clients to request
+   Unauthenticated access.  Clients SHOULD be implemented to require
+   user selection of the Unauthenticated Authentication Mechanism by
+   means other than user input of an empty password.  Clients SHOULD
+   disallow an empty password input to a Name/Password Authentication
+   user interface.  Additionally, Servers SHOULD by default fail
+   Unauthenticated Bind requests with a resultCode of
+   unwillingToPerform.
+
+5.1.3.  Name/Password Authentication Mechanism of Simple Bind
+
+   An LDAP client may use the name/password authentication mechanism of
+   the simple Bind method to establish an authenticated authorization
+   state by sending a Bind request with a name value (a distinguished
+   name in LDAP string form [RFC4514] of non-zero length) 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.
+
+   A resultCode of invalidDNSyntax indicates that the DN sent in the
+   name value is syntactically invalid.  A resultCode of
+   invalidCredentials indicates that the DN is syntactically correct but
+   not valid for purposes of authentication, that the password is not
+   valid for the DN, or that the server otherwise considers the
+   credentials invalid.  A resultCode of success indicates that the
+   credentials are valid and that the server is willing to provide
+   service to the entity these credentials identify.
+
+   Server behavior is undefined for Bind requests specifying the
+   name/password authentication mechanism with a zero-length name value
+   and a password value of non-zero length.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 15]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   The name/password authentication mechanism of the simple Bind method
+   is not suitable for authentication in environments without
+   confidentiality protection.
+
+5.2.  SASL Authentication Method
+
+   The sasl authentication method of the Bind Operation provides
+   facilities for using any SASL mechanism including authentication
+   mechanisms and other services (e.g., data security services).
+
+5.2.1.  SASL Protocol Profile
+
+   LDAP allows authentication via any SASL mechanism [RFC4422].  As LDAP
+   includes native anonymous and name/password (plain text)
+   authentication methods, the ANONYMOUS [RFC4505] 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 ([RFC4422], Section 4).  This section explains how each of
+   these profiling requirements is met by LDAP.
+
+5.2.1.1.  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.
+
+5.2.1.2.  SASL Authentication Initiation and Protocol Exchange
+
+   SASL authentication is initiated via a BindRequest message
+   ([RFC4511], 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
+        [RFC4422], Sections 3 and 5).
+
+   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 sending
+   BindRequest messages multiple times.  A challenge is indicated by the
+   server sending a BindResponse message with the resultCode set to
+
+
+
+Harrison                    Standards Track                    [Page 16]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   saslBindInProgress.  This indicates that the server requires the
+   client to send a new BindRequest message with the same SASL mechanism
+   to continue the authentication process.
+
+   To the LDAP message layer, these challenges and responses are opaque
+   binary tokens of arbitrary length.  LDAP servers use the
+   serverSaslCreds field (an OCTET STRING) in a BindResponse message to
+   transmit each challenge.  LDAP clients use the credentials field (an
+   OCTET STRING) in the SaslCredentials sequence of a BindRequest
+   message to transmit each response.  Note that unlike some Internet
+   protocols where SASL is used, LDAP is not text based and does not
+   Base64-transform these challenge and response values.
+
+   Clients sending a BindRequest message with the sasl choice selected
+   SHOULD send a zero-length value in the name field.  Servers receiving
+   a BindRequest message with the sasl choice selected SHALL ignore any
+   value in the name field.
+
+   A client may abort a SASL Bind negotiation by sending a BindRequest
+   message with a different value in the mechanism field of
+   SaslCredentials or with 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 a resultCode
+   of authMethodNotSupported.  This will allow the client 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 BindResponse in which the resultCode
+   value is not saslBindInProgress.
+
+   The serverSaslCreds field in the BindResponse can be used to include
+   an optional challenge with a success notification for mechanisms that
+   are defined to have the server send additional data along with the
+   indication of successful completion.
+
+5.2.1.3.  Optional Fields
+
+   As discussed above, LDAP provides an optional field for carrying an
+   initial response in the message initiating the SASL exchange and
+   provides an optional field for carrying additional data in the
+   message indicating the outcome of the authentication exchange.  As
+   the mechanism-specific content in these fields may be zero length,
+   SASL requires protocol specifications to detail how an empty field is
+   distinguished from an absent field.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 17]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   Zero-length initial response data is distinguished from no initial
+   response data in the initiating message, a BindRequest PDU, by the
+   presence of the SaslCredentials.credentials OCTET STRING (of length
+   zero) in that PDU.  If the client does not intend to send an initial
+   response with the BindRequest initiating the SASL exchange, it MUST
+   omit the SaslCredentials.credentials OCTET STRING (rather than
+   include an zero-length OCTET STRING).
+
+   Zero-length additional data is distinguished from no additional
+   response data in the outcome message, a BindResponse PDU, by the
+   presence of the serverSaslCreds OCTET STRING (of length zero) in that
+   PDU.  If a server does not intend to send additional data in the
+   BindResponse message indicating outcome of the exchange, the server
+   SHALL omit the serverSaslCreds OCTET STRING (rather than including a
+   zero-length OCTET STRING).
+
+5.2.1.4.  Octet Where Negotiated Security Layers Take Effect
+
+   SASL layers take effect following the transmission by the server and
+   reception by the client of the final BindResponse in the SASL
+   exchange with a resultCode of success.
+
+   Once a SASL 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 layer is not affected by a failed
+   or non-SASL Bind.
+
+5.2.1.5.  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) ([RFC4512], 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 all clients --
+   even those with an anonymous authorization -- to retrieve the
+   'supportedSASLMechanisms' attribute of the root DSE both before and
+   after the SASL authentication exchange.  The purpose of the latter is
+   to allow the client to detect possible downgrade attacks (see Section
+   6.4 and [RFC4422], Section 6.1.2).
+
+   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 session.
+
+
+
+
+Harrison                    Standards Track                    [Page 18]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+5.2.1.6.  Rules for Using SASL Layers
+
+   Upon installing a SASL layer, the client SHOULD discard or refresh
+   all information about the server that it obtained prior to the
+   initiation of the SASL negotiation and that it did not obtain through
+   secure mechanisms.
+
+   If a lower-level security layer (such as TLS) is installed, any SASL
+   layer SHALL be layered on top of such security layers regardless of
+   the order of their negotiation.  In all other respects, the SASL
+   layer and other security layers act independently, e.g., if both a
+   TLS layer and a SASL layer are in effect, then removing the TLS layer
+   does not affect the continuing service of the SASL layer.
+
+5.2.1.7.  Support for Multiple Authentications
+
+   LDAP supports multiple SASL authentications as defined in [RFC4422],
+   Section 4.
+
+5.2.1.8.  SASL Authorization Identities
+
+   Some SASL mechanisms allow clients to request a desired authorization
+   identity for the LDAP session ([RFC4422], Section 3.4).  The decision
+   to allow or disallow the current authentication identity to have
+   access to the requested authorization identity is a matter of local
+   policy.  The authorization identity is a string of UTF-8 [RFC3629]
+   encoded [Unicode] characters corresponding to the following Augmented
+   Backus-Naur Form (ABNF) [RFC4234] grammar:
+
+      authzId = dnAuthzId / uAuthzId
+
+      ; distinguished-name-based authz id
+      dnAuthzId =  "dn:" distinguishedName
+
+      ; unspecified authorization id, UTF-8 encoded
+      uAuthzId = "u:" userid
+      userid = *UTF8 ; syntax unspecified
+
+   where the distinguishedName rule is defined in Section 3 of [RFC4514]
+   and the UTF8 rule is defined in Section 1.4 of [RFC4512].
+
+   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 ([RFC4517], Section 4.2.15).
+   There is no requirement that the asserted distinguishedName value be
+   that of an entry in the directory.
+
+
+
+
+
+Harrison                    Standards Track                    [Page 19]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   The uAuthzId choice allows clients to assert an authorization
+   identity that is not in distinguished name form.  The format of
+   userid is defined only as a sequence of UTF-8 [RFC3629] encoded
+   [Unicode] characters, and any further interpretation is a local
+   matter.  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.  To compare
+   uAuthzId values, each uAuthzId value MUST be prepared as a "query"
+   string ([RFC3454], Section 7) using the SASLprep [RFC4013] algorithm,
+   and then the two values are compared octet-wise.
+
+   The above grammar is extensible.  The authzId production may be
+   extended to support additional forms of identities.  Each form is
+   distinguished by its unique prefix (see Section 3.12 of [RFC4520] for
+   registration requirements).
+
+5.2.2.  SASL Semantics within LDAP
+
+   Implementers must take care to maintain the semantics of SASL
+   specifications when handling data that has different semantics in the
+   LDAP protocol.
+
+   For example, the SASL DIGEST-MD5 authentication mechanism
+   [DIGEST-MD5] utilizes an authentication identity and a realm that are
+   syntactically simple strings and semantically simple username
+   [RFC4013] and realm values.  These values are not LDAP DNs, and there
+   is no requirement that they be represented or treated as such.
+
+5.2.3.  SASL EXTERNAL Authentication Mechanism
+
+   A client can use the SASL EXTERNAL ([RFC4422], Appendix A) 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).  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 LDAP session in an anonymous state
+   (Section 4), the state of any installed security layer is unaffected.
+
+   A client may either request that its authorization identity be
+   automatically derived from its authentication credentials exchanged
+   at a lower security layer, or it may explicitly provide a desired
+   authorization identity.  The former is known as an implicit
+   assertion, and the latter as an explicit assertion.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 20]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+5.2.3.1.  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 field (found within
+   the SaslCredentials sequence in the BindRequest).  The server will
+   derive the client's authorization identity from the authentication
+   identity supplied by a security layer (e.g., a public key certificate
+   used during TLS layer installation) according to local policy.  The
+   underlying mechanics of how this is accomplished are implementation
+   specific.
+
+5.2.3.2.  Explicit Assertion
+
+   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 field (found within the SaslCredentials
+   sequence in the BindRequest).  The value of the credentials field (an
+   OCTET STRING) is the asserted authorization identity and MUST be
+   constructed as documented in Section 5.2.1.8.
+
+6.  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.
+
+6.1.  General LDAP Security Considerations
+
+   LDAP itself provides no security or protection from accessing or
+   updating the directory by means other than through the LDAP protocol,
+   e.g., from inspection of server database files by database
+   administrators.
+
+   Sensitive data may be carried in almost any LDAP message, and its
+   disclosure may be subject to privacy laws or other legal regulation
+   in many countries.  Implementers should take appropriate measures to
+   protect sensitive data from disclosure to unauthorized entities.
+
+   A session on which the client has not established data 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 implementers SHOULD take
+   measures to protect sensitive data in the LDAP session from these
+   attacks by using data protection services as discussed in this
+   document.  Clients and servers should provide the ability to be
+   configured to require these protections.  A resultCode of
+
+
+
+Harrison                    Standards Track                    [Page 21]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   confidentialityRequired indicates that the server requires
+   establishment of (stronger) data confidentiality protection in order
+   to perform the requested operation.
+
+   Access control should always be applied when reading sensitive
+   information or updating directory information.
+
+   Various security factors, including authentication and authorization
+   information and data security services may change during the course
+   of the LDAP session, or even during the performance of a particular
+   operation.  Implementations should be robust in the handling of
+   changing security factors.
+
+6.2.  StartTLS Security Considerations
+
+   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 through 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-
+   protected session.  For example, the security level of the TLS layer
+   might have been negotiated down to plaintext.
+
+   Clients MUST 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 configurable to refuse to proceed
+   without an acceptable level of security.
+
+   As stated in Section 3.1.2, a server may use a local security policy
+   to determine whether to successfully complete TLS negotiation.
+   Information in the user's certificate that is originated or verified
+   by the certification authority should be used by the policy
+   administrator when configuring the identification and authorization
+   policy.
+
+   Server implementers 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 [RFC4346].
+
+
+
+Harrison                    Standards Track                    [Page 22]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+6.3.  Bind Operation Security Considerations
+
+   This section discusses several security considerations relevant to
+   LDAP authentication via the Bind operation.
+
+6.3.1.  Unauthenticated Mechanism Security Considerations
+
+   Operational experience shows that clients can (and frequently do)
+   misuse the unauthenticated authentication mechanism of the simple
+   Bind method (see Section 5.1.2).  For example, a client program might
+   make a decision to grant access to non-directory information on the
+   basis of successfully completing a Bind operation.  LDAP server
+   implementations may return a success response to an unauthenticated
+   Bind request.  This may erroneously leave the client with the
+   impression that the server has successfully authenticated the
+   identity represented by the distinguished name when in reality, an
+   anonymous authorization state 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.
+
+6.3.2.  Name/Password Mechanism Security Considerations
+
+   The name/password authentication mechanism of the simple Bind method
+   discloses the password to the server, which is an inherent security
+   risk.  There are other mechanisms, such as SASL DIGEST-MD5
+   [DIGEST-MD5], that do not disclose the password to the server.
+
+6.3.3.  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.  LDAP
+   implementations SHOULD NOT by default support authentication methods
+   using clear text passwords and other unprotected authentication
+   credentials unless the data on the session is protected using TLS or
+   other data confidentiality and data integrity protection.
+
+   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 [RFC4422]
+
+
+
+
+
+Harrison                    Standards Track                    [Page 23]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   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 that:
+
+         A TLS layer has been successfully installed.
+
+         OR
+
+         Some other data confidentiality mechanism that protects the
+         password value from eavesdropping has been provided.
+
+         OR
+
+         The server returns a resultCode of confidentialityRequired for
+         the operation (i.e., name/password 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.
+
+   Server implementations may also want to provide policy mechanisms to
+   invalidate or otherwise protect accounts in situations where a server
+   detects that a password for an account has been transmitted in the
+   clear.
+
+6.3.4.  Hashed Password Security Considerations
+
+   Some authentication mechanisms (e.g., DIGEST-MD5) transmit a hash of
+   the password value that may be vulnerable to offline dictionary
+   attacks.  Implementers should take care to protect such hashed
+   password values during transmission using TLS or other
+   confidentiality mechanisms.
+
+6.4.  SASL Security Considerations
+
+   Until data integrity service is installed on an LDAP session, an
+   attacker can modify the transmitted values of the
+   'supportedSASLMechanisms' attribute response and thus downgrade the
+   list of available SASL mechanisms to include only the least secure
+   mechanism.  To detect this type of attack, the client may retrieve
+   the SASL mechanisms the server makes available both before and after
+   data integrity service is installed on an LDAP session.  If the
+   client finds that the integrity-protected list (the list obtained
+
+
+
+Harrison                    Standards Track                    [Page 24]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   after data integrity service was installed) contains a stronger
+   mechanism than those in the previously obtained list, the client
+   should assume the previously obtained list was modified by an
+   attacker.  In this circumstance it is recommended that the client
+   close the underlying transport connection and then reconnect to
+   reestablish the session.
+
+6.5.  Related Security Considerations
+
+   Additional security considerations relating to the various
+   authentication methods and mechanisms discussed in this document
+   apply and can be found in [RFC4422], [RFC4013], [RFC3454], and
+   [RFC3629].
+
+7.  IANA Considerations
+
+   The IANA has updated the LDAP Protocol Mechanism registry to indicate
+   that this document and [RFC4511] provide the definitive technical
+   specification for the StartTLS (1.3.6.1.4.1.1466.20037) extended
+   operation.
+
+   The IANA has updated the LDAP LDAPMessage types registry to indicate
+   that this document and [RFC4511] provide the definitive technical
+   specification for the bindRequest (0) and bindResponse (1) message
+   types.
+
+   The IANA has updated the LDAP Bind Authentication Method registry to
+   indicate that this document and [RFC4511] provide the definitive
+   technical specification for the simple (0) and sasl (3) bind
+   authentication methods.
+
+   The IANA has updated the LDAP authzid prefixes registry to indicate
+   that this document provides the definitive technical specification
+   for the dnAuthzId (dn:) and uAuthzId (u:) authzid prefixes.
+
+8.  Acknowledgements
+
+   This document combines information originally contained in RFC 2251,
+   RFC 2829, and RFC 2830.  RFC 2251 was a product of the Access,
+   Searching, and Indexing of Directories (ASID) Working Group.  RFC
+   2829 and RFC 2830 were products of the LDAP Extensions (LDAPEXT)
+   Working Group.
+
+   This document is a product of the IETF LDAP Revision (LDAPBIS)
+   working group.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 25]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+9.  Normative References
+
+   [RFC791]     Postel, J., "Internet Protocol", STD 5, RFC 791,
+                September 1981.
+
+   [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
+                Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC2460]    Deering, S. and R. Hinden, "Internet Protocol, Version 6
+                (IPv6) Specification", RFC 2460, December 1998.
+
+   [RFC3454]    Hoffman, P. and M. Blanchet, "Preparation of
+                Internationalized Strings ("stringprep")", RFC 3454,
+                December 2002.
+
+   [RFC3490]    Faltstrom, P., Hoffman, P., and A. Costello,
+                "Internationalizing Domain Names in Applications
+                (IDNA)", RFC 3490, March 2003.
+
+   [RFC3629]    Yergeau, F., "UTF-8, a transformation format of ISO
+                10646", STD 63, RFC 3629, November 2003.
+
+   [RFC4013]    Zeilenga, K., "SASLprep: Stringprep Profile for User
+                Names and Passwords", RFC 4013, February 2005.
+
+   [RFC4234]    Crocker, D. and P. Overell, "Augmented BNF for Syntax
+                Specifications: ABNF", RFC 4234, October 2005.
+
+   [RFC4346]    Dierks, T. and E. Rescorla, "The TLS Protocol Version
+                1.1", RFC 4346, March 2006.
+
+   [RFC4422]    Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
+                Authentication and Security Layer (SASL)", RFC 4422,
+                June 2006.
+
+   [RFC4510]    Zeilenga, K., Ed., "Lightweight Directory Access
+                Protocol (LDAP): Technical Specification Road Map", RFC
+                4510, June 2006.
+
+   [RFC4511]    Sermersheim, J., Ed., "Lightweight Directory Access
+                Protocol (LDAP): The Protocol", RFC 4511, June 2006.
+
+   [RFC4512]    Zeilenga, K., "Lightweight Directory Access Protocol
+                (LDAP): Directory Information Models", RFC 4512, June
+                2006.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 26]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   [RFC4514]    Zeilenga, K., Ed., "Lightweight Directory Access
+                Protocol (LDAP): String Representation of Distinguished
+                Names", RFC 4514, June 2006.
+
+   [RFC4517]    Legg, S., Ed., "Lightweight Directory Access Protocol
+                (LDAP): Syntaxes and Matching Rules", RFC 4517, June
+                2006.
+
+   [RFC4519]    Sciberras, A., Ed., "Lightweight Directory Access
+                Protocol (LDAP): Schema for User Applications", RFC
+                4519, June 2006.
+
+   [RFC4520]    Zeilenga, K., "Internet Assigned Numbers Authority
+                (IANA) Considerations for the Lightweight Directory
+                Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006.
+
+   [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/).
+
+   [X.501]      ITU-T Rec. X.501, "The Directory: Models", 1993.
+
+10.  Informative References
+
+   [DIGEST-MD5] Leach, P., Newman, C., and A. Melnikov, "Using Digest
+                Authentication as a SASL Mechanism", Work in Progress,
+                March 2006.
+
+   [PLAIN]      Zeilenga, K., "The Plain SASL Mechanism", Work in
+                Progress, March 2005.
+
+   [RFC2828]    Shirey, R., "Internet Security Glossary", FYI 36, RFC
+                2828, May 2000.
+
+   [RFC4301]    Kent, S. and K. Seo, "Security Architecture for the
+                Internet Protocol", RFC 4301, December 2005.
+
+   [RFC4505]    Zeilenga, K., "The Anonymous SASL Mechanism", RFC 4505,
+                June 2006.
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 27]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+Appendix A.  Authentication and Authorization Concepts
+
+   This appendix is non-normative.
+
+   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.
+
+A.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.
+
+A.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.  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 transport
+   connection via which the request is transmitted; and others (e.g.,
+   time of day) may be "environmental".
+
+   Access control policies are expressed in terms of access control
+   factors; for example, "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.
+
+A.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 authorization 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.  X.509 certificates, Kerberos tickets, and simple
+   identity and password pairs are all examples of authentication
+
+
+
+Harrison                    Standards Track                    [Page 28]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   credential forms.  Note that an authentication mechanism may
+   constrain the form of authentication identities used with it.
+
+A.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; for example, "entity X can perform
+   operation Y on resource Z".
+
+   The authorization identity of an LDAP session is often semantically
+   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 [RFC4422].
+   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, thus 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 B.  Summary of Changes
+
+   This appendix is non-normative.
+
+   This appendix summarizes substantive changes made to RFC 2251, RFC
+   2829 and RFC 2830.  In addition to the specific changes detailed
+   below, the reader of this document should be aware that numerous
+   general editorial changes have been made to the original content from
+   the source documents.  These changes include the following:
+
+   - The material originally found in RFC 2251 Sections 4.2.1 and 4.2.2,
+     RFC 2829 (all sections except Sections 2 and 4), and RFC 2830 was
+     combined into a single document.
+
+   - The combined material was substantially reorganized and edited to
+     group related subjects, improve the document flow, and clarify
+     intent.
+
+   - Changes were made throughout the text to align with definitions of
+     LDAP protocol layers and IETF security terminology.
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 29]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+   - Substantial updates and additions were made to security
+     considerations from both documents based on current operational
+     experience.
+
+B.1.  Changes Made to RFC 2251
+
+   This section summarizes the substantive changes made to Sections
+   4.2.1 and 4.2.2 of RFC 2251 by this document.  Additional substantive
+   changes to Section 4.2.1 of RFC 2251 are also documented in
+   [RFC4511].
+
+B.1.1.  Section 4.2.1 ("Sequencing of the Bind Request")
+
+   - Paragraph 1: Removed the sentence, "If at any stage the client
+     wishes to abort the bind process it MAY unbind and then drop the
+     underlying connection".  The Unbind operation still permits this
+     behavior, but it is not documented explicitly.
+
+   - Clarified that the session is moved to an anonymous state upon
+     receipt of the BindRequest PDU and that it is only moved to a non-
+     anonymous state if and when the Bind request is successful.
+
+B.1.2.  Section 4.2.2 ("Authentication and Other Security Services")
+
+   - RFC 2251 states that anonymous authentication MUST be performed
+     using the simple bind method.  This specification defines the
+     anonymous authentication mechanism of the simple bind method and
+     requires all conforming implementations to support it.  Other
+     authentication mechanisms producing anonymous authentication and
+     authorization state may also be implemented and used by conforming
+     implementations.
+
+B.2.  Changes Made to RFC 2829
+
+   This section summarizes the substantive changes made to RFC 2829.
+
+B.2.1.  Section 4 ("Required security mechanisms")
+
+   - The name/password authentication mechanism (see Section B.2.5
+     below) protected by TLS replaces the SASL DIGEST-MD5 mechanism as
+     LDAP's mandatory-to-implement password-based authentication
+     mechanism.  Implementations are encouraged to continue supporting
+     SASL DIGEST-MD5 [DIGEST-MD5].
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 30]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+B.2.2.  Section 5.1 ("Anonymous authentication procedure")
+
+   - Clarified that anonymous authentication involves a name value of
+     zero length and a password value of zero length.  The
+     unauthenticated authentication mechanism was added to handle simple
+     Bind requests involving a name value with a non-zero length and a
+     password value of zero length.
+
+B.2.3.  Section 6 ("Password-based authentication")
+
+   - See Section B.2.1.
+
+B.2.4.  Section 6.1 ("Digest authentication")
+
+   - As the SASL-DIGEST-MD5 mechanism is no longer mandatory to
+     implement, this section is now historical and was not included in
+     this document.  RFC 2829, Section 6.1, continues to document the
+     SASL DIGEST-MD5 authentication mechanism.
+
+B.2.5.  Section 6.2 ("'simple' authentication choice under TLS
+        encryption")
+
+   - Renamed the "simple" authentication mechanism to the name/password
+     authentication mechanism to better describe it.
+
+   - The use of TLS was generalized to align with definitions of LDAP
+     protocol layers.  TLS establishment is now discussed as an
+     independent subject and is generalized for use with all
+     authentication mechanisms and other security layers.
+
+   - Removed the implication that the userPassword attribute is the sole
+     location for storage of password values to be used in
+     authentication.  There is no longer any implied requirement for how
+     or where passwords are stored at the server for use in
+     authentication.
+
+B.2.6.  Section 6.3 ("Other authentication choices with TLS")
+
+   - See Section B.2.5.
+
+B.2.7.  Section 7.1 ("Certificate-based authentication with TLS")
+
+   - See Section B.2.5.
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 31]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+B.2.8.  Section 8 ("Other mechanisms")
+
+   - All SASL authentication mechanisms are explicitly allowed within
+     LDAP.  Specifically, this means the SASL ANONYMOUS and SASL PLAIN
+     mechanisms are no longer precluded from use within LDAP.
+
+B.2.9.  Section 9 ("Authorization Identity")
+
+   - Specified matching rules for dnAuthzId and uAuthzId values.  In
+     particular, the DN value in the dnAuthzId form must be matched
+     using DN matching rules, and the uAuthzId value MUST be prepared
+     using SASLprep rules before being compared octet-wise.
+
+   - Clarified that uAuthzId values should not be assumed to be globally
+     unique.
+
+B.2.10.  Section 10 ("TLS Ciphersuites")
+
+   - TLS ciphersuite recommendations are no longer included in this
+     specification.  Implementations must now support the
+     TLS_RSA_WITH_3DES_EDE_CBC_SHA ciphersuite and should continue to
+     support the TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA ciphersuite.
+
+   - Clarified that anonymous authentication involves a name value of
+     zero length and a password value of zero length.  The
+     unauthenticated authentication mechanism was added to handle simple
+     Bind requests involving a name value with a non-zero length and a
+     password value of zero length.
+
+B.3.  Changes Made to RFC 2830
+
+   This section summarizes the substantive changes made to Sections 3
+   and 5 of RFC 2830.  Readers should consult [RFC4511] for summaries of
+   changes to other sections.
+
+B.3.1.  Section 3.6 ("Server Identity Check")
+
+   - Substantially updated the server identity check algorithm to ensure
+     that it is complete and robust.  In particular, the use of all
+     relevant values in the subjectAltName and the subjectName fields
+     are covered by the algorithm and matching rules are specified for
+     each type of value.  Mapped (derived) forms of the server identity
+     may now be used when the mapping is performed in a secure fashion.
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 32]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+B.3.2.  Section 3.7 ("Refresh of Server Capabilities Information")
+
+   - Clients are no longer required to always refresh information about
+     server capabilities following TLS establishment.  This is to allow
+     for situations where this information was obtained through a secure
+     mechanism.
+
+B.3.3.  Section 5 ("Effects of TLS on a Client's Authorization
+        Identity")
+
+   - Establishing a TLS layer on an LDAP session may now cause the
+     authorization state of the LDAP session to change.
+
+B.3.4.  Section 5.2 ("TLS Connection Closure Effects")
+
+   - Closing a TLS layer on an LDAP session changes the authentication
+     and authorization state of the LDAP session based on local policy.
+     Specifically, this means that implementations are not required to
+     change the authentication and authorization states to anonymous
+     upon TLS closure.
+
+   - Replaced references to RFC 2401 with RFC 4301.
+
+Author's Address
+
+   Roger Harrison
+   Novell, Inc.
+   1800 S.  Novell Place
+   Provo, UT 84606
+   USA
+
+   Phone: +1 801 861 2642
+   EMail: roger_harrison@novell.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 33]
+
+RFC 4513              LDAP Authentication Methods              June 2006
+
+
+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2006).
+
+   This document is subject to the rights, licenses and restrictions
+   contained in BCP 78, and except as set forth therein, the authors
+   retain all their rights.
+
+   This document and the information contained herein are provided on an
+   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
+   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
+   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
+   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
+   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+Intellectual Property
+
+   The IETF takes no position regarding the validity or scope of any
+   Intellectual Property Rights or other rights that might be claimed to
+   pertain to the implementation or use of the technology described in
+   this document or the extent to which any license under such rights
+   might or might not be available; nor does it represent that it has
+   made any independent effort to identify any such rights.  Information
+   on the procedures with respect to rights in RFC documents can be
+   found in BCP 78 and BCP 79.
+
+   Copies of IPR disclosures made to the IETF Secretariat and any
+   assurances of licenses to be made available, or the result of an
+   attempt made to obtain a general license or permission for the use of
+   such proprietary rights by implementers or users of this
+   specification can be obtained from the IETF on-line IPR repository at
+   http://www.ietf.org/ipr.
+
+   The IETF invites any interested party to bring to its attention any
+   copyrights, patents or patent applications, or other proprietary
+   rights that may cover technology that may be required to implement
+   this standard.  Please address the information to the IETF at
+   ietf-ipr@ietf.org.
+
+Acknowledgement
+
+   Funding for the RFC Editor function is provided by the IETF
+   Administrative Support Activity (IASA).
+
+
+
+
+
+
+
+Harrison                    Standards Track                    [Page 34]
+