Network Working Group J. Hodges
Request for Comments: 2830 Oblix Inc.
Category: Standards Track R. Morgan
Univ of Washington
M. Wahl
Sun Microsystems, Inc.
May 2000
Lightweight Directory Access Protocol (v3):
Extension for Transport Layer Security
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This document defines the "Start Transport Layer Security (TLS)
Operation" for LDAP [LDAPv3, TLS]. This operation provides for TLS
establishment in an LDAP association and is defined in terms of an
LDAP extended request.
1. Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [ReqsKeywords].
2. The Start TLS Request
This section describes the Start TLS extended request and extended
response themselves: how to form the request, the form of the
response, and enumerates the various result codes the client MUST be
prepared to handle.
The section following this one then describes how to sequence an
overall Start TLS Operation.
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RFC 2830 LDAPv3: Extension for Transport Layer Security May 2000
2.1. 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
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
ExtendedResponse is defined as follows:
ExtendedResponse ::= [APPLICATION 24] SEQUENCE {
COMPONENTS OF LDAPResult,
responseName [10] LDAPOID OPTIONAL,
response [11] OCTET STRING OPTIONAL }
A Start TLS extended response MUST contain a responseName field which
MUST be set to the same string as that in the responseName field
present in the Start TLS extended request. The response field is
absent. The server MUST set the resultCode field to either success or
one of the other values outlined in section 2.3.
2.2. "Success" Response
If the ExtendedResponse contains a resultCode of success, this
indicates that the server is willing and able to negotiate TLS. Refer
to section 3, below, for details.
2.3. Response other than "success"
If the ExtendedResponse contains a resultCode other than success,
this indicates that the server is unwilling or unable to negotiate
TLS.
Hodges, et al. Standards Track [Page 2]
RFC 2830 LDAPv3: Extension for Transport Layer Security May 2000
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
section 3, below.
If the server does not support TLS (whether by design or by current
configuration), 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 referral. 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
establish 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 operation, or it MAY proceed with any other LDAP
operation, or it MAY close the connection.
3. Sequencing of the Start TLS Operation
This section describes the overall procedures clients and servers
MUST follow for TLS establishment. These procedures take into
consideration various aspects of the overall security of the LDAP
association including discovery of resultant security level and
assertion of the client's authorization identity.
Note that the precise effects, on a client's authorization identity,
of establishing TLS on an LDAP association are described in detail in
section 5.
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RFC 2830 LDAPv3: Extension for Transport Layer Security May 2000
3.1. Requesting to Start TLS on an LDAP Association
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 a resultCode of
operationsError, as described above in section 2.3.
The client MAY have already performed a Bind operation when it sends
a Start TLS request, or the client might have not yet bound.
If the client did not establish a TLS connection before sending any
other requests, and the server requires the client to establish a TLS
connection before performing a particular request, the server MUST
reject that request with a confidentialityRequired or
strongAuthRequired result. The client MAY send a Start TLS extended
request, or it MAY choose to close the connection.
3.2. Starting TLS
The server will return an extended response with the resultCode of
success if it is willing and able to negotiate TLS. It will return
other resultCodes, documented above, if it is unable.
In the successful case, the client, which has ceased to transfer LDAP
requests on the connection, MUST either begin a TLS negotiation or
close the connection. The client will send PDUs in the TLS Record
Protocol directly over the underlying transport connection to the
server to initiate TLS negotiation [TLS].
3.3. TLS Version Negotiation
Negotiating the version of TLS or SSL to be used is a part of the TLS
Handshake Protocol, as documented in [TLS]. Please refer to that
document for details.
3.4. Discovery of Resultant Security Level
After a TLS connection is established on an LDAP association, both
parties MUST individually decide whether or not to continue based on
the privacy level achieved. Ascertaining the TLS connection's privacy
level is implementation dependent, and accomplished by communicating
with one's respective local TLS implementation.
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RFC 2830 LDAPv3: Extension for Transport Layer Security May 2000
If the client or server decides that the level of authentication or
privacy is not high enough for it to continue, it SHOULD gracefully
close the TLS connection immediately after the TLS negotiation has
completed (see sections 4.1 and