2 INTERNET-DRAFT Editor: R. Harrison
3 draft-ietf-ldapbis-authmeth-08.txt Novell, Inc.
4 Obsoletes: 2251, 2829, 2830 26 October 2003
5 Intended Category: Draft Standard
8 LDAP: Authentication Methods
10 Connection Level Security Mechanisms
14 This document is an Internet-Draft and is in full conformance with
15 all provisions of Section 10 of RFC2026.
17 This document is intended to be, after appropriate review and
18 revision, submitted to the RFC Editor as a Standard Track document.
19 Distribution of this memo is unlimited. Technical discussion of
20 this document will take place on the IETF LDAP Extension Working
21 Group mailing list <ietf-ldapbis@OpenLDAP.org>. Please send
22 editorial comments directly to the author
23 <roger_harrison@novell.com>.
25 Internet-Drafts are working documents of the Internet Engineering
26 Task Force (IETF), its areas, and its working groups. Note that
27 other groups may also distribute working documents as Internet-
28 Drafts. Internet-Drafts are draft documents valid for a maximum of
29 six months and may be updated, replaced, or obsoleted by other
30 documents at any time. It is inappropriate to use Internet-Drafts
31 as reference material or to cite them other than as "work in
34 The list of current Internet-Drafts can be accessed at
35 http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-
36 Draft Shadow Directories can be accessed at
37 http://www.ietf.org/shadow.html.
41 Copyright (C) The Internet Society (2003). All Rights Reserved.
45 This document describes authentication methods and connection level
46 security mechanisms of the Lightweight Directory Access Protocol
49 This document details the simple Bind authentication method
50 including anonymous, unauthenticated, and plain-text password
51 methods and the SASL (Simple Authentication and Security Layer) Bind
52 authentication method including the use of DIGEST-MD5 and EXTERNAL
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60 This document also details establishment of TLS (Transport Layer
61 Security) using the Start TLS operation.
63 This document describes various authentication and authorization
64 states through which a connection to an LDAP server may pass and the
65 actions that trigger these state changes.
67 This document also prescribes DIGEST-MD5 as LDAP's mandatory-to-
68 implement strong authentication mechanism.
72 The Lightweight Directory Access Protocol (LDAP) [Protocol] is a
73 powerful access protocol for directories. It offers means of
74 searching, retrieving and manipulating directory content, and ways
75 to access a rich set of security functions.
77 It is vital that these security functions be interoperable among all
78 LDAP clients and servers on the Internet; therefore there has to be
79 a minimum subset of security functions that is common to all
80 implementations that claim LDAP conformance.
82 Basic threats to an LDAP directory service include:
84 (1) Unauthorized access to directory data via data-retrieval
87 (2) Unauthorized access to reusable client authentication
88 information by monitoring others' access,
90 (3) Unauthorized access to directory data by monitoring others'
93 (4) Unauthorized modification of directory data,
95 (5) Unauthorized modification of configuration information,
97 (6) Unauthorized or excessive use of resources (denial of service),
100 (7) Spoofing of directory: Tricking a client into believing that
101 information came from the directory when in fact it did not,
102 either by modifying data in transit or misdirecting the client's
103 connection. Also, tricking a client into sending privileged
104 information to a hostile entity that appears to be the directory
107 Threats (1), (4), (5) and (6) are due to hostile clients. Threats
108 (2), (3) and (7) are due to hostile agents on the path between
109 client and server or hostile agents posing as a server.
111 LDAP can be protected with the following security mechanisms:
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119 (1) Client authentication by means of the Secure Authentication and
120 Security Layer (SASL) [SASL] mechanism set, possibly backed by
121 the Transport Layer Security (TLS) [TLS] credentials exchange
124 (2) Client authorization by means of access control based on the
125 requestor's authenticated identity,
127 (3) Data integrity protection by means of TLS or SASL mechanisms
128 with security layers that provide data integrity services,
130 (4) Data confidentiality protection against snooping by means of the
131 TLS protocol or SASL mechanisms that provide data
132 confidentiality services,
134 (5) Server resource usage limitation by means of administrative
135 service limits configured on the server, and
137 (6) Server authentication by means of the TLS protocol or SASL
140 At the moment, imposition of access controls is done by means
141 outside the scope of LDAP.
143 It seems clear that allowing any implementation, faced with the
144 above requirements, to simply pick and choose among the possible
145 alternatives is not a strategy that is likely to lead to
146 interoperability. In the absence of mandates, clients will be
147 written that do not support any security function supported by the
148 server, or worse, they will support only mechanisms like the LDAP
149 simple bind using clear text passwords that provide inadequate
150 security for most circumstances.
152 Given the presence of the Directory, there is a strong desire to see
153 mechanisms where identities take the form of an LDAP distinguished
154 name [LDAPDN] and authentication data can be stored in the
155 directory. This means that this data must be updated outside the
156 protocol or only updated in sessions well protected against
157 snooping. It is also desirable to allow authentication methods to
158 carry authorization identities based on existing--non-LDAP DN--forms
159 of user identities for backwards compatibility with non-LDAP-based
160 authentication services.
162 The set of security mechanisms provided in LDAP and described in
163 this document is intended to meet the security needs for a wide
164 range of deployment scenarios and still provide a high degree of
165 interoperability among various LDAP implementations and deployments.
166 Appendix A contains example deployment scenarios that list the
167 mechanisms that might be used to achieve a reasonable level of
168 security in various circumstances.
170 This document is an integral part of the LDAP Technical
171 Specification [Roadmap]. This document replaces RFC 2829 and
172 portions of RFC 2830 and RFC 2251.
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179 2. Conventions Used in this Document
181 2.1. Glossary of Terms
183 The following terms are used in this document. To aid the reader,
184 these terms are defined here.
186 - "user" represents any human or application entity which is
187 accessing the directory using a directory client. A directory
188 client (or client) is also known as a directory user agent
191 - "connection" and "LDAP connection" both refer to the underlying
192 transport protocol connection between two protocol peers.
194 - "TLS connection" refers to a TLS-protected LDAP connection.
196 - "association" and "LDAP association" both refer to the
197 association of the LDAP connection and its current
198 authentication and authorization state.
200 2.2. Security Terms and Concepts
202 In general, security terms in this document are used consistently
203 with the definitions provided in [RFC2828]. In addition, several
204 terms and concepts relating to security, authentication, and
205 authorization are presented in Appendix B of this document. While
206 the formal definition of these terms and concepts is outside the
207 scope of this document, an understanding of them is prerequisite to
208 understanding much of the material in this document. Readers who are
209 unfamiliar with security-related concepts are encouraged to review
210 Appendix B before reading the remainder of this document.
214 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
215 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
216 document are to be interpreted as described in RFC 2119 [RFC2119].
220 The Bind operation defined in section 4.2 of [Protocol] allows
221 authentication information to be exchanged between the client and
222 server to establish a new LDAP association. The new LDAP association
223 is established upon successful completion of the authentication
228 3.1. Implied Anonymous Bind on LDAP Association
230 Prior to the successful completion of a Bind operation and during
231 any subsequent authentication exchange, the session has an anonymous
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237 LDAP association. Among other things this implies that the client
238 need not send a Bind Request in the first PDU of the connection. The
239 client may send any operation request prior to binding, and the
240 server MUST treat it as if it had been performed after an anonymous
241 bind operation. This authentication state on an LDAP association is
242 sometimes referred to as an implied anonymous bind.
244 3.2. Simple Authentication
246 The simple authentication choice provides minimal facilities for
247 establishing an anonymous association or for establishing an LDAP
248 association based upon credentials consisting of a name (in the form
249 of an [LDAPDN] and a password.
251 The simple authentication choice provides two different methods
252 for establishing an anonymous association: anonymous bind and
253 unauthenticated bind (see section 6.1).
255 The simple authentication choice provides one method for
256 establishing a non-anonymous association: simple password bind.
258 3.3. SASL Authentication Profile
260 LDAP allows authentication via any SASL mechanism [SASL]. As LDAP
261 includes native anonymous and plaintext authentication methods, the
262 "ANONYMOUS" [ANONYMOUS] and "PLAIN" [PLAIN] SASL mechanisms are
263 typically not used with LDAP.
265 Each protocol that utilizes SASL services is required to supply
266 certain information profiling the way they are exposed through the
267 protocol ([SASL] section 5). This section explains how each of these
268 profiling requirements are met by LDAP.
270 3.3.1. SASL Service Name for LDAP
272 The SASL service name for LDAP is "ldap", which has been registered
273 with the IANA as a GSSAPI service name.
275 3.3.2. SASL authentication initiation and protocol exchange
277 SASL authentication is initiated via an LDAP bind request
278 ([Protocol] section 4.2) with the following parameters:
281 - The AuthenticationChoice is sasl.
282 - The mechanism element of the SaslCredentials sequence contains
283 the value of the desired SASL mechanism.
284 - The optional credentials field of the SaslCredentials sequence
285 may be used to provide an initial client response for
286 mechanisms that are defined to have the client send data first
287 (see [SASL] sections 5 and 6.1).
289 In general, a SASL authentication protocol exchange consists of a
290 series of server challenges and client responses, the contents of
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296 which are specific to and defined by the SASL mechanism. Thus for
297 some SASL authentication mechanisms, it may be necessary for the
298 client to respond to one or more server challenges by invoking the
299 BindRequest multiple times. A challenge is indicated by the server
300 sending a BindResponse with the resultCode set to
301 saslBindInProgress. This indicates that the server requires the
302 client to send a new bind request, with the same sasl mechanism to
303 continue the authentication process.
305 To the encapsulating protocol, these challenges and responses are
306 opaque binary tokens of arbitrary length. LDAP servers use the
307 serverSaslCreds field, an OCTET STRING, in a bind response message
308 to transmit each challenge. LDAP clients use the credentials field,
309 an OCTET STRING, in the SaslCredentials sequence of a bind request
310 message to transmit each response. Note that unlike some Internet
311 application protocols where SASL is used, LDAP is not text-based,
312 thus no Base64 transformations are performed on these challenge and
315 Clients sending a bind request with the sasl choice selected SHOULD
316 NOT send a value in the name field. Servers receiving a bind request
317 with the sasl choice selected SHALL ignore any value in the name
320 A client may abort a SASL bind negotiation by sending a BindRequest
321 with a different value in the mechanism field of SaslCredentials, or
322 an AuthenticationChoice other than sasl.
324 If the client sends a BindRequest with the sasl mechanism field as
325 an empty string, the server MUST return a BindResponse with
326 authMethodNotSupported as the resultCode. This will allow clients to
327 abort a negotiation if it wishes to try again with the same SASL
330 The server indicates completion of the SASL challenge-response
331 exchange by responding with a bind response in which the resultCode
332 is either success, or an error indication.
334 The serverSaslCreds field in the bind response can be used to
335 include an optional challenge with a success notification for
336 mechanisms which are defined to have the server send additional data
337 along with the indication of successful completion.
339 3.3.3. Octet where negotiated security mechanisms take effect
341 When negotiated, SASL security layers take effect following the
342 transmission by the server and reception by the client of the final
343 BindResponse in the exchange.
345 Once a SASL security layer providing integrity or confidentiality
346 services takes effect, the layer remains in effect until a new layer
347 is installed (i.e. at the first octet following the final
348 BindResponse of the bind operation that caused the new layer to take
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356 3.3.4. Determination of supported SASL mechanisms
358 An LDAP client may determine the SASL mechanisms a server supports
359 by performing a search request on the root DSE, requesting the
360 supportedSASLMechanisms attribute. The values of this attribute, if
361 any, list the mechanisms the server supports.
363 3.3.5. Rules for using SASL security layers
365 If a SASL security layer is negotiated, the client SHOULD discard
366 information about the server fetched prior to the initiation of the
367 SASL negotiation and not obtained through secure mechanisms.
369 If the client is configured to support multiple SASL mechanisms, it
370 SHOULD fetch the supportedSASLmechanisms list both before and after
371 the SASL security layer is negotiated. This allows the client to
372 detect active attacks that remove supported SASL mechanisms from the
373 supportedSASLMechanisms list and allows the client to ensure that it
374 is using the best mechanism supported by both client and server. (In
375 particular, this allows for environments where the
376 supportedSASLMechanisms list is provided to the client through a
377 different trusted source, e.g. as part of a digitally signed
380 If a lower level security layer (such as TLS) is negotiated, any
381 SASL security services SHALL be layered on top of such security
382 layers regardless of the order of their negotiation.
384 3.3.6. Use of EXTERNAL SASL Mechanism
386 A client can use the "EXTERNAL" SASL mechanism to request the LDAP
387 server to make use of security credentials exchanged by a lower
388 layer. If authentication credentials have not been established at a
389 lower level (such as by TLS authentication or IP-level security
390 [RFC2401]), the SASL EXTERNAL bind MUST fail with a resultCode of
391 inappropriateAuthentication. Any client authentication and
392 authorization state of the LDAP association is lost, so the LDAP
393 association is in an anonymous state after the failure (see
394 [Protocol] section 4.2.1).
396 3.4. SASL Authorization Identity
398 When the "EXTERNAL" SASL mechanism is being negotiated, if the
399 SaslCredentials credentials field is present, it contains an
400 authorization identity. Other mechanisms define the location of the
401 authorization identity in the credentials field. In either case, the
402 authorization identity is represented in the authzId form described
405 3.4.1. Authorization Identity Syntax
407 The authorization identity is a string of [UTF-8] encoded [Unicode]
408 characters corresponding to the following ABNF grammar [RFC2234]:
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415 ; Specific predefined authorization (authz) id schemes are
416 ; defined below -- new schemes may be defined in the future.
418 authzId = dnAuthzId / uAuthzId
420 DNCOLON = %x64 %x6e %x3a ; "dn:"
421 UCOLON = %x75 %x3a ; "u:"
423 ; distinguished-name-based authz id.
424 dnAuthzId = DNCOLON dn
425 dn = utf8string ; with syntax defined in [LDAPDN] section 3.
428 ; unspecified authorization id, UTF-8 encoded.
429 uAuthzId = UCOLON userid
430 userid = utf8string ; syntax unspecified
432 The dnAuthzId choice allows client applications to assert
433 authorization identities in the form of a distinguished name to be
434 matched in accordance with the distinguishedName matching rule
435 [Syntaxes]. The decision to allow or disallow an authentication
436 identity to have access to the requested authorization identity is a
437 matter of local policy ([SASL] section 4.2). For this reason there
438 is no requirement that the asserted dn be that of an entry in
441 The uAuthzId choice allows for compatibility with client
442 applications that wish to assert an authorization identity to a
443 local directory but do not have that identity in distinguished name
444 form. The value contained within a uAuthzId MUST be prepared using
445 SASLprep before being compared octet-wise. The format of utf8string
446 is defined as only a sequence of of [UTF-8] encoded [Unicode]
447 characters, and further interpretation is subject to prior agreement
448 between the client and server.
450 For example, the userid could identify a user of a specific
451 directory service or be a login name or the local-part of an RFC 822
452 email address. A uAuthzId SHOULD NOT be assumed to be globally
455 Additional authorization identity schemes may be defined in future
456 versions of this document.
458 4. Start TLS Operation
460 The Start Transport Layer Security (StartTLS) operation defined in
461 section 4.13 of [Protocol] provides the ability to establish [TLS]
462 on an LDAP association.
464 4.1. Sequencing of the Start TLS Operation
466 This section describes the overall procedures clients and servers
467 must follow for TLS establishment. These procedures take into
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473 consideration various aspects of the overall security of the LDAP
474 association including discovery of resultant security level and
475 assertion of the client's authorization identity.
477 Note that the precise effects, on a client's authorization identity,
478 of establishing TLS on an LDAP association are described in detail
481 4.1.1. Requesting to Start TLS on an LDAP Connection
483 The client MAY send the Start TLS extended request at any time after
484 establishing an LDAP connection, except:
486 - when TLS is currently established on the connection,
487 - when a multi-stage SASL negotiation is in progress on the
489 - when there are one or more outstanding LDAP operations on the
492 The result of violating any of these requirements is a resultCode of
493 operationsError, as described in [Protocol] section 4.13.2.2. Client
494 implementers should note that it is possible to receive a resultCode
495 of success for a Start TLS operation that is sent on a connection
496 with outstanding LDAP operations and the server has sufficient time
497 to process them prior to its receiving the Start TLS request.
498 Implementors should ensure that they do not inadvertently depend
499 upon this race condition for proper functioning of their
502 In particular, there is no requirement that the client have or have
503 not already performed a Bind operation before sending a Start TLS
504 operation request. The client may have already performed a Bind
505 operation when it sends a Start TLS request, or the client might
508 If the client did not establish a TLS connection before sending any
509 other requests, and the server requires the client to establish a
510 TLS connection before performing a particular request, the server
511 MUST reject that request by sending a resultCode of
512 confidentialityRequired or strongAuthRequired.
516 The server will return an extended response with the resultCode of
517 success if it is willing and able to negotiate TLS. It will return
518 other resultCodes (documented in [Protocol] section 4.13.2.2) if it
521 In the successful case, the client (which has ceased to transfer
522 LDAP requests on the connection) MUST either begin a TLS negotiation
523 or close the connection. The client will send PDUs in the TLS Record
524 Protocol directly over the underlying transport connection to the
525 server to initiate [TLS] negotiation.
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532 4.1.3. TLS Version Negotiation
534 Negotiating the version of TLS or SSL to be used is a part of the
535 [TLS] Handshake Protocol. Please refer to that document for details.
537 4.1.4. Discovery of Resultant Security Level
539 After a TLS connection is established on an LDAP association, both
540 parties MUST individually decide whether or not to continue based on
541 the security level achieved. Ascertaining the TLS connection's
542 security level is implementation dependent and accomplished by
543 communicating with one's respective local TLS implementation.
545 If the client or server decides that the level of authentication or
546 security is not high enough for it to continue, it SHOULD gracefully
547 close the TLS connection immediately after the TLS negotiation has
548 completed (see [Protocol] section 4.13.3.1 and section 4.2.3 below).
549 If the client decides to continue, it may gracefully close the TLS
550 connection and attempt to Start TLS again, it may send an unbind
551 request, or it may send any other LDAP request.
553 4.1.5. Server Identity Check
555 The client MUST check its understanding of the server's hostname
556 against the server's identity as presented in the server's
557 Certificate message in order to prevent man-in-the-middle attacks.
559 Matching is performed according to these rules:
561 - The client MUST use the server provided by the user (or other
562 trusted entity) as the value to compare against the server name
563 as expressed in the server's certificate. A hostname derived
564 from the user input is to be considered provided by the user
565 only if derived in a secure fashion (e.g., DNSSEC).
567 - If a subjectAltName extension of type dNSName is present in the
568 certificate, it SHOULD be used as the source of the server's
571 - Matching is case-insensitive.
573 - The "*" wildcard character is allowed. If present, it applies
574 only to the left-most name component.
576 For example, *.bar.com would match a.bar.com and b.bar.com, but
577 it would not match a.x.bar.com nor would it match bar.com. If
578 more than one identity of a given type is present in the
579 certificate (e.g. more than one dNSName name), a match in any
580 one of the set is considered acceptable.
582 If the hostname does not match the dNSName-based identity in the
583 certificate per the above check, user-oriented clients SHOULD either
584 notify the user (clients may give the user the opportunity to
585 continue with the connection in any case) or terminate the
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591 connection and indicate that the server's identity is suspect.
592 Automated clients SHOULD close the connection, returning and/or
593 logging an error indicating that the server's identity is suspect.
595 Beyond the server identity checks described in this section, clients
596 SHOULD be prepared to do further checking to ensure that the server
597 is authorized to provide the service it is observed to provide. The
598 client may need to make use of local policy information in making
601 4.1.6. Refresh of Server Capabilities Information
603 Upon TLS session establishment, the client SHOULD discard or refresh
604 all information about the server fetched prior to the initiation of
605 the TLS negotiation and not obtained through secure mechanisms. This
606 protects against active-intermediary attacks that may have altered
607 any server capabilities information retrieved prior to TLS
610 The server may advertise different capabilities after TLS
611 establishment. In particular, the value of supportedSASLMechanisms
612 may be different after TLS has been negotiated (specifically, the
613 EXTERNAL and [PLAIN] mechanisms are likely to be listed only after a
614 TLS negotiation has been performed).
616 4.2. Effects of TLS on a Client's Authorization Identity
618 This section describes the effects on a client's authorization
619 identity brought about by establishing TLS on an LDAP association.
620 The default effects are described first, and next the facilities for
621 client assertion of authorization identity are discussed including
622 error conditions. Finally, the effects of closing the TLS connection
625 Authorization identities and related concepts are described in
628 4.2.1. Default Effects
630 Upon establishment of the TLS session onto the LDAP association, any
631 previously established authentication and authorization identities
632 MUST remain in force, including anonymous state. This holds even in
633 the case where the server requests client authentication via TLS --
634 e.g. requests the client to supply its certificate during TLS
637 4.2.2. Client Assertion of Authorization Identity
639 The client MAY, upon receipt of a Start TLS response indicating
640 success, assert that a specific authorization identity be utilized
641 in determining the client's authorization status. The client
642 accomplishes this via an LDAP Bind request specifying a SASL
643 mechanism of "EXTERNAL" [SASL]. A client may either implicitly
644 request that its LDAP authorization identity be derived from its
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650 authenticated TLS credentials or it may explicitly provide an
651 authorization identity and assert that it be used in combination
652 with its authenticated TLS credentials. The former is known as an
653 implicit assertion, and the latter as an explicit assertion.
655 4.2.2.1. Implicit Assertion
657 An implicit authorization identity assertion is accomplished after
658 TLS establishment by invoking a Bind request of the SASL form using
659 the "EXTERNAL" mechanism name [SASL] [Protocol] that SHALL NOT
660 include the optional credentials octet string (found within the
661 SaslCredentials sequence in the Bind Request). The server will
662 derive the client's authorization identity from the authentication
663 identity supplied in the client's TLS credentials (typically a
664 public key certificate) according to local policy. The underlying
665 mechanics of how this is accomplished are implementation specific.
667 4.2.2.2. Explicit Assertion
669 An explicit authorization identity assertion is accomplished after
670 TLS establishment by invoking a Bind request of the SASL form using
671 the "EXTERNAL" mechanism name [SASL] [Protocol] that SHALL include
672 the credentials octet string. This string MUST be constructed as
673 documented in section 3.4.1.
675 The server MUST verify that the client's authentication identity as
676 supplied in its TLS credentials is permitted to be mapped to the
677 asserted authorization identity. The server MUST reject the Bind
678 operation with an invalidCredentials resultCode in the Bind response
679 if the client is not so authorized.
681 4.2.2.3. Error Conditions
683 Additionally, with either form of assertion, if a TLS session has
684 not been established between the client and server prior to making
685 the SASL EXTERNAL Bind request and there is no other external source
686 of authentication credentials (e.g. IP-level security [RFC2401]), or
687 if during the process of establishing the TLS session, the server
688 did not request the client's authentication credentials, the SASL
689 EXTERNAL bind MUST fail with a resultCode of
690 inappropriateAuthentication.
692 After the above Bind operation failures, any client authentication
693 and authorization state of the LDAP association is lost (see
694 [Protocol] section 4.2.1), so the LDAP association is in an
695 anonymous state after the failure. The TLS session state is
696 unaffected, though a server MAY end the TLS session, via a TLS
697 close_notify message, based on the Bind failure (as it MAY at any
700 4.2.3. TLS Connection Closure Effects
702 Closure of the TLS session MUST cause the LDAP association to move
703 to an anonymous authentication and authorization state regardless of
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709 the state established over TLS and regardless of the authentication
710 and authorization state prior to TLS session establishment.
712 5. LDAP Association State Transition Tables
714 To comprehensively diagram the various authentication and TLS states
715 through which an LDAP association may pass, this section provides a
716 state transition table to represent a state diagram for the various
717 states through which an LDAP association may pass during the course
718 of its existence and the actions that cause these changes in state.
720 5.1. LDAP Association States
722 The following table lists the valid LDAP association states and
723 provides a description of each state. The ID for each state is used
724 in the state transition table in section 5.4.
727 -- --------------------------------------------------------------
729 no Authentication ID is associated with the LDAP connection
730 no Authorization ID is in force
731 No security layer is in effect.
732 No TLS credentials have been provided
739 [TLS: Creds Auth ID "I", ON]
748 [TLS: Creds Auth ID "I", ON]
751 [TLS: Creds Auth ID "I", ON]
754 [TLS: Creds Auth ID "I", ON]
756 5.2. Actions that Affect LDAP Association State
758 The following table lists the actions that can affect the state of
759 an LDAP association. The ID for each action is used in the state
760 transition table in section 5.4.
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769 -- ------------------------------------------------
770 A1 Client binds anonymously
771 A2 Inappropriate authentication: client attempts an anonymous
772 bind or a bind without supplying credentials to a server that
773 requires the client to provide some form of credentials.
774 A3 Client Start TLS request
775 Server: client auth NOT required
776 A4 Client: Start TLS request
777 Server: client creds requested
778 Client: [TLS creds: Auth ID "I"]
779 A5 Client or Server: send TLS closure alert ([Protocol] section
781 A6 Client: Bind w/simple password or SASL mechanism (e.g. DIGEST-
782 MD5 password, Kerberos, etc., except EXTERNAL [Auth ID "X"
783 maps to AuthZ ID "Y"]
784 A7 Client Binds SASL EXTERNAL with credentials: AuthZ ID "J"
785 [Explicit Assertion (section 4.2.1.2.2)]
786 A8 Client Bind SASL EXTERNAL without credentials [Implicit
787 Assertion (section 4.2.1.2.1)]
788 A9 Client abandons a bind operation or bind operation fails
790 5.3. Decisions Used in Making LDAP Association State Changes
792 Certain changes in the state of an LDAP association are only allowed
793 if the server can affirmatively answer a question. These questions
794 are applied as part of the criteria for allowing or disallowing a
795 state change in the state transition table in section 5.4.
798 -- --------------------------------------------------------------
799 D1 Can TLS Credentials Auth ID "I" be mapped to AuthZ ID "J"?
800 D2 Can a valid AuthZ ID "K" be derived from TLS Credentials Auth
803 5.4. LDAP Association State Transition Table
805 The LDAP Association table below lists the valid states for an LDAP
806 association and the actions that could affect them. For any given
807 row in the table, the Current State column gives the state of an
808 LDAP association, the Action column gives an action that could
809 affect the state of an LDAP assocation, and the Next State column
810 gives the resulting state of an LDAP association after the action
813 The initial state for the state machine described in this table is
817 State Action State Comment
818 ------- ------------- ----- -----------------------------------
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825 S1 A2 S1 Error: Inappropriate authentication
829 S1 A7 ? identity could be provided by
830 another underlying mechanism such
832 S1 A8 ? identity could be provided by
833 another underlying mechanism such
836 S2 A2 S2 Error: Inappropriate authentication
839 S2 A7 ? identity could be provided by
840 another underlying mechanism such
842 S2 A8 ? identity could be provided by
843 another underlying mechanism such
846 S3 A2 S3 Error: Inappropriate authentication
849 S3 A7 and D1=NO S3 Error: InvalidCredentials
851 S3 A8 and D2=NO S3 Error: InvalidCredentials
854 S4 A2 S1 Error: Inappropriate Authentication
859 S4 A7 ? identity could be provided by
860 another underlying mechanism such
862 S4 A8 ? identity could be provided by
863 another underlying mechanism such
866 S5 A2 S2 Error: Inappropriate Authentication
869 S5 A7 ? identity could be provided by
870 another underlying mechanism such
872 S5 A8 ? identity could be provided by
873 another underlying mechanism such
876 S6 A2 S2 Error: Inappropriate Authentication
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884 S6 A7 and D1=NO S6 Error: InvalidCredentials
886 S6 A8 and D2=NO S3 Error: InvalidCredentials
889 S7 A2 S2 Error: Inappropriate Authentication
893 S7 A8 and D2=NO S3 Error: InvalidCredentials
896 S8 A2 S2 Error: Inappropriate Authentication
899 S8 A7 and D1=NO S6 Error: InvalidCredentials
902 Any A9 S1 See [Protocol] section 4.2.1.
905 6. Anonymous Authentication
907 Directory operations that modify entries or access protected
908 attributes or entries generally require client authentication.
909 Clients that do not intend to perform any of these operations
910 typically use anonymous authentication. Servers SHOULD NOT allow
911 clients with anonymous authentication to modify directory entries or
912 access sensitive information in directory entries.
914 LDAP implementations MUST support anonymous authentication, as
915 defined in section 6.1.
917 LDAP implementations MAY support anonymous authentication with TLS,
918 as defined in section 6.2.
920 While there MAY be access control restrictions to prevent access to
921 directory entries, an LDAP server SHOULD allow an anonymously-bound
922 client to retrieve the supportedSASLMechanisms attribute of the root
925 An LDAP server MAY use other information about the client provided
926 by the lower layers or external means to grant or deny access even
927 to anonymously authenticated clients.
929 6.1. Anonymous Authentication Procedure
931 Prior to successfully completing a Bind operation, the LDAP
932 association is anonymous. See section 3.1.
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940 An LDAP client may also explicitly establish an anonymous
941 association. A client that wishes to do so MUST choose the simple
942 authentication option in the Bind Request and set the password to be
943 of zero length. (This is often done by LDAPv2 clients.) Typically
944 the name is also of zero length. A bind request where both the name
945 and password are of zero length is said to be an anonymous bind. A
946 bind request where the name, a DN, is of non-zero length, and the
947 password is of zero length is said to be an unauthenticated bind.
948 Both variations produce an anonymous association.
950 6.2. Anonymous Authentication and TLS
952 An LDAP client MAY use the Start TLS operation (section 5) to
953 negotiate the use of [TLS] security. If the client has not bound
954 beforehand, then until the client uses the EXTERNAL SASL mechanism
955 to negotiate the recognition of the client's certificate, the client
956 is anonymously authenticated.
958 Recommendations on TLS ciphersuites are given in section 9.
960 An LDAP server which requests that clients provide their certificate
961 during TLS negotiation MAY use a local security policy to determine
962 whether to successfully complete TLS negotiation if the client did
963 not present a certificate which could be validated.
965 7. Password-based Authentication
967 This section discusses various options for performing password-based
968 authentication to LDAP compliant servers and the environments
969 suitable for their use.
971 7.1. Simple Authentication
973 The LDAP "simple" authentication choice is not suitable for
974 authentication in environments where there is no network or
975 transport layer confidentiality. LDAP implementations SHOULD support
976 authentication with the "simple" authentication choice when the
977 connection is protected against eavesdropping using TLS, as defined
978 in section 4. LDAP implementations SHOULD NOT support authentication
979 with the "simple" authentication choice unless the data on the
980 connection is protected using TLS or other data confidentiality and
981 data integrity protection.
983 7.2. Digest Authentication
985 LDAP servers that implement any authentication method or mechanism
986 (other than simple anonymous bind) MUST implement the SASL
987 DIGEST-MD5 mechanism [DigestAuth].
989 Support for subsequent authentication is OPTIONAL in clients and
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999 Implementors must take care to ensure that they maintain the
1000 semantics of the DIGEST-MD5 specification even when handling data
1001 that has different semantics in the LDAP protocol.
1002 For example, the SASL DIGEST-MD5 authentication mechanism utilizes
1003 realm and username values ([DigestAuth section 2.1) which are
1004 syntactically simple strings and semsantically simple realm and
1005 username values. These values are not LDAP DNs, and there is no
1006 requirement that they be represented or treated as such. Username
1007 and realm values that look like LDAP DNs in form, e.g. "cn=bob,
1008 o=Ace Industry ", are syntactically allowed, however DIGEST-MD5
1009 treats them as simple strings for comparison purposes. To illustrate
1010 further, the two DNs "cn=bob, o=Ace Industry" (space between RDNs)
1011 and "cn=bob,o=Ace Industry" (no space between RDNs) would be
1012 equivalent when being compared semantically as LDAP DNs, however
1013 they are not equivalent if they were used to represent username
1014 values in DIGEST-MD5 because simple octet-wise comparision semantics
1015 are used by DIGEST-MD5.
1018 7.3. "simple" authentication choice under TLS encryption
1020 Following the negotiation of an appropriate TLS ciphersuite
1021 providing connection confidentiality, a client MAY authenticate to a
1022 directory that supports the simple authentication choice by
1023 performing a simple bind operation
1025 Simple authentication with TLS encryption protection is performed as
1028 1. The client will use the Start TLS operation [Protocol] to
1029 negotiate the use of TLS security [TLS] on the connection to
1030 the LDAP server. The client need not have bound to the
1031 directory beforehand.
1033 For the subsequent authentication procedure to be performed
1034 securely, the client and server MUST negotiate a ciphersuite
1035 which contains a bulk encryption algorithm of appropriate
1036 strength. Recommendations on cipher suites are given in
1039 2. Following the successful completion of TLS negotiation, the
1040 client MUST send an LDAP bind request with the version number
1041 of 3, the name field containing a DN, and the "simple"
1042 authentication choice, containing a password.
1044 7.3.1. "simple" Authentication Choice
1046 DSAs that map the DN sent in the bind request to a directory entry
1047 with an associated set of one or more passwords will compare the
1048 presented password to the set of passwords associated with that
1049 entry. If the presented password matches any member of that set,
1050 then the server will respond with a success resultCode, otherwise
1051 the server will respond with an invalidCredentials resultCode.
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1058 7.4. Other authentication choices with TLS
1060 It is also possible, following the negotiation of TLS, to perform a
1061 SASL authentication that does not involve the exchange of plaintext
1062 reusable passwords. In this case the client and server need not
1063 negotiate a ciphersuite that provides confidentiality if the only
1064 service required is data integrity.
1066 8. Certificate-based authentication
1068 LDAP server implementations SHOULD support authentication via a
1069 client certificate in TLS, as defined in section 8.1.
1071 8.1. Certificate-based authentication with TLS
1073 A user who has a public/private key pair in which the public key has
1074 been signed by a Certification Authority may use this key pair to
1075 authenticate to the directory server if the user's certificate is
1076 requested by the server. The user's certificate subject field SHOULD
1077 be the name of the user's directory entry, and the Certification
1078 Authority that issued the user's certificate must be sufficiently
1079 trusted by the directory server in order for the server to process
1080 the certificate. The means by which servers validate certificate
1081 paths is outside the scope of this document.
1083 A server MAY support mappings for certificates in which the subject
1084 field name is different from the name of the user's directory entry.
1085 A server which supports mappings of names MUST be capable of being
1086 configured to support certificates for which no mapping is required.
1088 The client will use the Start TLS operation [Protocol] to negotiate
1089 the use of TLS security [TLS] on the connection to the LDAP server.
1090 The client need not have bound to the directory beforehand.
1092 In the TLS negotiation, the server MUST request a certificate. The
1093 client will provide its certificate to the server, and the server
1094 MUST perform a private key-based encryption, proving it has the
1095 private key associated with the certificate.
1097 In deployments that require protection of sensitive data in transit,
1098 the client and server MUST negotiate a ciphersuite that contains a
1099 bulk encryption algorithm of appropriate strength. Recommendations
1100 of cipher suites are given in section 9.
1102 The server MUST verify that the client's certificate is valid. The
1103 server will normally check that the certificate is issued by a known
1104 certification authority (CA), and that none of the certificates on
1105 the client's certificate chain are invalid or revoked. There are
1106 several procedures by which the server can perform these checks.
1108 Following the successful completion of TLS negotiation, the client
1109 will send an LDAP bind request with the SASL "EXTERNAL" mechanism.
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1118 A client or server that supports TLS MUST support
1119 TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA and MAY support other ciphersuites
1120 offering equivalent or better protection.
1122 Several issues should be considered when selecting TLS ciphersuites
1123 that are appropriate for use in a given circumstance. These issues
1124 include the following:
1126 - The ciphersuite's ability to provide adequate confidentiality
1127 protection for passwords and other data sent over the LDAP
1128 connection. Client and server implementers should recognize that
1129 some TLS ciphersuites provide no confidentiality protection
1130 while other ciphersuites that do provide confidentiality
1131 protection may be vulnerable to being cracked using brute force
1132 methods, especially in light of ever-increasing CPU speeds that
1133 reduce the time needed to successfully mount such attacks.
1135 Client and server implementers SHOULD carefully consider the
1136 value of the password or data being protected versus the level
1137 of confidentially protection provided by the ciphersuite to
1138 ensure that the level of protection afforded by the ciphersuite
1141 - The ciphersuite's vulnerability (or lack thereof) to man-in-the-
1142 middle attacks. Ciphersuites vulnerable to man-in-the-middle
1143 attacks SHOULD NOT be used to protect passwords or sensitive
1144 data, unless the network configuration is such that the danger
1145 of a man-in-the-middle attack is tolerable.
1147 9.1. TLS Ciphersuites Recommendations
1149 As of the writing of this document, the following recommendations
1150 regarding TLS ciphersuites are applicable. Because circumstances are
1151 constantly changing, this list must not be considered exhaustive,
1152 but is hoped that it will serve as a useful starting point for
1155 The following ciphersuites defined in [TLS] MUST NOT be used for
1156 confidentiality protection of passwords or data:
1158 TLS_NULL_WITH_NULL_NULL
1159 TLS_RSA_WITH_NULL_MD5
1160 TLS_RSA_WITH_NULL_SHA
1162 The following ciphersuites defined in [TLS] can be cracked easily
1163 (less than a day of CPU time on a standard CPU in 2000) and are NOT
1164 RECOMMENDED for use in confidentiality protection of passwords or
1167 TLS_RSA_EXPORT_WITH_RC4_40_MD5
1168 TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
1169 TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
1170 TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA
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1176 TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA
1177 TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA
1178 TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA
1179 TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
1180 TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
1182 The following ciphersuites are vulnerable to man-in-the-middle
1185 TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
1186 TLS_DH_anon_WITH_RC4_128_MD5
1187 TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
1188 TLS_DH_anon_WITH_DES_CBC_SHA
1189 TLS_DH_anon_WITH_3DES_EDE_CBC_SHA
1193 10. Security Considerations
1195 Security issues are discussed throughout this memo; the
1196 (unsurprising) conclusion is that mandatory security is important
1197 and that session confidentiality protection is required when
1198 snooping is a problem.
1200 Servers are encouraged to prevent modifications by anonymous users.
1202 Servers may also wish to minimize denial of service attacks by
1203 timing out idle connections, and returning the unwillingToPerform
1204 resultCode rather than performing computationally expensive
1205 operations requested by unauthorized clients.
1207 The use of cleartext passwords is strongly discouraged over open
1208 networks when the underlying transport service cannot guarantee
1211 Operational experience shows that clients can misuse unauthenticated
1212 access (simple bind with name but no password). For example, a
1213 client program might authenticate a user via LDAP and then grant
1214 access to information not stored in the directory on the basis of
1215 completing a successful bind. Some implementations will return a
1216 success response to a simple bind that consists of a user name and
1217 an empty password thus leaving the impression that the client has
1218 successfully authenticated the identity represented by the user
1219 name, when in reality, the directory server has simply performed an
1220 anonymous bind. For this reason, servers SHOULD by default reject
1221 authentication requests that have a DN with an empty password with
1222 an error of invalidCredentials.
1224 Access control SHOULD always be applied when reading sensitive
1225 information or updating directory information.
1227 A connection on which the client has not performed the Start TLS
1228 operation or negotiated a suitable SASL mechanism for connection
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1235 integrity and encryption services is subject to man-in-the-middle
1236 attacks to view and modify information in transit.
1238 10.1. Start TLS Security Considerations
1240 The goals of using the TLS protocol with LDAP are to ensure
1241 connection confidentiality and integrity, and to optionally provide
1242 for authentication. [TLS] expressly provides these capabilities.
1244 All security gained via use of the Start TLS operation is gained by
1245 the use of TLS itself. The Start TLS operation, on its own, does not
1246 provide any additional security.
1248 Once established, TLS only provides for and ensures confidentiality
1249 and integrity of the operations and data in transit over the LDAP
1250 association--and only if the implementations on the client and
1251 server support and negotiate it. The use of TLS does not provide or
1252 ensure for confidentiality and/or non-repudiation of the data housed
1253 by an LDAP-based directory server. Nor does it secure the data from
1254 inspection by the server administrators.
1256 The level of security provided though the use of TLS depends
1257 directly on both the quality of the TLS implementation used and the
1258 style of usage of that implementation. Additionally, an active-
1259 intermediary attacker can remove the Start TLS extended operation
1260 from the supportedExtension attribute of the root DSE. Therefore,
1261 both parties SHOULD independently ascertain and consent to the
1262 security level achieved once TLS is established and before beginning
1263 use of the TLS connection. For example, the security level of the
1264 TLS connection might have been negotiated down to plaintext.
1266 Clients SHOULD either warn the user when the security level achieved
1267 does not provide confidentiality and/or integrity protection, or be
1268 configurable to refuse to proceed without an acceptable level of
1271 Client and server implementors SHOULD take measures to ensure proper
1272 protection of credentials and other confidential data where such
1273 measures are not otherwise provided by the TLS implementation.
1275 Server implementors SHOULD allow for server administrators to elect
1276 whether and when connection confidentiality and/or integrity is
1277 required, as well as elect whether and when client authentication
1278 via TLS is required.
1280 Additional security considerations relating to the EXTERNAL
1281 mechanism to negotiate TLS can be found in [SASL] and [TLS].
1283 11. IANA Considerations
1285 The following IANA considerations apply to this document:
1287 Please update the GSSAPI service name registry to point to [Roadmap]
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1299 This document combines information originally contained in RFC 2829
1300 and RFC 2830. The editor acknowledges the work of Harald Tveit
1301 Alvestrand, Jeff Hodges, Tim Howes, Steve Kille, RL "Bob" Morgan ,
1302 and Mark Wahl, each of whom authored one or more of these documents.
1306 This document is based upon input of the IETF LDAP Revision working
1307 group. The contributions and suggestions made by its members in
1308 shaping the contents and technical accuracy of this document is
1309 greatly appreciated.
1311 Normative References
1313 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
1314 Requirement Levels", BCP 14, RFC 2119, March 1997.
1316 [RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
1317 Specifications: ABNF", RFC 2234, November 1997.
1319 [DigestAuth] Leach, P. C. Newman, and A. Melnikov, "Using Digest
1320 Authentication as a SASL Mechanism", draft-ietf-sasl-rfc2831bis-
1321 xx.txt, a work in progress.
1323 [LDAPDN] Zeilenga, Kurt D. (editor), "LDAP: String Representation of
1324 Distinguished Names", draft-ietf-ldapbis-dn-xx.txt, a work in
1327 [Model] Zeilenga, Kurt D. (editor), "LDAP: Directory Information
1328 Models", draft-ietf-ldapbis-models-xx.txt, a work in progress.
1330 [Protocol] Sermersheim, J., "LDAP: The Protocol", draft-ietf-
1331 ldapbis-protocol-xx.txt, a work in progress.
1333 [Roadmap] K. Zeilenga, "LDAP: Technical Specification Road Map",
1334 draft-ietf-ldapbis-roadmap-xx.txt, a work in progress.
1336 [SASL] Melnikov, A. (editor), "Simple Authentication and Security
1337 Layer (SASL)", draft-ietf-sasl-rfc2222bis-xx.txt, a work in
1340 [Syntaxes] Legg, S. (editor), "LDAP: Syntaxes and Matching Rules",
1341 draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress.
1343 [TLS] Dierks, T. and C. Allen. "The TLS Protocol Version 1.1",
1344 draft-ietf-tls-rfc2246-bis-xx.txt, a work in progress.
1346 [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
1347 RFC 2279, January 1998.
1349 Harrison Expires April 2004 [Page 23]
1351 Internet-Draft LDAP Authentication Methods 7 October 2003
1354 [Unicode] International Organization for Standardization, "Universal
1355 Multiple-Octet Coded Character Set (UCS) - Architecture and
1356 Basic Multilingual Plane", ISO/IEC 10646-1 : 1993.
1358 Informative References
1360 [ANONYMOUS] Zeilenga, K.,"Anonymous SASL Mechanism", draft-zeilenga-
1361 sasl-anon-xx.txt, a work in progress.
1363 [PLAIN] Zeilenga, K.,"Plain SASL Mechanism", draft-zeilenga-sasl-
1364 plain-xx.txt, a work in progress.
1366 [RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828, May
1369 [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
1370 Internet Protocol", RFC 2401, November 1998.
1377 1800 S. Novell Place
1380 roger_harrison@novell.com
1382 Full Copyright Statement
1384 Copyright (C) The Internet Society (2003). All Rights Reserved.
1386 This document and translations of it may be copied and furnished to
1387 others, and derivative works that comment on or otherwise explain it
1388 or assist in its implementation may be prepared, copied, published
1389 and distributed, in whole or in part, without restriction of any
1390 kind, provided that the above copyright notice and this paragraph
1391 are included on all such copies and derivative works. However, this
1392 document itself may not be modified in any way, such as by removing
1393 the copyright notice or references to the Internet Society or other
1394 Internet organizations, except as needed for the purpose of
1395 developing Internet standards in which case the procedures for
1396 copyrights defined in the Internet Standards process must be
1397 followed, or as required to translate it into languages other than
1400 The limited permissions granted above are perpetual and will not be
1401 revoked by the Internet Society or its successors or assigns.
1403 This document and the information contained herein is provided on an
1404 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
1405 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
1406 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
1408 Harrison Expires April 2004 [Page 24]
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1412 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
1413 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
1415 Appendix A. Example Deployment Scenarios
1417 The following scenarios are typical for LDAP directories on the
1418 Internet, and have different security requirements. (In the
1419 following discussion, "sensitive data" refers to information whose
1420 disclosure, alteration, destruction, or loss would adversely affect
1421 the interests or business of its owner or user. Also note that there
1422 may be data that is protected but not sensitive.) This is not
1423 intended to be a comprehensive list; other scenarios are possible,
1424 especially on physically protected networks.
1426 (1) A read-only directory, containing no sensitive data, accessible
1427 to "anyone", and TCP connection hijacking or IP spoofing is not
1428 a problem. Anonymous authentication, described in section 7, is
1429 suitable for this type of deployment, and requires no additional
1430 security functions except administrative service limits.
1432 (2) A read-only directory containing no sensitive data; read access
1433 is granted based on identity. TCP connection hijacking is not
1434 currently a problem. This scenario requires data confidentiality
1435 for sensitive authentication information AND data integrity for
1436 all authentication information.
1438 (3) A read-only directory containing no sensitive data; and the
1439 client needs to ensure the identity of the directory server and
1440 that the directory data is not modified while being returned
1441 from the server. A data origin authentication service AND data
1442 integrity service are required.
1444 (4) A read-write directory, containing no sensitive data; read
1445 access is available to "anyone", update access to properly
1446 authorized persons. TCP connection hijacking is not currently a
1447 problem. This scenario requires data confidentiality for
1448 sensitive authentication information AND data integrity for all
1449 authentication information.
1451 (5) A directory containing sensitive data. This scenario requires
1452 data confidentiality protection AND secure authentication.
1454 Appendix B. Authentication and Authorization: Definitions and Concepts
1456 This appendix defines basic terms, concepts, and interrelationships
1457 regarding authentication, authorization, credentials, and identity.
1458 These concepts are used in describing how various security
1459 approaches are utilized in client authentication and authorization.
1461 B.1. Access Control Policy
1463 An access control policy is a set of rules defining the protection
1464 of resources, generally in terms of the capabilities of persons or
1465 other entities accessing those resources. A common expression of an
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1471 access control policy is an access control list. Security objects
1472 and mechanisms, such as those described here, enable the expression
1473 of access control policies and their enforcement. Access control
1474 policies are typically expressed in terms of access control factors
1477 B.2. Access Control Factors
1479 A request, when it is being processed by a server, may be associated
1480 with a wide variety of security-related factors (section 4.2 of
1481 [Protocol]). The server uses these factors to determine whether and
1482 how to process the request. These are called access control factors
1483 (ACFs). They might include source IP address, encryption strength,
1484 the type of operation being requested, time of day, etc. Some
1485 factors may be specific to the request itself, others may be
1486 associated with the connection via which the request is transmitted,
1487 others (e.g. time of day) may be "environmental".
1489 Access control policies are expressed in terms of access control
1490 factors. E.g., a request having ACFs i,j,k can perform operation Y
1491 on resource Z. The set of ACFs that a server makes available for
1492 such expressions is implementation-specific.
1494 B.3. Authentication, Credentials, Identity
1496 Authentication credentials are the evidence supplied by one party to
1497 another, asserting the identity of the supplying party (e.g. a user)
1498 who is attempting to establish an association with the other party
1499 (typically a server). Authentication is the process of generating,
1500 transmitting, and verifying these credentials and thus the identity
1501 they assert. An authentication identity is the name presented in a
1504 There are many forms of authentication credentials -- the form used
1505 depends upon the particular authentication mechanism negotiated by
1506 the parties. For example: X.509 certificates, Kerberos tickets,
1507 simple identity and password pairs. Note that an authentication
1508 mechanism may constrain the form of authentication identities used
1511 B.4. Authorization Identity
1513 An authorization identity is one kind of access control factor. It
1514 is the name of the user or other entity that requests that
1515 operations be performed. Access control policies are often expressed
1516 in terms of authorization identities; e.g., entity X can perform
1517 operation Y on resource Z.
1519 The authorization identity bound to an association is often exactly
1520 the same as the authentication identity presented by the client, but
1521 it may be different. SASL allows clients to specify an authorization
1522 identity distinct from the authentication identity asserted by the
1523 client's credentials. This permits agents such as proxy servers to
1524 authenticate using their own credentials, yet request the access
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1530 privileges of the identity for which they are proxying [SASL]. Also,
1531 the form of authentication identity supplied by a service like TLS
1532 may not correspond to the authorization identities used to express a
1533 server's access control policy, requiring a server-specific mapping
1534 to be done. The method by which a server composes and validates an
1535 authorization identity from the authentication credentials supplied
1536 by a client is implementation-specific.
1538 Appendix C. RFC 2829 Change History
1540 This appendix lists the changes made to the text of RFC 2829 in
1541 preparing this document.
1543 C.0. General Editorial Changes
1546 - Changed other instances of the term LDAP to LDAP where v3 of the
1547 protocol is implied. Also made all references to LDAP use the
1550 - Miscellaneous grammatical changes to improve readability.
1552 - Made capitalization in section headings consistent.
1556 - Changed title to reflect inclusion of material from RFC 2830 and
1559 C.1. Changes to Section 1
1563 - Moved conventions used in document to a separate section.
1565 C.2. Changes to Section 2
1569 - Moved section to an appendix.
1571 C.3. Changes to Section 3
1575 - Moved section to an appendix.
1577 C.4 Changes to Section 4
1581 - Changed "Distinguished Name" to "LDAP distinguished name".
1583 C.5. Changes to Section 5
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1592 - Added the following sentence: "Servers SHOULD NOT allow clients
1593 with anonymous authentication to modify directory entries or
1594 access sensitive information in directory entries."
1596 C.5.1. Changes to Section 5.1
1600 - Replaced the text describing the procedure for performing an
1601 anonymous bind (protocol) with a reference to section 4.2 of RFC
1602 2251 (the protocol spec).
1606 - Brought text describing procedure for performing an anonymous
1607 bind from section 4.2 of RFC 2251 bis. This text will be
1608 removed from the draft standard version of that document.
1610 C.6. Changes to Section 6.
1614 Reorganized text in section 6.1 as follows:
1616 1. Added a new section (6.1) titled "Simple Authentication" and
1617 moved one of two introductory paragraphs for section 6 into
1618 section 6.1. Added sentences to the paragraph indicating:
1620 a. simple authentication is not suitable for environments where
1621 confidentiality is not available.
1623 b. LDAP implementations SHOULD NOT support simple
1624 authentication unless confidentiality and data integrity
1625 mechanisms are in force.
1627 2. Moved first paragraph of section 6 (beginning with "LDAP
1628 implementations MUST support authentication with a password...")
1629 to section on Digest Authentication (Now section 6.2).
1631 C.6.1. Changes to Section 6.1.
1633 Version -00 Renamed section to 6.2
1635 - Added sentence from original section 6 indicating that the
1636 DIGEST-MD5 SASL mechanism is required for all conforming LDAP
1639 C.6.2. Changes to Section 6.2
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1646 Internet-Draft LDAP Authentication Methods 7 October 2003
1648 - Renamed section to 6.3
1650 - Reworded first paragraph to remove reference to user and the
1651 userPassword password attribute Made the first paragraph more
1652 general by simply saying that if a directory supports simple
1653 authentication that the simple bind operation MAY performed
1654 following negotiation of a TLS ciphersuite that supports
1657 - Replaced "the name of the user's entry" with "a DN" since not
1658 all bind operations are performed on behalf of a "user."
1660 - Added Section 6.3.1 heading just prior to paragraph 5.
1662 - Paragraph 5: replaced "The server" with "DSAs that map the DN
1663 sent in the bind request to a directory entry with a
1664 userPassword attribute."
1666 C.6.3. Changes to section 6.3.
1670 - Renamed to section 6.4.
1672 C.7. Changes to section 7.
1676 C.7.1. Changes to section 7.1.
1680 - Clarified the entity issuing a certificate by moving the phrase
1681 "to have issued the certificate" immediately after
1682 "Certification Authority."
1684 C.8. Changes to section 8.
1688 - Removed the first paragraph because simple authentication is
1689 covered explicitly in section 6.
1691 - Added section 8.1. heading just prior to second paragraph.
1693 - Added section 8.2. heading just prior to third paragraph.
1695 - Added section 8.3. heading just prior to fourth paragraph.
1699 - Moved entire section 8 of RFC 2829 into section 3.4 (Using SASL
1700 for Other Security Services) to bring material on SASL
1701 mechanisms together into one location.
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1708 C.9. Changes to section 9.
1712 - Paragraph 2: changed "EXTERNAL mechanism" to "EXTERNAL SASL
1715 - Added section 9.1. heading.
1717 - Modified a comment in the ABNF from "unspecified userid" to
1718 "unspecified authz id".
1720 - Deleted sentence, "A utf8string is defined to be the UTF-8
1721 encoding of one or more ISO 10646 characters," because it is
1724 - Added section 9.1.1. heading.
1726 - Added section 9.1.2. heading.
1730 - Moved entire section 9 to become section 3.5 so that it would be
1731 with other SASL material.
1733 C.10. Changes to Section 10.
1737 - Updated reference to cracking from a week of CPU time in 1997 to
1738 be a day of CPU time in 2000.
1740 - Added text: "These ciphersuites are NOT RECOMMENDED for use...
1741 and server implementers SHOULD" to sentence just prior the
1742 second list of ciphersuites.
1744 - Added text: "and MAY support other ciphersuites offering
1745 equivalent or better protection," to the last paragraph of the
1748 C.11. Changes to Section 11.
1752 - Moved to section 3.6 to be with other SASL material.
1754 C.12. Changes to Section 12.
1758 - Inserted new section 12 that specifies when SASL protections
1759 begin following SASL negotiation, etc. The original section 12
1760 is renumbered to become section 13.
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1769 - Moved to section 3.7 to be with other SASL material.
1771 C.13. Changes to Section 13 (original section 12).
1775 Appendix D. RFC 2830 Change History
1777 This appendix lists the changes made to the text of RFC 2830 in
1778 preparing this document.
1780 D.0. General Editorial Changes
1782 - Material showing the PDUs for the Start TLS response was broken
1783 out into a new section.
1785 - The wording of the definition of the Start TLS request and Start
1786 TLS response was changed to make them parallel. NO changes were
1787 made to the ASN.1 definition or the associated values of the
1790 - A separate section heading for graceful TLS closure was added
1791 for parallelism with section on abrupt TLS closure.
1793 Appendix E. RFC 2251 Change History
1795 This appendix lists the changes made to the text of RFC 2251 in
1796 preparing this document.
1798 E.0. General Editorial Changes
1800 - All material from section 4.2 of RFC 2251 was moved into this
1803 - A new section was created for the Bind Request
1805 - Section 4.2.1 of RFC 2251 (Sequencing Bind Request) was moved
1806 after the section on the Bind Response for parallelism with the
1807 presentation of the Start TLS operations. The section was also
1808 subdivided to explicitly call out the various effects being
1809 described within it.
1811 - All SASL profile information from RFC 2829 was brought within
1812 the discussion of the Bind operation (primarily sections 4.4 -
1815 Appendix F. Change History to Combined Document
1817 F.1. Changes for draft-ldap-bis-authmeth-02
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1826 - Added references to other LDAP standard documents, to sections
1827 within the document, and fixed broken references.
1829 - General editorial changes--punctuation, spelling, formatting,
1834 - Added glossary of terms and added sub-section headings
1838 - Clarified security mechanisms 3, 4, & 5 and brought language in
1839 line with IETF security glossary.
1843 - Brought language in requirement (3) in line with security
1846 - Clarified that information fetched prior to initiation of TLS
1847 negotiation must be discarded
1849 -Clarified that information fetched prior to initiation of SASL
1850 negotiation must be discarded
1852 - Rewrote paragraph on SASL negotiation requirements to clarify
1857 - Added stipulation that sasl choice allows for any SASL mechanism
1858 not prohibited by this document. (Resolved conflict between this
1859 statement and one that prohibited use of ANONYMOUS and PLAIN
1864 - Added a.x.bar.com to wildcard matching example on hostname
1869 - Added LDAP Association State Transition Tables to show the
1870 various states through which an LDAP association may pass along
1871 with the actions and decisions required to traverse from state
1876 - Brought security terminology in line with IETF security glossary
1877 throughout the appendix.
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1884 F.2. Changes for draft-ldap-bis-authmeth-03
1888 - Added introductory notes and changed title of document and
1889 references to conform to WG chair suggestions for the overall
1890 technical specification.
1892 - Several issues--G.13, G.14, G.16, G.17--were resolved without
1893 requiring changes to the document.
1897 - Removed reference to /etc/passwd file and associated text.
1901 - Removed sections 4.1, 4.2 and parts of section 4.3. This
1902 information was being duplicated in the protocol specification
1903 and will now reside there permanently.
1906 - changed words, "not recommended" to "strongly discouraged"
1910 - Based on ldapbis WG discussion at IETF52 two sentences were
1911 added indicating that clients SHOULD NOT send a DN value when
1912 binding with the sasl choice and servers SHALL ignore any value
1913 received in this circumstance.
1918 - Generalized the language of this section to not refer to any
1919 specific password attribute or to refer to the directory entry
1924 - Added security consideration regarding misuse of unauthenticated
1927 - Added security consideration requiring access control to be
1928 applied only to authenticated users and recommending it be
1929 applied when reading sensitive information or updating directory
1933 F.3. Changes for draft-ldap-bis-authmeth-04
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1943 - Changed references to use [RFCnnnn] format wherever possible.
1944 (References to works in progress still use [name] format.)
1945 - Various edits to correct typos and bring field names, etc. in
1946 line with specification in [Protocol] draft.
1948 - Several issues--G.13, G.14, G.16, G.17--were resolved without
1949 requiring changes to the document.
1953 - Changed ABNF grammar to use productions that are like those in
1958 - Removed sections 5.1, 5.2, and 5.4 that will be added to
1959 [Protocol]. Renumbered sections to accommodate this change.
1964 - Reviewed LDAP Association State table for completeness and
1965 accuracy. Renumbered actions A3, A4, and A5 to be A5, A3, and A4
1966 respectively. Re-ordered several lines in the table to ensure
1967 that actions are in ascending order (makes analyzing the table
1968 much more logical). Added action A2 to several states where it
1969 was missing and valid. Added actions A7 and A8 placeholders to
1970 states S1, S2, S4 and S5 pending resolution of issue G.28.
1974 - Modified security consideration (originally added in -03)
1975 requiring access control to be applied only to authenticated
1976 users. This seems nonsensical because anonymous users may have
1977 access control applied to limit permissible actions.
1981 - Verified all normative references and moved informative
1982 references to a new section 14.
1984 F.4. Changes for draft-ldap-bis-authmeth-05
1988 - General editory changes to fix punctuation, spelling, line
1990 - Verified and updated intra- and inter-document references
1992 - Document-wide review for proper usage of RFC 2119 keywords with
1993 several changes to correct improper usage.
1998 Harrison Expires April 2004 [Page 34]
2000 Internet-Draft LDAP Authentication Methods 7 October 2003
2002 - Updated to match current contents of documents. This was needed
2003 due to movement of material on Bind and Start TLS operations to
2004 [Protocol] in this revision.
2008 - Renamed section to "Rationale for LDAP Security Mechanisms" and
2009 removed text that did not support this theme. Part of the
2010 motivation for this change was to remove the implication of the
2011 previous section title, "Required Security Mechanisms", and
2012 other text found in the section that everything in the section
2015 - Information from several removed paragraphs that describe
2016 deployment scenarios will be added Appendix A in the next
2017 revision of the draft.
2020 - Paragraph beginning, " If TLS is negotiated, the client MUST
2021 discard all information..." was moved to section 5.1.7 and
2022 integrated with related material there.
2024 - Paragraph beginning, "If a SASL security layer is negotiated..."
2025 was moved to section 4.2
2029 - Changed wording of first paragraph to clarify meaning.
2032 - Added paragraph from section 3 of -04 beginning, "If a SASL
2033 security layer is negotiated..."
2036 - Renamed to "Other SASL Mechanisms" and completely rewrote the
2037 section (one sentence) to generalize the treatment of SASL
2038 mechanisms not explicitly mentioned in this document.
2042 - Added paragraph beginning, "The dnAuthzID choice allows client
2043 applications..." to clarify whether DN form authorization
2044 identities have to also have a corresponding directory entry.
2045 This change was based on editor's perception of WG consensus.
2047 - Made minor clarifying edits in the paragraph beginning, "The
2048 uAuthzID choice allows for compatibility..."
2052 - Made minor clarifying edits in the last paragraph of the
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2062 - Wording from section 3 paragraph beginning " If TLS is
2063 negotiated, the client MUST discard all information..." was
2064 moved to this section and integrated with existing text.
2068 - Changed usage of "TLS connection" to "TLS session" throughout.
2070 - Removed empty section 5.2.1 and renumbered sections it had
2071 previously contained.
2075 - Added introductory paragraph at beginning of section.
2079 - Changed term "data privacy" to "data confidentiality" to be
2080 consistent with usage in rest of document.
2084 - Changed first paragraph to require implementations that
2085 implement *password-based* authentication to implement and
2086 support DIGEST-MD5 SASL authentication.
2090 - First paragraph: changed "session encryption" to "session
2091 confidentiality protection" to be consistent with usage in rest
2096 - Began changes to incorporate information on deployment scenarios
2097 removed from section 3.
2099 F.5. Changes for draft-ldap-bis-authmeth-06
2104 - Combined Section 2 (Introduction) and Section 3 (Motivation) and
2105 moved Introduction to section 1. All following sections numbers
2106 were decremented by one as result.
2108 - Edits to fix typos, I-D nits, etc.
2110 - Opened several new issues in Appendix G based on feedback from
2111 WG. Some of these have been resolved. Others require further
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2121 - Added additional example of spoofing under threat (7).
2125 - Changed definition of "LDAP association" and added terms,
2126 "connection" and "TLS connection" to bring usage in line with
2131 - Clarified sentence stating that the client MUST NOT use derived
2136 - Began edits to LDAP Association state table to clarify meaning
2137 of various states and actions.
2139 - Added action A9 to cover abandoned bind operation and added
2140 appropriate transitions to the state transition table to
2145 - Replaced first paragraph to clarify that the "DIGEST-MD5" SASL
2146 mechanism is required to implement.
2150 - Rewrote the section to make the advice more applicable over the
2151 long term, i.e. more "timeless." The intent of content in the
2152 original section was preserved.
2156 - Added a clarifying example to the consideration regarding misuse
2157 of unauthenticated access.
2159 F.6. Changes for draft-ldap-bis-authmeth-07
2164 - Updated external and internal references to accommodate changes
2167 - Opened several new issues in Appendix G based on feedback from
2168 WG. Some of these have been resolved. Others require further
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2179 - Rewrote much of section 3.3 to mee the SASL profile requirements
2180 of draft-ietf-sasl-rfc2222bis-xx.txt section 5.
2182 - Changed treatement of SASL ANONYMOUS and PLAIN mechanisms to
2183 bring in line with WG consensus.
2187 - Note to implementers in section 4.1.1 based on operational
2190 - Clarification on client continuing by performing a Start TLS
2191 with TLS already established in section 4.1.4.
2193 - Moved verification of mapping of client's authentication ID to
2194 asserted authorization ID to apply only to explicit assertion.
2195 The local policy in place for implicit assertion is adequate.
2199 - Removed most of section 7.2 as the information is now covered
2200 adequately via the new SASL profile in section 3.3. Added note
2201 to implementors regarding the treatment of username and realm
2202 values in DIGEST-MD5.
2204 - Section 7.3. Minor clarifications in wording.
2206 - Section 7.3.1. Clarification that a match of the presented value
2207 to any member of the set of stored passwords constitutes a
2208 successful authentication.
2210 F.6. Changes for draft-ldap-bis-authmeth-08
2215 - Changed usage from LDAPv3 to LDAP for usage consistency across
2216 LDAP technical specification.
2217 - Fixed a number of usage nits for consistency and to bring doc in
2218 conformance with publication guidelines.
2222 - Significant cleanup and rewording of abstract based on WG
2227 - New definition of user.
2231 - Added 1.5 sentences at end of introductory paragraph indicating
2232 the effect of the Bind op on the LDAP association.
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2241 - Retitled section and clarified wording
2245 - Clarified that simple authentication choice provides three types
2246 of authentication: anonymous, unauthenticated, and simple
2251 - New wording clarifying when negotiated security mechanisms take
2256 - Changed requirement to discard information about server fetched
2257 prior to SASL negotion from MUST to SHOULD to allow for
2258 information obtained through secure mechanisms.
2262 - Simplified wording of first paragraph based on suggestion from
2267 - Minor clarifications in wording.
2271 - Minor larifications in wording in first sentence.
2272 - Explicitly called out that the DN value in the dnAuthzID form is
2273 to be matched using DN matching rules.
2274 - Called out that the uAuthzID MUST be prepared using SASLprep
2275 rules before being compared.
2276 - Clarified requirement on assuming global uniqueness by changing
2277 a "generally... MUST" wording to "SHOULD".
2281 - Simplified wording describing conditions when Start TLS cannot
2283 - Simplified wording in note to implementers regarding race
2284 condition with outstanding LDAP operations on connection.
2288 - Removed section and moved relevant text to section 4.2.2.
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2297 - Renumbered to 4.1.5.
2298 - Updated server identity check rules for server's name based on
2303 - Renumbered to 4.1.6
2304 - Changed requirement to discard information about server fetched
2305 prior to TLS negotion from MUST to SHOULD to allow for
2306 information obtained through secure mechanisms.
2310 - Clarified wording.
2311 - Added definition of anonymous and unauthenticated binds.
2315 - Added security consideration (moved from elsewhere) discouraging
2316 use of cleartext passwords on unprotected communication
2321 - Added an IANA consideration to update GSSAPI service name
2322 registry to point to [Roadmap] and [Authmeth]
2324 Appendix G. Issues to be Resolved
2326 This appendix lists open questions and issues that need to be
2327 resolved before work on this document is deemed complete.
2331 Section 1 lists 6 security mechanisms that can be used by LDAP
2332 servers. I'm not sure what mechanism 5, "Resource limitation by
2333 means of administrative limits on service controls" means.
2335 Status: resolved. Changed wording to "administrative service limits"
2340 Section 2 paragraph 1 defines the term, "sensitive." Do we want to
2341 bring this term and other security-related terms in alignment with
2342 usage with the IETF security glossary (RFC 2828)?
2344 Status: resolved. WG input at IETF 51 was that we should do this, so
2345 the appropriate changes have been made.
2349 Section 2, deployment scenario 2: What is meant by the term "secure
2350 authentication function?"
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2357 Status: resolved. Based on the idea that a "secure authentication
2358 function" could be provided by TLS, I changed the wording to require
2359 data confidentiality for sensitive authentication information and
2360 data integrity for all authentication information.
2364 Section 3, deployment scenario 3: What is meant by the phrase,
2365 "directory data is authenticated by the server?"
2367 Status: resolved. I interpreted this to mean the ability to ensure
2368 the identity of the directory server and the integrity of the data
2369 sent from that server to the client, and explictly stated such.
2373 Section 4 paragraph 3: What is meant by the phrase, "this means that
2374 either this data is useless for faking authentication (like the Unix
2375 "/etc/passwd" file format used to be)?"
2377 Status: resolved. Discussion at IETF 52 along with discussions with
2378 the original authors of this material have convinced us that this
2379 reference is simply too arcane to be left in place. In -03 the text
2380 has been modified to focus on the need to either update password
2381 information in a protected fashion outside of the protocol or to
2382 update it in session well protected against snooping, and the
2383 reference to /etc/passwd has been removed.
2387 Section 4 paragraph 7 begins: "For a directory needing session
2388 protection..." Is this referring to data confidentiality or data
2391 Status: resolved. Changed wording to say, "For a directory needing
2392 data security (both data integrity and data confidentiality)..."
2396 Section 4 paragraph 8 indicates that "information about the server
2397 fetched fetched prior to the TLS negotiation" must be discarded. Do
2398 we want to explicitly state that this applies to information fetched
2399 prior to the *completion* of the TLS negotiation or is this going
2402 Status: resolved. Based on comments in the IETF 51 LDAPBIS WG
2403 meeting, this has been changed to explicitly state, "fetched prior
2404 to the initiation of the TLS negotiation..."
2408 Section 4 paragraph 9 indicates that clients SHOULD check the
2409 supportedSASLMechanisms list both before and after a SASL security
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2415 layer is negotiated to ensure that they are using the best available
2416 security mechanism supported mutually by the client and server. A
2417 note at the end of the paragraph indicates that this is a SHOULD
2418 since there are environments where the client might get a list of
2419 supported SASL mechanisms from a different trusted source.
2421 I wonder if the intent of this could be restated more plainly using
2422 one of these two approaches (I've paraphrased for the sake of
2425 Approach 1: Clients SHOULD check the supportedSASLMechanisms
2426 list both before and after SASL negotiation or clients SHOULD
2427 use a different trusted source to determine available supported
2430 Approach 2: Clients MUST check the supportedSASLMechanisms list
2431 both before and after SASL negotiation UNLESS they use a
2432 different trusted source to determine available supported SASL
2435 Status: resolved. WG input at IETF 51 was that Approach 1 was
2436 probably best. I ended up keeping the basic structure similar to the
2437 original to meet this intent.
2441 Section 6.3.1 states: "DSAs that map the DN sent in the bind request
2442 to a directory entry with a userPassword attribute will... compare
2443 [each value in the named user's entry]... with the presented
2444 password." This implies that this applies only to user entries with
2445 userPassword attributes. What about other types of entries that
2446 might allow passwords and might store in the password information in
2447 other attributes? Do we want to make this text more general?
2449 Status: resolved in -03 draft by generalizing section 8.3.1 to not
2450 refer to any specific password attribute and by removing the term
2451 "user" in referring to the directory entry specified by the DN in
2454 G.10 userPassword and simple bind
2456 We need to be sure that we don't require userPassword to be the only
2457 attribute used for authenticating via simple bind. (See 2251 sec 4.2
2458 and authmeth 6.3.1. Work with Jim Sermersheim on resolution to this.
2459 On publication state something like: "This is the specific
2460 implementation of what we discussed in our general reorg
2461 conversation on the list." (Source: Kurt Zeilenga)
2463 Status: resolved in -03 draft by generalizing section 8.3.1 to not
2464 refer to any specific password attribute and by removing the term
2465 "user" in referring to the directory entry specified by the DN in
2468 G.11. Meaning of LDAP Association
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2475 The original RFC 2830 uses the term "LDAP association" in describing
2476 a connection between an LDAP client and server regardless of the
2477 state of TLS on that connection. This term needs to be defined or
2480 Status: resolved. at IETF 51 Bob Morgan indicated that the term
2481 "LDAP association" was intended to distinguish the LDAP-level
2482 connection from the TLS-level connection. This still needs to be
2483 clarified somewhere in the draft. Added "LDAP association" to a
2484 glossary in section 1.
2486 G.12. Is DIGEST-MD5 mandatory for all implementations?
2488 Reading 2829bis I think DIGEST-MD5 is mandatory ONLY IF your server
2489 supports password based authentication...but the following makes it
2490 sound mandatory to provide BOTH password authentication AND DIGEST-
2493 "6.2. Digest authentication
2495 LDAP implementations MUST support authentication with a password
2496 using the DIGEST-MD5 SASL mechanism for password protection, as
2497 defined in section 6.1."
2499 The thing is for acl it would be nice (though not critical) to be
2500 able to default the required authentication level for a subject to a
2501 single "fairly secure" mechanism--if there is no such mandatory
2502 authentication scheme then you cannot do that. (Source: Rob Byrne)
2504 Status: resolved. -00 version of the draft added a sentence at the
2505 beginning of section 8.2 stating that LDAP server implementations
2506 must support this method.
2508 G.13. Ordering of authentication levels requested
2510 Again on the subject of authentication level, is it possible to
2511 define an ordering on authentication levels which defines their
2512 relative "strengths" ? This would be useful in acl as you could say
2513 things like"a given aci grants access to a given subject at this
2514 authentication level AND ABOVE". David Chadwick raised this before
2515 in the context of denying access to a subject at a given
2516 authentication level, in which case he wanted to express "deny
2517 access to this subject at this authentication level AND TO ALL
2518 IDENTITIES AUTHENTICATED BELOW THAT LEVEL". (Source: Rob Byrne)
2520 Status: out of scope. This is outside the scope of this document and
2521 will not be addressed.
2523 G.14. Document vulnerabilities of various mechanisms
2525 While I'm here...in 2829, I think it would be good to have some
2526 comments or explicit reference to a place where the security
2527 properties of the particular mandatory authentication schemes are
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2533 outlined. When I say "security properties" I mean stuff like "This
2534 scheme is vulnerable to such and such attacks, is only safe if the
2535 key size is > 50, this hash is widely considered the best, etc...".
2536 I think an LDAP implementor is likely to be interested in that
2537 information, without having to wade through the security RFCs.
2540 Status: out of scope. This is outside the scope of this document and
2541 will not be addressed.
2543 G.15. Include a StartTLS state transition table
2545 The pictoral representation it is nominally based on is here (URL
2548 http://www.stanford.edu/~hodges/doc/LDAPAssociationStateDiagram-
2551 (Source: Jeff Hodges)
2553 Status: In Process. Table provided in -03. Review of content for
2554 accuracy in -04. Additional review is needed, plus comments from WG
2555 members indicate that additional description of each state's meaning
2558 G.16. Empty sasl credentials question
2560 I spent some more time looking microscopically at ldap-auth-methods
2561 and ldap-ext-tls drafts. The drafts say that the credential must
2562 have the form dn:xxx or u:xxx or be absent, and although they don't
2563 say what to do in the case of an empty octet string I would say that
2564 we could send protocolError (claim it is a bad PDU).
2566 There is still the question of what to do if the credential is 'dn:'
2567 (or 'u:') followed by the empty string. (Source: ariel@columbia.edu
2570 Status: resolved. Kurt Zeilenga indicated during ldapbis WG
2571 discussion at IETF 52 that SASL AuthzID credentials empty and absent
2572 are equivalent in the latest SASL ID. This resolves the issue.
2574 G.17. Hostname check from MUST to SHOULD?
2576 I am uneasy about the hostname check. My experience from PKI with
2577 HTTP probably is a contributing factor; we have people using the
2578 short hostname to get to a server which naturally has the FQDN in
2579 the certificate, no end of problems. I have a certificate on my
2580 laptop which has the FQDN for the casse when the system is on our
2581 Columbia network with a fixed IP; when I dial in however, I have
2582 some horrible dialup name, and using the local https server becomes
2583 annoying. Issuing a certificate in the name 'localhost' is not a
2584 solution! Wildcard match does not solve this problem. For these
2585 reasons I am inclined to argue for 'SHOULD' instead of
2586 'MUST' in paragraph...
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2593 Also, The hostname check against the name in the certificate is a
2594 very weak means of preventing man-in-the-middle attacks; the proper
2595 solution is not here yet (SecureDNS or some equivalent). Faking out
2596 DNS is not so hard, and we see this sort of thing in the press on a
2597 pretty regular basis, where site A hijacks the DNS server for site B
2598 and gets all their requests. Some mention of this should be made in
2599 the draft. (Source: ariel@columbia.edu via Jeff Hodges)
2601 Status: resolved. Based on discussion at IETF 52 ldapbis WG meeting,
2602 this text will stand as it is. The check is a MUST, but the behavior
2603 afterward is a SHOULD. This gives server implementations the room to
2606 G.18. Must SASL DN exist in the directory?
2608 If the 'dn:' form of sasl creds is used, is it the intention of the
2609 draft(ers) that this DN must exist in the directory and the client
2610 will have the privileges associated with that entry, or can the
2611 server map the sasl DN to perhaps some other DN in the directory,
2612 in an implementation-dependent fashion?
2614 We already know that if *no* sasl credentials are presented, the DN
2615 or altname in the client certificate may be mapped to a DN in an
2616 implementation-dependent fashion, or indeed to something not in the
2617 directory at all. (Right?) (Source: ariel@columbia.edu via Jeff
2620 Status: resolved. (11/12/02)Based on my research I propose that the
2621 DN MUST exist in the directory when the DN form of sasl creds is
2622 used. I have made this proposal to the ldapbis mailing list.
2624 (11/21/02) Feedback from mailing list has proposed removing this
2625 paragraph entirely because (1) explicit assertion of authorization
2626 identity should only be done when proxying (2) mapping of the
2627 asserted authorization identity is implementation specific and
2628 policy driven [SASL] section 4.2, and (3) keeping this paragraph is
2629 not required for interoperability.
2631 G.19. DN used in conjunction with SASL mechanism
2633 We need to specify whether the DN field in Bind operation can/cannot
2634 be used when SASL mechanism is specified. (source: RL Bob)
2636 Status: resolved. (-03) Based on ldapbis WG discussion at IETF52 two
2637 sentences were added to section 4.3 indicating that clients SHOULD
2638 NOT send a DN value when binding with the sasl choice and servers
2639 SHALL ignore any value received in this circumstance. During edits
2640 for -04 version of draft it was noted that [Protocol] section 4.2
2641 conflicts with this draft. The editor of [Protocol] has been
2642 notified of the discrepancy, and they have been handled.
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2651 Differences between unauthenticated and anonymous. There are four
2652 states you can get into. One is completely undefined (this is now
2653 explicitly called out in [Protocol]). This text needs to be moved
2654 from [Protocol] to this draft. (source: Jim Sermersheim)
2656 Status: Resolved. There are four states: (1) no name, no password
2657 (anon); (2) name, no password (anon); (3) no name, password
2658 (invalid); (4) name, password (simple bind). States 1, 2, and 4 are
2659 called out in [AuthMeth]. State 3 is called out in [Protocol]; this
2660 seems appropriate based on review of alternatives.
2662 G.21. Misuse of unauthenticated access
2664 Add a security consideration that operational experience shows that
2665 clients can misuse unauthenticated access (simple bind with name but
2666 no password). Servers SHOULD by default reject authentication
2667 requests that have a DN with an empty password with an error of
2668 invalidCredentials. (Source: Kurt Zeilenga and Chris Newman (Sun))
2670 Status: Resolved. Added to security considerations in -03.
2672 G.22. Need to move StartTLS protocol information to [Protocol]
2674 Status: Resolved. Removed Sections 5.1, 5.2, and 5.4 for -04 and
2675 they are [Protocol] -11.
2677 G.23. Split Normative and Non-normative references into separate
2680 Status: Resolved. Changes made in -04
2682 G.24. What is the authentication state if a Bind operation is
2687 (3/24/03) This following text appears in section 4.2.1 of [Protocol]
2688 revision -13 to cover what happens if a bind operation is abandoned:
2690 A failed or abandoned Bind Operation has the effect of leaving the
2691 connection in an anonymous state. To arrive at a known
2692 authentication state after abandoning a bind operation, clients may
2693 unbind, rebind, or make use of the BindResponse.
2695 (6/28/03): The state table in section 6 of [AuthMeth] has been
2696 updated to reflect this wording.
2698 G.25. Difference between checking server hostname and server's
2699 canonical DNS name in Server Identity Check?
2701 Section 4.1.6: I now understand the intent of the check (prevent
2702 man-in-the-middle attacks). But what is the subtle difference
2703 between the "server hostname" and the "server's canonical DNS name"?
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2713 (11/12/02) Sent suggested wording change to this paragraph to the
2714 ldapbis mail list and also asked for opinion as to whether we should
2715 discuss the distinction between server DNS hostname and server
2716 canonical DNS hostname in [AuthMeth].
2718 (11/21/02): RL Bob Morgan will provide wording that allows
2719 derivations of the name that are provided securely.
2721 (6/28/03): posted to the WG list asking Bob or any other WG member
2722 who is knowledgeable about the issues involved to help me with
2723 wording or other information I can use to make this change and close
2726 (10/08/03): Based on WG list feedback, I've updated this text to
2727 read what I judge to be the WG consensus, "The client MUST use the
2728 server provided by the user (or other trusted entity) as the value
2729 to compare against the server name as expressed in the server's
2730 certificate. A hostname derived from the user input is to be
2731 considered provided by the user only if derived in a secure fashion
2735 G.26. Server Identity Check using servers located via SRV records
2737 Section 4.1.6: What should be done if the server was found using SRV
2738 records based on the "locate" draft/RFC? (Source: Tim Hahn).
2740 Status: Resolved. Section 5 of draft-ietf-ldapext-locate-08
2741 specifically calls out how the server identity should be performed
2742 if the server is located using the method defined in that draft.
2743 This is the right location for this information, and the coverage
2744 appears to be adequate.
2746 G.27 Inconsistency in effect of TLS closure on LDAP association.
2748 Section 4.4.1 of authmeth -03 (section 4.1 of RFC2830) states that
2749 TLS closure alert will leave the LDAP association intact. Contrast
2750 this with Section 4.5.2 (section 5.2 of RFC2830) that says that the
2751 closure of the TLS connection MUST cause the LDAP association to
2752 move to an anonymous authentication.
2754 Status: Resolved. (11/12/02) This is actually a [Protocol] issue
2755 because these sections have now been moved to [Protocol] -11. I have
2756 proposed the following text for Section 4.4.1 of [AuthMeth] -03
2757 (section 4.13.3.1 of [Protocol]) to resolve this apparent
2760 "Either the client or server MAY terminate the TLS connection on an
2761 LDAP association by sending a TLS closure alert. The LDAP
2762 connection remains open for further communication after TLS closure
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2769 occurs although the authentication state of the LDAP connection is
2770 affected (see [AuthMeth] section 4.2.2).
2772 (11/21/02): resolution to this is expected in [Protocol] -12
2774 (06/28/03): [Protocol]-15 clarifies that a TLS closure alert
2775 terminates the TLS connection while leaving the LDAP connection
2776 intact. The authentication state table in [AuthMeth] specifies the
2777 effect on the LDAP association.
2779 G.28 Ordering of external sources of authorization identities
2781 Section 4.3.2 implies that external sources of authorization
2782 identities other than TLS are permitted. What is the behavior when
2783 two external sources of authentication credentials are available
2784 (e.g. TLS and IPsec are both present (is this possible?)) and a SASL
2785 EXTERNAL Bind operation is performed?
2787 Status: resolved. 11/20/02: Resolved by Section 4.2 of [SASL] which
2788 states that the decision to allow or disallow the asserted identity
2789 is based on an implementation defined policy.
2791 G.29 Rewrite of Section 9, TLS Ciphersuites
2793 This section contains anachronistic references and needs to be
2794 updated/rewritten in a way that provides useful guidance for future
2795 readers in a way that will transcend the passage of time.
2797 Status: Resolved. (6/28/03): Rewrote the section to cover the
2798 general issues and considerations involved in selecting TLS
2801 G.30 Update to Appendix A, Example Deployment Scenarios
2803 This section needs to be updated to indicate which security
2804 mechanisms and/or combinations of security mechanisms described
2805 elsewhere in the document can provide the types of protections
2806 suggested in this appendix.
2808 G.31 Use of PLAIN SASL Mechanism
2810 At least one LDAP server implementer has found the SASL "PLAIN"
2811 mechanism useful in authenticating to legacy systems that do not
2812 represent authentication identities as DNs. Section 3.3.1 appears to
2813 implicitly disallow the use of the SASL "PLAIN" mechanism with LDAP.
2814 Should we allow the use of this mechanism? I.e. is this "SASL"
2815 "PLAIN" MUST NOT be used with LDAP, or is it simply that LDAP
2816 doesn't define bindings for these mechanism. If SASL "PLAIN" is
2817 allowed, the following adjustments will be needed to section 3.3.1:
2818 (a) change section heading, (b) remove reference to "PLAIN" in the
2819 section, (c) ensure wording of last sentence regarding non-DN
2820 AuthZIDs is consistent with rest of the section.
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2829 (6/28/03): email to WG list stating issue and asking if we should
2830 remove the reference to SASL "PLAIN".
2832 For -07 draft I've generalized the SASL profile in section 3.3 to
2833 allow any SASL mechanism.
2836 G.32 Clarification on use of SASL mechanisms
2838 Section 3.3.1: BTW, what _are_ the "ANONYMOUS" and "PLAIN" SASL
2839 mechanisms? They are not defined in RFC2222. If you refer to other
2840 SASL mechanisms than those in rfc2222, Maybe you should only list
2841 which mechanisms _are_used, instead of which ones are _not. (Source:
2844 I (Kurt Zeilenga) note[s] as well that the ANONYMOUS/PLAIN section
2846 be deleted. ANONYMOUS and PLAIN, like in other mechanism,
2847 can be used in LDAP if a) supported and b) enabled. I note
2848 that they each offer capabilities not found in their simple
2849 bind equivalents (and hence are used in some deployments).
2850 For example, PLAIN (over TLS) is quite useful when interacting
2851 with legacy authentication subsystems. (Source: Kurt Zeilenga)
2855 For -07 draft I've generalized the SASL profile in section 3.3 to
2856 allow any SASL mechanism.
2860 G.33 Clarification on use of password protection based on AuthZID form
2862 Section 3.3.1: "If an authorization identity of a form different
2863 from a DN is requested by the client, a mechanism that protects the
2864 password in transit SHOULD be used." What has that to do with DNs?
2865 A mechanism that protects the password in transit should be used in
2866 any case, shouldn't it?
2869 G.34 Clarification on use of matching rules in Server Identity Check
2871 The text in section 4.1.6 isn't explicit on whether all rules apply
2872 to both CN and dNSName values. The text should be clear as to which
2873 rules apply to which values.... in particular, the wildcard
2874 rules. (Source: Kurt Zeilenga)
2877 G.35 Requested Additions to Security Considerations
2879 Requested to mention hostile servers which the user might have been
2880 fooled to into contacting. Which mechanisms that are standardized by
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2886 the LDAP standard do/do not disclose the user's password to the
2887 server? (Or to servers doing man-in-the-middle attack? Or is that a
2890 Requested to mention denial of service attacks.
2892 Requested list of methods that need/don't need the server to know
2893 the user's plaintext password. (I say 'know' instead of 'store'
2894 because it could still store the password encrypted, but in a way
2895 which it knows how to decrypt.)
2897 (Source: Hallvard Furuseth)
2899 G.36 Add reference to definition of DIGEST-MD5
2901 Need a reference to the definition of DIGEST-MD5 SASL mechanism in
2902 section 7.2 (Source: Hallvard Furuseth)
2904 Status: Resolved. A reference to to the DIGEST-MD5 SASL mechanism,
2905 [DigestAuth], is included in the -07 revision.
2907 G.37 Clarification on procedure for certificate-based authentication
2910 8.1. Certificate-based authentication with TLS states: "Following
2911 the successful completion of TLS negotiation, the client will send
2912 an LDAP bind request with the SASL "EXTERNAL" mechanism." Is this
2913 immediately following, or just some time later? Should the wording,
2914 "the client will send..." actually read, "the client MUST send..."?
2916 G.38 Effect of StartTLS on authentication state
2918 Should the server drop all knowledge of connection, i.e. return to
2919 anonymous state, if it gets a StartTLS request on a connection that
2920 has successfully bound using the simple method?
2922 G.39 Be sure that there is a consideration in [SCHEMA] that discusses
2923 multiple password values in userPassword
2925 Allowing multiple values obviously does raise a number of security
2926 considerations and these need to be discussed in the document.
2928 Certainly applications which intend to replace the userPassword with
2929 new value(s) should use modify/replaceValues (or
2930 modify/deleteAttribute+addAttribute). Additionally, server
2931 implementations should be encouraged to provide administrative
2932 controls which, if enabled, restrict userPassword to one value.
2934 G.40. Clarify need to verify mapping between authentication identity
2935 and resulting authorization identity on implicit assertion of AuthZID.
2937 4.2.2.3. Error Conditions
2939 "For either form of assertion, the server MUST verify that the
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2945 client's authentication identity as supplied in its TLS credentials
2946 is permitted to be mapped to the asserted authorization identity."
2948 This makes sense for the explicit assertion case, but seems to be
2949 ambiguous for the implicit case.
2950 IMHO, the mapping can be done as two steps:
2951 a). deriving LDAP authentication identity from TLS credentials; If t
2952 this steps fails, EXTERNAL mechanism returns failure.
2953 b). verify that the authorization identity is allowed for the
2954 derived authentication identity. This is always "noop" for the
2956 I am not sure that the text is saying this.
2957 (Source: Alexey Melnikov email 8/1/2003 5:30:43 PM)
2959 Status: Resolved in -07. After reading the comments and the text of
2960 the draft, I believe that this should be clarified. The local policy
2961 used to map the AuthNID to the AuthZID in the implicit case is
2962 sufficient and that no additional verification is useful or needed.
2963 This text has been moved to apply only to the explicit assertion
2966 G.41. Section 7.2 contains unnecessary and misleading detail.
2968 " I am not sure why this section is required in the document.
2969 DIGEST-MD5 is defined in a separate document and there should be
2970 nothing magical about its usage in LDAP. If DIGEST-MD5 description
2971 creates confusion for LDAP implementors, let's fix the DIGEST-MD5
2972 document! Also, this section tries to redefine DIGEST-MD5 behavior,
2973 which is explicitly prohibited by the SASL specification."
2974 (Source: Alexey Melnikov: email 8/1/2003 5:30:43 PM)
2978 After reading the comments and the text of the draft plus the
2979 related text in draft-ietf-sasl-rfc2831bis-02.txt plus
2980 http://www.ietf.org/internet-drafts/draft-ietf-sasl-rfc2222bis-
2981 02.txt, I am inclined to agree with Alexey. In -07 I rewrote section
2982 3.3 (SASL mechanisms) to match the profiling requirements
2983 rfc2831bis. I then dramatically reduced the material in section 7.2
2984 to a bare minimum and let the SASL profile stand on its own.
2986 G.42. Does change for G.41 cause interoperability issue?
2988 There is one issue with the way the authmeth draft is currently
2989 written that changes the SASL DIGEST-MD5 behavior on the way the
2990 server responds with the subsequent authentication information .
2991 This has been documented in this fashion since RFC 2829 (section
2992 6.1) was originally published and may cause an interoperability
2993 issue at this point if it changed to follow the DIGEST-MD5 spec (as
2994 it was in -07 of AuthMeth). Take this issue to the list.
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3004 (10/08/03) This item was discussed on the WG list between 5/2/03 and
3005 5/9/03. Consensus apppears to support the notion that RFC 2829 was
3006 in error and that the semantics of RFC 2831 are correct and should
3007 be reflected in authmeth. This is already the case as of the -07
3010 G.43. DIGEST-MD5 Realms recommendations for LDAP
3012 From http://www.ietf.org/internet-drafts/draft-ietf-sasl-rfc2222bis-
3013 02.txt: A protocol profile SHOULD provide a guidance how realms are
3014 to be constructed and used in the protocol and MAY further restrict
3015 its syntax and protocol-specific semantics."
3017 I don't believe that any such guidance exists within the LDAP TS.
3018 The most likely place for this to reside is in the authmeth draft.
3020 Related email from Alexey Melnikov (8/4/2003 1:08:40 PM):
3022 "The problem I have with the document is that it references realm
3023 without explaining what it is (or at least some examples of valid
3024 values). For LDAP, some recommendations should be given. For
3026 1). Use a hardcoded string as the realm (one of the implementations
3027 I worked on was doing that)
3028 2). Use hostname (realm==host) or domain/cluster name (realm
3029 includes multiple hosts).
3030 3). Use a node in DIT above user entry, for example for "cn=Barbara
3031 Jensen, ou=Accounting, o=Ace Industry, c=US"
3032 and "cn=John Doe, ou=Accounting, o=Ace Industry, c=US" realm can be
3033 "ou=Accounting, o=Ace Industry, c=US"
3034 (or "o=Ace Industry, c=US"); for "cn=Gern Jensen, ou=Product
3035 Testing,o=Ace Industry, c=US" realm can be "ou=Product Testing,
3036 o=Ace Industry, c=US".
3038 Of course other choices are possible.
3042 To summarize: I'd like authmeth to define a realm name for use with
3043 Digest-MD5 that corresponds to LDAP DNs known to this server.
3044 Authzid is okay, but perhaps could be better put into context.
3047 John McMeeking (5/12/2003)
3049 G.44. Use of DNs in usernames and realms in DIGEST-MD5
3051 In reading the discussion on the mailing list, I reach the following
3054 DIGEST-MD5 username and realm are simple strings. The syntax of
3055 these strings allows strings that look like DNs in form, however,
3056 DIGEST-MD5 treats them a simple strings for comparision purposes.
3057 For example, the DNs cn=roger, o=US and cn=roger,o=us are equivalent
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3063 when being compared semantically as DNs, however, these would be
3064 considered two different username values in DIGEST-MD5 because
3065 simple octet-wise semantics (rather than DN semantics) are used to
3066 compare username values in DIGEST-MD5. Ditto for realm values.
3070 In -07 revision I added notes to implementors expressing this issue
3073 G.45: Open Issue: Is Simple+TLS mandatory to implement?
3075 Going forward, it would be much better to clarify that simple
3076 +TLS is to be used for DN/password credentials and DIGEST-MD5
3077 (or PLAIN+TLS) be used for username/password credentials. (Kurt
3078 Zeilenga, 5/12/2003)
3080 I don't believe you can mandate simple/TLS! At the time RFC 2829 was
3081 debated, a large number on the WG wanted this. They did not get
3082 their way because of the complexity of the solution. It was argued
3083 that a password-based method would be better. I think they believed
3084 it would still be DN/password, though. (Ron Ramsay, 5/12/2003)
3086 This was officially opened as an issue by WG co-chair Kurt Zeilenga
3087 on 5/12/03. Little direct discussion has occurred since, however
3088 there has been significant discussion on the use of DN values as the
3089 username for DIGEST-MD5.
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