ASID Working Group Jeff Hodges, Stanford INTERNET-DRAFT RL "Bob" Morgan, Stanford Mark Wahl, Critical Angle Inc. June, 1997 Lightweight Directory Access Protocol (v3): Extension for Transport Layer Security draft-ietf-asid-ldapv3-tls-01.txt 1. Status of this Memo This document is an Internet-Draft. Internet-Drafts are working docu- ments 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). 2. Abstract This document defines the "Start Transport Layer Security (TLS) Opera- tion" for LDAP [LDAPv3, TLS]. This operation provides for TLS establish- ment in an LDAP association and is defined in terms of an LDAP extended request. The key words "MUST", "SHOULD", and "MAY" used in this document are to be interpreted as described in [Bradner97]. 3. The Start TLS Operation 3.1. Requesting TLS Establishment A client may perform a Start TLS operation by transmitting an LDAP PDU containing an ExtendedRequest [LDAPv3] specifying the OID for the Start TLS operation: 1.3.6.1.4.1.1466.20037 Hodges, Morgan, Wahl [Page 1] LDAPv3: Extension for Transport Layer Security June 1997 An LDAP ExtendedRequest is defined as follows: ExtendedRequest ::= [APPLICATION 23] SEQUENCE { requestName [0] LDAPOID, requestValue [1] OCTET STRING OPTIONAL } A Start TLS extended request is formed by setting the requestName field to the OID string given above. The requestValue field is absent. The client MUST NOT send any PDUs on this connection following this request until it receives a Start TLS extended response. When a Start TLS extended request is made, the server MUST return an LDAP PDU containing a Start TLS extended response. An LDAP Exten- dedResponse is defined as follows: ExtendedResponse ::= [APPLICATION 24] SEQUENCE { responseName [0] LDAPOID OPTIONAL, response [1] OCTET STRING OPTIONAL, standardResponse [2] LDAPResult } A Start TLS extended response MUST contain a responseName field which MUST be set to the same string as that present in the Start TLS extended request. The response field is absent. The server MUST set the resultCode of the standardResponse field to either success or one of the other values outlined in section 3.3. 3.2. "Success" Response If the standardResponse field contains a resultCode of success, this indicates that the server is willing and able to negotiate TLS. At this point the client, which has ceased to transfer LDAP requests on the con- nection, MUST either begin a TLS negotiation, or close the connection. In the former case, the client will send PDUs in the TLS Record Protocol directly over the underlying TCP bytestream to the server. After the TLS connection is established, both parties MUST individually decide whether or not to continue based on the privacy level achieved. Ascertaining the TLS connection's privacy level is implementation depen- dent, and accomplished by communicating with one's respective local TLS implementation. If the client or server decides that the level of authentication or privacy is not high enough for it to continue, it SHOULD close the TLS connection immediately after the TLS negotiation has completed, to disconnect the TLS service and return to an LDAP state (see section 5, below). This will cause the client's authorization identity to be reset to anonymous. The client MAY attempt to Start TLS again, or MAY send an unbind request, or send any other LDAP request. Hodges, Morgan, Wahl [Page 2] LDAPv3: Extension for Transport Layer Security June 1997 3.3. Response other than "success" If the standardResponse field contains a resultCode other than success, this indicates that the server is unwilling or unable to negotiate TLS. If the Start TLS extended request was not successful, the resultCode will be one of: - operationsError (operations sequencing incorrect; e.g. TLS already established) - protocolError (TLS not supported or incorrect PDU structure) - referral (this server doesn't do TLS, try this one) - unavailable (e.g. some major problem with TLS, or server is shutting down) The server MUST return operationsError if the client violates any of the Start TLS extended operation sequencing requirements described in sec- tion 4, below. If the server does not support TLS (whether by design or by current con- figuration), it MUST set the resultCode to protocolError (see section 4.1.1 of [LDAPv3]), or to referral. The server MUST include an actual referral value in the LDAP Result if it returns a resultCode of refer- ral. The client's current session is unaffected if the server does not support TLS. The client MAY proceed with any LDAP operation, or it MAY close the connection. The server MUST return unavailable if it supports TLS but cannot estab- lish a TLS connection for some reason, e.g. the certificate server not responding, it cannot contact its TLS implementation, or if the server is in process of shutting down. The client MAY retry the StartTLS opera- tion, or it MAY proceed with any other LDAP operation, or it MAY close the connection. 4. Sequencing of the Start TLS Operation The client MAY send the Start TLS extended request at any time after establishing an LDAP association, except that in the following cases the client MUST NOT send a Start TLS extended request: - if TLS is currently established on the connection, or - during a multi-stage SASL negotiation, or - if there are any LDAP operations outstanding on the connection. The result of violating any of these requirements is described above in section 3.3. Hodges, Morgan, Wahl [Page 3] LDAPv3: Extension for Transport Layer Security June 1997 The client MAY have already perfomed a Bind operation when it sends a Start TLS request, or the client might have not yet bound. If the client did not establish a TLS connection before sending any other requests, and the server requires the client to establish a TLS connection before performing a particular request, the server MUST reject that request with a confidentialityRequired or strongAuthRequired result. The client MAY send a Start TLS extended request, or it MAY choose to close the connection. 5. Closing a TLS Connection 5.1. Graceful Closure Either the client or server MAY terminate the TLS connection on an LDAP association by sending a TLS closure alert. This will leave the LDAP association intact. Before closing a TLS connection, the client MUST either wait for any outstanding LDAP operations to complete, or explicitly abandon them [LDAPv3]. After the initiator of a close has sent a closure alert, it MUST discard any TLS messages until it has received an alert from the other party. It will cease to send TLS Record Protocol PDUs, and following the reciept of the alert, MAY send and receive LDAP PDUs. The other party, if it receives a closure alert, MUST immediately transmit a TLS closure alert. It will subequently cease to send TLS Record Protocol PDUs, and MAY send and receive LDAP PDUs. 5.2. Abrupt Closure Either the client or server MAY abruptly close the entire LDAP associa- tion and any TLS connection established on it by dropping the underlying TCP connection. A server MAY beforehand send the client a Notice of Disconnection [LDAPv3] in this case. 6. Effects of TLS Establishment on the Client's Authorization Identity Upon establishment of the TLS connection onto the LDAP association, the server MAY base the client's authorization identity on the client's negotiated TLS credentials, overriding any previously established credentials and authorization identity. Otherwise, any previously esta- blished credentials and authorization identity MUST remain in force, including anonymous cedentials and identity in the case where the client had not previously bound. Hodges, Morgan, Wahl [Page 4] LDAPv3: Extension for Transport Layer Security June 1997 A client MAY explicitly request that its authenticated TLS credentials be used as the source for its LDAP authorization identity. This is accomplished after TLS establishment by invoking a Bind request of the SASL form with a negotiated mechanism name of "EXTERNAL" [SASL]. The credentials field MAY contain the client's distinguished name (as an LDAP string), or it MAY be empty. If it does contain a distinguished name, this name MUST match the authorization identity negotiated by TLS as the client's identity. It is a matter of local policy what consti- tutes a match. In the absence of local policy, the default matching pol- icy compares for equality. The server MUST reject the Bind operation with an invalidCredentials resultCode in the Bind response if they do not match. Closure of the TLS connection MUST cause the LDAP association to move to an anonymous authentication and authorization state regardless of the state established over TLS and regardless of the authentication and authorization state prior to TLS connection establishment. 7. Security Considerations The goals of using the TLS protocol with LDAP are to ensure connection confidentiality and integrity, and to optionally provide for authentica- tion. TLS expressly provides these capabilities, as described in [TLS]. All security gained via use of the Start TLS operation is gained by the use of TLS itself. The Start TLS operation, on its own, does not provide any additional security. The use of TLS does not provide or ensure for confidentiality and/or non-repudiation of the data housed by an LDAP-based directory server. Once established, TLS only provides for and ensures confidentiality and integrity of the operations and data in transit over the LDAP associa- tion, and only if the implementations on the client and server support and negotiate it. The level of security provided though the use of TLS depends directly on both the quality of the TLS implementation used and the style of usage of that implementation. Both parties SHOULD independently ascertain and consent to the privacy level achieved once TLS is established and before begining use of the TLS connection. For example, the privacy level of the TLS connection might have been negotiated down to plaintext. Client and server implementors SHOULD take measures to ensure proper protection of credentials and other confidential data where such meas- ures are not otherwise provided by the TLS implementation. Server implementors SHOULD allow for server administrators to elect whether and when connection confidentiality is required. Hodges, Morgan, Wahl [Page 5] LDAPv3: Extension for Transport Layer Security June 1997 8. Acknowledgements The authors thank Tim Howes and Paul Hoffman for their contributions to this document. 9. References [Bradner97] Scott Bradner, "Key Words for use in RFCs to Indicate Requirement Levels", Internet Draft, RFC 2119. [LDAPv3] M. Wahl, S. Kille and T. Howes, "Lightweight Directory Access Pro- tocol (v3)", Internet Draft, February, 1997. Available as draft- ietf-asid-ldapv3-protocol-04.txt. [TLS]Tim Dierks, C. Allen, "The TLS Protocol Version 1.0", Internet Draft, March 1997. Available as draft-ietf-tls-protocol-03.txt [SASL]J. Myers, "Simple Authentication and Security Layer (SASL)", Internet Draft, April 1997. Available as draft-myers-auth-sasl- 10.txt 10. Author's Address Jeff Hodges Computing & Communication Services Stanford University 115 Pine Hall Stanford, CA 94305-4122 USA Phone: +1-415-723-2452 EMail: Jeff.Hodges@Stanford.edu RL "Bob" Morgan Computing & Communication Services Stanford University 115 Pine Hall Stanford, CA 94305-4122 USA Phone: +1-415-723-9711 EMail: Bob.Morgan@Stanford.edu Mark Wahl Hodges, Morgan, Wahl [Page 6] LDAPv3: Extension for Transport Layer Security June 1997 Critical Angle Inc. 4815 W. Braker Lane #502-385 Austin, TX 78759 USA EMail: M.Wahl@critical-angle.com Hodges, Morgan, Wahl [Page 7]