

Internet-Draft                                      Editor: R. Harrison 
Intended Category: Draft Standard                          Novell, Inc. 
Document: draft-ietf-ldapbis-authmeth-05.txt                 March 2003 
Obsoletes: RFC 2829, RFC 2830                                           
 
 
                      LDAP: Authentication Methods 
                                  and  
                  Connection Level Security Mechanisms 
 
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>. 
    
   Internet-Drafts are working documents of the Internet Engineering 
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   The list of current Internet-Drafts can be accessed at 
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Abstract 
    
   This document describes LDAPv3 (Lightweight Directory Access 
   Protocol v3) 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 
      
     - various forms of authentication including anonymous 
       authentication, password-based authentication, and certificate 
       based authentication 
     - the use of SASL mechanisms with LDAPv3 
     - the use of TLS (Transport Layer Security) with LDAPv3 
      
 
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     - the various authentication and authorization states through 
       which a connection to an LDAP server may pass and the actions 
       that trigger these state changes. 
      
    
1. Conventions Used in this Document 
    
1.1. Glossary of Terms 
    
   The following terms are used in this document. To aid the reader, 
   these terms are defined here. 
    
     - "user" represents any application which is an LDAP client using 
       the directory to retrieve or store information. 
      
     - "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 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 [RFC2119]. 
 
2. Introduction 
    
   This document is an integral part of the LDAP Technical 
   Specification [ROADMAP]. This document replaces RFC 2829 and 
   portions of RFC 2830. Changes to RFC 2829 are summarized in Appendix 
   C and changes to RFC 2830 are summarized in Appendix D. 
    
   LDAPv3 is a powerful access protocol for 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 LDAPv3 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 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 
 
   (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 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 [RFC2222] mechanism 
       set, possibly backed by the TLS [RFC2246] 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 SASL 
       mechanisms that provide data integrity services, 
 
   (4) Data confidentiality protection against snooping by means of the 
       TLS protocol or SASL mechanisms that provide data 
       confidentiality services, 
 
   (5) Server resource usage limitation by means of administrative 
       service limits configured on 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 LDAPv3 protocol. 
 
3. Rationale for LDAPv3 Security Mechanisms 
 

 
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   It seems clear that allowing any implementation, faced with the 
   above requirements, to simply 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, they will support only mechanisms like the LDAPv3 
   simple bind using clear text passwords that provide inadequate 
   security for most circumstances. 
 
   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 means that this data must be updated outside the 
   protocol or only updated in sessions well protected against 
   snooping. It is also desirable to allow authentication methods to 
   carry authorization identities based on existing--non-LDAP DN--forms 
   of user identities for backwards compatibility with non-LDAP-based 
   authentication services. 
    
   The set of security mechanisms provided in LDAPv3 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 LDAPv3 implementations and 
   deployments. 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 defined in section 4.2 of [Protocol] allows 
   authentication information to be exchanged between the client and 
   server.  
    
4.1. Unbound Connection Treated as Anonymous ("Implied Anonymous Bind") 
    
   Unlike LDAP version 2, the client need not send a Bind Request in 
   the first PDU of the connection. The client may send any operation 
   request prior to binding, and the server MUST treat it as if it had 
   been performed after an anonymous bind operation. 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. 
    
 
4.2. Simple Authentication  
    
   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 strongly discouraged over open networks when the 
   underlying transport service cannot guarantee confidentiality (see 
   section 8).  
    
4.3. SASL Authentication 
 
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   The sasl authentication option allows for any mechanism defined for 
   use with SASL [RFC2222] not specifically prohibited by this document 
   (see section 4.3.1).  
    
   Clients sending a bind request with the sasl choice selected SHOULD 
   NOT send a value in the name field. Servers receiving a bind request 
   with the sasl choice selected SHALL ignore any value in the name 
   field. 
    
   The mechanism field in SaslCredentials contains the name of the 
   mechanism. The credentials field contains the arbitrary data used 
   for authentication, inside an OCTET STRING wrapper. Note that unlike 
   some Internet application protocols where SASL is used, LDAP is not 
   text-based, thus no Base64 transformations are performed on the 
   credentials. 
    
   If any SASL-based integrity or confidentiality services are enabled, 
   they take effect following the transmission by the server and 
   reception by the client of the final BindResponse with a resultCode 
   of success.  
    
   If a SASL security layer is negotiated, the client MUST discard all 
   information about the server fetched prior to the initiation of the 
   SASL negotiation. If the client is configured to support multiple 
   SASL mechanisms, it SHOULD fetch the supportedSASLmechanisms list 
   both before and after the SASL security layer is negotiated. This 
   allows the client to detect active attacks that remove supported 
   SASL mechanisms from the supportedSASLMechanisms list and allows the 
   client to ensure that it is using the best mechanism supported by 
   both client and server. (This requirement is a SHOULD to allow for 
   environments where the supportedSASLMechanisms list is provided to 
   the client through a different trusted source, e.g. as part of a 
   digitally signed object.) 
    
   The client can request that the server use authentication 
   information from a lower layer protocol by using the SASL EXTERNAL 
   mechanism (see section 5.2.2.). 
    
4.3.1. 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 data confidentiality mechanism that 
   protects the password in transit should be used. 
 
4.3.2. 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 
 
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   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 resultCode 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 (see 
   [Protocol] section 4.2.1). 
 
4.3.3. Other SASL Mechanisms 
    
   Other SASL mechanisms may be used with LDAP, but their usage is not 
   considered in this document. 
 
4.4. SASL Authorization Identity 
 
   The authorization identity is carried as part of the SaslCredentials 
   credentials field in the 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. 
 
4.4.1. Authorization Identity Syntax 
    
   The authorization identity is a string in the UTF-8 character set, 
   corresponding to the following ABNF grammar [RFC2234]: 
 
   ; Specific predefined authorization (authz) id schemes are 
   ; defined below -- new schemes may be defined in the future. 
 
   authzId = dnAuthzId / uAuthzId 
 
   DNCOLON  = %x64 %x6e %x3a ; "dn:" 
   UCOLON = %x75 %x3a ; "u:" 
    
   ; distinguished-name-based authz id. 
   dnAuthzId = DNCOLON dn 
   dn = utf8string    ; with syntax defined in [LDAPDN] section 3. 
 
 
   ; unspecified authorization id, UTF-8 encoded. 
   uAuthzId = UCOLON userid 
   userid = utf8string    ; syntax unspecified 
    
   The dnAuthzId choice allows client applications to assert 
   authorization identities in the form of a distinguished name. The 
   decision to allow or disallow an authentication identity to have 
   access to the requested authorization identity is a matter of local 
   policy ([SASL] section 4.2). For this reason there is no requirement 
   that the asserted dn be that of an entry in directory. 
    
 
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   The uAuthzId choice allows for compatibility with client 
   applications that wish to assert an authorization identity to a 
   local directory but do not have that identity in distinguished name 
   form. 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. 
 
4.5. SASL Service Name for LDAP 
 
   For use with SASL [RFC2222], 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. 
    
4.6. SASL Integrity and Privacy Protections 
    
   Any negotiated SASL integrity and privacy protections SHALL start on 
   the first octet of the first LDAP PDU following successful 
   completion of the SASL bind operation. If lower level security layer 
   is negotiated, such as TLS, any SASL security services SHALL be 
   layered on top of such security layers regardless of the order of 
   their negotiation. 
 
5. Start TLS Operation 
    
   The Start Transport Layer Security (StartTLS) operation defined in 
   section 4.13 of [Protocol] provides the ability to establish 
   Transport Layer Security [RFC2246] on an LDAP association. 
    
5.1. 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. 
 
5.1.1. 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: 
 
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        - if TLS is currently established on the connection, or 
        - during a multi-stage SASL negotiation, or 
        - if there are any LDAP operations outstanding on the 
          connection. 
    
   The result of violating any of these requirements is a resultCode of 
   operationsError, as described above in [Protocol] section 14.3.2.2. 
    
   In particular, there is no requirement that the client have or have 
   not already performed a Bind operation before sending a Start TLS 
   operation request. 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 by sending a resultCode of 
   confidentialityRequired or strongAuthRequired. In response, the 
   client MAY send a Start TLS extended request, or it MAY choose to 
   close the connection. 
 
5.1.2. Starting TLS 
 
   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 in [Protocol] section 4.13.2.2) if it 
   is unable to do so. 
    
   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 [RFC2246]. 
 
5.1.3. TLS Version Negotiation 
 
   Negotiating the version of TLS or SSL to be used is a part of the 
   TLS Handshake Protocol, as documented in [RFC2246]. Please refer to 
   that document for details. 
 
5.1.4. 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 [Protocol] section 4.13.3.1 and section 5.2.3 below). 
 
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   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. 
 
5.1.5. Assertion of Client's Authorization Identity 
 
   The client MAY, upon receipt of a Start TLS response indicating 
   success, assert that a specific authorization identity be utilized 
   in determining the client's authorization status. The client 
   accomplishes this via an LDAP Bind request specifying a SASL 
   mechanism of "EXTERNAL" [RFC2222] (see section 5.5.1.2 below). 
 
5.1.6. 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 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 any other derived form of name including the server's 
       canonical DNS name. 
    
     - 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. 
    
   For example, *.bar.com would match a.bar.com and b.bar.com, but it 
   would not match a.x.bar.com nor would it match bar.com.  If more 
   than one identity of a given type is present in the certificate 
   (e.g. more than one dNSName name), a match in any one of the set is 
   considered acceptable. 
    
   If the hostname does not match the dNSName-based identity in the 
   certificate per the above check, user-oriented clients SHOULD either 
   notify the user (clients MAY give the user the opportunity to 
   continue with the connection in any case) or terminate the 
   connection and indicate that the server's identity is suspect. 
   Automated clients SHOULD close the connection, returning and/or 
   logging an error indicating that the server's identity is suspect. 
    
   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. 
 
 
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5.1.7. Refresh of Server Capabilities Information 
 
   Upon TLS session establishment, the client MUST discard all 
   information about the server fetched prior to the initiation of the 
   TLS negotiation and MUST refresh any cached server capabilities 
   information (e.g. from the server's root DSE; see section 3.4 of 
   [Protocol]). This is necessary to protect against active-
   intermediary attacks that may have altered any server capabilities 
   information retrieved prior to TLS establishment.  
    
   The server MAY advertise different capabilities after TLS 
   establishment. 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). 
    
5.2. Effects of TLS on a Client's Authorization Identity 
 
   This section describes the effects on a client's authorization 
   identity brought about by establishing TLS on an LDAP association. 
   The default effects are described first, and next the facilities for 
   client assertion of authorization identity are discussed including 
   error conditions. Finally, the effects of closing the TLS connection 
   are described. 
 
   Authorization identities and related concepts are described in 
   Appendix B. 
 
5.2.1. Default Effects 
    
   Upon establishment of the TLS session 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 [RFC2246]). 
    
5.2.2. 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. 
    
5.2.2.1. Implicit Assertion 
    
   An implicit authorization identity assertion is accomplished after 
   TLS establishment by invoking a Bind request of the SASL form using 
   the "EXTERNAL" mechanism name [RFC2222] [Protocol] 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 
 
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   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. 
    
5.2.2.2. 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 [RFC2222] [Protocol] that SHALL 
   include the credentials octet string. This string MUST be 
   constructed as documented in section 4.4.1. 
    
5.2.2.3. 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 [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. 
    
   After the above Bind operation failures, any client authentication 
   and authorization state of the LDAP association is lost (see 
   [Protocol] section 4.2.1), so the LDAP association is in an 
   anonymous state after the failure.  The TLS session state is 
   unaffected, though a server MAY end the TLS session, via a TLS 
   close_notify message, based on the Bind failure (as it MAY at any 
   time). 
    
5.2.3. TLS Connection Closure Effects 
    
   Closure of the TLS session 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 session establishment. 
    
6. LDAP Association State Transition Tables 
    
   To comprehensively diagram the various authentication and TLS states 
   through which an LDAP association may pass, this section provides a 
   state transition table to represent a state diagram for the various 
   states through which an LDAP association may pass during the course 
   of its existence and the actions that cause these changes in state. 
    
6.1. LDAP Association States 
    
 
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   The following table lists the 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= Y 
       [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= J 
       [TLS: Creds Auth ID "I", ON] 
   S8 Auth ID = I 
       AuthZ ID= K 
       [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 Inappropriate authentication: client attempts an anonymous 
       bind or a bind without supplying credentials to a server that 
       requires the client to provide some form of credentials. 
   A3 Client Start TLS request 
       Server: client auth NOT required 
   A4 Client: Start TLS request 
       Server: client creds requested 
       Client: [TLS creds: Auth ID "I"] 
   A5 Client or Server: send TLS closure alert ([Protocol] section 
       X) 
   A6 Client: Bind w/simple password or SASL mechanism (e.g. DIGEST-
       MD5 password, Kerberos, etc. -ū except EXTERNAL [Auth ID "X" 
 
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       maps to AuthZ ID "Y"] 
   A7 Client Binds SASL EXTERNAL with credentials: AuthZ ID "J" 
       [Explicit Assertion (section 5.2.1.2.2)] 
   A8 Client Bind SASL EXTERNAL without credentials [Implicit 
       Assertion (section 5.2 .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 "K" 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. 
    
   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    A3              S2    
      S1    A4              S3    
      S1    A6              S4    
      S1    A7               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
      S1    A8               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
      S2    A1              S2    
      S2    A2              S2   Error: Inappropriate authentication 
      S2    A5              S1    
      S2    A6              S5    
      S2    A7               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
 
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      S2    A8               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
      S3    A1              S3    
      S3    A2              S3   Error: Inappropriate authentication 
      S3    A5              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    A1              S1    
      S4    A2              S4   Error: Inappropriate Authentication 
      S4    A3              S5    
      S4    A4              S6    
      S4    A5              S1    
      S4    A6              S4    
      S4    A7               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
      S4    A8               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
      S5    A1              S2    
      S5    A2              S5   Error: Inappropriate Authentication 
      S5    A5              S1    
      S5    A6              S5    
      S5    A7               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
      S5    A8               ?   identity could be provided by 
                                  another underlying mechanism such 
                                  as IPSec. 
      S6    A1              S3    
      S6    A2              S6   Error: Inappropriate Authentication 
      S6    A5              S1    
      S6    A6              S6    
      S6    A7 and D1=NO    S6   Error: InvalidCredentials 
      S6    A7 and D1=YES   S7    
      S6    A8 and D2=NO    S6   Error: InvalidCredentials 
      S6    A8 and D2=YES   S8    
      S7    A1              S3    
      S7    A2              S7   Error: Inappropriate Authentication 
      S7    A5              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    A2              S8   Error: Inappropriate Authentication 
      S8    A5              S1    
      S8    A6              S6    
 
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      S8    A7 and D1=NO    S6   Error: InvalidCredentials 
      S8    A7 and D1=YES   S7    
      S8    A8              S8    
 
 
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. 
 
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 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.  
 
7.2. Anonymous Authentication and TLS 
 
   An LDAP client MAY use the Start TLS operation (section 5) to 
   negotiate the use of TLS security [RFC2246]. 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. 
 
   An LDAP server which requests that clients provide their certificate 
   during TLS negotiation MAY use a local security policy to determine 

 
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   whether to successfully complete TLS negotiation if the client did 
   not present a certificate which could be validated. 
 
8. Password-based Authentication 
    
   This section discusses various options for performing password-based 
   authentication to LDAPv3 compliant servers and the environments 
   suitable for their use. 
 
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 with the "simple" authentication choice when the 
   connection is protected against eavesdropping using TLS, as defined 
   in section 5. LDAP implementations SHOULD NOT support authentication 
   with the "simple" authentication choice unless the data on the 
   connection is protected using TLS or other data confidentiality and 
   data integrity protection. 
 
8.2. Digest Authentication 
    
   LDAP servers that implement any password-based authentication method 
   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 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 
 
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   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 [RFC2831]. Support 
   for subsequent authentication is OPTIONAL in clients and servers. 
 
8.3. "simple" authentication choice under TLS encryption 
    
   Following the negotiation of an appropriate TLS ciphersuite 
   providing connection confidentiality [RFC2246], a client MAY 
   authenticate to a directory that supports the simple authentication 
   choice by performing a simple bind operation. 
    
   The client will use the Start TLS operation [Protocol] to negotiate 
   the use of TLS security [RFC2246] 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. 
    
   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. 
    
8.3.1. "simple" Authentication Choice  
 
   DSAs that map the DN sent in the bind request to a directory entry 
   with an associated set of one or more passwords will compare the 
   presented password to the set of passwords associated with that 
   entry. If there is a match, then the server will respond with 
   resultCode success, otherwise the server will respond with 
   resultCode invalidCredentials. 
    
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 that provides confidentiality if the only 
   service required is data integrity. 
    
9. Certificate-based authentication 
 
   LDAP server implementations SHOULD support authentication via a 
   client certificate in TLS, as defined in section 5.2.2. 
 
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 
 
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   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 user's certificate must be sufficiently 
   trusted by the directory server in order for the server to process 
   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. 
 
   The client will use the Start TLS operation [Protocol] to negotiate 
   the use of TLS security [RFC2246] 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 that contains a 
   bulk encryption algorithm of appropriate strength. Recommendations 
   of cipher suites are given in section 10. 
 
   The server MUST verify that the client's certificate is valid. The 
   server will normally check that the certificate is issued by a known 
   certification authority (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. 
 
10. TLS Ciphersuites 
 
   The following ciphersuites defined in [RFC2246] 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 [RFC2246] 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 
 
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         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, and 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: 
 
         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. 
 
11. Security Considerations 
    
   Security issues are discussed throughout this memo; the 
   (unsurprising) conclusion is that mandatory security is important 
   and that session confidentiality protection 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. 
    
   Operational experience shows that clients can misuse unauthenticated 
   access (simple bind with name but no password).  For this reason, 
   servers SHOULD by default reject authentication requests that have a 
   DN with an empty password with an error of invalidCredentials. 
    
   Access control SHOULD be applied when reading sensitive information 
   or updating directory information. 
 
   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. 
    
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 [RFC2246]. 
 
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   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. 
    
   Once established, TLS only provides for and ensures confidentiality 
   and integrity of the operations and data in transit over the LDAP 
   association--and only if the implementations on the client and 
   server support and negotiate it. The 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.  
     
   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-
   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 [RFC2222] and [RFC2246]. 
    
    
12. Acknowledgements 
 
   This document combines information originally contained in RFC 2829 
   and RFC 2830. 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. 
    
13. Normative References 
 
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   [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate 
       Requirement Levels", BCP 14, RFC 2119, March 1997. 
    
   [RFC2222] Myers, J., "Simple Authentication and Security Layer 
       (SASL)", draft-myers-saslrev-xx.txt, a work in progress. 
    
   [RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 
       Specifications: ABNF", RFC 2234, November 1997. 
 
   [RFC2246] Dierks, T. and C. Allen. "The TLS Protocol Version 1.0", 
       RFC 2246, January 1999. 
 
    [RFC2831] Leach, P. and C. Newman, "Using Digest Authentication as 
      a SASL Mechanism", RFC 2831, May 2000.  
    
   [LDAPDN] Zeilenga, Kurt D. (editor), "LDAP: String Representation of 
      Distinguished Names", draft-ietf-ldapbis-dn-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. 
     
14. Informative References 
 
   [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. 
 
 
15. Author's Address 
 
   Roger Harrison 
   Novell, Inc. 
   1800 S. Novell Place 
   Provo, UT 84606 
   +1 801 861 2642 
   roger_harrison@novell.com 
 
16. 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 
 
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   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. 
 
   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 discussion, "sensitive data" refers to information whose 
   disclosure, alteration, destruction, or loss would adversely affect 
   the interests or business of its owner or user. Also note that there 
   may be data that is protected but not sensitive.) This is not 
   intended to be a comprehensive list; other scenarios are possible, 
   especially on physically protected networks. 
    
   (1) A read-only directory, containing no sensitive data, accessible 
       to "anyone", and TCP connection hijacking or IP spoofing is not 
       a problem. Anonymous authentication, described in section 7, is 
       suitable for this type of deployment, and requires no additional 
       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 data confidentiality 
       for sensitive authentication 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 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 data confidentiality for 
       sensitive authentication information AND data integrity for all 
       authentication information. 
    
 
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   (5) A directory containing sensitive data. This scenario requires 
       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. 
   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 
   [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 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. 
 
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B.4. Authorization Identity 
 
   An authorization identity is one kind of access control factor. It 
   is the name of the user or other entity that requests that 
   operations be performed. Access control policies are often expressed 
   in terms of authorization identities; e.g., entity X can perform 
   operation Y on resource Z. 
 
   The authorization identity bound to an association is often exactly 
   the same as the authentication identity presented by the client, but 
   it may be different. SASL allows clients to specify an authorization 
   identity distinct from the authentication identity asserted by the 
   client's credentials. This permits agents such as proxy servers to 
   authenticate using their own credentials, yet request the access 
   privileges of the identity for which they are proxying [RFC2222]. 
   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. 
    
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 
    
 
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     - Moved section to an appendix. 
    
C.3. Changes to Section 3 
    
   Version -01 
    
     - Moved section to an appendix. 
    
C.4 Changes to Section 4 
    
   Version -00 
    
     - Changed "Distinguished Name" to "LDAP distinguished name". 
 
C.5. Changes to Section 5 
    
   Version -00 
    
     - Added the following sentence: "Servers SHOULD NOT allow clients 
       with anonymous authentication to modify directory entries or 
       access sensitive information in directory entries." 
    
C.5.1. Changes to Section 5.1 
    
   Version -00 
    
     - Replaced the text describing the procedure for performing an 
       anonymous bind (protocol) with a reference to section 4.2 of RFC 
       2251 (the protocol spec). 
      
   Version -01 
      
     - Brought text describing procedure for performing an anonymous 
       bind from section 4.2 of RFC 2251 bis.  This text will be 
       removed from the draft standard version of that document.  
    
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. 
    

 
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     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. 
    
   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. 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. 
 
 
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   Version -00 
      
     - Removed the first paragraph because simple authentication is 
       covered explicitly in section 6. 
      
     - Added section 8.1. heading just prior to second paragraph. 
      
     - Added section 8.2. heading just prior to third paragraph. 
      
     - Added section 8.3. heading just prior to fourth paragraph. 
      
   Version -01 
      
     - Moved entire section 8 of RFC 2829 into section 3.4 (Using SASL 
       for Other Security Services) to bring material on SASL 
       mechanisms together into one location. 
 
C.9. Changes to section 9. 
 
   Version -00 
      
     - Paragraph 2: changed "EXTERNAL mechanism" to "EXTERNAL SASL 
       mechanism." 
      
     - Added section 9.1. heading. 
      
     - Modified a comment in the ABNF from "unspecified userid" to 
       "unspecified authz id". 
      
     - Deleted sentence, "A utf8string is defined to be the UTF-8 
       encoding of one or more ISO 10646 characters," because it is 
       redundant. 
      
     - Added section 9.1.1. heading. 
      
     - Added section 9.1.2. heading. 
      
   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. 
      

 
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     - Added text: "and MAY support other ciphersuites offering 
       equivalent or better protection," to the last paragraph of the 
       section. 
      
C.11. Changes to Section 11. 
      
   Version -01 
      
     - Moved to section 3.6 to be with other SASL material. 
      
C.12. Changes to Section 12. 
      
   Version -00 
    
     - Inserted new section 12 that specifies when SASL protections 
       begin following SASL negotiation, etc. The original section 12 
       is renumbered to become section 13. 
      
   Version -01 
    
     - Moved to section 3.7 to be with other SASL material. 
      
C.13. Changes to Section 13 (original section 12). 
 
   None 
    
Appendix D. RFC 2830 Change History 
    
   This appendix lists the changes made to the text of RFC 2830 in 
   preparing this document. 
    
D.0. General Editorial Changes 
    
     - Material showing the PDUs for the 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. 
      
 
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     - A new section was created for the Bind Request 
      
     - Section 4.2.1 of RFC 2251 (Sequencing Bind Request) was moved 
       after the section on the Bind Response for parallelism with the 
       presentation of the Start TLS operations. The section was also 
       subdivided to explicitly call out the various effects being 
       described within it. 
       
     - All SASL profile information from RFC 2829 was brought within 
       the discussion of the Bind operation (primarily sections 4.4 - 
       4.7). 
 
Appendix F. 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 changesłpunctuation, 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.) 
    
 
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   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. 
    
F.2. Changes for draft-ldap-bis-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--G.13, G.14, G.16, G.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. 
 
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   Section 11 
    
     - Added security consideration regarding misuse of unauthenticated 
       access. 
      
     - Added security consideration requiring access control to be 
       applied only to authenticated users and recommending it be 
       applied when reading sensitive information or updating directory 
       information. 
      
 
F.3. Changes for draft-ldap-bis-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--G.13, G.14, G.16, G.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 LDAP Association State table for completeness and 
       accuracy. Renumbered actions A3, A4, 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 G.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 
    
 
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     - Verified all normative references and moved informative 
       references to a new section 14. 
      
F.4. Changes for draft-ldap-bis-authmeth-05 
    
   General 
    
     - General editory changes to fix punctuation, spelling, line 
       length issues, etc. 
     - Verified and updated intra- and inter-document references 
       throughout. 
     - Document-wide review for proper usage of RFC 2119 keywords with 
       several changes to correct improper usage. 
 
   Abstract 
     - Updated to match current contents of documents. This was needed 
       due to movement of material on Bind and Start TLS operations to  
       [Protocol] in this revision. 
    
   Section 3. 
    
     - Renamed section to "Rationale for LDAPv3 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. 
 
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     - Added paragraph beginning, "The dnAuthzID choice allows client 
       applications..." to clarify whether DN form authorization 
       identities have to also have a corresponding directory entry. 
       This change was based on editor's perception of WG consensus. 
      
     - Made minor clarifying edits in the paragraph beginning, "The 
       uAuthzID choice allows for compatibility..." 
    
   Section 5.1.1. 
      
     - Made minor clarifying edits in the last paragraph of the 
       section. 
      
   Section 5.1.7. 
      
     - Wording from section 3 paragraph beginning " If TLS is 
       negotiated, the client MUST discard all information..." was 
       moved to this section and integrated with existing text. 
      
   Section 5.2. 
    
     - Changed usage of "TLS connection" to "TLS session" throughout. 
      
     - Removed empty section 5.2.1 and renumbered sections it had 
       previously contained. 
    
   Section 8. 
    
     - Added introductory paragraph at beginning of section. 
 
   Section 8.1. 
    
     - Changed term  "data privacy" to "data confidentiality" to be 
       consistent with usage in rest of document.  
    
   Section 8.2. 
    
     - 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 A. 
    
     - Began changes to incorporate information on deployment scenarios 
       removed from section 3. 
      
 
 
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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. 
 
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. 
    
   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)? 
    
   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?" 
    
   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?" 
    
   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. 
 
   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)?" 
    
   Status: resolved. Discussion at IETF 52 along with discussions with 
   the original authors of this material have convinced us that this 
   reference is simply too arcane to be left in place. In -03 the text 
   has been modified to focus on the need to either update password 
   information in a protected fashion outside of the protocol or to 

 
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   update it in session well protected against snooping, and the 
   reference to /etc/passwd has been removed. 
 
G.6. 
 
   Section 4 paragraph 7 begins: "For a directory needing session 
   protection..." Is this referring to data confidentiality or data 
   integrity or both? 
    
   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? 
    
   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 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. 
    
   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. 
 
G.9. 
 
 
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   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 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? 
    
   Status: resolved in -03 draft by generalizing section 8.3.1 to not 
   refer to any specific password attribute and by removing the term 
   "user" in referring to the directory entry specified by the DN in 
   the bind request. 
    
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) 
    
   Status: resolved in -03 draft by generalizing section 8.3.1 to not 
   refer to any specific password attribute and by removing the term 
   "user" in referring to the directory entry specified by the DN in 
   the bind request. 
 
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.  
    
   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 
 
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   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) 
    
   Status: resolved. -00 version of the draft added a sentence at the 
   beginning of section 8.2 stating that LDAP server implementations 
   must support this method. 
    
G.13. Ordering of authentication levels requested 
 
   Again on the subject of authentication level, is it possible to  
   define an ordering on authentication levels which defines their 
   relative "strengths" ? This would be useful in acl as you could say 
   things like"a given aci grants access to a given subject at this 
   authentication level AND ABOVE". David Chadwick raised this before 
   in the context of denying access to a subject at a given 
   authentication level, in which case he wanted to express "deny 
   access to this subject at this authentication level AND TO ALL 
   IDENTITIES AUTHENTICATED BELOW THAT LEVEL". (Source: Rob Byrne) 
    
   Status: out of scope. This is outside the scope of this document and 
   will not be addressed. 
    
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) 
    
   Status: out of scope. This is outside the scope of this document and 
   will not be addressed. 
    
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) 
    
   Status: In Process. Table provided in -03. Review of content for 
   accuracy in -04. Additional review is needed, plus comments from WG 
   members indicate that additional description of each state's meaning 
   would be helpful. 
    

 
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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) 
    
   Status: resolved. Kurt Zeilenga indicated during ldapbis WG 
   discussion at IETF 52 that SASL AuthzID credentials empty and absent 
   are equivalent in the latest SASL ID. This resolves the issue.  
    
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 
   laptop which has the FQDN for the casse when the system is on our 
   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) 
    
   Status: resolved. Based on discussion at IETF 52 ldapbis WG meeting, 
   this text will stand as it is. The check is a MUST, but the behavior 
   afterward is a SHOULD. This gives server implementations the room to 
   maneuver as needed. 
    
   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 
 
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   directory at all. (Right?)  (Source: ariel@columbia.edu via Jeff 
   Hodges) 
    
   Status: resolved. (11/12/02)Based on my research I propose that the 
   DN MUST exist in the directory when the DN form of sasl creds is 
   used. I have made this proposal to the ldapbis mailing list. 
    
   (11/21/02) Feedback from mailing list has proposed removing this 
   paragraph entirely because (1) explicit assertion of authorization 
   identity should only be done when proxying (2) mapping of the 
   asserted authorization identity is implementation specific and 
   policy driven [SASL] section 4.2, and (3) keeping this paragraph is 
   not required for interoperability. 
    
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) 
    
   Status: resolved. (-03) Based on ldapbis WG discussion at IETF52 two 
   sentences were added to section 4.3 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. During edits 
   for -04 version of draft it was noted that [Protocol] section 4.2 
   conflicts with this draft. The editor of [Protocol] has been 
   notified of the discrepancy, and they have been handled. 
    
G.20. Bind states 
    
   Differences between unauthenticated and anonymous. There are four 
   states you can get into. One is completely undefined (this is now 
   explicitly called out in [Protocol]).  This text needs to be moved 
   from [Protocol] to this draft. (source: Jim Sermersheim) 
    
   Status: Resolved. There are four states: (1) no name, no password 
   (anon); (2) name, no password (anon); (3) no name, password 
   (invalid); (4) name, password (simple bind).  States 1, 2, and 4 are 
   called out in [AuthMeth]. State 3 is called out in [Protocol]; this 
   seems appropriate based on review of alternatives. 
 
G.21. Misuse of unauthenticated access 
 
   Add a security consideration that operational experience shows that 
   clients can misuse unauthenticated access (simple bind with name but 
   no password).  Servers SHOULD by default reject authentication 
   requests that have a DN with an empty password with an error of 
   invalidCredentials. (Source: Kurt Zeilenga and Chris Newman (Sun)) 
    
   Status: Resolved. Added to security considerations in ū03. 
    
G.22. Need to move StartTLS protocol information to [Protocol] 
 
   Status: Resolved. Removed Sections 5.1, 5.2, and 5.4 for -04 and 
   they are [Protocol] -11. 
 
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G.23. Split Normative and Non-normative references into separate 
sections. 
 
   Status: Resolved. Changes made in -04 
 
G.24. What is the authentication state if a Bind operation is 
abandoned? 
 
   Status: In process. (11/12/02) This text was suggested to be added 
   to [Protocol] -11 to cover what happens if a bind operation is 
   abandoned: 
     
   "If a server receives an Abandon request for a Bind operation, the 
   server SHOULD leave the connection in the anonymous state. Clients 
   that abandon a Bind operation MUST rebind after abandoning the Bind 
   request in order to have a known authentication state on the 
   connection." 
    
   (11/21/02) Jim Sermersheim prposed the following wording on the 
   ldapbis mail list:  "Authentication from earlier binds are 
   subsequently ignored. A failed or abandoned Bind Operation has the 
   effect of leaving the connection in an anonymous state. Clients MUST 
   rebind after abandoning a bind operation in order to determine a 
   known authentication state." 
    
   Once this is resolved in [Protocol] the state table in section 6 of 
   [AuthMeth] will need to be updated to reflect the consensus wording. 
 
G.25. Difference between checking server hostname and server's 
canonical DNS name in Server Identity Check? 
 
   Section 5.1.6: I now understand the intent of the check (prevent 
   man-in-the-middle attacks).  But what is the subtle difference 
   between the "server hostname" and the "server's canonical DNS name"? 
   (Source: Tim Hahn) 
    
   Status: In Process. (11/12/02) Sent suggested wording change to this 
   paragraph to the ldapbis mail list and also asked for opinion as to 
   whether we should discuss the distinction between server DNS 
   hostname and server canonical DNS hostname in [AuthMeth]. 
    
   (11/21/02): RL Bob Morgan will provide wording that allows 
   derivations of the name that are provided securely. 
    
6.26. Server Identity Check using servers located via SRV records 
    
   Section 5.1.6: What should be done if the server was found using SRV 
   records based on the "locate" draft/RFC? (Source: Tim Hahn). 
         
   Status: Resolved. Section 5 of draft-ietf-ldapext-locate-08 
   specifically calls out how the server identity should be performed 
   if the server is located using the method defined in that draft. 

 
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   This is the right location for this information, and the coverage 
   appears to be adequate. 
    
G.27 Inconsistency in effect of TLS closure on LDAP association. 
    
   Section 5.4.1 of authmeth -03 (section 4.1 of RFC2830) states that 
   TLS closure alert will leave the LDAP association intact. Contrast 
   this with Section 5.5.2 (section 5.2 of RFC2830) that says that the 
   closure of the TLS connection MUST cause the LDAP association to 
   move to an anonymous authentication. 
    
   Status: in process. (11/12/02) This is actually a [Protocol] issue 
   because these sections have now been moved to [Protocol] -11. I have 
   proposed the following text for Section 5.4.1 of [AuthMeth] -03 
   (section 4.13.3.1 of [Protocol]) to resolve this apparent 
   discrepancy: 
    
   "Either the client or server MAY terminate the TLS connection on an 
   LDAP association by sending a TLS closure alert.  The LDAP 
   connection remains open for further communication after TLS closure 
   occurs although the authentication state of the LDAP connection is 
   affected (see [AuthMeth] section 5.2.2). 
    
   (11/21/02): resolution to this is expected in [Protocol] -12 
 
G.28 Ordering of external sources of authorization identities 
    
   Section 4.3.2 implies that external sources of authorization 
   identities other than TLS are permitted. What is the behavior when 
   two external sources of authentication credentials are available 
   (e.g. TLS and IPsec are both present (is this possible?)) and a SASL 
   EXTERNAL Bind operation is performed? 
    
   Status: resolved. 11/20/02: Resolved by Section 4.2 of [SASL] which 
   states that the decision to allow or disallow the asserted identity 
   is based on an implementation defined policy. 
    
G.29 Rewrite of Section 10, TLS Ciphersuites 
    
   This section contains anachronistic references and needs to be 
   updated/rewritten in a way that provides useful guidance for future 
   readers in a way that will transcend the passage of time. 
    
G.30 Update to Appendix A, Example Deployment Scenarios 
    
   This section needs to be updated to indicate which security 
   mechanisms and/or combinations of security mechanisms described 
   elsewhere in the document can provide the types of protections 
   suggested in this appendix. 
     



 
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