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

INTERNET-DRAFT                                      Editor: R. Harrison 
draft-ietf-ldapbis-authmeth-09.txt                         Novell, Inc. 
Obsoletes: 2251, 2829, 2830                             5 December 2003 
Intended Category: Draft Standard                                       
 
 
                      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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Copyright Notice 
    
   Copyright (C) The Internet Society (2003).  All Rights Reserved. 
    
Abstract 
    
   This document describes authentication methods and connection level 
   security mechanisms of the Lightweight Directory Access Protocol 
   (LDAP).  
 
   This document details the simple Bind authentication method 
   including anonymous, unauthenticated, and plain-text password 
   methods and the SASL (Simple Authentication and Security Layer) Bind 
   authentication method including the use of DIGEST-MD5 and EXTERNAL 
   mechanisms. 
    
 
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   This document also details establishment of TLS (Transport Layer 
   Security) using the Start TLS operation. 
    
   This document describes various authentication and authorization 
   states through which a connection to an LDAP server may pass and the 
   actions that trigger these state changes. 
 
1. Introduction 
    
   The Lightweight Directory Access Protocol (LDAP) [Protocol] 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 LDAP conformance. 
 
   Basic threats to an LDAP directory service include: 
 
   (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. Also, tricking a client into sending privileged 
       information to a hostile entity that appears to be the directory 
       but is not. 
 
   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. 
 
   LDAP can be protected with the following security mechanisms: 
 
   (1) Client authentication by means of the Secure Authentication and 
       Security Layer (SASL) [SASL] mechanism set, possibly backed by 
       the Transport Layer Security (TLS) [TLS] credentials exchange 
       mechanism, 
 
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   (2) Client authorization by means of access control based on the 
       requestor's authenticated identity, 
 
   (3) Data integrity protection by means of TLS or SASL mechanisms 
       with security layers 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 LDAP. 
    
   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 LDAP 
   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 identities not represented as LDAP DNs that are familiar to 
   the user or that are used in other systems. 
    
     The set of security mechanisms provided in LDAP and described in 
     this document is intended to meet the security needs for a wide 
     range of deployment scenarios and still provide a high degree of 
     interoperability among various LDAP implementations and 
     deployments. Appendix A contains example deployment scenarios that 
     list the mechanisms that might be used to achieve a reasonable 
     level of security in various circumstances. 
    
1.1. Relationship to Other Documents 
 
   This document is an integral part of the LDAP Technical 
   Specification [Roadmap].  
    
   This document obsoletes RFC 2829. 
    

 
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   Sections 2 and 4 of RFC 2830 are obsoleted by [Protocol].  The 
   remainder of RFC 2830 is obsoleted by this document.  
    
2. Conventions Used in this Document 
    
2.1. Glossary of Terms 
    
   The following terms are used in this document. To aid the reader, 
   these terms are defined here. 
    
     - "user" represents any human or application entity which is 
       accessing the directory using a directory client.  A directory 
       client (or client) is also known as a directory user agent 
       (DUA). 
      
     - "connection" and "LDAP connection" both refer to the underlying 
       transport protocol connection between two protocol peers.  
      
     - "TLS connection" refers to a TLS-protected LDAP connection.  
      
     - "association" and "LDAP association" both refer to the 
       association of the LDAP connection and its current 
       authentication and authorization state. 
    
2.2. Security Terms and Concepts 
    
   In general, security terms in this document are used consistently 
   with the definitions provided in [RFC2828]. In addition, several 
   terms and concepts relating to security, authentication, and 
   authorization are presented in Appendix 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. 
 
2.3. Keywords 
    
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 
   document are to be interpreted as described in RFC 2119 [RFC2119]. 
 
3. Bind Operation 
     
   The Bind operation defined in section 4.2 of [Protocol] allows 
   authentication information to be exchanged between the client and 
   server to establish a new LDAP association. The new LDAP association 
   is established upon successful completion of the authentication 
   exchange. 
    
3.1. Implied Anonymous Bind on LDAP Association  
    
   Prior to the successful completion of a Bind operation and during 
   any subsequent authentication exchange, the session has an anonymous 
 
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   LDAP association. Among other things this implies that the client 
   need not send a Bind Request in the first PDU of the connection. The 
   client may send any operation request prior to binding, and the 
   server MUST treat it as if it had been performed after an anonymous 
   bind operation. This authentication state on an LDAP association is 
   sometimes referred to as an implied anonymous bind. 
 
3.2. Simple Authentication  
    
   The simple authentication choice provides minimal facilities for 
   establishing an anonymous association or for establishing an LDAP 
   association based upon credentials consisting of a name (in the form 
   of an [LDAPDN] and a password. 
 
   The simple authentication choice provides two different methods 
   for establishing an anonymous association: anonymous bind and 
   unauthenticated bind (see section 5.1). 
 
   The simple authentication choice provides one method for 
   establishing a non-anonymous association: simple password bind.  
    
3.3. SASL Authentication Profile 
    
   LDAP allows authentication via any SASL mechanism [SASL]. As LDAP 
   includes native anonymous and plaintext authentication methods, the 
   ANONYMOUS [ANONYMOUS] and PLAIN [PLAIN] SASL mechanisms are 
   typically not used with LDAP. 
 
   Each protocol that utilizes SASL services is required to supply 
   certain information profiling the way they are exposed through the 
   protocol ([SASL] section 5). This section explains how each of these 
   profiling requirements are met by LDAP. 
    
3.3.1. SASL Service Name for LDAP 
 
   The SASL service name for LDAP is "ldap", which has been registered 
   with the IANA as a GSSAPI service name. 
    
3.3.2. SASL authentication initiation and protocol exchange 
    
   SASL authentication is initiated via an LDAP bind request 
   ([Protocol] section 4.2) with the following parameters: 
    
      - The version is 3. 
      - The AuthenticationChoice is sasl.  
      - The mechanism element of the SaslCredentials sequence contains 
        the value of the desired SASL mechanism.  
      - The optional credentials field of the SaslCredentials sequence 
        may be used to provide an initial client response for 
        mechanisms that are defined to have the client send data first 
        (see [SASL] sections 5 and 5.1). 
    
   In general, a SASL authentication protocol exchange consists of a 
   series of server challenges and client responses, the contents of 
 
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   which are specific to and defined by the SASL mechanism. Thus for 
   some SASL authentication mechanisms, it may be necessary for the 
   client to respond to one or more server challenges by invoking the 
   BindRequest multiple times. A challenge is indicated by the server 
   sending a BindResponse with the resultCode set to 
   saslBindInProgress. This indicates that the server requires the 
   client to send a new bind request, with the same sasl mechanism to 
   continue the authentication process. 
    
   To the encapsulating protocol, these challenges and responses are 
   opaque binary tokens of arbitrary length. LDAP servers use the 
   serverSaslCreds field, an OCTET STRING, in a bind response message 
   to transmit each challenge. LDAP clients use the credentials field, 
   an OCTET STRING, in the SaslCredentials sequence of a bind request 
   message to transmit each response. Note that unlike some Internet 
   protocols where SASL is used, LDAP is not text-based, thus no Base64 
   transformations are performed on these challenge and response 
   values. 
    
   Clients sending a bind request with the sasl choice selected SHOULD 
   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. 
    
   A client may abort a SASL bind negotiation by sending a BindRequest 
   with a different value in the mechanism field of SaslCredentials, or 
   an AuthenticationChoice other than sasl.  
        
   If the client sends a BindRequest with the sasl mechanism field as 
   an empty string, the server MUST return a BindResponse with 
   authMethodNotSupported as the resultCode. This will allow clients to 
   abort a negotiation if it wishes to try again with the same SASL 
   mechanism. 
    
   The server indicates completion of the SASL challenge-response 
   exchange by responding with a bind response in which the resultCode 
   is either success, or an error indication. 
    
   The serverSaslCreds field in the bind response can be used to 
   include an optional challenge with a success notification for 
   mechanisms which are defined to have the server send additional data 
   along with the indication of successful completion. 
 
3.3.3. Octet where negotiated security mechanisms take effect 
 
   When negotiated, SASL security layers take effect following the 
   transmission by the server and reception by the client of the final 
   BindResponse in the exchange. 
 
   Once a SASL security layer providing integrity or confidentiality 
   services takes effect, the layer remains in effect until a new layer 
   is installed (i.e. at the first octet following the final 
   BindResponse of the bind operation that caused the new layer to take 
   effect). 
 
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3.3.4. Determination of supported SASL mechanisms 
    
   An LDAP client may determine the SASL mechanisms a server supports 
   by performing a search request on the root DSE, requesting the 
   supportedSASLMechanisms attribute. The values of this attribute, if 
   any, list the mechanisms the server supports. 
    
3.3.5. Rules for using SASL security layers 
    
   If a SASL security layer is negotiated, the client SHOULD discard 
   information about the server it obtained prior to the initiation of 
   the SASL negotiation and not obtained through secure mechanisms.  
    
   If a lower level security layer (such as TLS) is negotiated, any 
   SASL security services SHALL be layered on top of such security 
   layers regardless of the order of their negotiation. In all other 
   respects, SASL security services and other security layers act 
   independently, e.g. if both TLS and SASL security service are in 
   effect removing the SASL security service does not affect the 
   continuing service of TLS and vice versa. 
    
   Because SASL mechanisms provide critical security functions, clients 
   and servers should allow the user to specify what mechanisms are 
   acceptable and allow only those mechanisms to be used. 
 
3.3.6. Use of EXTERNAL SASL Mechanism 
    
   A client can use the EXTERNAL SASL [SASL] mechanism to request the 
   LDAP server to make use of security credentials exchanged by a lower 
   security layer (such as by TLS authentication or IP-level security 
   [RFC2401]).  
    
   If the client's authentication credentials have not been established 
   at a lower security layer, the SASL EXTERNAL bind MUST fail with a 
   resultCode of inappropriateAuthentication.  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). In such a situation, the 
   state of any established security layer is unaffected. 
 
   A client may either implicitly request that its LDAP authorization 
   identity be derived from a lower layer 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. 
    
3.3.6.1. Implicit Assertion 
    
   An implicit authorization identity assertion is performed by 
   invoking a Bind request of the SASL form using the EXTERNAL 
   mechanism name that 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 
 
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   from the authentication identity supplied by the security layer 
   (e.g., a public key certificate used during TLS establishment) 
   according to local policy. The underlying mechanics of how this is 
   accomplished are implementation specific. 
    
3.3.6.2. Explicit Assertion 
    
   An explicit authorization identity assertion is performed by 
   invoking a Bind request of the SASL form using the EXTERNAL 
   mechanism name that SHALL include the credentials octet string. This 
   string MUST be constructed as documented in section 3.4.1. 
    
   The server MUST 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. 
 
3.3.6.3. SASL Authorization Identity 
 
   When the EXTERNAL SASL mechanism is being negotiated, if the 
   SaslCredentials credentials field is present, it contains an 
   authorization identity. Other mechanisms define the location of the 
   authorization identity in the credentials field. In either case, the 
   authorization identity is represented in the authzId form described 
   below. 
 
3.3.6.4 Authorization Identity Syntax 
    
   The authorization identity is a string of [UTF-8] encoded [Unicode] 
   characters corresponding to the following [ABNF] grammar: 
 
   authzId = dnAuthzId / uAuthzId 
 
   DNCOLON  = %x64 %x6e %x3a ; "dn:" 
   UCOLON = %x75 %x3a ; "u:" 
    
   ; distinguished-name-based authz id. 
   dnAuthzId = DNCOLON distinguishedName 
 
   ; unspecified authorization id, UTF-8 encoded. 
   uAuthzId = UCOLON userid 
   userid = *UTF8    ; syntax unspecified 
    
   where the <distinguishedName> production is defined in section 3 of 
   [LDAPDN] and <UTF8> production is defined in section 1.3 of 
   [Models]. 
 
   In order to support additional specific authorization identity 
   forms, future updates to this specification may add new choices 
   supporting other forms may be added to the authzId production.  
    
   The dnAuthzId choice allows clients to assert authorization 
   identities in the form of a distinguished name to be matched in 
 
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   accordance with the distinguishedName matching rule [Syntaxes]. The 
   decision to allow or disallow an authentication identity to have 
   access to the requested authorization identity is a matter of local 
   policy ([SASL] section 4.2). For this reason there is no requirement 
   that the asserted dn be that of an entry in directory. 
    
   The uAuthzId choice allows for compatibility with clients that wish 
   to assert an authorization identity to a local directory but do not 
   have that identity in distinguished name form. The value contained 
   within a uAuthzId MUST be prepared using [SASLPrep] before being 
   compared octet-wise. The format of utf8string is defined as only a 
   sequence of [UTF-8] encoded [Unicode] 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. A uAuthzId SHOULD NOT be assumed to be globally 
   unique. 
 
4. Start TLS Operation 
    
   The Start Transport Layer Security (Start TLS) operation defined in 
   section 4.13 of [Protocol] provides the ability to establish [TLS] 
   on an LDAP association. 
    
4.1. 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 4.2. 
 
4.1.1. Start TLS Request  
 
   The client MAY send the Start TLS extended request at any time after 
   establishing an LDAP connection, except: 
    
      - when TLS is currently established on the connection, 
      - when a multi-stage SASL negotiation is in progress on the 
        connection, or 
      - when there are one or more outstanding LDAP operations on the 
        connection. 
    
   The result of violating any of these requirements is a resultCode of 
   operationsError, as described in [Protocol] section 4.13.2.2. Client 
   implementers should note that it is possible to receive a resultCode 
   of success for a Start TLS operation that is sent on a connection 
   with outstanding LDAP operations and the server has sufficient time 
 
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   to process them prior to its receiving the Start TLS request. 
   Implementors of clients should ensure that they do not inadvertently 
   depend upon this race condition. 
    
   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. 
 
4.1.2. Start TLS Response 
 
   The server will return an extended response with the resultCode of 
   success if it is willing and able to negotiate TLS.  It will return 
   other resultCode values (documented in [Protocol] section 4.13.2.2) 
   if it is unwilling or 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. 
 
4.1.3. TLS Version Negotiation 
 
   Negotiating the version of TLS or SSL to be used is a part of the 
   [TLS] Handshake Protocol. Please refer to that document for details. 
 
4.1.4. 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 security level achieved. Ascertaining the TLS connection's 
   security 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 
   security 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 4.2.3 below). 
   If the client decides to continue, it may gracefully close the TLS 
   connection and attempt to Start TLS again, it may send an unbind 
   request, or it may send any other LDAP request. 
 
4.1.5. Server Identity Check 
 


 
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   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 provided by the user (or other 
       trusted entity) as the value to compare against the server name 
       as expressed in the server's certificate. A hostname derived 
       from the user input is to be considered provided by the user 
       only if derived in a secure fashion (e.g., DNSSEC). 
    
     - If a subjectAltName extension of type dNSName is present in the 
       certificate, it SHOULD be used as the source of the server's 
       identity. 
         
     - 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 in making 
   this determination. 
 
4.1.6. Refresh of Server Capabilities Information 
 
   Upon TLS session establishment, the client SHOULD discard or refresh 
   all information about the server it obtained prior to the initiation 
   of the TLS negotiation and not obtained through secure mechanisms. 
   This protects against 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 

 
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   EXTERNAL and PLAIN [PLAIN] mechanisms are likely to be listed only 
   after a TLS negotiation has been performed). 
    
4.2. 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. 
 
4.2.1. TLS Connection Establishment Effects 
    
   The decision to keep or invalidate the established authentication 
   and authorization identities in place after TLS is negotiated is a 
   matter of local server policy. If a server chooses to invalidate 
   established authentication and authorization identities after TLS is 
   negotiated, it MUST reply to subsequent valid operation requests 
   until the next TLS closure or successful bind request with a 
   resultCode of strongAuthRequired to indicate that the client needs 
   to bind to reestablish its authentication. If the client attempts to 
   bind using a method the server is unwilling to support, it responds 
   to the with a resultCode of authMethodNotSupported (per [Protocol]) 
   to indicate that a different authentication method should be used.  
 
4.2.2. Client Assertion of Authorization Identity 
    
   After successfully establishing a TLS session, a client may request 
   that its credentials exchanged during the TLS establishment be 
   utilized to determine the client's authorization status. The client 
   accomplishes this via an LDAP Bind request specifying a SASL 
   mechanism of EXTERNAL [SASL]. See section 3.3.6 for additional 
   details. 
    
4.2.3. TLS Connection Closure Effects 
    
   The decision to keep or invalidate the established authentication 
   and authorization identities in place after TLS closure is a matter 
   of local server policy. If a server chooses to invalidate 
   established authentication and authorization identities after TLS is 
   negotiated, it MUST reply to subsequent valid operation requests 
   until the next TLS closure or successful bind request with a 
   resultCode of strongAuthRequired to indicate that the client needs 
   to bind to reestablish its authentication. If the client attempts to 
   bind using a method the server is unwilling to support, it responds 
   to the with a resultCode of authMethodNotSupported (per [Protocol]) 
   to indicate that a different authentication method should be used. 
 
5. Anonymous Authentication 
 
 
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   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. 
 
   LDAP implementations MUST support anonymous authentication, as 
   defined in section 5.1. 
 
   LDAP implementations MAY support anonymous authentication with TLS, 
   as defined in section 5.2. 
 
   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. 
 
5.1. Anonymous Authentication Procedure 
 
   Prior to successfully completing a Bind operation, the LDAP 
   association is anonymous. See section 3.1. 
 
   An LDAP client may also explicitly establish an anonymous 
   association by sending a Bind Request with the simple authentication 
   option and a password of zero length. A bind request where both the 
   name and password are of zero length is said to be an anonymous 
   bind. A bind request where the name, a DN, is of non-zero length, 
   and the password is of zero length is said to be an unauthenticated 
   bind. Both variations produce an anonymous association. 
    
   Unauthenticated binds can have significant security issues (see 
   section 10). Servers SHOULD by default reject unauthenticated bind 
   requests with a resultCode of invalidCredentials, and clients may 
   need to actively detect situations where they would make an 
   unauthenticated bind request. 
 
5.2. Anonymous Authentication and TLS 
 
   An LDAP client may use the Start TLS operation (section 5) to 
   negotiate the use of [TLS] security. 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 9. 
 
   An LDAP server which requests that clients provide their certificate 
   during TLS negotiation MAY use a local security policy to determine 
   whether to successfully complete TLS negotiation if the client did 
   not present a certificate which could be validated. 
 
 
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6. Password-based Authentication 
    
   This section discusses various options for performing password-based 
   authentication to LDAP compliant servers and the environments 
   suitable for their use. 
    
   The transmission of passwords in the clear--typically for 
   authentication or modification--poses a significant security risk. 
   This risk can be avoided by using SASL bind [SASL] mechanisms that 
   do not transmit passwords in the clear and by negotiating transport 
   or session layer confidentiality services before transmitting 
   password values. 
    
   To mitigate the security risks associated with the use of passwords, 
   a server implementation MUST implement a configuration that at the 
   time of authentication or password modification, requires: 
    
     1) A Start TLS encryption layer has been successfully negotiated. 
      
      OR 
      
     2) Some other confidentiality mechanism that protects the password 
        value from snooping has been provided. 
      
      OR 
      
     3) The server returns a resultCode of confidentialityRequired for 
        the operation (i.e. simple bind with password value, SASL bind 
        transmitting a password value in the clear, add or modify 
        including a userPassword value, etc.), even if the password 
        value is correct. 
 
6.1. 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 4. 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. 
 
6.2. Digest Authentication 
    
   LDAP servers that implement any authentication method or mechanism 
   (other than simple anonymous bind) MUST implement the SASL 
   DIGEST-MD5 mechanism [DIGEST-MD5].  This provides client 
   authentication with protection against passive eavesdropping 
   attacks, but does not provide protection against active intermediary 
   attacks.  DIGEST-MD5 also provides data integrity and data 
   confidentiality capabilities. 
    
 
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   Support for subsequent authentication is OPTIONAL in clients and 
   servers. 
    
   Implementors must take care to ensure that they maintain the 
   semantics of the DIGEST-MD5 specification even when handling data 
   that has different semantics in the LDAP protocol. 
   For example, the SASL DIGEST-MD5 authentication mechanism utilizes 
   realm and username values ([DigestAuth section 2.1) which are 
   syntactically simple strings and semsantically simple realm and 
   username values. These values are not LDAP DNs, and there is no 
   requirement that they be represented or treated as such. Username 
   and realm values that look like LDAP DNs in form, e.g. <cn=bob, 
   dc=example,dc=com>, are syntactically allowed, however DIGEST-MD5 
   treats them as simple strings for comparison purposes. To illustrate 
   further, the two DNs <cn=Bob,dc=example,dc=com> (upper case "B") and 
   <cn=bob,dc=example,dc=com> (lower case "b") are equivalent when 
   being compared semantically as LDAP DNs because the cn attribute is 
   defined to be case insensitive, however the two values are not 
   equivalent if they represent username values in DIGEST-MD5 because 
   [SASLPrep] semantics are used by DIGEST-MD5.  
 
6.3. simple authentication choice under TLS encryption 
    
   Following the negotiation of an appropriate TLS ciphersuite 
   providing connection confidentiality, a client MAY authenticate to a 
   directory that supports the simple authentication choice by 
   performing a simple bind operation 
    
   Simple authentication with TLS encryption protection is performed as 
   follows:   
    
      1. The client will use the Start TLS operation [Protocol] to 
        negotiate the use of TLS security [TLS] on the connection to 
        the LDAP server. The client need not have bound to the 
        directory beforehand. 
      
         For the subsequent authentication procedure to be performed 
         securely, 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 9. 
    
      2. 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. 
    
6.3.1. 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 the presented password matches any member of that set, 
 
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   then the server will respond with a success resultCode, otherwise 
   the server will respond with an invalidCredentials resultCode. 
    
6.4. 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. 
    
7. Certificate-based authentication 
 
   LDAP server implementations SHOULD support authentication via a 
   client certificate in TLS, as defined in section 7.1. 
 
7.1. Certificate-based authentication with TLS 
 
   A user who has a public/private key pair in which the public key has 
   been signed by a Certification Authority may use this key pair to 
   authenticate to the directory server if the user's certificate is 
   requested by the server. The user's certificate subject field SHOULD 
   be the name of the user's directory entry, and the Certification 
   Authority that issued the 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 [TLS] 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 9. 
 
   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. 
 

 
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   Following the successful completion of TLS negotiation, the client 
   will send an LDAP bind request with the SASL EXTERNAL mechanism. 
 
8. LDAP Association State Transition Tables 
    
   To comprehensively diagram the various authentication and TLS states 
   through hich 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. 
    
8.1. LDAP Association States 
    
   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 8.4. 
 
   ID State Description 
   -- -------------------------------------------------------------- 
   S1 Anonymous 
          no Authentication ID is associated with the LDAP connection 
          no Authorization ID is in force 
   S2 Authenticated 
          Authentication ID = I 
          Authorization ID = X 
   S3 Authenticated SASL EXTERNAL, implicit authorization ID 
          Authentication ID = J 
          Authorization ID = Y 
   S4 Authenticated SASL EXTERNAL, explicit authorization ID  
          Authentication ID = J 
          Authorization ID = Z 
 
8.2. Actions that Affect LDAP Association State 
    
   The following table lists the actions that can affect the 
   authentication and authorization state of an LDAP association. The 
   ID for each action is used in the state transition table in section 
   8.4. 
    
   ID  Action 
   --  -------------------------------------------------------------- 
   A1  Client bind request fails 
   A2  Client successfully performs anonymous simple bind 
   A3  Client successfully performs unauthenticated simple bind 
   A4  Client successfully performs simple bind with name and 
        password OR SASL bind with any mechanism except EXTERNAL using 
        an authentication ID = I that maps to authorization ID X 
   A5  Client Binds SASL EXTERNAL with implicit assertion of 
        authorization ID (section 3.3.6.1)]. The current 
        authentication ID maps to authorization ID = Y. 
   A6  Client Binds SASL EXTERNAL with explicit assertion of 
        authorization ID = Z (section 3.3.6.2)] 

 
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   A7  Client abandons a bind operation, and server processes the 
        abandon 
   A8  Client abandons a bind operation, and server does not process 
        the abandon 
   A9  Client Start TLS request fails 
   A10 Client Start TLS request succeeds 
   A11 Client or Server: graceful TLS closure ([Protocol] section 
        4.13.3.1.) 
                                                  
8.3. Decisions Used in Making LDAP Association State Changes 
    
   Certain changes in the authentication and authorization 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 transition in the state 
   transition table in section 8.4.  
 
   ID Decision Question 
   -- -------------------------------------------------------------- 
   D1 Are lower-layer credentials available? 
   D2 Can lower-layer credentials for Auth ID "K" be mapped asserted 
       AuthZID "L"? 
 
8.4. LDAP Association State Transition Table 
    
   The LDAP Association table below lists the valid authentication and 
   authorization 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. 
    
   S1, the initial state for the state machine described in this table, 
   is the authentication state when an LDAP connection is initially 
   established. 
 
   Current            Next    
    State  Action     State  Comment 
   ------- -------    -----  --------------------------------------- 
     Any   A1          S1    [Protocol] section 4.2.1 
     Any   A2          S1    Section 6 
     Any   A3          S1    Section 6 
     Any   A4          S2    Sections 6.1, 6.2 
     Any   A5,         S1    Failed bind, section 3.3.6 
            D1=no 
     Any   A5,         S3     
            D1=yes 
     Any   A6,         S1    failed bind, section 3.3.6 
            D1=no 
     Any   A6,         S1    failed bind, section 3.3.6.2 
            D1=yes,  
            D2=no 
 
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     Any   A6,         S4     
            D1=yes, 
            D2=yes 
     Any   A7          S1    [Protocol] section 4.2.1. Clients 
                               cannot detect this state. 
     Any   A8          no    [Protocol] section 4.2.1. Clients 
                      change  cannot detect this state.  
     Any   A9          no    [Protocol] section 4.13.2.2 
                      change 
     Any   A10         no    Section 4.2.1 
                      change 
     Any   A11         S1    Section 4.2.3 
 
9. TLS Ciphersuites 
 
   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. 
    
   Several issues should be considered when selecting TLS ciphersuites 
   that are appropriate for use in a given circumstance. These issues 
   include the following: 
    
     - The ciphersuite's ability to provide adequate confidentiality 
       protection for passwords and other data sent over the LDAP 
       connection. Client and server implementers should recognize that 
       some TLS ciphersuites provide no confidentiality protection 
       while other ciphersuites that do provide confidentiality 
       protection may be vulnerable to being cracked using brute force 
       methods, especially in light of ever-increasing CPU speeds that 
       reduce the time needed to successfully mount such attacks. 
      
       Client and server implementers SHOULD carefully consider the 
       value of the password or data being protected versus the level 
       of confidentially protection provided by the ciphersuite to 
       ensure that the level of protection afforded by the ciphersuite 
       is appropriate. 
      
     - The ciphersuite's vulnerability (or lack thereof) to man-in-the-
       middle attacks. Ciphersuites vulnerable to man-in-the-middle 
       attacks SHOULD NOT be used to protect passwords or sensitive 
       data, unless the network configuration is such that the danger 
       of a man-in-the-middle attack is tolerable. 
 
9.1. TLS Ciphersuites Recommendations 
    
   As of the writing of this document, the following recommendations 
   regarding TLS ciphersuites are applicable. Because circumstances are 
   constantly changing, this list must not be considered exhaustive, 
   but is hoped that it will serve as a useful starting point for 
   implementers.  
    

 
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   The following ciphersuites defined in [TLS] MUST NOT be used for 
   confidentiality protection of passwords or data: 
 
         TLS_NULL_WITH_NULL_NULL 
         TLS_RSA_WITH_NULL_MD5 
         TLS_RSA_WITH_NULL_SHA 
 
   The following ciphersuites defined in [TLS] can be cracked easily 
   (less than a day of CPU time on a standard CPU in 2000) and are NOT 
   RECOMMENDED for use in confidentiality protection of passwords or 
   data. 
 
         TLS_RSA_EXPORT_WITH_RC4_40_MD5 
         TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 
         TLS_RSA_EXPORT_WITH_DES40_CBC_SHA 
         TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA 
         TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA 
         TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA 
         TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA 
         TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 
         TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA 
 
   The following ciphersuites are vulnerable to man-in-the-middle 
   attacks: 
 
         TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 
         TLS_DH_anon_WITH_RC4_128_MD5 
         TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA 
         TLS_DH_anon_WITH_DES_CBC_SHA 
         TLS_DH_anon_WITH_3DES_EDE_CBC_SHA 
 
    
 
10. 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 can minimize denial of service attacks by timing out idle 
   connections, and returning the unwillingToPerform resultCode rather 
   than performing computationally expensive operations requested by 
   unauthorized clients. 
    
   The use of cleartext passwords and other unprotected authentication 
   credentials is strongly discouraged over open networks when the 
   underlying transport service cannot guarantee confidentiality. 
    
   Operational experience shows that clients can (and frequently do) 
   misuse unauthenticated bind (see section 5.1).  For example, a 
   client program might make a decision to grant access to non-
 
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   directory information on the basis of completing a successful bind 
   operation. Some LDAP server implementations will return a success 
   response to an unauthenticated bind thus leaving the client with the 
   impression that the server has successfully authenticated the 
   identity represented by the user name, when in effect, an anonymous 
   LDAP association has been created. Clients that use the results from 
   a simple bind operation to make authorization decisions should 
   actively detect unauthenticated bind requests (via the empty 
   password value) and react appropriately. 
    
   Access control SHOULD always 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. 
    
10.1. 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. 
    
   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. 
 
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   Server implementors SHOULD allow for server administrators to elect 
   whether and when connection confidentiality and/or integrity is 
   required, as well as elect whether and when client authentication 
   via TLS is required. 
    
   Additional security considerations relating to the EXTERNAL 
   mechanism to negotiate TLS can be found in [SASL] and [TLS]. 
    
11. IANA Considerations 
    
   The following IANA considerations apply to this document: 
    
   Please update the GSSAPI service name registry to point to [Roadmap] 
   and this document. 
    
   [To be completed] 
    
Acknowledgements 
    
   This document combines information originally contained in RFC 2829 
   and RFC 2830. The editor acknowledges the work of Harald Tveit 
   Alvestrand, Jeff Hodges, Tim Howes, Steve Kille, RL "Bob" Morgan , 
   and Mark Wahl, each of whom authored one or more of these documents. 
 
   This document is based upon input of the IETF LDAP Revision working 
   group. The contributions and suggestions made by its members in 
   shaping the contents and technical accuracy of this document is 
   greatly appreciated. 
    
Normative References 
 
   [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate 
       Requirement Levels", BCP 14, RFC 2119, March 1997. 
    
   [ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 
       Specifications: ABNF", RFC 2234, November 1997. 
 
   [DIGEST-MD5] Leach, P. C. Newman, and A. Melnikov, "Using Digest 
      Authentication as a SASL Mechanism", draft-ietf-sasl-rfc2831bis-
      xx.txt, a work in progress.  
    
   [LDAPDN] Zeilenga, Kurt D. (editor), "LDAP: String Representation of 
      Distinguished Names", draft-ietf-ldapbis-dn-xx.txt, a work in 
      progress. 
    
   [Models] Zeilenga, Kurt D. (editor), "LDAP: Directory Information 
       Models", draft-ietf-ldapbis-models-xx.txt, a work in progress. 
    
   [Protocol] Sermersheim, J., "LDAP: The Protocol", draft-ietf-
       ldapbis-protocol-xx.txt, a work in progress. 
    
   [Roadmap] K. Zeilenga, "LDAP: Technical Specification Road Map", 
       draft-ietf-ldapbis-roadmap-xx.txt, a work in progress. 
 
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   [SASL] Melnikov, A. (editor), "Simple Authentication and Security 
       Layer (SASL)", draft-ietf-sasl-rfc2222bis-xx.txt, a work in 
       progress. 
    
   [SASLPrep] Zeilenga, K., "Stringprep profile for user names and 
       passwords", draft-ietf-sasl-saslprep-xx.txt, (a work in 
       progress). 
    
   [StringPrep]  Hoffman P. and M. Blanchet, "Preparation of 
       Internationalized Strings ('stringprep')", draft-hoffman-
       rfc3454bis-xx.txt, a work in progress.  
    
   [Syntaxes] Legg, S. (editor), "LDAP: Syntaxes and Matching Rules", 
       draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress. 
    
   [TLS] Dierks, T. and C. Allen. "The TLS Protocol Version 1.1", 
       draft-ietf-tls-rfc2246-bis-xx.txt, a work in progress. 
 
   [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", 
       RFC 3629, STD 63, November 2003. 
    
   [Unicode] The Unicode Consortium, "The Unicode Standard, Version 
       3.2.0" is defined by "The Unicode Standard, Version 3.0" 
       (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), as 
       amended by the "Unicode Standard Annex #27: Unicode 3.1" 
       (http://www.unicode.org/reports/tr27/) and by the <20>Unicode 
       Standard Annex #28: Unicode 3.2" 
       (http://www.unicode.org/reports/tr28/). 
 
Informative References 
 
   [ANONYMOUS] Zeilenga, K.,"Anonymous SASL Mechanism", draft-zeilenga-
       sasl-anon-xx.txt, a work in progress. 
    
   [PLAIN] Zeilenga, K.,"Plain SASL Mechanism", draft-zeilenga-sasl-
       plain-xx.txt, a work in progress. 
    
    [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. 
 
 
Author's Address 
 
   Roger Harrison 
   Novell, Inc. 
   1800 S. Novell Place 
   Provo, UT 84606 
   +1 801 861 2642 
   roger_harrison@novell.com 
 
 
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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. 
    
   (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 
 
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   policies are typically expressed in terms of access control factors 
   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. 
 
B.4. Authorization Identity 
 
   An authorization identity is one kind of access control factor. It 
   is the name of the user or other entity that requests that 
   operations be performed. Access control policies are often expressed 
   in terms of authorization identities; e.g., entity X can perform 
   operation Y on resource Z. 
 
   The authorization identity bound to an association is often exactly 
   the same as the authentication identity presented by the client, but 
   it may be different. SASL allows clients to specify an authorization 
   identity distinct from the authentication identity asserted by the 
   client's credentials. This permits agents such as proxy servers to 
   authenticate using their own credentials, yet request the access 
   privileges of the identity for which they are proxying [SASL]. Also, 
   the form of authentication identity supplied by a service like TLS 
   may not correspond to the authorization identities used to express a 
 
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   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 LDAP where v3 of the 
       protocol is implied. Also made all references to LDAP use the 
       same wording. 
    
     - Miscellaneous grammatical changes to improve readability. 
      
     - Made capitalization in section headings consistent. 
      
   Version -01 
      
     - Changed title to reflect inclusion of material from RFC 2830 and 
       2251. 
    
C.1. Changes to Section 1 
    
   Version -01 
    
     - Moved conventions used in document to a separate section. 
    
C.2. Changes to Section 2 
    
   Version -01 
    
     - Moved section to an appendix. 
    
C.3. Changes to Section 3 
    
   Version -01 
    
     - 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 
    
 
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     - Added the following sentence: "Servers SHOULD NOT allow clients 
       with anonymous authentication to modify directory entries or 
       access sensitive information in directory entries." 
    
C.5.1. Changes to Section 5.1 
    
   Version -00 
    
     - Replaced the text describing the procedure for performing an 
       anonymous bind (protocol) with a reference to section 4.2 of RFC 
       2251 (the protocol spec). 
      
   Version -01 
      
     - Brought text describing procedure for performing an anonymous 
       bind from section 4.2 of RFC 2251 bis.  This text will be 
       removed from the draft standard version of that document.  
    
C.6. Changes to Section 6. 
    
   Version -00 
      
     Reorganized text in section 6.1 as follows: 
    
     1. Added a new section (6.1) titled "Simple Authentication" and 
       moved one of two introductory paragraphs for section 6 into 
       section 6.1. Added sentences to the paragraph indicating: 
    
        a. simple authentication is not suitable for environments where 
        confidentiality is not available. 
         
        b. LDAP implementations SHOULD NOT support simple 
        authentication unless confidentiality and data integrity 
        mechanisms are in force. 
    
     2. Moved first paragraph of section 6 (beginning with "LDAP 
       implementations MUST support authentication with a password...") 
       to section on Digest Authentication (Now section 6.2). 
      
C.6.1. Changes to Section 6.1. 
    
   Version -00 Renamed section to 6.2 
    
     - Added sentence from original section 6 indicating that the 
       DIGEST-MD5 SASL mechanism is required for all conforming LDAP 
       implementations 
    
C.6.2. Changes to Section 6.2 
    
   Version -00 
      
     - Renamed section to 6.3 
    

 
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     - Reworded first paragraph to remove reference to user and the 
       userPassword password attribute Made the first paragraph more 
       general by simply saying that if a directory supports simple 
       authentication that the simple bind operation MAY performed 
       following negotiation of a TLS ciphersuite that supports 
       confidentiality. 
    
     - Replaced "the name of the user's entry" with "a DN" since not 
       all bind operations are performed on behalf of a "user." 
    
     - Added Section 6.3.1 heading just prior to paragraph 5. 
    
     - Paragraph 5: replaced "The server" with "DSAs that map the DN 
       sent in the bind request to a directory entry with a 
       userPassword attribute." 
    
C.6.3. Changes to section 6.3. 
    
     Version -00 
      
     - Renamed to section 6.4. 
    
C.7. Changes to section 7. 
    
   none 
    
C.7.1. Changes to section 7.1. 
    
   Version -00 
      
     - Clarified the entity issuing a certificate by moving the phrase 
       "to have issued the certificate" immediately after 
       "Certification Authority." 
 
C.8. Changes to section 8. 
 
   Version -00 
      
     - Removed the first paragraph because simple authentication is 
       covered explicitly in section 6. 
      
     - Added section 8.1. heading just prior to second paragraph. 
      
     - 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. 
 
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   Version -00 
      
     - Paragraph 2: changed "EXTERNAL mechanism" to "EXTERNAL SASL 
       mechanism." 
      
     - Added section 9.1. heading. 
      
     - Modified a comment in the ABNF from "unspecified userid" to 
       "unspecified authz id". 
      
     - Deleted sentence, "A utf8string is defined to be the UTF-8 
       encoding of one or more ISO 10646 characters," because it is 
       redundant. 
      
     - Added section 9.1.1. heading. 
      
     - Added section 9.1.2. heading. 
      
   Version -01 
      
     - Moved entire section 9 to become section 3.5 so that it would be 
       with other SASL material. 
 
C.10. Changes to Section 10. 
      
   Version -00 
      
     - Updated reference to cracking from a week of CPU time in 1997 to 
       be a day of CPU time in 2000. 
      
     - Added text: "These ciphersuites are NOT RECOMMENDED for use... 
       and server implementers SHOULD" to sentence just prior the 
       second list of ciphersuites. 
      
     - Added text: "and MAY support other ciphersuites offering 
       equivalent or better protection," to the last paragraph of the 
       section. 
      
C.11. Changes to Section 11. 
      
   Version -01 
      
     - 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 
 
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     - 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. 
      
     - 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 
    

 
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     - Added references to other LDAP standard documents, to sections 
       within the document, and fixed broken references. 
      
     - General editorial changes--punctuation, spelling, formatting, 
       etc. 
    
   Section 1. 
    
     - Added glossary of terms and added sub-section headings 
    
   Section 2. 
    
     - Clarified security mechanisms 3, 4, & 5 and brought language in 
       line with IETF security glossary. 
    
   Section 3. 
    
     - Brought language in requirement (3) in line with security 
       glossary. 
      
     - Clarified that information fetched prior to initiation of TLS 
       negotiation must be discarded 
      
     -Clarified that information fetched prior to initiation of SASL 
       negotiation must be discarded 
      
     - Rewrote paragraph on SASL negotiation requirements to clarify 
       intent 
    
   Section 4.4. 
 
     - Added stipulation that sasl choice allows for any SASL mechanism 
       not prohibited by this document. (Resolved conflict between this 
       statement and one that prohibited use of ANONYMOUS and PLAIN 
       SASL mechanisms.) 
    
   Section 5.3.6 
    
     - Added a.x.bar.com to wildcard matching example on hostname 
       check. 
    
   Section 6 
    
     - 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 
 
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   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. 
    
   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.) 
 
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     - 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 
    
     - 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. 
 
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   Section 3. 
    
     - Renamed section to "Rationale for LDAP Security Mechanisms" and 
       removed text that did not support this theme. Part of the 
       motivation for this change was to remove the implication of the 
       previous section title, "Required Security Mechanisms", and 
       other text found in the section that everything in the section 
       was a requirement 
      
     - Information from several removed paragraphs that describe 
       deployment scenarios will be added Appendix A in the next 
       revision of the draft. 
 
      
     - Paragraph beginning, " If TLS is negotiated, the client MUST 
       discard all information..." was moved to section 5.1.7 and 
       integrated with related material there. 
      
     - Paragraph beginning, "If a SASL security layer is negotiated..." 
       was moved to section 4.2 
      
   Section 4.l. 
    
     - Changed wording of first paragraph to clarify meaning. 
    
   Section 4.2. 
     - Added paragraph from section 3 of -04 beginning, "If a SASL 
       security layer is negotiated..." 
    
   Section 4.3.3. 
     - Renamed to "Other SASL Mechanisms" and completely rewrote the 
       section (one sentence) to generalize the treatment of SASL 
       mechanisms not explicitly mentioned in this document.  
    
   Section 4.4.1. 
    
     - Added paragraph beginning, "The dnAuthzID choice allows client 
       applications..." to clarify whether DN form authorization 
       identities have to also have a corresponding directory entry. 
       This change was based on editor's perception of WG consensus. 
      
     - Made minor clarifying edits in the paragraph beginning, "The 
       uAuthzID choice allows for compatibility..." 
    
   Section 5.1.1. 
      
     - Made minor clarifying edits in the last paragraph of the 
       section. 
      
   Section 5.1.7. 
      


 
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     - 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. 
 
F.5. Changes for draft-ldap-bis-authmeth-06 
 
      
   General 
    
     - Combined Section 2 (Introduction) and Section 3 (Motivation) and 
       moved Introduction to section 1. All following sections numbers 
       were decremented by one as result. 
      
     - Edits to fix typos, I-D nits, etc. 
      
     - Opened several new issues in Appendix G based on feedback from 
       WG. Some of these have been resolved. Others require further 
       discussion. 
      
   Section 1 
      
 
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     - Added additional example of spoofing under threat (7). 
      
   Section 2.1 
      
     - Changed definition of "LDAP association" and added terms, 
       "connection" and "TLS connection" to bring usage in line with 
       [Protocol]. 
      
   Section 4.1.6 
      
     - Clarified sentence stating that the client MUST NOT use derived 
       forms of DNS names. 
    
   Section 5.1 
    
     - Began edits to LDAP Association state table to clarify meaning 
       of various states and actions. 
      
     - Added action A9 to cover abandoned bind operation and added 
       appropriate transitions to the state transition table to 
       accommodate it. 
      
   Section 7.2 
      
     - Replaced first paragraph to clarify that the "DIGEST-MD5" SASL 
       mechanism is required to implement. 
    
   Section 9 
      
     - Rewrote the section to make the advice more applicable over the 
       long term, i.e. more "timeless." The intent of content in the 
       original section was preserved. 
 
   Section 10 
      
     - Added a clarifying example to the consideration regarding misuse 
       of unauthenticated access.  
 
F.6. Changes for draft-ldap-bis-authmeth-07 
 
      
   General 
      
     - Updated external and internal references to accommodate changes 
       in recent drafts. 
      
     - Opened several new issues in Appendix G based on feedback from 
       WG. Some of these have been resolved. Others require further 
       discussion. 
      
   Section 3 
    
     - Rewrote much of section 3.3 to meet the SASL profile 
       requirements of draft-ietf-sasl-rfc2222bis-xx.txt section 5. 
 
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     - Changed treatement of SASL ANONYMOUS and PLAIN mechanisms to 
       bring in line with WG consensus. 
    
   Section 4 
    
     - Note to implementers in section 4.1.1 based on operational 
       experience. 
    
     - Clarification on client continuing by performing a Start TLS 
       with TLS already established in section 4.1.4. 
    
     - Moved verification of mapping of client's authentication ID to 
       asserted authorization ID to apply only to explicit assertion. 
       The local policy in place for implicit assertion is adequate. 
    
   Section 7 
    
     - Removed most of section 7.2 as the information is now covered 
       adequately via the new SASL profile in section 3.3. Added note 
       to implementors regarding the treatment of username and realm 
       values in DIGEST-MD5. 
    
     - Section 7.3. Minor clarifications in wording. 
    
     - Section 7.3.1. Clarification that a match of the presented value 
       to any member of the set of stored passwords constitutes a 
       successful authentication. 
    
F.6. Changes for draft-ldap-bis-authmeth-08 
 
      
   General 
      
     - Changed usage from LDAPv3 to LDAP for usage consistency across 
       LDAP technical specification. 
      
     - Fixed a number of usage nits for consistency and to bring doc in 
       conformance with publication guidelines. 
 
   Abstract 
      
     - Significant cleanup and rewording of abstract based on WG 
       feedback. 
      
   Section 2.1 
      
     - New definition of user. 
      
   Section 3 
      
     - Added 1.5 sentences at end of introductory paragraph indicating 
       the effect of the Bind op on the LDAP association. 
      
 
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   Section 3.1 
      
     - Retitled section and clarified wording 
      
   Section 3.2 
 
     - Clarified that simple authentication choice provides three types 
       of authentication: anonymous, unauthenticated, and simple 
       password. 
      
   Section 3.3.3 
      
     - New wording clarifying when negotiated security mechanisms take 
       effect. 
      
   Section 3.3.5 
      
     - Changed requirement to discard information about server fetched 
       prior to SASL negotiation from MUST to SHOULD to allow for 
       information obtained through secure mechanisms. 
      
   Section 3.3.6 
      
     - Simplified wording of first paragraph based on suggestion from 
       WG. 
      
   Section 3.4 
      
     - Minor clarifications in wording. 
      
   Section 3.4.1 
      
     - Minor clarifications in wording in first sentence. 
     - Explicitly called out that the DN value in the dnAuthzID form is 
       to be matched using DN matching rules. 
     - Called out that the uAuthzID MUST be prepared using SASLprep 
       rules before being compared. 
     - Clarified requirement on assuming global uniqueness by changing 
       a "generally... MUST" wording to "SHOULD". 
      
   Section 4.1.1 
      
     - Simplified wording describing conditions when Start TLS cannot 
       be sent. 
     - Simplified wording in note to implementers regarding race 
       condition with outstanding LDAP operations on connection. 
 
   Section 4.1.5 
      
     - Removed section and moved relevant text to section 4.2.2. 
 
   Section 4.1.6  
      
     - Renumbered to 4.1.5. 
 
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     - Updated server identity check rules for server's name based on 
       WG list discussion. 
      
   Section 4.1.7 
      
     - Renumbered to 4.1.6 
     - Changed requirement to discard information about server fetched 
       prior to TLS negotion from MUST to SHOULD to allow for 
       information obtained through secure mechanisms. 
 
   Section 6.1 
      
     - Clarified wording. 
     - Added definition of anonymous and unauthenticated binds. 
 
   Section 10 
      
     - Added security consideration (moved from elsewhere) discouraging 
       use of cleartext passwords on unprotected communication 
       channels. 
 
   Section 11 
      
     - Added an IANA consideration to update GSSAPI service name 
       registry to point to [Roadmap] and [Authmeth] 
      
F.7. Changes for draft-ldap-bis-authmeth-09 
 
      
   General 
      
     - Updated section references within document 
     - Changed reference tags to match other docs in LDAP TS 
     - Used non-quoted names for all SAL mechanisms 
    
   Abstract 
 
     - Inspected keyword usage and removed several improper usages. 
      
     - Removed sentence saying DIGEST-MD5 is LDAP's mandatory-to-
       implement mechanism. This is covered elsewhere in document. 
 
     - Moved section 5, authentication state table, of -08 draft to 
       section 8 of -09 and completely rewrote it. 
 
   Section 1 
      
     - Reworded sentence beginning, "It is also desireable to allow 
       authentication methods to carry identities based on existing<6E>
       non-LDAP DN<44>forms..." 
     - Clarified relationship of this document to other documents in 
       the LDAP TS. 
    
   Section 3.3.5 
 
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     - Removed paragraph beginning,"If the client is configured to 
       support multiple SASL mechanisms..." because the actions 
       specified in the paragraph do not provide the protections 
       indicated. Added a new paragraph indicating that clients and 
       server should allow specification of acceptable mechanisms and 
       only allow those mechanisms to be used. 
      
     - Clarified independent behavior when TLS and SASL security layers 
       are both in force (e.g. one being removed doesn't affect the 
       other). 
    
   Section 3.3.6 
      
     - Moved most of section 4.2.2, Client Assertion of Authorization 
       Identity, to sections 3.3.6, 3.3.6.1, and 3.3.6.2.  
    
   Section 3.3.6.4 
      
     - Moved some normative comments into text body. 
    
   Section 4.1.2 
      
     - Non success resultCode values are valid if server is *unwilling* 
       or unable to negotiate TLS. 
    
   Section 4.2.1 
      
     - Rewrote entire section based on WG feedback. 
 
   Section 4.2.2 
      
     - Moved most of this section to 3.3.6 for better document flow. 
 
   Section 4.2.3 
      
     - Rewrote entire section based on WG feedback. 
 
   Section 5.1 
      
     - Moved imperative language regarding unauthenticated access from 
       security considerations to here. 
    
   Section 6 
      
     - Added several paragraphs regarding the risks of transmitting 
       passwords in the clear and requiring server implementations to 
       provide a specific configuration that reduces these risks. 
 
   Section 6.2 
      
     - Added sentence describing protections provided by DIGEST-MD5 
       method. 
     - Changed DNs in exmple to be dc=example,dc=com. 
 
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   Section 10 
      
     - Updated consideration on use of cleartext passwords to include 
       other unprotected authentication credentials 
     - Substantial rework of consideration on misuse of unauthenticated 
       bind. 
 
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. 
 


 
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   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 
   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 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 

 
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        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. 
 
   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-
 
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   MD5:  
    
   "6.2. Digest authentication  
    
   LDAP implementations MUST support authentication with a password  
   using the DIGEST-MD5 SASL mechanism for password protection, as  
   defined in section 6.1."  
    
   The thing is for acl it would be nice (though not critical) to be 
   able to default the required authentication level for a subject to a 
   single "fairly secure" mechanism--if there is no such mandatory 
   authentication scheme then you cannot do that. (Source: Rob Byrne) 
    
   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 Start TLS 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 
 
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   (Source: Jeff Hodges) 
    
   Status: Resolved.  
    
   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. 
    
   Did a significant revision of state transition table in -09. Changes 
   were based on suggestions from WG and greatly simplified overall 
   table. 
    
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 
 
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   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 
   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. 
 
 
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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 -03. 
    
G.22. Need to move Start TLS protocol information to [Protocol] 
 
   Status: Resolved. Removed Sections 5.1, 5.2, and 5.4 for -04 and 
   they are [Protocol] -11. 
 
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: Resolved. 
    
   (3/24/03) This following text appears in section 4.2.1 of [Protocol] 
   revision -13 to cover what happens if a bind operation is abandoned: 
     
   A failed or abandoned Bind Operation has the effect of leaving the 
   connection in an anonymous state. To arrive at a known 
   authentication state after abandoning a bind operation, clients may 
   unbind, rebind, or make use of the BindResponse. 
    
   (6/28/03): The state table in section 6 of [AuthMeth] has been 
   updated to reflect this wording.  
 
G.25. Difference between checking server hostname and server's 
canonical DNS name in Server Identity Check? 
 
   Section 4.1.6: 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: Resolved.  
    
   (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. 
    
 
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   (6/28/03): posted to the WG list asking Bob or any other WG member 
   who is knowledgeable about the issues involved to help me with 
   wording or other information I can use to make this change and close 
   the work item. 
    
   (10/08/03): Based on WG list feedback, I've updated this text to 
   read what I judge to be the WG consensus, "The client MUST use the 
   server provided by the user (or other trusted entity) as the value 
   to compare against the server name as expressed in the server's 
   certificate. A hostname derived from the user input is to be 
   considered provided by the user only if derived in a secure fashion 
   (e.g., DNSSEC)." 
    
    
G.26. Server Identity Check using servers located via SRV records 
    
   Section 4.1.6: 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. 
   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 4.4.1 of authmeth -03 (section 4.1 of RFC2830) states that 
   TLS closure alert will leave the LDAP association intact. Contrast 
   this with Section 4.5.2 (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: Resolved. (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 4.4.1 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 4.2.2). 
    
   (11/21/02): resolution to this is expected in [Protocol] -12 
    
   (06/28/03): [Protocol]-15 clarifies that a TLS closure alert 
   terminates the TLS connection while leaving the LDAP connection 
   intact. The authentication state table in [AuthMeth] specifies the 
   effect on the LDAP association.  
 
G.28 Ordering of external sources of authorization identities 
    
 
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   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 9, 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. 
    
   Status: Resolved. (6/28/03): Rewrote the section to cover the 
   general issues and considerations involved in selecting TLS 
   ciphersuites. 
    
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. 
 
G.31 Use of PLAIN SASL Mechanism 
    
   At least one LDAP server implementer has found the SASL "PLAIN" 
   mechanism useful in authenticating to legacy systems that do not 
   represent authentication identities as DNs. Section 3.3.1 appears to 
   implicitly disallow the use of the SASL "PLAIN" mechanism with LDAP. 
   Should we allow the use of this mechanism? I.e. is this "SASL" 
   "PLAIN" MUST NOT be used with LDAP, or is it simply that LDAP 
   doesn't define bindings for these mechanism. If SASL "PLAIN" is 
   allowed, the following adjustments will be needed to section 3.3.1: 
   (a) change section heading, (b) remove reference to "PLAIN" in the 
   section, (c) ensure wording of last sentence regarding non-DN 
   AuthZIDs is consistent with rest of the section. 
    
   Status: Resolved. 
    
   (6/28/03): email to WG list stating issue and asking if we should 
   remove the reference to SASL "PLAIN". 
    
   For -07 draft I've generalized the SASL profile in section 3.3 to 
   allow any SASL mechanism. 
    
    
G.32 Clarification on use of SASL mechanisms 
    
   Section 3.3.1: BTW, what _are_ the "ANONYMOUS" and "PLAIN" SASL 
   mechanisms?  They are not defined in RFC2222.  If you refer to other 
 
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   SASL mechanisms than those in rfc2222, Maybe you should only list 
   which mechanisms _are_used, instead of which ones are _not. (Source: 
   Hallvard Furuseth) 
    
   I (Kurt Zeilenga) note[s] as well that the ANONYMOUS/PLAIN section 
   (4.2) should 
   be deleted.  ANONYMOUS and PLAIN, like in other mechanism, 
   can be used in LDAP if a) supported and b) enabled.  I note 
   that they each offer capabilities not found in their simple 
   bind equivalents (and hence are used in some deployments). 
   For example, PLAIN (over TLS) is quite useful when interacting 
   with legacy authentication subsystems.  (Source: Kurt Zeilenga) 
    
   Status: Resolved. 
    
   For -07 draft I've generalized the SASL profile in section 3.3 to 
   allow any SASL mechanism. 
    
    
    
G.33 Clarification on use of password protection based on AuthZID form 
    
   Section 3.3.1: "If an authorization identity of a form different 
   from a DN is requested by the client, a mechanism that protects the 
   password in transit SHOULD be used." What has that to do with DNs?  
   A mechanism that protects the password in transit should be used in 
   any case, shouldn't it? 
    
   Status: Resolved. 
    
   In -08 draft this text was removed. There is already a general 
   security consideration that covers this issue. 
    
    
G.34 Clarification on use of matching rules in Server Identity Check 
    
   The text in section 4.1.6 isn't explicit on whether all rules apply 
   to both CN and dNSName values.  The text should be clear as to which 
   rules apply to which values....  in particular, the wildcard 
   rules. (Source: Kurt Zeilenga) 
    
    
G.35 Requested Additions to Security Considerations 
    
   Requested to mention hostile servers which the user might have been 
   fooled to into contacting. Which mechanisms that are standardized by 
   the LDAP standard do/do not disclose the user's password to the 
   server? (Or to servers doing man-in-the-middle attack? Or is that a 
   stupid question?) 
    
   Requested to mention denial of service attacks.  
    
   Requested list of methods that need/don't need the server to know 
   the user's plaintext password. (I say 'know' instead of 'store' 
 
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   because it could still store the password encrypted, but in a way 
   which it knows how to decrypt.) 
    
   (Source: Hallvard Furuseth) 
    
G.36 Add reference to definition of DIGEST-MD5 
    
   Need a reference to the definition of DIGEST-MD5 SASL mechanism in 
   section 7.2 (Source: Hallvard Furuseth) 
    
   Status: Resolved. A reference to to the DIGEST-MD5 SASL mechanism, 
   [DigestAuth], is included in the -07 revision. 
    
G.37 Clarification on procedure for certificate-based authentication 
 
    
   8.1. Certificate-based authentication with TLS states: "Following 
   the successful completion of TLS negotiation, the client will send 
   an LDAP bind request with the SASL "EXTERNAL" mechanism." Is this 
   immediately following, or just some time later? Should the wording, 
   "the client will send..." actually read, "the client MUST send..."? 
    
G.38 Effect of Start TLS on authentication state 
    
   Should the server drop all knowledge of connection, i.e. return to 
   anonymous state, if it gets a Start TLS request on a connection that 
   has successfully bound using the simple method? 
    
G.39 Be sure that there is a consideration in [SCHEMA] that discusses 
multiple password values in userPassword 
 
   Allowing multiple values obviously does raise a number of security 
   considerations and these need to be discussed in the document. 
    
   Certainly applications which intend to replace the userPassword with 
   new value(s) should use modify/replaceValues (or 
   modify/deleteAttribute+addAttribute). Additionally, server 
   implementations should be encouraged to provide administrative 
   controls which, if enabled, restrict userPassword to one value. 
    
G.40. Clarify need to verify mapping between authentication identity 
and resulting authorization identity on implicit assertion of AuthZID. 
 
   4.2.2.3. 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." 
    
   This makes sense for the explicit assertion case, but seems to be  
   ambiguous for the implicit case. 
   IMHO, the mapping can be done as two steps: 
   a). deriving LDAP authentication identity from TLS credentials; If t 
   this steps fails, EXTERNAL mechanism returns failure. 
 
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   b). verify that the authorization identity is allowed for the 
   derived authentication identity. This is always "noop" for the 
   implicit case. 
   I am not sure that the text is saying this. 
   (Source: Alexey Melnikov email 8/1/2003 5:30:43 PM) 
    
   Status: Resolved in -07. After reading the comments and the text of 
   the draft, I believe that this should be clarified. The local policy 
   used to map the AuthNID to the AuthZID in the implicit case is 
   sufficient and that no additional verification is useful or needed. 
   This text has been moved to apply only to the explicit assertion 
   case. 
    
G.41. Section 7.2 contains unnecessary and misleading detail. 
    
   " I am not sure why this section is required in the document. 
   DIGEST-MD5 is defined in a separate document and there should be 
   nothing magical about its usage in LDAP. If DIGEST-MD5 description 
   creates confusion for LDAP implementors, let's fix the DIGEST-MD5 
   document! Also, this section tries to redefine DIGEST-MD5 behavior, 
   which is explicitly prohibited by the SASL specification." 
   (Source: Alexey Melnikov: email 8/1/2003 5:30:43 PM) 
    
   Status: Resolved. 
    
   After reading the comments and the text of the draft plus the 
   related text in draft-ietf-sasl-rfc2831bis-02.txt plus 
   http://www.ietf.org/internet-drafts/draft-ietf-sasl-rfc2222bis-
   02.txt, I am inclined to agree with Alexey. In -07 I rewrote section 
   3.3 (SASL mechanisms) to match the profiling requirements 
   rfc2831bis. I then dramatically reduced the material in section 7.2 
   to a bare minimum and let the SASL profile stand on its own.   
 
G.42. Does change for G.41 cause interoperability issue? 
    
   There is one issue with the way the authmeth draft is currently 
   written that changes the SASL DIGEST-MD5 behavior on the way the 
   server responds with the subsequent authentication information . 
   This has been documented in this fashion since RFC 2829 (section 
   6.1) was originally published and may cause an interoperability 
   issue at this point if it changed to follow the DIGEST-MD5 spec (as 
   it was in -07 of AuthMeth). Take this issue to the list. 
    
   Status: Resolved 
    
   (10/08/03) This item was discussed on the WG list between 5/2/03 and 
   5/9/03. Consensus apppears to support the notion that RFC 2829 was 
   in error and that the semantics of RFC 2831 are correct and should 
   be reflected in authmeth. This is already the case as of the -07 
   draft. 
 
G.43. DIGEST-MD5 Realms recommendations for LDAP 
    

 
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   From http://www.ietf.org/internet-drafts/draft-ietf-sasl-rfc2222bis-
   02.txt: A protocol profile SHOULD provide a guidance how realms are 
   to be constructed and used in the protocol and MAY further restrict 
   its syntax and protocol-specific semantics." 
    
   I don't believe that any such guidance exists within the LDAP TS. 
   The most likely place for this to reside is in the authmeth draft. 
    
   Related email from Alexey Melnikov (8/4/2003 1:08:40 PM): 
    
   "The problem I have with the document is that it references realm 
   without explaining what it is (or at least some examples of valid 
   values). For LDAP, some recommendations should be given. For 
   example: 
   1). Use a hardcoded string as the realm (one of the implementations 
   I worked on was doing that) 
   2). Use hostname (realm==host) or domain/cluster name (realm 
   includes multiple hosts). 
   3). Use a node in DIT above user entry, for example for "cn=Barbara  
   Jensen, ou=Accounting, o=Ace Industry, c=US" 
    and "cn=John Doe, ou=Accounting, o=Ace Industry, c=US" realm can be  
   "ou=Accounting, o=Ace Industry, c=US" 
   (or "o=Ace Industry, c=US"); for "cn=Gern Jensen, ou=Product 
   Testing,o=Ace Industry, c=US" realm can be "ou=Product Testing, 
   o=Ace Industry, c=US". 
    
   Of course other choices are possible. 
    
   Alexey 
    
   To summarize:  I'd like authmeth to define a realm name for use with 
   Digest-MD5 that corresponds to LDAP DNs known to this server.  
   Authzid is okay, but perhaps could be better put into context. 
    
    
   John  McMeeking (5/12/2003) 
    
   Status: Resolved. 
    
   draft-ietf-sasl-rfc2222bis-03.txt no longer requires this 
   information in a SASL protocol. In addition, the ldapbis WG chairs 
   have ruled this work out of scope. Individuals are welcome to make 
   submissions to provide guidance on the use of realm and realm values 
   in LDAP. 
    
G.44. Use of DNs in usernames and realms in DIGEST-MD5 
    
   In reading the discussion on the mailing list, I reach the following 
   conclusions: 
    
   DIGEST-MD5 username and realm are simple strings. The syntax of 
   these strings allows strings that look like DNs in form, however, 
   DIGEST-MD5 treats them a simple strings for comparision purposes. 
   For example, the DNs cn=roger, o=US and cn=roger,o=us are equivalent 
 
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   when being compared semantically as DNs, however, these would be 
   considered two different username values in DIGEST-MD5 because 
   simple octet-wise semantics (rather than DN semantics) are used to 
   compare username values in DIGEST-MD5. Ditto for realm values. 
    
   Status: Resolved. 
    
   In -07 revision I added notes to implementors expressing this issue 
   in section 7.2.  
    
G.45: Open Issue: Is Simple+TLS mandatory to implement? 
    
   Going forward, it would be much better to clarify that simple 
   +TLS is to be used for DN/password credentials and DIGEST-MD5 
   (or PLAIN+TLS) be used for username/password credentials. (Kurt 
   Zeilenga, 5/12/2003) 
    
   I don't believe you can mandate simple/TLS! At the time RFC 2829 was 
   debated, a large number on the WG wanted this. They did not get 
   their way because of the complexity of the solution. It was argued 
   that a password-based method would be better. I think they believed 
   it would still be DN/password, though. (Ron Ramsay, 5/12/2003) 
    
   This was officially opened as an issue by WG co-chair Kurt Zeilenga 
   on 5/12/03. Little direct discussion has occurred since, however 
   there has been significant discussion on the use of DN values as the 
   username for DIGEST-MD5. 
    
   Status: Resolved. 
    
   Based on WG list discussion, Kurt Zeilenga has gaged a lack of WG 
   consensus that Simple+TLS should be mandatory to implement. No 
   further discussion is necessary. 
    
 
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