INTERNET-DRAFT Kurt D. Zeilenga Intended Category: Experimental OpenLDAP Foundation Expires in six months 28 October 2005 LDAP Turn Operation 1. Status of this Memo This document is intended to be, after appropriate review and revision, submitted to the RFC Editor for publication as an Experimental document. Distribution of this memo is unlimited. Technical discussion of this document will take place on the IETF LDAP Extensions mailing list . Please send editorial comments directly to the author . By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright (C) The Internet Society (2005). All Rights Reserved. Please see the Full Copyright section near the end of this document for more information. Abstract Zeilenga LDAP Turn Op [Page 1] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 This specification describes a Lightweight Directory Access Protocol (LDAP) extended operation to reverse (or "turn") the roles of client and server for subsequent protocol exchanges in the session, or to enable each peer to act as both client and server with respect to the other. 1. Background and Intent of Use The Lightweight Directory Access Protocol (LDAP) [Roadmap][Protocol] is a client-server protocol which typically operates over reliable octet-stream transports such as the Transport Control Protocol (TCP). Generally, the client initiates the stream by connecting to the server's listener at some well-known address. There are cases where it is desirable for the server to initiate the stream. While it certainly is possible to write a technical specification detailing how to implement server-initiated LDAP sessions, this would require the design of new authentication and other security mechanisms to support server-initiated LDAP sessions. Instead, this document introduces an operation, the Turn operation, which may be used to reverse the client-servers roles of the protocol peers. This allows the initiating protocol peer to become server (after the reversal). As an additional feature, the Turn operation may be used to allow both peers to act in both roles. This is useful where both peers are directory servers that desire to request, as LDAP clients, operations be performed by the other. This may be useful in replicated and/or distributed environments. This operation is intended to be used between protocol peers which have established a mutual agreement, by means outside of the protocol, which requires reversal of client-server roles, or allows both peers to act both as client and server. 1.1 Terminology Protocol elements are described using ASN.1 [X.680] with implicit tags. The term "BER-encoded" means the element is to be encoded using the Basic Encoding Rules [X.690] under the restrictions detailed in Section 5.2 of [Protocol]. 2. Turn Operation Zeilenga LDAP Turn Op [Page 2] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 The Turn operation is defined as a LDAP Extended Operation [Protocol, Section 4.12] identified by the IANA-ASSIGNED-OID. The function of the Turn Operation is to request that the client-server roles be reversed, or, optionally to request that both protocol peers to be able to act both as client and server in respect to the other. 2.1. Turn Request The Turn request is an ExtendedRequest with the requestName field containing the IANA-ASSIGNED-OID and a requestValue field is a BER-encoded turnValue: turnValue ::= SEQUENCE { mutual BOOLEAN DEFAULT FALSE, identifier LDAPString } A TRUE mutual field value indicates a request to allow both peers to act both as client and server. A FALSE mutual field value indicates a request to reserve the client and server roles. The value of the identifier field is a locally-defined policy identifier (typically associated with a mutual agreement for which this turn is be executed as part of). 2.2. Turn Response A Turn response is an ExtendedResponse where the responseName and responseValue fields are absent. A resultCode of success is returned if and only if the responder is willing and able to turn the session as requested. Otherwise, a different resultCode is returned. 3. Authentication This extension's authentication model assumes separate authentication of the peers in each of their roles. A separate Bind exchange is expected between the peers in their new roles to establish identities in these roles. Upon completion of the Turn, the responding peer in its new client role has an anonymous association at the initiating peer in its new server role. If the turn was mutual, the authentication association of the initiating peer in its pre-existing client role is left intact at the responding peer in its pre-existing server role. If the turn was not mutual, this association is void. Zeilenga LDAP Turn Op [Page 3] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 The responding peer may establish its identity in its client role by requesting and successfully completing a Bind operation. The remainder of this section discuss some authentication scenarios. In the protocol exchange illustrations, A refers to the initiating peer (the original client) and B refers to the responding peer (the original server). 3.1. Use with TLS and Simple Authentication A->B: StartTLS Request B->A: StartTLS(success) Response A->B: Bind(Simple(cn=B,dc=example,dc=net,B's secret)) Request B->A: Bind(success) Response A->B: Turn(TRUE,"XXYYZ") Request B->A: Turn(success) Response A->B: Bind(Simple(DN/Password)) Request B->A: Bind(Simple(cn=A,dc=example,dc=net,A's secret)) Request A->B: Bind(success) Response In this scenario, TLS (Transport Layer Security) [TLS] is started and the initiating peer (the original client) establishes its identity with the responding peer prior to the Turn using the the DN/password mechanism of the Simple method of the Bind operation. After the turn, the responding peer in its new client role establishes its identity with the initiating peer in its new server role. 3.2. Use with TLS and SASL EXTERNAL A->B: StartTLS Request B->A: StartTLS(success) Response A->B: Bind(SASL(EXTERNAL)) Request B->A: Bind(success) Response A->B: Turn(TRUE,"XXYYZ") Request B->A: Turn(success) Response B->A: Bind(SASL(EXTERNAL)) Request A->B: Bind(success) Response In this scenario, TLS is started prior with each peer providing a valid certificate and the initiating peer (the original client) establishes its identity through the use of the EXTERNAL mechanism of the SASL (Simple Authentication and Security Layer) [SASL] method of the Bind operation prior to the Turn. After the turn, the responding peer in its new client role establishes its identity with the initiating peer in its new server role. Zeilenga LDAP Turn Op [Page 4] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 3.3. Use of mutual authentication and SASL EXTERNAL A number of SASL mechanisms, such as GSSAPI [GSSAPI] and DIGEST-MD5 [DIGEST-MD5], support mutual authentication. The initiating peer, it its new server role, may use the identity of the responding peer established by a prior authentication exchange, as its source for "external" identity in subsequent EXTERNAL exchange. A->B: Bind(SASL(GSSAPI)) Request B->A: Bind(success) Response A->B: Turn(TRUE,"XXYYZ") Request B->A: Turn(success) Response B->A: Bind(SASL(EXTERNAL)) Request A->B: Bind(success) Response In this scenario, a GSSAPI mutual-authentication exchange is completed between the initiating peer (the original client) and the the responding server (the original server) prior to the turn. After the turn, the responding peer in its new client role requests the initiating peer utilize an "external" identity to establish its LDAP authorization identity. 4. TLS and SASL security layers As described in [Protocol], LDAP supports both Transport Layer Security (TLS) [TLS] and Simple Authentication and Security Layer (SASL) [SASL] security frameworks. The following table illustrates the relationship between the LDAP message layer, SASL layer, TLS layer, and transport connection within an LDAP session. +----------------------+ | LDAP message layer | +----------------------+ > LDAP PDUs +----------------------+ < data | SASL layer | +----------------------+ > SASL-protected data +----------------------+ < data | TLS layer | Application +----------------------+ > TLS-protected data ------------+----------------------+ < data Transport | transport connection | +----------------------+ This extension does not alter this relationship, nor does it remove the general restriction against multiple TLS layers, nor does it remove the general restriction against multiple SASL layers. Zeilenga LDAP Turn Op [Page 5] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 As specified in [Protocol], the StartTLS operation is used to initiate negotiation of a TLS layer. If a TLS is already installed, the StartTLS operation must fail. Upon establishment of the TLS layer, regardless of which peer issued the request to start TLS, the peer which initiated the LDAP session (the original client) performs the "server identity check" as described in Section 3.1.5 of [AuthMeth] treating itself as the "client" and its peer as the "server". As specified in [SASL], newly negotiated SASL security layer replace the installed SASL security layer. Though the client/server roles in LDAP, and hence SASL, may be reversed in subsequent exchanges, only one SASL security layer may be installed at any instance. 5. Security Considerations Implementors should be aware that the reversing of client/server roles and/or allowing both peers to act as client and server likely introduces security considerations not foreseen by the authors of this document. In particular, the security implications of the design choices made in the authentication and data security models for this extension (discussed in sections 3 and 4, respectively) are not fully studied. It is hoped that experimentation with this extension will lead to better understanding of the security implications of these models and other aspects of this extension, and that appropriate considerations will be documented in a future document. The following security considerations are apparent at this time. Implementors should take special care to process LDAP, SASL, TLS, and other events the appropriate roles for the peers. It is noted that while the Turn reverses the client/server roles with LDAP, and in SASL authentication exchanges, it does not reverse the roles within the TLS layer or the transport connection. The responding server (the original server) should restrict use of this operation to authorized clients. Client knowledge of a valid identifier should not be the sole factor in determining authorization to turn. Where the peers except to establish TLS, TLS should be started prior to the Turn and any request to authenticate via the Bind operation. LDAP security considerations [Protocol][AuthMeth] generally apply to this extension. 6. IANA Considerations Zeilenga LDAP Turn Op [Page 6] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 Registration of the following values [BCP64bis] is requested. 6.1. Object Identifier It is requested that IANA assign an LDAP Object Identifier to identify the LDAP Turn Operation as defined in this document. Subject: Request for LDAP Object Identifier Registration Person & email address to contact for further information: Kurt Zeilenga Specification: RFC XXXX Author/Change Controller: Author Comments: Identifies the LDAP Turn Operation 6.2. LDAP Protocol Mechanism It is requested that IANA register the LDAP Protocol Mechanism described in this document. Subject: Request for LDAP Protocol Mechanism Registration Object Identifier: IANA-ASSIGNED-OID Description: LDAP Turn Operation Person & email address to contact for further information: Kurt Zeilenga Usage: Extended Operation Specification: RFC XXXX Author/Change Controller: Author Comments: none 7. Author's Address Kurt D. Zeilenga OpenLDAP Foundation Email: Kurt@OpenLDAP.org 8. References [[Note to the RFC Editor: please replace the citation tags used in referencing Internet-Drafts with tags of the form RFCnnnn where possible.]] Zeilenga LDAP Turn Op [Page 7] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 8.1. Normative References [Roadmap] Zeilenga, K. (editor), "LDAP: Technical Specification Road Map", draft-ietf-ldapbis-roadmap-xx.txt, a work in progress. [Protocol] Sermersheim, J. (editor), "LDAP: The Protocol", draft-ietf-ldapbis-protocol-xx.txt, a work in progress. [AuthMeth] Harrison, R. (editor), "LDAP: Authentication Methods and Connection Level Security Mechanisms", draft-ietf-ldapbis-authmeth-xx.txt, a work in progress. [SASL] Melnikov, A. (Editor), "Simple Authentication and Security Layer (SASL)", draft-ietf-sasl-rfc2222bis-xx.txt, a work in progress. [TLS] Dierks, T. and, E. Rescorla, "The TLS Protocol Version 1.1", draft-ietf-tls-rfc2246-bis-xx.txt, a work in progress. [X.680] International Telecommunication Union - Telecommunication Standardization Sector, "Abstract Syntax Notation One (ASN.1) - Specification of Basic Notation", X.680(2002) (also ISO/IEC 8824-1:2002). [X.690] International Telecommunication Union - Telecommunication Standardization Sector, "Specification of ASN.1 encoding rules: Basic Encoding Rules (BER), Canonical Encoding Rules (CER), and Distinguished Encoding Rules (DER)", X.690(2002) (also ISO/IEC 8825-1:2002). 8.2. Informative References [BCP64bis] Zeilenga, K., "IANA Considerations for LDAP", draft-ietf-ldapbis-bcp64-xx.txt, a work in progress. [GSSAPI] Linn, J., "Generic Security Service Application Program Interface, Version 2, Update 1", RFC 2743, January 2000. [DIGEST-MD5] Leach, P., C. Newman, and A. Melnikov, "Using Digest Authentication as a SASL Mechanism", draft-ietf-sasl-rfc2831bis-xx.txt, a work in progress. Zeilenga LDAP Turn Op [Page 8] INTERNET-DRAFT draft-zeilenga-ldap-turn-03 28 October 2005 Intellectual Property Rights The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Full Copyright Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Zeilenga LDAP Turn Op [Page 9]