One document matched: draft-ietf-asid-ldapv3-tls-00.txt
ASID Working Group Jeff Hodges, Stanford
INTERNET-DRAFT RL "Bob" Morgan, Stanford
Mark Wahl, Critical Angle Inc.
May, 1997
Lightweight Directory Access Protocol (v3):
Extension for Transport Layer Security
draft-ietf-asid-ldapv3-tls-00.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
operation.
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:
[To Be Determined]
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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 begin a TLS negotiation. 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
and LDAP connection as discussed in section 5 [see Open Issues, below].
3.3. Response other than "success"
If the standardResponse field contains a resultCode other than success,
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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)
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 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 once the
LDAP association has been established, except during a SASL negotiation,
or if TLS is currently established on the connection.
The client may have already completed the bind process when it sends a
Start TLS request, or the client may 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
Closing a TLS connection requires termination of the overlying LDAP
association [see Open Issues, below]. The TLS protocol interactions for
TLS closure are described in [TLS]. The LDAP operations specified below
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LDAPv3: Extension for Transport Layer Security May 1997
are described in [LDAPv3].
5.1. Client-initiated Closure
A client MAY initiate TLS, and thus LDAP, connection closure at any
time. It MAY initiate the termination by first performing an LDAP Unbind
Operation. It MUST then initiate TLS and underlying transport closure
according to the procedures required by the particular TLS implementa-
tion being utilized.
5.2. Server-initiated Closure
A server MAY initiate TLS, and thus LDAP, connection closure at any
time. It SHOULD first send an LDAP Notice of Disconnection with the
appropriate resultCode value to the client. It MUST then immediately
initiate TLS and underlying transport closure according to the pro-
cedures required by the particular TLS implementation being utilized.
6. Effects of TLS Establishment on an LDAP Connection
The establishment of TLS into the LDAP protocol stack causes any out-
standing requests from the client to be implicitly abandoned. However,
it does not affect the authentication credentials of the client nor its
associated authorization identity. If the client had bound to the
server previously on this association, that authorization identity MUST
remain in force. If the client had not bound, then the connection MUST
remain in an anonymous authentication and authorization state.
The client MAY request that its authenticated TLS credentials be used as
the source for its LDAP authorization identity, or it MAY request use of
other credentials.
Requesting that the server use the negotiated TLS credentials for LDAP
authorization is accomplished by invoking a Bind request of the SASL
form with a negotiated mechanism name of "EXTERNAL" [SASL]. The creden-
tials field MAY contain the client's distinguished name (as an LDAP
string). If it does contain a distinguished name, this name MUST match
that negotiated by TLS as the client's identity. The client MAY leave
the credentials field empty.
The termination of TLS MUST cause the connection to move to an anonymous
authentication and authorization state irregardless of the state esta-
blished over TLS and irregardless of the authentication and authoriza-
tion state prior to TLS connection establishment.
7. Security Considerations
The goals of using the TLS protocol with LDAP are to ensure connection
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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.
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 and for what
portions of the DIT (served by the server) it applies to.
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8. 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
9. Open Issues
9.1. TLS Closure
[TLS] discusses TLS closure in section 7.2.1. This section implies that
closing a TLS connection assumes closure of the underlying transport.
Thus, closing TLS, but retaining both the overlying application layer
(LDAP, in this case) and the underlying transport is not explicitly sup-
ported.
Modifications to [TLS] are required if there are requirements for con-
tinuing an LDAP association across a TLS connection closure.
Below is suggested alternative text for the "Closing a TLS Connection"
section of this document that COULD be used if [TLS] is so modified:
Either the client or server MAY terminate the TLS service on the
connection by sending a TLS closure alert. TLS closure has the
effect of abandoning any outstanding LDAP protocol requests.
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.
Additionally, below is suggested alternative text for the last paragraph
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of the "Success Response" section:
If the client or server decides that the level of authentication or
privacy is not high enough for it to continue, it SHOULD send a TLS
closure alert immediately after the TLS negotiation has completed,
to disconnect the TLS service and return to an LDAP state. (This
will cause the authorization 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.
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
Critical Angle Inc.
4815 W. Braker Lane #502-385
Austin, TX 78759
USA
EMail: M.Wahl@critical-angle.com
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