Fix prev commit, spawns unnecessary threads.

[openldap] / doc / drafts / draft-ietf-ldapbis-authmeth-xx.txt

INTERNET-DRAFT                                      Editor: R. Harrison
draft-ietf-ldapbis-authmeth-14.txt                         Novell, Inc.
Obsoletes: 2829, 2830                                    February, 2005
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
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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....................................................5
   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........................8
   3.1.6. Server Identity Check........................................9
   3.1.7. Refresh of Server Capabilities Information...................9
   3.2. Effects of TLS on a Client's Authorization Identity...........10
   3.3. TLS Ciphersuites..............................................10
   3.3.1. TLS Ciphersuites Recommendations............................10
   4. Associations....................................................11
   4.1. Anonymous Association on Unbound Connections..................11
   4.2. Anonymous Association After Failed Bind.......................12
   4.3. Invalidated Associations......................................12
   5. Bind Operation..................................................12
   5.1. Simple Authentication Choice..................................12
   5.2. SASL Authentication Choice....................................12
   6. Anonymous Authentication Mechanism of Simple Bind...............13
   7. Unauthenticated Authentication Mechanism of Simple Bind.........13
   8. Simple Authentication Mechanism of Simple Bind .................13
   9. SASL Protocol Profile...........................................14
   9.1. SASL Service Name for LDAP....................................14
   9.2. SASL Authentication Initiation and Protocol Exchange..........14
   9.3. Octet Where Negotiated Security Mechanisms Take Effect........15
   9.4. Determination of Supported SASL Mechanisms....................15


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   9.5. Rules for Using SASL Layers...................................16
   9.6 Support for Multiple Authentications...........................16
   9.7. SASL Authorization Identities.................................16
   10. SASL DIGEST-MD5 Authentication Mechanism.......................17
   11. SASL EXTERNAL Authentication Mechanism.........................17
   11.1. Implicit Assertion...........................................18
   11.2. Explicit Assertion...........................................18
   12. Security Considerations........................................18
   12.1. General LDAP Security Considerations.........................18
   12.1.1. Password-related Security Considerations...................19
   12.2. StartTLS Security Considerations.............................20
   12.3. Unauthenticated Mechanism Security Considerations............20
   12.4. Simple Mechanism Security Considerations.....................21
   12.5. SASL DIGEST-MD5 Mechanism Security Considerations............21
   12.6. Related Security Considerations..............................21
   13. IANA Considerations............................................21
   Acknowledgments....................................................21
   Normative References...............................................21
   Informative References.............................................23
   Author's Address...................................................23
   Appendix A. Association State Transition Tables....................23
   A.1. Association States............................................23
   A.2. Actions that Affect Association State.........................24
   A.3. Association State Transition Table............................24
   Appendix B. Authentication and Authorization Concepts..............25
   B.1. Access Control Policy.........................................25
   B.2. Access Control Factors........................................25
   B.3. Authentication, Credentials, Identity.........................25
   B.4. Authorization Identity........................................25
   Appendix C. RFC 2829 Change History................................26
   Appendix D. RFC 2830 Change History................................30
   Appendix E. RFC 2251 Change History................................30
   Appendix F. Change History to Combined Document....................31
   Intellectual Property Rights.......................................45


1. Introduction

   The Lightweight Directory Access Protocol (LDAP) [Roadmap] 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:




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   (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.

   (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,

   (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,



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   (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
       mechanisms.

   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.

   Sections 2 and 4 of RFC 2830 are obsoleted by [Protocol].  The
   remainder of RFC 2830 is obsoleted by this document. 

1.2. Conventions


   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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   The term "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).

   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.

   The term "association" refers to the association that exists between
   the transport connection and 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.

   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.

2. Implementation Requirements

   LDAP server implementations MUST support the anonymous
   authentication mechanism of simple bind (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 (section
   10).  DIGEST-MD5 is a reasonably strong authentication mechanism
   that provides (mandatory-to-implement) data security (data integrity
   and data confidentiality) services.

   LDAP implementations SHOULD support the simple (DN and password)
   authentication mechanism of simple bind (section 8).
   Implementations that support this authentication mechanism MUST be
   capable of protecting using TLS as established by the StartTLS
   operation (section 3), SHOULD disallow the use of this

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   authentication mechanism by default when suitable data security
   services are not in place, and 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 (sections
   3.2.2 and 9).

   LDAP server implementations SHOULD support the StartTLS operation
   (section 3), 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 11), 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.

   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.



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   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.

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 (as 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 during 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 a client that has provided a suitable certificate subsequently
   binds using the SASL EXTERNAL authentication mechanism (section 9),
   information in the certificate may be used by the server to
   establish the client's authorization identity.

3.1.5. Discovery of Resultant Security Level

   After a TLS layer is established on a transport connection, both
   parties are to individually decide whether or not to continue based
   on the security level achieved. The procedure for ascertaining the
   TLS layer's security level is implementation dependent.



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   If the client or server decides that the security level is not high
   enough for it to continue, it SHOULD gracefully remove 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 transport 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 with 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 LDAP session in this case) or close the transport
   connection and indicate that the server's identity is suspect.
   Automated clients SHOULD close the connection and then  return
   and/or log an error indicating that the server's identity is suspect.

   Beyond the server identity checks described in this section, clients
   SHOULD be prepared to do further checking to ensure that the server
   is authorized to provide the service it is requested 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



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   Upon installing a TLS layer, 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
   layer installation. 

   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. Effects of TLS on a Client's Authorization Identity

   The decision to keep or invalidate the established state of the
   association (section 4.3) after TLS layer installation or removal is
   a matter of local server policy. 

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 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

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   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
         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 LDAP
   message layer. 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.


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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 LDAP
   session has an invalidated association, the server may reject any
   operation request other than Bind, Unbind, and StartTLS by
   responding with a resultCode of strongerAuthRequired 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 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

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   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
   specifying 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
   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] 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, or the password is not
   valid for the DN, or the server otherwise considers the credentials
   to be invalidA resultCode of success indicates that the credentials
   are valid and the server is willing to provide service to the entity
   these credentials identify.



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   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.x

9. SASL Protocol Profile

   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
   Bind operation multiple times. A challenge is indicated by the
   server sending a BindResponse PDU with the resultCode set to
   saslBindInProgress. This indicates that the server requires the
   client to send a new BindRequest PDU with the same sasl mechanism to
   continue the authentication process.

   To 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 PDU
   message to transmit each challenge. LDAP clients use the credentials

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   field, an OCTET STRING, in the SaslCredentials sequence of a
   BindRequest PDU 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 BindRequest 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.

   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 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
   is not saslBindInProgress (either success or another 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 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 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.

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

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   current LDAP session state. LDAP servers SHOULD allow a client with
   an anonymous association 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 Layers

   If a SASL layer is installed, 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 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 SASL
   layer does not affect the continuing service of the TLS layer and
   vice versa.

9.6 Support for Multiple Authentications

   LDAP supports multiple SASL authentications as defined in [SASL]
   section 6.3.

9.7. SASL Authorization Identities

   Some SASL mechanisms allow clients to request a desired
   authorization identity for the association. The decision to allow or
   disallow the current authentication identity to have access to the
   requested authorization identity is a matter of local policy ([SASL]
   section 4.2). 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 the <UTF8> production is defined in section 1.3 of
   [Models].

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   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]. There is no
   requirement that the asserted distinguishedName value 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.  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 using
   [SASLPrep] and then the two values are compared octet-wise.

10. SASL DIGEST-MD5 Authentication Mechanism

   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.
   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.

11. 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

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   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 resulting
   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 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 an
   authorization identity desired for the association.  The former is
   known as an implicit assertion, and the latter as an explicit
   assertion.

11.1. 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.

11.2. 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 9.7.

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


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   control SHOULD always be applied when reading sensitive information
   or updating directory information.

   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 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 confidentialityRequired indicates that the server
   requires establishment of (stronger) data confidentiality protection
   in order to perform the requested operation.

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.  LDAP
   implementations SHOULD NOT support authentication methods using
   cleartext passwords and other unprotected authentication credentials
   unless the data on the connection 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 [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 TLS layer has been successfully installed.

      OR

        Some other data confidentiality mechanism that protects the
        password value from snooping has been provided.

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      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

   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 layer 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 reality, 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.


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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

   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



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   [[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. 

   [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.



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   [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

   [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.3.

   ID Association State Description
   -- --------------------------------------------------------------


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   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 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.3.

   ID  Action
   --  --------------------------------------------------------------
   A1  Client bind request fails
   A2  Client successfully performs anonymous simple bind or
        unauthenticated simple bind
   A3  Client successfully binds producing an authentication ID of I.
        Authentication ID I maps to authorization ID X. Depending on
        the bind mechanism and associated parameters authorization ID X
        was either derived from authentication ID I or was explicitly
        requested as part of the bind operation.
   A4  Client StartTLS request fails
   A5  Client StartTLS request succeeds
   A6  Client or Server: graceful TLS layer removal 
   A7  Server decides to invalidate current association state

A.3. 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.

                        Next State
        Action                                     Comment
   ----------------  ---------------  -------------------------------
   A1                       S1        Section 4
   A2                       S1        Sections 6 and 7
   A3                       S2
   A4                   no change     [Protocol] section 4.14.2.2
   A5                no change or S3* [Protocol] section 4.14.2.1
   A6                no change or S3* [Protocol] section 4.14.3.1
   A7                       S3

     * The server may invalidate the association after installing or
       removing a TLS layer (section 3.2).



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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
   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


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   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.

     - 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


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     - 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. 

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

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     - 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.

     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.


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     - 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.

   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


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     - 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.

     - 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.
      

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     - 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.

     - 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




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     - 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.
   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

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       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

     - 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.

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     - 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.

     - 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..."


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   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.

     - 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.


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     - 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.

   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.

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   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.

     - 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

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     - 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

     - 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.

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   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

     - 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..."


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     - 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

     - 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

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     - 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

   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




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     - 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
       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


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     - 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.
     - Made usage of data confidentiality consistent throughout
       document.

   Section 1
     - Reworded mechanisms 3 and 4 for more parallelism.
     - Changed language on rationale for required mechanisms 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
       resultCode when for invalidated associations.

   Section 8
     - Clarified action when simple bind request has a DN with invalid
       syntax.

   Section 12.1

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     - 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.



F.13. Changes for draft-ldapbis-authmeth-14

   General

     - Moved to standardized LDAP TS terms: transport connection, TLS
       layer, SASL layer, and LDAP message layer. Reworked usage of
       terminology throughout document to conform to latest usage.
     - Changed language on resultCode values to be less prescriptive
       and more descriptive.

   Section 1
     - Changed format and definitions of terms to parallel latest
       revision of [Protocol].

   Section 2
     - Updated implementation requirements for protecting LDAP simple
       bind mechanism to conform to WG consensus.

   Section 3.1.1
     - Moved last paragraph to security considerations and made
       generalized discussion of use of confidentialityRequired
       resultCode general for all data confidentiality services not
       just TLS.

   Section 3.1.4
       ûRewrote last paragraph to clarify that SASL EXTERNAL is a
         client action when server uses certificate information to
         derive authorization ID.

   Section 3.2
       ûCollapsed three subsections into a single subsection. Removed
         text that implied that the TLS credentials were the only lower
         layer credentials that are used by SASL EXTERNAL in determining
         authentication ID and authorization ID.

   Section 8
     - Removed most of last paragraph that was redundant with
       implementation requirements in section 2.

   Section 10

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     - Changed to SASL DIGEST-MD5 (was section 11 in -13 revision)

   Section 11
     - Changed to SASL EXTERNAL (was section 10 in -13 revision). Moved
       discussion of SASL authorization identities to Section 9.7.
       Clarified language around implicit and explicit assertion of
       authroization identities.

   Appendix A
     - Further collapsed identical states and actions continuing work
       in previous revisions.

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