ASID Working Group Jeff Hodges, Stanford INTERNET-DRAFT RL "Bob" Morgan, Stanford Category: Standards Track Mark Wahl, Critical Angle Inc. August, 1997 Lightweight Directory Access Protocol (v3): Extension for Transport Layer Security draft-ietf-asid-ldapv3-tls-02.txt Status of this Document 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 doc- uments 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). This document expires in February 1998. 1. 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. 2. Conventions Used in this Document The key words "MUST", "SHOULD", and "MAY" used in this document are to be interpreted as described in [ReqsKeywords]. 3. The Start TLS Operation 3.1. Requesting TLS Establishment A client may perform a Start TLS operation by transmitting an LDAP PDU Hodges, Morgan, Wahl [Page 1] I-D LDAPv3: Extension for Transport Layer Security August 1997 containing an ExtendedRequest [LDAPv3] specifying the OID for the Start TLS operation: 1.3.6.1.4.1.1466.20037 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 Extende- dResponse 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 result- Code 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 pri- vacy is not high enough for it to continue, it SHOULD close the TLS Hodges, Morgan, Wahl [Page 2] I-D LDAPv3: Extension for Transport Layer Security August 1997 connection immediately after the TLS negotiation has completed, to dis- connect 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. 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 Hodges, Morgan, Wahl [Page 3] I-D LDAPv3: Extension for Transport Layer Security August 1997 - 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. 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 trans- mit 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 Dis- connection [LDAPv3] in this case. 6. Effects of TLS on the Client's Authorization Identity This section first defines terms, and then describes the effects of TLS establishment and closure on the client's authorization identity in terms of those definitions. Hodges, Morgan, Wahl [Page 4] I-D LDAPv3: Extension for Transport Layer Security August 1997 6.1. Authorization-Related Definitions 6.1.1. Security policy A security policy is a set of rules defining the protection of resources, generally in terms of the capabilities of persons or other agents accessing those resources. A common example of a security policy is an access control list. Security mechanisms such as those described here work in support of the enforcement of security policies. 6.1.2. Authentication, Credentials, Identity An authentication credential is the evidence supplied by one party to another, asserting the identity of the supplying party (typically a user) who is attempting to establish an association with the other party (typically a server). Authentication is the process of generating, transmitting, and verifying these credentials. An authentication iden- tity is the name presented in a credential. There are many forms of authentication credentials -- the form used depends upon the particular authentication mechanism negotiated by the parties. For example: X.509 certificates, Kerberos tickets, simple identity and password pairs. Note that an authentication mechanism may constrain the form of authentication identities used with it. 6.1.3. Authorization Identity An authorization identity is a name used in expressions of security policies, in particular the name of a user or other agent that may access a resource or request that an operation be performed. Typically a server, when processing a request, will use its security policies and the authorization identity associated with the request to determine whether and how to process the request. The authorization identity bound to an association is often exactly the same as the authentication identity presented by the client, but it MAY be different. SASL allows clients to specify an authorization identity distinct from the authentication identity supplied by the client's cre- dentials. This permits agents such as proxy servers to authenticate using their own credentials, yet request the access privileges of the identity for which they are proxying [SASL]. Also, the form of authen- tication identity supplied by a service like TLS may not correspond to the authorization identities used to express a server's security policy, requiring a server-specific mapping to be done. The method by which a server composes and validates an authorization identity from the creden- tials and identities supplied by a client is implementation-specific. Hodges, Morgan, Wahl [Page 5] I-D LDAPv3: Extension for Transport Layer Security August 1997 6.2. Session Establishment Effects 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 cre- dentials and authorization identity. Otherwise, any previously estab- lished credentials and authorization identity MUST remain in force, including anonymous credentials and identity in the case where the client had not previously bound. A client MAY explicitly request that its authenticated TLS credentials be used as a source for its LDAP authorization identity. This is accom- plished after TLS establishment by invoking a Bind request of the SASL form with a negotiated mechanism name of "EXTERNAL" [SASL]. The credentials field (in the SaslCredentials field in the Bind Request) MAY contain an authorization identity, or it MAY be empty. If it does contain an identity, the server uses its security policy to determine whether the client is authorized to authenticate as that identity. The server MUST reject the Bind operation with an invalidAuthorizationId resultCode in the Bind response if the client is not so authorized. 6.3. Session Closure Effects 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 Hodges, Morgan, Wahl [Page 6] I-D LDAPv3: Extension for Transport Layer Security August 1997 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 mea- sures are not otherwise provided by the TLS implementation. Server implementors SHOULD allow for server administrators to elect whether and when connection confidentiality is required. 8. Acknowledgements The authors thank Tim Howes, Paul Hoffman, and John Kristian for their contributions to this document. 9. References [LDAPv3] M. Wahl, S. Kille and T. Howes, "Lightweight Directory Access Pro- tocol (v3)", Internet Draft (work in progress), February, 1997. Available as draft-ietf-asid-ldapv3-protocol-06.txt. [ReqsKeywords] Scott Bradner, "Key Words for use in RFCs to Indicate Requirement Levels", RFC 2119. [SASL]J. Myers, "Simple Authentication and Security Layer (SASL)", Internet Draft (work in progress), April 1997. Available as draft- myers-auth-sasl-11.txt [TLS]Tim Dierks, C. Allen, "The TLS Protocol Version 1.0", Internet Draft (work in progress), March 1997. Available as draft-ietf-tls- protocol-03.txt 10. Author's Address Jeff Hodges Computing & Communication Services Stanford University Pine Hall 241 Panama Street Stanford, CA 94305-4122 USA Phone: +1-415-723-2452 EMail: Jeff.Hodges@Stanford.edu Hodges, Morgan, Wahl [Page 7] I-D LDAPv3: Extension for Transport Layer Security August 1997 RL "Bob" Morgan Computing & Communication Services Stanford University Pine Hall 241 Panama Street Stanford, CA 94305-4122 USA Phone: +1-415-723-9711 EMail: Bob.Morgan@Stanford.edu Mark Wahl Critical Angle Inc. 4815 W. Braker Lane #502-385 Austin, TX 78759 USA EMail: M.Wahl@critical-angle.com Hodges, Morgan, Wahl [Page 8]