Individual Submission                               R. Harrison, Editor
Internet Draft                                             Novell, Inc.
Document: draft-ietf-ldapbis-authmeth-01.txt              July 19, draft-ietf-ldapbis-authmeth-02.txt          November 14, 2001
Intended Category: Draft Standard
Obsoletes: RFC 2829, RFC 2830

                         Authentication Methods
                                  and
                  Connection Level Security Mechanisms
                               for LDAPv3

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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 Extension Working
   Group mailing list <ietf-ldapbis@OpenLDAP.org>.  Please send
   editorial comments directly to the author
   <roger_harrison@novell.com>.

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Abstract

   This document describes LDAPv3 authentication methods and connection
   level security mechanisms that are required of all conforming LDAPv3
   server implementations and makes recommendations for combinations of
   these mechanisms to be used in various deployment circumstances.

   Among the mechanisms described are

     - the LDAPv3 Bind operation used for authenticating LDAP clients
       to LDAP servers.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

     - the Start TLS operation used to initiate Transport Layer
       Security on an established connection between an LDAP client and
       server.

                  Authentication Methods for LDAPv3     July 19, 2001

     - various forms of authentication including anonymous
       authentication, password-based authentication, and certificate
       based authentication.

1. Conventions Used in this Document

   In
1.1. Glossary of Terms

   The following terms are used in this document, document. To aid the term reader,
   these terms are defined here.

     - "user" represents any application which is an LDAP client using
       the directory to retrieve or store information.

   Several

     - "LDAP association" is used to distinguish the LDAP-level
       connection from any underlying TLS-level connection that may or
       may not exist.

1.2. Security Terms and Concepts

   In general, security terms in this document are used consistently
   with the definitions provided in [RFC2828]. In addition, several
   terms and concepts relating to authentication security, authentication, and
   authorization are presented in Appendix B 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 B before reading the remainder of this document.

1.3. Keywords

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

2. Introduction

   LDAPv3 is a powerful access protocol for directories. It offers
   means of searching, fetching and manipulating directory content, and
   ways to access a rich set of security functions.

   It is vital that these security functions be interoperable among all
   LDAP clients and servers on the Internet; therefore there has to be
   a minimum subset of security functions that is common to all
   implementations that claim LDAPv3 conformance.

   Basic threats to an LDAP directory service include:

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   (1) Unauthorized access to directory data via data-fetching
       operations,

   (2) Unauthorized access to reusable client authentication
       information by monitoring others' access,

   (3) Unauthorized access to directory data by monitoring others'
       access,

   (4) Unauthorized modification of directory data,

   (5) Unauthorized modification of configuration information,

   (6) Unauthorized or excessive use of resources (denial of service),
       and
                  Authentication Methods for LDAPv3     July 19, 2001

   (7) Spoofing of directory: Tricking a 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.

   Threats (1), (4), (5) and (6) are due to hostile clients. Threats
   (2), (3) and (7) are due to hostile agents on the path between
   client and server, server or hostile agents posing as a server.

   The LDAP protocol suite can be protected with the following security
   mechanisms:

   (1) Client authentication by means of the SASL [SASL] mechanism set,
       possibly backed by the TLS [TLS] credentials exchange mechanism,

   (2) Client authorization by means of access control based on the
       requestor's authenticated identity,

   (3) Data integrity protection by means of the TLS protocol or data-
       integrity SASL mechanisms,
       mechanisms that provide data integrity services,

   (4) Protection Data confidentiality protection against snooping by means of the
       TLS protocol or
       data-encrypting SASL mechanisms, mechanisms that provide data
       confidentiality services,

   (5) Resource Server resource usage limitation by means of administrative
       service limits configured on
       service controls, the server, and

   (6) Server authentication by means of the TLS protocol or SASL
       mechanism.

   At the moment, imposition of access controls is done by means
   outside the scope of the LDAP protocol.

3. Required Security Mechanisms
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   It is clear that allowing any implementation, faced with the above
   requirements, to pick and choose among the possible alternatives is
   not a strategy that is likely to lead to interoperability. In the
   absence of mandates, clients will be written that do not support any
   security function supported by the server, or worse, support only
   mechanisms like cleartext passwords that provide clearly inadequate
   security.

   Active intermediary attacks are the most difficult for an attacker
   to perform, and for an implementation to protect against. Methods
   that protect only against hostile client and passive eavesdropping
   attacks are useful in situations where the cost of protection
   against active intermediary attacks is not justified based on the
   perceived risk of active intermediary attacks.

   Given the presence of the Directory, there is a strong desire to see
   mechanisms where identities take the form of an LDAP distinguished
   name [LDAPDN] and authentication data can be stored in the
   directory; this
                  Authentication Methods for LDAPv3     July 19, 2001 means that either this data is useless for faking
   authentication (like the Unix "/etc/passwd" file format used to be),
   or its content is never passed across the wire unprotected - that
   is, it's either updated outside the protocol or it is only updated
   in sessions well protected against snooping. It is also desirable to
   allow authentication methods to carry authorization identities based
   on existing forms of user identities for backwards compatibility
   with non-LDAP-based authentication services.

   Therefore, the following implementation conformance requirements are
   in place:

   (1) For a read-only, public directory, anonymous authentication,
       described in section 5, 7, can be used.

   (2) Implementations providing password-based authenticated access
       MUST support authentication using the DIGEST-MD5 SASL mechanism
       [4], as described in section 6.2. 8.2. This provides client
       authentication with protection against passive eavesdropping
       attacks, but does not provide protection against active
       intermediary attacks.

   (3) For a directory needing session protection data security (both data integrity and
       data confidentiality) and authentication, the Start TLS
       operation described in section 5, and either the simple
       authentication choice or the SASL EXTERNAL mechanism, are to be
       used together. Implementations SHOULD support authentication
       with a password as described in section 7.2, 8.3, and SHOULD support
       authentication with a certificate as described in section 8.1. 9.1.
       Together, these can provide integrity and disclosure protection
       of transmitted data, and authentication of client and server,
       including protection against active intermediary attacks.

   If TLS is negotiated, the client MUST discard all information about
   the server fetched prior to the initiation of the TLS negotiation.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   In particular, the value of supportedSASLMechanisms MAY be different
   after TLS has been negotiated (specifically, the EXTERNAL mechanism
   or the proposed PLAIN mechanism are likely to only be listed after a
   TLS negotiation has been performed).

   If a SASL security layer is negotiated, the client MUST discard all
   information about the server fetched prior to SASL. In particular,
   if the initiation of the
   SASL negotiation. If the client is configured to support multiple
   SASL mechanisms, it SHOULD fetch supportedSASLMechanisms the supportedSASLmechanisms list
   both before and after the SASL security layer is negotiated and verify that the value has not
   changed after the SASL security layer was negotiated. This detects
   allows the client to detect active attacks which that remove supported
   SASL mechanisms from the supportedSASLMechanisms list, list and allows the
   client to ensure that it is using the best mechanism supported by
   both client and server
   (additionally, this server. (This requirement is a SHOULD to allow for
   environments where the
   supported SASL mechanisms supportedSASLMechanisms list is provided to
   the client through a different trusted source, e.g. as part of a
   digitally signed
   object).

                  Authentication Methods for LDAPv3     July 19, 2001 object.)

   Appendix A contains example deployment scenarios that list the
   mechanisms that might be used to achieve a reasonable level of
   security in various circumstances.

4. Bind Operation

   The Bind operation allows authentication information to be exchanged
   between the client and server.

4.1

4.1. Bind Request

   The Bind Request is defined in section 4.2 of [LDAPv3] as follows:

        BindRequest ::= [APPLICATION 0] SEQUENCE {
                version                 INTEGER (1 .. 127),
                name                    LDAPDN,
                authentication          AuthenticationChoice }

        AuthenticationChoice ::= CHOICE {
                simple                  [0] OCTET STRING,
                                        -- 1 and 2 reserved
                sasl                    [ReqsKeywords]                    SaslCredentials }

        SaslCredentials ::= SEQUENCE {
                mechanism               LDAPString,
                credentials             OCTET STRING OPTIONAL }

   Parameters of the Bind Request are:

     - version: A version number indicating the version of the protocol
       to be used in this protocol session. This document describes
       version 3 of the LDAP protocol. Note that there is no version
       negotiation, and the client just sets this parameter to the
       version it desires. If the client requests protocol version 2, a
                  Authentication Methods for LDAPv3     Nov. 14, 2001

       server that supports the version 2 protocol as described in
       [RFC1777] will not return any v3-specific protocol fields. (Note
       that not all LDAP servers will support protocol version 2, since
       they may be unable to generate the attribute syntaxes associated
       with version 2.)

     - name: The name of the directory object that the client wishes to
       bind as. This field may take on a null value (a zero length
       string) for the purposes of anonymous binds, when authentication
       has been performed at a lower layer, or when using SASL
       credentials with a mechanism that includes the name in the
       credentials. Server behavior is undefined when the name is a
       null value, simple authentication is used, and a password is
       specified. Note that the server SHOULD NOT perform any alias
       dereferencing in determining the object to bind as.

                  Authentication Methods for LDAPv3     July 19, 2001

     - authentication: information used to authenticate the name, if
       any, provided in the Bind Request.

   Upon receipt of a Bind Request, a protocol server will authenticate
   the requesting client, if necessary. The server will then return a
   Bind Response to the client indicating the status of the
   authentication.

   Authorization is the use of this authentication information when
   performing operations. Authorization MAY be affected by factors
   outside of the LDAP Bind request, such as lower layer security
   services.

4.2. Bind Response

   The Bind Response is defined in section 4.2 of [LDAPv3] as follows.

        BindResponse ::= [APPLICATION 1] SEQUENCE {
             COMPONENTS OF LDAPResult,
             serverSaslCreds    [ABNF] OCTET STRING OPTIONAL }

   BindResponse consists simply of an indication from the server of the
   status of the client's request for authentication.

   If the bind was successful, the resultCode will be success.
   Otherwise it will be one of:

     - operationsError: server encountered an internal error.

     - protocolError: unrecognized version number or incorrect PDU
       structure.

     - authMethodNotSupported: unrecognized SASL mechanism name.

     - strongAuthRequired: the server requires authentication be
       performed with a SASL mechanism.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

     - referral: this server cannot accept this bind and the client
       should try another.

     - saslBindInProgress: the server requires the client to send a new
       bind request, with the same sasl mechanism, to continue the
       authentication process.

     - inappropriateAuthentication: the server requires the client
       which had attempted to bind anonymously or without supplying
       credentials to provide some form of credentials.

     - invalidCredentials: the wrong password was supplied or the SASL
       credentials could not be processed.

     - unavailable: the server is shutting down.

                  Authentication Methods for LDAPv3     July 19, 2001

   If the server does not support the client's requested protocol
   version it MUST set the resultCode to protocolError.

   If the client receives a BindResponse response where the resultCode
   was protocolError it MUST close the connection as the server will be
   unwilling to accept further operations. (This is for compatibility
   with earlier versions of LDAP, in which the bind was always the
   first operation and there was no negotiation.)

   The serverSaslCreds are used as part of a SASL-defined bind
   mechanism to allow the client to authenticate the server to which it
   is communicating, or to perform "challenge-response" authentication.
   If the client bound with the password choice, or the SASL mechanism
   does not require the server to return information to the client,
   then this field is not to be included in the result.

4.3. Sequencing of the Bind Operation

4.3.1. Effect of Multiple Bind Requests

   Subsequent to sending a bind request, A client MAY send a bind
   request to change its identity. Such a bind request has the effect
   of abandoning all operations outstanding on the connection. (This
   simplifies server implementation.) Authentication from earlier binds
   are subsequently ignored, and so if the bind fails, the connection
   will be treated as anonymous (see section 4.3.3). If a SASL transfer
   encryption or integrity mechanism has been negotiated, and that
   mechanism does not support the changing of credentials from one
   identity to another, then the client MUST instead establish a new
   connection.

   For some SASL authentication mechanisms, it may be necessary for the
   client to invoke the BindRequest multiple times. If at any stage the
   client wishes to abort the bind process it MAY unbind and then drop
   the underlying connection. Clients MUST NOT invoke operations
   between two Bind requests made as part of a multi-stage bind.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

4.3.2. Aborting SASL Bind Negotiation

   A client may abort a SASL bind negotiation by sending a BindRequest
   with a different value in the mechanism field of SaslCredentials, or
   an AuthenticationChoice other than sasl.

   If the client sends a BindRequest with the sasl mechanism field as
   an empty string, the server MUST return a BindResponse with
   authMethodNotSupported as the resultCode. This will allow clients to
   abort a negotiation if it wishes to try again with the same SASL
   mechanism.

4.3.3. Unbound Connection Treated as Anonymous

   Unlike LDAP v2, the client need not send a Bind Request in the first
   PDU of the connection. The client may request any operations and the
                  Authentication Methods for LDAPv3     July 19, 2001
   server MUST treat these as anonymous. If the server requires that
   the client bind before browsing or modifying the directory, the
   server MAY reject a request other than binding, unbinding or an
   extended request with the "operationsError" result.

   If the client did not bind before sending a request and receives an
   operationsError, it may then send a Bind Request. If this also fails
   or the client chooses not to bind on the existing connection, it
   will close the connection, reopen it and begin again by first
   sending a PDU with a Bind Request. This will aid in interoperating
   with servers implementing other versions of LDAP.

4.4. Using SASL for Other Security Services

   The simple authentication option provides minimal authentication
   facilities, with the contents of the authentication field consisting
   only of a cleartext password. Note that the use of cleartext
   passwords is not recommended over open networks when the underlying
   transport service cannot guarantee confidentiality; see the
   "Security Considerations" section.

   The sasl choice allows for any mechanism defined for use with SASL
   [RFC2222].
   [RFC2222] not specifically prohibited by this document (see section
   4.4.1). The mechanism field contains the name of the mechanism. The
   credentials field contains the arbitrary data used for
   authentication, inside an OCTET STRING wrapper. Note that unlike
   some Internet application protocols where SASL is used, LDAP is not
   text-based, thus no base64 Base64 transformations are performed on the
   credentials.

   If any SASL-based integrity or confidentiality services are enabled,
   they take effect following the transmission by the server and
   reception by the client of the final BindResponse with resultCode
   success.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   The client can request that the server use authentication
   information from a lower layer protocol by using the SASL EXTERNAL
   mechanism.
   mechanism (see section 5.5.1.2).

4.4.1. Use of ANONYMOUS and PLAIN SASL Mechanisms

   As LDAP includes native anonymous and plaintext authentication
   methods, the "ANONYMOUS" and "PLAIN" SASL mechanisms are not used
   with LDAP. If an authorization identity of a form different from a
   DN is requested by the client, a mechanism that protects the
   password in transit SHOULD be used.

4.4.2. Use of EXTERNAL SASL Mechanism

   The "EXTERNAL" SASL mechanism can be used to request the LDAP server
   make use of security credentials exchanged by a lower layer. If a
   TLS session has not been established between the client and server
   prior to making the SASL EXTERNAL Bind request and there is no other
   external source of authentication credentials (e.g. IP-level
                  Authentication Methods for LDAPv3     July 19, 2001
   security [RFC2401]), or if, during the process of establishing the
   TLS session, the server did not request the client's authentication
   credentials, the SASL EXTERNAL bind MUST fail with a result code of
   inappropriateAuthentication. Any client authentication and
   authorization state of the LDAP association is lost, so the LDAP
   association is in an anonymous state after the failure.

4.4.3. SASL Mechanisms not Considered in this Document

   The following SASL-based mechanisms are not considered in this
   document: KERBEROS_V4, GSSAPI and SKEY.

4.5. SASL Authorization Identity

   The authorization identity is carried as part of the SASL
   credentials field in the LDAP Bind request and response.

   When the "EXTERNAL" SASL mechanism is being negotiated, if the
   credentials field is present, it contains an authorization identity
   of the authzId form described below.

   Other mechanisms define the location of the authorization identity
   in the credentials field.

4.5.1. Authorization Identity Syntax

   The authorization identity is a string in the UTF-8 character set,
   corresponding to the following ABNF grammar [ABNF]:

   ; Specific predefined authorization (authz) id schemes are
   ; defined below -- new schemes may be defined in the future.

   authzId = dnAuthzId / uAuthzId
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   ; distinguished-name-based authz id.
   dnAuthzId = "dn:" dn
   dn = utf8string    ; with syntax defined in RFC 2253 [LDAPDN] section 3.

   ; unspecified authorization id, UTF-8 encoded.
   uAuthzId = "u:" userid
   userid = utf8string    ; syntax unspecified

4.5.1.1. DN-based Authorization Identity

   All servers that support the storage of authentication credentials,
   such as passwords or certificates, in the directory MUST support the
   dnAuthzId choice. The format for distinguishedName is defined in
   Section
   section 3 of draft-zeilenga-ldapbis-rfc2253-01.txt. [LDAPDN].

4.5.1.2. Unspecified Authorization Identity
                  Authentication Methods for LDAPv3     July 19, 2001

   The uAuthzId choice allows for compatibility with client
   applications that wish to authenticate to a local directory but do
   not know their own distinguished name or that do not have a
   directory entry. The format of utf8string is defined as only a
   sequence of UTF-8 encoded ISO 10646 characters, and further
   interpretation is subject to prior agreement between the client and
   server.

   For example, the userid could identify a user of a specific
   directory service, or be a login name or the local-part of an RFC
   822 email address. In general a uAuthzId MUST NOT be assumed to be
   globally unique.

   Additional authorization identity schemes MAY be defined in future
   versions of this document.

4.6. SASL Service Name for LDAP

   For use with SASL [SASL], a protocol must specify a service name to
   be used with various SASL mechanisms, such as GSSAPI. For LDAP, the
   service name is "ldap", which has been registered with the IANA as a
   GSSAPI service name.

4.7.  SASL Integrity and Privacy Protections

   Any negotiated SASL integrity and privacy protections SHALL start on
   the first octet of the first LDAP PDU following successful
   completion of the SASL bind operation. If lower level security layer
   is negotiated, such as TLS, any SASL security services SHALL be
   layered on top of such security layers regardless of the order of
   their negotiation.

5. Start TLS Operation

   The Start
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   The Start Transport Layer Security (StartTLS) operation provides the
   ability to establish Transport Layer Security [TLS] on an LDAP
   association.

5.1. Start TLS Request

   A client requests TLS establishment by transmitting a Start TLS
   request PDU to the server. The Start TLS request is defined in terms
   of the [LDAPv3] ExtendedRequest as follows:

       ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
           requestName             [0] LDAPOID,
           requestValue            [LDAPv3] OCTET STRING OPTIONAL }

   The requestName portion of the Start TLS request MUST be the OID
   "1.3.6.1.4.1.1466.20037".

   The requestValue field is absent.

                  Authentication Methods for LDAPv3     July 19, 2001

   The client MUST NOT send any PDUs on this connection following this
   request until it receives a Start TLS extended response.

5.2. Start TLS Response

   When a Start TLS request is made, the server MUST return a Start TLS
   response PDU to the requestor.  The Start TLS response id defined in
   terms of the [LDAPv3] ExtendedResponse as follows:

        ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
                COMPONENTS OF LDAPResult,
                responseName     [10] LDAPOID OPTIONAL,
                response         [11] OCTET STRING OPTIONAL }

   The responseName portion of the Start TLS response MUST be the OID
   "1.3.6.1.4.1.1466.20037". (Note that this OID is the same OID value
   used in the requestName of the Start TLS request.)

   The response field is absent.

   The server MUST set the resultCode field to either success or one of
   the other values outlined in section 5.2.2.

5.2.1. "Success" Response

   If the ExtendedResponse contains a resultCode of success, this
   indicates that the server is willing and able to negotiate TLS.
   Refer to section 3, 5.3, below, for details.

5.2.2. Response other than "success"

   If the ExtendedResponse contains a resultCode other than success,
   this indicates that the server is unwilling or unable to negotiate
   TLS.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   If the Start TLS extended request was not successful, the resultCode
   will be one of:

   operationsError  (operations sequencing incorrect; e.g. TLS already
                     established)

   protocolError    (TLS not supported or incorrect PDU structure)

   referral         (this server doesn't do TLS, try this one)

   unavailable      (e.g. some major problem with TLS, or server is
                     shutting down)

   The server MUST return operationsError if the client violates any of
   the Start TLS extended operation sequencing requirements described
   in section 5.3, below.

                  Authentication Methods for LDAPv3     July 19, 2001

   If the server does not support TLS (whether by design or by current
   configuration), it MUST set the resultCode to protocolError (see
   section 4.1.1 of [LDAPv3]), or to referral. The server MUST include
   an actual referral value in the LDAP Result if it returns a
   resultCode of referral. The client's current session is unaffected
   if the server does not support TLS. The client MAY proceed with any
   LDAP operation, or it MAY close the connection.

   The server MUST return unavailable if it supports TLS but cannot
   establish a TLS connection for some reason, e.g. the certificate
   server not responding, it cannot contact its TLS implementation, or
   if the server is in process of shutting down. The client MAY retry
   the StartTLS operation, or it MAY proceed with any other LDAP
   operation, or it MAY close the connection.

5.3.  Sequencing of the Start TLS Operation

   This section describes the overall procedures clients and servers
   MUST follow for TLS establishment. These procedures take into
   consideration various aspects of the overall security of the LDAP
   association including discovery of resultant security level and
   assertion of the client's authorization identity.

   Note that the precise effects, on a client's authorization identity,
   of establishing TLS on an LDAP association are described in detail
   in section 5.5.

5.3.1.  Requesting to Start TLS on an LDAP Association

   The client MAY send the Start TLS extended request at any time after
   establishing an LDAP association, except that in the following cases
   the client MUST NOT send a Start TLS extended request:

        - if TLS is currently established on the connection, or
        - during a multi-stage SASL negotiation, or
                  Authentication Methods for LDAPv3     Nov. 14, 2001

        - if there are any LDAP operations outstanding on the
          connection.

   The result of violating any of these requirements is a resultCode of
   operationsError, as described above in section 2.3. 5.2.2.

   The client MAY have already performed a Bind operation when it sends
   a Start TLS request, or the client might have not yet bound.

   If the client did not establish a TLS connection before sending any
   other requests, and the server requires the client to establish a
   TLS connection before performing a particular request, the server
   MUST reject that request with a confidentialityRequired or
   strongAuthRequired result. The client MAY send a Start TLS extended
   request, or it MAY choose to close the connection.

5.3.2.  Starting TLS
                  Authentication Methods for LDAPv3     July 19, 2001

   The server will return an extended response with the resultCode of
   success if it is willing and able to negotiate TLS.  It will return
   other resultCodes, documented above, if it is unable.

   In the successful case, the client, which has ceased to transfer
   LDAP requests on the connection, MUST either begin a TLS negotiation
   or close the connection. The client will send PDUs in the TLS Record
   Protocol directly over the underlying transport connection to the
   server to initiate TLS negotiation [TLS].

5.3.3.  TLS Version Negotiation

   Negotiating the version of TLS or SSL to be used is a part of the
   TLS Handshake Protocol, as documented in [TLS]. Please refer to that
   document for details.

5.3.4.  Discovery of Resultant Security Level

   After a TLS connection is established on an LDAP association, both
   parties MUST individually decide whether or not to continue based on
   the privacy level achieved. Ascertaining the TLS connection's
   privacy level is implementation dependent, and accomplished by
   communicating with one's respective local TLS implementation.

   If the client or server decides that the level of authentication or
   privacy is not high enough for it to continue, it SHOULD gracefully
   close the TLS connection immediately after the TLS negotiation has
   completed (see sections 5.4.1 and 5.5.2 below). If the client
   decides to continue, it MAY attempt to Start TLS again, it MAY send
   an unbind request, or it MAY send any other LDAP request.

5.3.5.  Assertion of Client's Authorization Identity

   The client MAY, upon receipt of a Start TLS response indicating
   success, assert that a specific authorization identity be utilized
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   in determining the client's authorization status. The client
   accomplishes this via an LDAP Bind request specifying a SASL
   mechanism of "EXTERNAL" [SASL] (see section 5.5.1.2 below).

5.3.6.  Server Identity Check

   The client MUST check its understanding of the server's hostname
   against the server's identity as presented in the server's
   Certificate message, in order to prevent man-in-the-middle attacks.

   Matching is performed according to these rules:

     - The client MUST use the server hostname it used to open the LDAP
       connection as the value to compare against the server name as
       expressed in the server's certificate.  The client MUST NOT use
       the server's canonical DNS name or any other derived form of
       name.

                  Authentication Methods for LDAPv3     July 19, 2001

     - If a subjectAltName extension of type dNSName is present in the
       certificate, it SHOULD be used as the source of the server's
       identity.

     - Matching is case-insensitive.

     - The "*" wildcard character is allowed.  If present, it applies
       only to the left-most name component.

   E.g.

   For example, *.bar.com would match a.bar.com, a.bar.com and b.bar.com, etc. but it
   would not match a.x.bar.com nor would it match bar.com.  If more
   than one identity of a given type is present in the certificate
   (e.g. more than one dNSName name), a match in any one of the set is
   considered acceptable.

   If the hostname does not match the dNSName-based identity in the
   certificate per the above check, user-oriented clients SHOULD either
   notify the user (clients MAY give the user the opportunity to
   continue with the connection in any case) or terminate the
   connection and indicate that the server's identity is suspect.
   Automated clients SHOULD close the connection, returning and/or
   logging an error indicating that the server's identity is suspect.

   Beyond the server identity checks described in this section, clients
   SHOULD be prepared to do further checking to ensure that the server
   is authorized to provide the service it is observed to provide. The
   client MAY need to make use of local policy information.

5.3.7. Refresh of Server Capabilities Information

   The client MUST refresh any cached server capabilities information
   (e.g. from the server's root DSE; see section 3.4 of [LDAPv3]) upon
   TLS session establishment. This is necessary to protect against
   active-intermediary attacks that may have altered any server
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   capabilities information retrieved prior to TLS establishment. The
   server MAY advertise different capabilities after TLS establishment.

5.4. Closing a TLS Connection

   Two forms of TLS connection closure--graceful and abrupt--are
   supported.

5.4.1. Graceful Closure

   Either the client or server MAY terminate the TLS connection on an
   LDAP association by sending a TLS closure alert. This will leave the
   LDAP association intact.

   Before closing a TLS connection, the client MUST [RGH18]either [RGH10]either wait
   for any outstanding LDAP operations to complete, or explicitly
   abandon them [LDAPv3].

   After the initiator of a close has sent a TLS closure alert, it MUST
   discard any TLS messages until it has received a TLS closure alert
                  Authentication Methods for LDAPv3     July 19, 2001
   from the other party.  It will cease to send TLS Record Protocol
   PDUs, and following the receipt of the alert, MAY send and receive
   LDAP PDUs.

   The other party, if it receives a TLS closure alert, MUST
   immediately transmit a TLS closure alert.  It will subsequently
   cease to send TLS Record Protocol PDUs, and MAY send and receive
   LDAP PDUs.

5.4.2. Abrupt Closure

   Either the client or server MAY abruptly close the entire LDAP
   association and any TLS connection established on it by dropping the
   underlying TCP connection. In this circumstance, a server MAY send
   the client a Notice of Disconnection [LDAPv3] before dropping the
   TCP connection.

5.5. Effects of TLS on a Client's Authorization Identity

   This section describes the effects on a client's authorization
   identity brought about by establishing TLS on an LDAP association.
   The default effects are described first, and next the facilities for
   client assertion of authorization identity are discussed including
   error conditions. Lastly, the effects of closing the TLS connection
   are described.

   Authorization identities and related concepts are described in
   Appendix B.

5.5.1. TLS Connection Establishment Effects

5.5.1.1. Default Effects
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   Upon establishment of the TLS connection onto the LDAP association,
   any previously established authentication and authorization
   identities MUST remain in force, including anonymous state. This
   holds even in the case where the server requests client
   authentication via TLS -- e.g. requests the client to supply its
   certificate during TLS negotiation (see [TLS]).

5.5.1.2. Client Assertion of Authorization Identity

   A client MAY either implicitly request that its LDAP authorization
   identity be derived from its authenticated TLS credentials or it MAY
   explicitly provide an authorization identity and assert that it be
   used in combination with its authenticated TLS credentials. The
   former is known as an implicit assertion, and the latter as an
   explicit assertion.

5.5.1.2.1. Implicit Assertion

   An implicit authorization identity assertion is accomplished after
   TLS establishment by invoking a Bind request of the SASL form using
                  Authentication Methods for LDAPv3     July 19, 2001
   the "EXTERNAL" mechanism name [SASL, LDAPv3] that SHALL NOT include
   the optional credentials octet string (found within the
   SaslCredentials sequence in the Bind Request). The server will
   derive the client's authorization identity from the authentication
   identity supplied in the client's TLS credentials (typically a
   public key certificate) according to local policy. The underlying
   mechanics of how this is accomplished are implementation specific.

5.5.1.2.2. Explicit Assertion

   An explicit authorization identity assertion is accomplished after
   TLS establishment by invoking a Bind request of the SASL form using
   the "EXTERNAL" mechanism name [SASL, LDAPv3] that SHALL include the
   credentials octet string. This string MUST be constructed as
   documented in section 9 of [AuthMeth]. 4.5.

5.5.1.2.3. Error Conditions

   For either form of assertion, the server MUST verify that the
   client's authentication identity as supplied in its TLS credentials
   is permitted to be mapped to the asserted authorization identity.
   The server MUST reject the Bind operation with an invalidCredentials
   resultCode in the Bind response if the client is not so authorized.

   Additionally, with either form of assertion, if a TLS session has
   not been established between the client and server prior to making
   the SASL EXTERNAL Bind request and there is no other external source
   of authentication credentials (e.g. IP-level security [IPSEC]), or
   if, during the process of establishing the TLS session, the server
   did not request the client's authentication credentials, the SASL
   EXTERNAL bind MUST fail with a result code of
   inappropriateAuthentication.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   After the above Bind operation failures, any client authentication
   and authorization state of the LDAP association is lost, so the LDAP
   association is in an anonymous state after the failure.  TLS
   connection state is unaffected, though a server MAY end the TLS
   connection, via a TLS close_notify message, based on the Bind
   failure (as it MAY at any time).

5.5.2. TLS Connection Closure Effects

   Closure of the TLS connection MUST cause the LDAP association to
   move to an anonymous authentication and authorization state
   regardless of the state established over TLS and regardless of the
   authentication and authorization state prior to TLS connection
   establishment.

6. Anonymous Authentication

   Directory operations that modify entries or access protected
   attributes or entries generally require client authentication.
   Clients that do not intend to perform any of these operations
                  Authentication Methods for LDAPv3     July 19, 2001

   typically use anonymous authentication. Servers SHOULD NOT allow
   clients with anonymous authentication to modify directory entries or
   access sensitive information in directory entries.

   LDAP implementations MUST support anonymous authentication, as
   defined in section 6.1. LDAP implementations MAY support anonymous Association State Transition Tables

   To comprehensively diagram the various authentication with TLS,
   as defined in and TLS states
   through which an LDAP association may pass, this section 6.2.

   While there MAY be access control restrictions to prevent access provides a
   state transition table to
   directory entries, represent a state diagram for the various
   states through which an LDAP server SHOULD allow an anonymously-bound
   client to retrieve association may pass during the supportedSASLMechanisms attribute course
   of its existence and the root
   DSE.

   An actions that cause these changes in state.

6.1. LDAP server MAY use other information about the client provided
   by Association States

   The following table lists the lower layers or external means to grant or deny access even
   to anonymously valid LDAP association states and
   provides a description of each state. The ID for each state is used
   in the state transition table in section 6.4.

   ID State Description
   -- --------------------------------------------------------------
   S1 no Auth ID
       no AuthZ ID
       TLS: no Creds OFF
   S2 no Auth ID
       no AuthZ ID
       TLS: no Creds ON
   S3 no Auth ID
       no AuthZ ID
       TLS: Creds Auth ID "I", ON.
   S4 Auth ID = Xn
       AuthZ ID= Yn
       [TLS: no Creds, Off]
   S5 Auth ID = Xn
       AuthZ ID= Yn
       [TLS: no Creds, On]
   S6 Auth ID = Xn
       AuthZ ID= Yn
       [TLS: Creds Auth ID "I", On]
   S7 Auth ID = I
       AuthZ ID= Jn
                  Authentication Methods for LDAPv3     Nov. 14, 2001

       [TLS: Creds Auth ID "I", On]
   S8 Auth ID = I
       AuthZ ID= is based on "I"
       [TLS: Creds Auth ID "I", On]

6.2. Actions that Affect LDAP Association State

   The following table lists the actions that can affect the state of
   an LDAP association. The ID for each action is used in the state
   transition table in section 6.4.

   ID Action
   -- ------------------------------------------------
   A1 Client binds anonymously
   A2 Error: Inappropriate authentication
   A3 Client or Server: close TLS connection (section 5.5.2)
   A4 Client StartTLS
       Server: client auth NOT required

   A5 Client: StartTLS
       Server: client creds requested
       Client: {TLS creds: Auth ID "I"]
   A6 Client: Bind w/simple password or SASL mechanism (e.g. DIGEST-
       MD5 password, Kerberos, etc. ū except EXTERNAL [Auth ID "X"
       maps to AuthZ ID "Y"]
   A7 Client Binds SASL EXTERNAL w/ credentials: AuthZ ID "J"
       [Explicit Assertion (section 5.5.1.2.2)]
   A8 Client Bind SASL EXTERNAL w/saslcredentials: NULL [Implicit
       Assertion (section 5.5.1.2.1)]

6.3. Decisions Used in Making LDAP Association State Changes

   Certain changes in the state of an LDAP association are only allowed
   if the server can affirmatively answer a question. These questions
   are applied as part of the criteria for allowing or disallowing a
   state change in the state transition table in section 6.4.

   ID Decision Question
   -- --------------------------------------------------------------
   D1 Can TLS Credentials Auth ID "I" be mapped to AuthZ ID "J"?
   D2 Can a valid AuthZ ID "J" be derived from TLS Credentials Auth
       ID "I"?

6.4. LDAP Association State Transition Table

   The LDAP Association table below lists the valid states for an LDAP
   association and the actions that could affect them. For any given
   row in the table, the Current State column gives the state of an
   LDAP association, the Action column gives an action that could
   affect the state of an LDAP assocation, and the Next State column
   gives the resulting state of an LDAP association after the action
   occurs.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   The initial state for the state machine described in this table is
   S1.

   Current                 Next
    State  Action         State Comment
   ------- -------------  ----- -----------------------------------
      S1    A1              S1
      S1    A2              S1   Error: Inappropriate authentication
      S1    A4              S2
      S1    A5              S3
      S1    A6              S4
      S2    A1              S2
      S2    A2              S2   Error: Inappropriate authentication
      S2    A3              S1
      S2    A6              S5
      S3    A1              S3
      S3    A3              S1
      S3    A6              S6
      S3    A7 and D1=NO    S3   Error: InvalidCredentials
      S3    A7 and D1=YES   S7
      S3    A8 and D2=NO    S3   Error: InvalidCredentials
      S3    A8 and D2=YES   S8
      S4    A6              S4
      S4    A2              S4   Error: Inappropriate Authentication
      S4    A3              S1
      S4    A4              S5
      S4    A5              S6
      S5    A6              S5
      S5    A2              S5   Error: Inappropriate Authentication
      S5    A3              S1
      S5    A1              S2
      S6    A6              S6
      S6    A3              S1
      S6    A1              S3
      S6    A7 and D1=NO    S6   Error: InvalidCredentials
      S6    A7 and D1=YES   S10
      S6    A8 and D2=NO    S6   Error: InvalidCredentials
      S6    A8 and D2=YES   S8
      S7    A1              S3
      S7    A3              S1
      S7    A6              S6
      S7    A7              S7
      S7    A8 and D2=NO    S3   Error: InvalidCredentials
      S7    A8 and D2=YES   S8
      S8    A1              S3
      S8    A3              S1
      S8    A8              S8
      S8    A7 and D1=NO    S6   Error: InvalidCredentials
      S8    A7 and D1=YES   S7
      S8    A6              S6
                  Authentication Methods for LDAPv3     Nov. 14, 2001

7. Anonymous Authentication

   Directory operations that modify entries or access protected
   attributes or entries generally require client authentication.
   Clients that do not intend to perform any of these operations
   typically use anonymous authentication. Servers SHOULD NOT allow
   clients with anonymous authentication to modify directory entries or
   access sensitive information in directory entries.

   LDAP implementations MUST support anonymous authentication, as
   defined in section 7.1.

   LDAP implementations MAY support anonymous authentication with TLS,
   as defined in section 7.2.

   While there MAY be access control restrictions to prevent access to
   directory entries, an LDAP server SHOULD allow an anonymously-bound
   client to retrieve the supportedSASLMechanisms attribute of the root
   DSE.

   An LDAP server MAY use other information about the client provided
   by the lower layers or external means to grant or deny access even
   to anonymously authenticated clients.

6.1.

7.1. Anonymous Authentication Procedure

   An LDAPv3 client that has not successfully completed a bind
   operation on a connection is anonymously authenticated. See section
   4.3.3.

   An LDAP client MAY also choose to explicitly bind anonymously. A
   client that wishes to do so MUST choose the simple authentication
   option in the Bind Request (see section XXX) 4.1) and set the password to
   be of zero length. (This is often done by LDAPv2 clients.) Typically
   the name is also of zero length.

6.2.

7.2. Anonymous Authentication and TLS

   An LDAP client MAY use the Start TLS operation (section 4) 5) to
   negotiate the use of TLS security [TLS]. If the client has not bound
   beforehand, then until the client uses the EXTERNAL SASL mechanism
   to negotiate the recognition of the client's certificate, the client
   is anonymously authenticated.

   Recommendations on TLS ciphersuites are given in section 10. 11.

   An LDAP server which requests that clients provide their certificate
   during TLS negotiation MAY use a local security policy to determine
   whether to successfully complete TLS negotiation if the client did
   not present a certificate which could be validated.

7.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

8. Password-based authentication

7.1.

8.1. Simple authentication

   The LDAP "simple" authentication choice is not suitable for
   authentication in environments where there is no network or
   transport layer confidentiality. LDAP implementations SHOULD support
                  Authentication Methods for LDAPv3     July 19, 2001
   authentication with the "simple" authentication choice when the
   connection is protected against eavesdropping using TLS, as defined
   in section 6.3. 7.3. LDAP implementations SHOULD NOT support
   authentication with the "simple" authentication choice unless the
   data on the connection is protected using TLS or other privacy and
   data-integrity protection.

7.2.

8.2. Digest Authentication

   LDAP implementations MUST support authentication with a password
   using the DIGEST-MD5 SASL mechanism for password protection.

   An LDAP client MAY determine whether the server supports this
   mechanism by performing a search request on the root DSE, requesting
   the supportedSASLMechanisms attribute, and checking whether the
   string "DIGEST-MD5" is present as a value of this attribute.

   In the first stage of authentication, when the client is perfCorming performing
   an "initial authentication" as defined in section 2.1 of [RFC2831],
   the client sends a bind request in which the version number is 3,
   the authentication choice is sasl, the sasl mechanism name is
   "DIGEST- MD5", and the credentials are absent. The client then waits
   for a response from the server to this request.

   The server will respond with a bind response in which the resultCode
   is saslBindInProgress, and the serverSaslCreds field is present. The
   contents of this field is a string defined by "digest-challenge" in
   section 2.1.1 of [RFC2831]. The server SHOULD include a realm
   indication and MUST indicate support for UTF-8.

   The client will send a bind request with a distinct message id, in
   which the version number is 3, the authentication choice is sasl,
   the sasl mechanism name is "DIGEST-MD5", and the credentials contain
   the string defined by "digest-response" in section 2.1.2 of
   [RFC2831]. The serv-type is "ldap".

   The server will respond with a bind response in which the resultCode
   is either success, or an error indication. If the authentication is
   successful and the server does not support subsequent
   authentication, then the credentials field is absent. If the
   authentication is successful and the server supports subsequent
   authentication, then the credentials field contains the string
   defined by "response-auth" in section 2.1.3 of [4]. Support for
   subsequent authentication is OPTIONAL in clients and servers.

7.3.

8.3. "simple" authentication choice under TLS encryption
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   Following the negotiation of an appropriate TLS ciphersuite
   providing connection confidentiality [6], a client MAY authenticate
   to a directory that supports the simple authentication choice by
   performing a simple bind operation.

                  Authentication Methods for LDAPv3     July 19, 2001

   The client will use the Start TLS operation [5] to negotiate the use
   of TLS security [6] on the connection to the LDAP server. The client
   need not have bound to the directory beforehand.

   For this authentication procedure to be successful, the client and
   server MUST negotiate a ciphersuite which contains a bulk encryption
   algorithm of appropriate strength. Recommendations on cipher suites
   are given in section 10. 11.

   Following the successful completion of TLS negotiation, the client
   MUST send an LDAP bind request with the version number of 3, the
   name field containing a DN , and the "simple" authentication choice,
   containing a password.

7.3.1

8.3.1. "simple" Authentication Choice

   DSAs that map the DN sent in the bind request to a directory entry
   with a userPassword attribute will, for each value of the
   userPassword attribute in the named user's entry, compare these for
   case-sensitive equality with the client's presented password. If
   there is a match, then the server will respond with resultCode
   success, otherwise the server will respond with resultCode
   invalidCredentials.

7.4.

8.4. Other authentication choices with TLS

   It is also possible, following the negotiation of TLS, to perform a
   SASL authentication that does not involve the exchange of plaintext
   reusable passwords. In this case the client and server need not
   negotiate a ciphersuite which that provides confidentiality if the only
   service required is data integrity.

8.

9. Certificate-based authentication

   LDAP implementations SHOULD support authentication via a client
   certificate in TLS, as defined in section 7.1. 8.1.

9.1. Certificate-based authentication with TLS

   A user who has a public/private key pair in which the public key has
   been signed by a Certification Authority may use this key pair to
   authenticate to the directory server if the user's certificate is
   requested by the server. The user's certificate subject field SHOULD
   be the name of the user's directory entry, and the Certification
   Authority that issued the userĘs certificate must be sufficiently
   trusted by the directory server in order for the server to process
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   the certificate. The means by which servers validate certificate
   paths is outside the scope of this document.

   A server MAY support mappings for certificates in which the subject
   field name is different from the name of the user's directory entry.
   A server which supports mappings of names MUST be capable of being
   configured to support certificates for which no mapping is required.

                  Authentication Methods for LDAPv3     July 19, 2001

   The client will use the Start TLS operation [5] to negotiate the use
   of TLS security [6] on the connection to the LDAP server. The client
   need not have bound to the directory beforehand.

   In the TLS negotiation, the server MUST request a certificate. The
   client will provide its certificate to the server, and the server
   MUST perform a private key-based encryption, proving it has the
   private key associated with the certificate.

   In deployments that require protection of sensitive data in transit,
   the client and server MUST negotiate a ciphersuite which that contains a
   bulk encryption algorithm of appropriate strength. Recommendations
   of cipher suites are given in section 10. 11.

   The server MUST verify that the client's certificate is valid. The
   server will normally check that the certificate is issued by a known
   CA, and that none of the certificates on the client's certificate
   chain are invalid or revoked. There are several procedures by which
   the server can perform these checks.

   Following the successful completion of TLS negotiation, the client
   will send an LDAP bind request with the SASL "EXTERNAL" mechanism.

9.

10. TLS Ciphersuites

   The following ciphersuites defined in [6] 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 [6] can be cracked easily
   (less than a day of CPU time on a standard CPU in 2000). These
   ciphersuites are NOT RECOMMENDED for use in confidentiality
   protection of passwords or data. Client and server implementers
   SHOULD carefully consider the value of the password or data being
   protected before using these ciphersuites:

         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
                  Authentication Methods for LDAPv3     Nov. 14, 2001

         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, and SHOULD NOT be used to protect passwords or sensitive
                  Authentication Methods for LDAPv3     July 19, 2001
   data, unless the network configuration is such that the danger of a
   man-in-the-middle attack is tolerable:

         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

   A client or server that supports TLS MUST support
   TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA and MAY support other ciphersuites
   offering equivalent or better protection.

10.

11. Security Considerations

   Security issues are discussed throughout this memo; the
   (unsurprising) conclusion is that mandatory security is important,
   and that session encryption is required when snooping is a problem.

   Servers are encouraged to prevent modifications by anonymous users.
   Servers may also wish to minimize denial of service attacks by
   timing out idle connections, and returning the unwillingToPerform
   result code rather than performing computationally expensive
   operations requested by unauthorized clients.

   A connection on which the client has not performed the Start TLS
   operation or negotiated a suitable SASL mechanism for connection
   integrity and encryption services is subject to man-in-the-middle
   attacks to view and modify information in transit.

10.1.

11.1.  Start TLS Security Considerations

   The goals of using the TLS protocol with LDAP are to ensure
   connection confidentiality and integrity, and to optionally provide
   for authentication. TLS expressly provides these capabilities, as
   described in [TLS].

   All security gained via use of the Start TLS operation is gained by
   the use of TLS itself. The Start TLS operation, on its own, does not
   provide any additional security.

   The use of TLS does not provide or ensure for confidentiality and/or
   non-repudiation of the data housed by an LDAP-based directory
   server. Nor does it secure the data from inspection by the server
   administrators.  Once established, TLS only provides for and ensures
   confidentiality and integrity of the operations and data in transit
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   over the LDAP association, and only if the implementations on the
   client and server support and negotiate it.

   The level of security provided though the use of TLS depends
   directly on both the quality of the TLS implementation used and the
   style of usage of that implementation. Additionally, an active-
                  Authentication Methods for LDAPv3     July 19, 2001
   intermediary attacker can remove the Start TLS extended operation
   from the supportedExtension attribute of the root DSE. Therefore,
   both parties SHOULD independently ascertain and consent to the
   security level achieved once TLS is established and before beginning
   use of the TLS connection. For example, the security level of the
   TLS connection might have been negotiated down to plaintext.

   Clients SHOULD either warn the user when the security level achieved
   does not provide confidentiality and/or integrity protection, or be
   configurable to refuse to proceed without an acceptable level of
   security.

   Client and server implementors SHOULD take measures to ensure proper
   protection of credentials and other confidential data where such
   measures are not otherwise provided by the TLS implementation.

   Server implementors SHOULD allow for server administrators to elect
   whether and when connection confidentiality and/or integrity is
   required, as well as elect whether and when client authentication
   via TLS is required.

   Additional security considerations relating to the EXTERNAL
   mechanism to negotiate TLS can be found in [SASL] and [6].

11.

12. Acknowledgements

   This document combines information originally contained in RFC 2829,
   RFC 2830 and portions of RFC 2251. The author 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. RFC 2829 and RFC 2830 were products of the IETF
   LDAPEXT Working Group. RFC 2251 was a product of the ASID Working
   Group.

   This document is based upon input of the IETF LDAP Revision working
   group. The contributions of its members is greatly appreciated.

12.

13. Bibliography

   [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
       Specifications: ABNF", RFC 2234, November 1997.

   [IPSEC] Kent, S. and R. Atkinson, "Security Architecture for the
       Internet Protocol", RFC 2401, November 1998.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   [LDAPDN] Zeilenga, Kurt D., "Lightweight Directory Access Protocol
       (v3): UTF-8 String Representation of Distinguished Names",
       draft-ietf-ldapbis-dn-06.txt, July, 2001.

   [LDAPv3] Wahl, M., Kille S. and T. Howes, "Lightweight Directory
       Access Protocol (v3)", RFC 2251, December 1997.

   [RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828, May
       2000.

   [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
       Internet Protocol", RFC 2401, November 1998.

   [RFC2831] Leach, P. and C. Newman, "Using Digest Authentication as a
       SASL Mechanism", RFC 2831, May 2000.

                  Authentication Methods for LDAPv3     July 19, 2001

   [ReqsKeywords] Bradner, S., "Key Words for use in RFCs to Indicate
       Requirement Levels", BCP 14, RFC 2119, March 1997.

   [SASL] Myers, J., "Simple Authentication and Security Layer (SASL)",
       RFC 2222, October 1997.

   [TLS] Dierks, T. and C. Allen. "The TLS Protocol Version 1.0", RFC
       2246, January 1999.

13.

14. Author's Address

   Roger Harrison
   Novell, Inc.
   1800 S. Novell Place
   Provo, UT 84606
   +1 801 861 2642
   roger_harrison@novell.com

14.

15. Full Copyright Statement

   Copyright (C) The Internet Society (2000). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Appendix A. Example Deployment Scenarios

   The following scenarios are typical for LDAP directories on the
   Internet, and have different security requirements. (In the
   following, "sensitive" means data that will cause real damage
   following discussion, "sensitive data" refers to information whose
   disclosure, alteration, destruction, or loss would adversely affect
   the
                  Authentication Methods for LDAPv3     July 19, 2001 interests or business of its owner if revealed; or user. Also note that there
   may be data that is protected but not
   sensitive). sensitive.) This is not
   intended to be a comprehensive list, list; other scenarios are possible,
   especially on physically protected networks.

   (1) A read-only directory, containing no sensitive data, accessible
       to "anyone", and TCP connection hijacking or IP spoofing is not
       a problem. This directory requires no security functions except
       administrative service limits.

   (2) A read-only directory containing no sensitive data; read access
       is granted based on identity. TCP connection hijacking is not
       currently a problem. This scenario requires a secure data confidentiality
       for sensitive authentication function. information AND data integrity for
       all authentication information.

   (3) A read-only directory containing no sensitive data; and the
       client needs to ensure the identity of the directory server and
       that the directory data is authenticated
       by the server and not modified while being returned
       from the server. A data origin authentication service AND data
       integrity service are required.

   (4) A read-write directory, containing no sensitive data; read
       access is available to "anyone", update access to properly
       authorized persons. TCP connection hijacking is not currently a
       problem. This scenario requires a secure data confidentiality for
       sensitive authentication information AND data integrity for all
       authentication
       function. information.

   (5) A directory containing sensitive data. This scenario requires
       session
       data confidentiality protection AND secure authentication.

Appendix B. Authentication and Authorization: Definitions and Concepts

   This appendix defines basic terms, concepts, and interrelationships
   regarding authentication, authorization, credentials, and identity.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   These concepts are used in describing how various security
   approaches are utilized in client authentication and authorization.

B.1. Access Control Policy

   An access control policy is a set of rules defining the protection
   of resources, generally in terms of the capabilities of persons or
   other entities accessing those resources. A common expression of an
   access control policy is an access control list. Security objects
   and mechanisms, such as those described here, enable the expression
   of access control policies and their enforcement. Access control
   policies are typically expressed in terms of access control
   attributes as described below.

B.2. Access Control Factors

   A request, when it is being processed by a server, may be associated
   with a wide variety of security-related factors (section 4.2 of
   [LDAPv3]). The server uses these factors to determine whether and
   how to process the request. These are called access control factors
   (ACFs). They might include source IP address, encryption strength,
                  Authentication Methods for LDAPv3     July 19, 2001
   the type of operation being requested, time of day, etc. Some
   factors may be specific to the request itself, others may be
   associated with the connection via which the request is transmitted,
   others (e.g. time of day) may be "environmental".

   Access control policies are expressed in terms of access control
   factors. E.g., a request having ACFs i,j,k can perform operation Y
   on resource Z. The set of ACFs that a server makes available for
   such expressions is implementation-specific.

B.3. Authentication, Credentials, Identity

   Authentication credentials are the evidence supplied by one party to
   another, asserting the identity of the supplying party (e.g. a user)
   who is attempting to establish an association with the other party
   (typically a server). Authentication is the process of generating,
   transmitting, and verifying these credentials and thus the identity
   they assert. An authentication identity is the name presented in a
   credential.

   There are many forms of authentication credentials -- the form used
   depends upon the particular authentication mechanism negotiated by
   the parties. For example: X.509 certificates, Kerberos tickets,
   simple identity and password pairs. Note that an authentication
   mechanism may constrain the form of authentication identities used
   with it.

B.4. Authorization Identity

   An authorization identity is one kind of access control factor. It
   is the name of the user or other entity that requests that
   operations be performed. Access control policies are often expressed
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   in terms of authorization identities; e.g., entity X can perform
   operation Y on resource Z.

   The authorization identity bound to an association is often exactly
   the same as the authentication identity presented by the client, but
   it may be different. SASL allows clients to specify an authorization
   identity distinct from the authentication identity asserted by the
   client's credentials. This permits agents such as proxy servers to
   authenticate using their own credentials, yet request the access
   privileges of the identity for which they are proxying [SASL]. Also,
   the form of authentication identity supplied by a service like TLS
   may not correspond to the authorization identities used to express a
   server's access control policy, requiring a server-specific mapping
   to be done. The method by which a server composes and validates an
   authorization identity from the authentication credentials supplied
   by a client is implementation-specific.

Appendix C. RFC 2829 Change History

   This appendix lists the changes made to the text of RFC 2829 in
   preparing this document.

                  Authentication Methods for LDAPv3     July 19, 2001

C.0. General Editorial Changes
   Version -00

     - Changed other instances of the term LDAP to LDAPv3 where v3 of
       the protocol is implied. Also made all references to LDAPv3 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
                  Authentication Methods for LDAPv3     Nov. 14, 2001

     - 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
                  Authentication Methods for LDAPv3     July 19, 2001

     - Replaced the text describing the procedure for performing an
       anonymous bind (protocol) with a reference to section 4.2 of RFC
       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 passwordą") to
section on Digest Authentication (Now section 6.2).

C.6.1. Changes to Section 6.1.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   Version -00 Renamed section to 6.2

     - Added sentence from original section 6 indicating that the
       DIGEST-MD5 SASL mechanism is required for all conforming LDAPv3
       implementations

C.6.2

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.

                  Authentication Methods for LDAPv3     July 19, 2001

     - 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.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

     - Added section 8.1. heading just prior to second paragraph.

     - Added section 8.2. heading just prior to third paragraph.

     - Added section 8.3. heading just prior to fourth paragraph.

   Version -01

     - Moved entire section 8 of RFC 2829 into section 3.4 (Using SASL
       for Other Security Services) to bring material on SASL
       mechanisms together into one location.

C.9. Changes to section 9.

   Version -00

     - Paragraph 2: changed "EXTERNAL mechanism" to "EXTERNAL SASL
       mechanism."
                  Authentication Methods for LDAPv3     July 19, 2001

     - 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.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

C.11. Changes to Section 11.

   Version -01

     - Moved to section 3.6 to be with other SASL material.

C.12. Changes to Section 12.

   Version -00

     - Inserted new section 12 that specifies when SASL protections
       begin following SASL negotiation, etc. The original section 12
       is renumbered to become section 13.

   Version -01

     - Moved to section 3.7 to be with other SASL material.

C.13

C.13. Changes to Section 13 (original section 12).

                  Authentication Methods for LDAPv3     July 19, 2001

   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 Start TLS response was broken
       out into a new section.

     - The wording of the definition of the Start TLS request and Start
       TLS response was changed to make them parallel. NO changes were
       made to the ASN.1 definition or the associated values of the
       parameters.

     - A separate section heading for graceful TLS closure was added
       for parallelism with section on abrupt TLS closure.

Appendix E. RFC 2251 Change History

   This appendix lists the changes made to the text of RFC 2251 in
   preparing this document.

E.0. General Editorial Changes

     - All material from section 4.2 of RFC 2251 was moved into this
       document.

     - A new section was created for the Bind Request
                  Authentication Methods for LDAPv3     Nov. 14, 2001

     - Section 4.2.1 of RFC 2251 (Sequencing Bind Request) was moved
       after the section on the Bind Response for parallelism with the
       presentation of the Start TLS operations. The section was also
       subdivided to explicitly call out the various effects being
       described within it.

     - All SASL profile information from RFC 2829 was brought within
       the discussion of the Bind operation (primarily sections 4.4 -
       4.7).

Appendix F. Change History to Combined Document

F.1. Changes for draft-ldap-bis-authmeth-02.doc

   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
     - Added LDAP Association State Transition Tables to show the
       various states through which an LDAP 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.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   General
     - Added references to other LDAP standard documents, to sections
       within the document, and fixed broken references.

     - General editorial changesłpunctuation, spelling, formatting,
       etc.

Appendix G. Issues to be Resolved

   This appendix lists open questions and issues that need to be
   resolved before work on this document is deemed complete.

F.1.

G.1.

   Section 1 lists 6 security mechanisms that can be used by LDAP
   servers. I'm not sure what mechanism 5, "Resource limitation by
   means of administrative limits on service controls" means.

                  Authentication Methods for LDAPv3     July 19, 2001

F.2. controls" means.

   Status: resolved. Changed wording to "administrative service limits"
   to clarify meaning.

G.2.

   Section 2 paragraph 1 defines the term, "sensitive." Do we want to
   bring this term and other security-related terms in alignment with
   usage with the IETF security glossary (RFC 2828)?

F.3.

   Status: resolved. WG input at IETF 51 was that we should do this, so
   the appropriate changes have been made.

G.3.

   Section 2, deployment scenario 2: What is meant by the term "secure
   authentication function?"

F.4.

   Status: resolved. Based on the idea that a "secure authentication
   function" could be provided by TLS, I changed the wording to require
   data confidentiality for sensitive authentication information and
   data integrity for all authentication information.

G.4.

   Section 3, deployment scenario 3: What is meant by the phrase,
   "directory data is authenticated by the server?"

F.5.

   Status: resolved. I interpreted this to mean the ability to ensure
   the identity of the directory server and the integrity of the data
   sent from that server to the client, and explictly stated such.

G.5.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

   Section 4 paragraph 3: What is meant by the phrase, "this means that
   either this data is useless for faking authentication (like the Unix
   "/etc/passwd" file format used to be)?"

F.6.

G.6.

   Section 4 paragraph 7 begins: "For a directory needing session
   protection..." Is this referring to data confidentiality or data
   integrity or both?

F.7.

   Status: resolved. Changed wording to say, "For a directory needing
   data security (both data integrity and data confidentiality)..."

G.7.

   Section 4 paragraph 8 indicates that "information about the server
   fetched fetched prior to the TLS negotiation" must be discarded. Do
   we want to explicitly state that this applies to information fetched
   prior to the *completion* of the TLS negotiation or is this going
   too far?

F.8.

   Status: resolved. Based on comments in the IETF 51 LDAPBIS WG
   meeting, this has been changed to explicitly state, "fetched prior
   to the initiation of the TLS negotiation..."

G.8.

   Section 4 paragraph 9 indicates that clients SHOULD check the
   supportedSASLMechanisms list both before and after a SASL security
   layer is negotiated to ensure that they are using the best available
   security mechanism supported mutually by the client and server. A
   note at the end of the paragraph indicates that this is a SHOULD
   since there are environments where the client might get a list of
   supported SASL mechanisms from a different trusted source.

   I wonder if the intent of this could be restated more plainly using
   one of these two approaches (I've paraphrased for the sake of
   brevity):

        Approach 1: Clients SHOULD check the supportedSASLMechanisms
        list both before and after SASL negotiation or clients SHOULD
        use a
                  Authentication Methods for LDAPv3     July 19, 2001 different trusted source to determine available supported
        SASL mechanisms.

        Approach 2: Clients MUST check the supportedSASLMechanisms list
        both before and after SASL negotiation UNLESS they use a
        different trusted source to determine available supported SASL
        mechanisms.

F.9.

   Status: Resolved. WG input at IETF 51 was that Approach 1 was
   probably best. I ended up keeping the basic structure similar to the
   original to meet this intent.

                  Authentication Methods for LDAPv3     Nov. 14, 2001

G.9.

   Section 6.3.1 states: "DSAs that map the DN sent in the bind request
   to a directory entry with a userPassword attribute will... compare
   [each value in the named user's entry]... with the presented
   password."  This implies that this this applies only to user entries
   with userPassword attributes.  What about other types of entries
   that might allow passwords and might store in the password
   information in other attributes?  Do we want to make this text more
   general?

F.10

G.10 userPassword and simple bind

   We need to be sure that we don't require userPassword to be the only
   attribute used for authenticating via simple bind. (See 2251 sec 4.2
   and authmeth 6.3.1. Work with Jim Sermersheim on resolution to this.
   On publication state something like: "This is the specific
   implementation of what we discussed in our general reorg
   conversation on the list." (Source: Kurt Zeilenga)

F.11

G.11. Meaning of LDAP Association

   The original RFC 2830 uses the term "LDAP association" in describing
   a connection between an LDAP client and server regardless of the
   state of TLS on that connection. This term needs to be defined or
   possibly changed.

F.12.

   Status: Resolved. at IETF 51 Bob Morgan indicated that the term
   "LDAP association" was intended to distinguish the LDAP-level
   connection from the TLS-level connection.  This still needs to be
   clarified somewhere in the draft. Added "LDAP association" to a
   glossary in section 1.

G.12. Is DIGEST-MD5 mandatory for all implementations?

   Reading 2829bis I think DIGEST-MD5 is mandatory ONLY IF your server
   supports password based authentication...but the following makes it
   sound mandatory to provide BOTH password authentication AND DIGEST-
   MD5:

   "6.2. Digest authentication

   LDAP implementations MUST support authentication with a password
   using the DIGEST-MD5 SASL mechanism for password protection, as
   defined in section 6.1."

   The thing is for acl it would be nice (though not critical) to be
   able to default the required authentication level for a subject to a
   single "fairly secure" mechanism--if there is no such mandatory
   authentication scheme then you cannot do that. (Source: Rob Byrne)
                  Authentication Methods for LDAPv3     July 19, 2001

F.13.

G.13. Ordering of authentication levels requested
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   Again on the subject of authentication level, is it possible to
   define an ordering on authentication levels which defines their
   relative "strengths" ? This would be useful in acl as you could say
   things like"a given aci grants access to a given subject at this
   authentication level AND ABOVE". David Chadwick raised this before
   in the context of denying access to a subject at a given
   authentication level, in which case he wanted to express "deny
   access to this subject at this authentication level AND TO ALL
   IDENTITIES AUTHENTICATED BELOW THAT LEVEL". (Source: Rob Byrne)

F.14.

G.14. Document vulnerabilities of various mechanisms

   While I'm here...in 2829, I think it would be good to have some
   comments or explicit reference to a place where the security
   properties of the particular mandatory authentication schemes are
   outlined. When I say "security properties" I mean stuff like "This
   scheme is vulnerable to such and such attacks, is only safe if the
   key size is > 50, this hash is widely considered the best, etc...".
   I think an LDAP implementor is likely to be interested in that
   information, without having to wade through the security RFCs.
   (Source: Rob Byrne)

F.15.

G.15. Include a StartTLS state transition table

   The pictoral representation it is nominally based on is here (URL
   possibly folded):

   http://www.stanford.edu/~hodges/doc/LDAPAssociationStateDiagram-
   1999-12-14.html

   (Source: Jeff Hodges)

F.16.

   Status: Table provided. Final review of content for accuracy is
   still needed.

G.16. Empty sasl credentials question

   I spent some more time looking microscopically at ldap-auth-methods
   and ldap-ext-tls drafts. The drafts say that the credential must
   have the form dn:xxx or u:xxx or be absent, and although they don't
   say what to do in the case of an empty octet string I would say that
   we could send protocolError (claim it is a bad PDU).

   There is still the question of what to do if the credential is 'dn:'
   (or 'u:') followed by the empty string. (Source: ariel@columbia.edu
   via Jeff Hodges)

F.17.

G.17. Hostname check from MUST to SHOULD?

   I am uneasy about the hostname check. My experience from PKI with
   HTTP probably is a contributing factor; we have people using the
   short hostname to get to a server which naturally has the FQDN in
   the certificate, no end of problems. I have a certificate on my
                  Authentication Methods for LDAPv3     Nov. 14, 2001

   laptop which has the FQDN for the casse when the system is on our
                  Authentication Methods for LDAPv3     July 19, 2001
   Columbia network with a fixed IP; when I dial in however, I have
   some horrible dialup name, and using the local https server becomes
   annoying. Issuing a certificate in the name 'localhost' is not a
   solution! Wildcard match does not solve this problem. For these
   reasons I am inclined to argue for 'SHOULD' instead of
   'MUST' in paragraph...

   Also, The hostname check against the name in the certificate is a
   very weak means of preventing man-in-the-middle attacks; the proper
   solution is not here yet (SecureDNS or some equivalent). Faking out
   DNS is not so hard, and we see this sort of thing in the press on a
   pretty regular basis, where site A hijacks the DNS server for site B
   and gets all their requests. Some mention of this should be made in
   the draft. (Source: ariel@columbia.edu via Jeff Hodges)

F.18.

G.18. Must SASL DN exist in the directory?

   If the 'dn:' form of sasl creds is used, is it the intention of the
   draft(ers) that this DN must exist in the directory and the client
   will have the privileges associated with that entry, or can the
   server map the sasl DN to perhaps some other DN in the directory,
   in an implementation-dependent fashion?

   We already know that if *no* sasl credentials are presented, the DN
   or altname in the client certificate may be mapped to a DN in an
   implementation-dependent fashion, or indeed to something not in the
   directory at all. (Right?)  (Source: ariel@columbia.edu via Jeff
   Hodges)

G.19. DN used in conjunction with SASL mechanism

   We need to specify whether the DN field in Bind operation can/cannot
   be used when SASL mechanism is specified. (source: RL Bob)

G.20. Bind states

   Differences between unauthenticated and anonymous. four states you
   can get into. One is completely undefined (this is now explicitly
   called out in document).  This text needs to be moved from
   RFC2251bis to this draft. (source: Jim Sermersheim)