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


Status of this Memo 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
documents 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 (US East Coast), (Europe), (US West Coast), or (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

2.  Conventions Used in this Document

The key words "MUST", "SHOULD", and "MAY" used in this document are to
be interpreted as described in [Bradner97]. [ReqsKeywords].

3.  The Start TLS Operation

3.1.  Requesting TLS Establishment

A client may perform a Start TLS operation by transmitting an LDAP PDU

I-D     LDAPv3: Extension for Transport Layer Security       August 1997

containing an ExtendedRequest [LDAPv3] specifying the OID for the Start
TLS operation:

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 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
resultCode 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

If the client or server decides that the level of authentication or
privacy pri-
vacy is not high enough for it to continue, it SHOULD close the TLS

I-D     LDAPv3: Extension for Transport Layer Security       August 1997

connection immediately after the TLS negotiation has completed, to
disconnect 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
     - 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

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

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 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
Disconnection Dis-
connection [LDAPv3] in this case.

6.  Effects of TLS Establishment 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.

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.

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
credentials cre-
dentials and authorization identity. Otherwise, any previously esta-
blished estab-
lished credentials and authorization identity MUST remain in force,
including anonymous cedentials 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  the a source for its LDAP authorization identity.  This is
accomplished 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 the client's  distinguished  name  (as an
LDAP  string), authorization identity, or it MAY be empty.  If it does
contain a distinguished
name, this name MUST match the authorization identity negotiated by  TLS
as an identity, the  client's  identity. It is a matter of local server uses its security policy what consti-
tutes a match. In the absence of local policy, to determine
whether the default matching pol-
icy  compares  for  equality. client is authorized to authenticate as that identity.  The
server MUST reject the Bind operation with an invalidCredentials invalidAuthorizationId
resultCode in the Bind response if  they  do the client is not match. 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

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 meas-
ures 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 and Howes, Paul Hoffman Hoffman, and John Kristian for their
contributions to this document.

9.  References

     Scott Bradner, "Key Words for use in RFCs to  Indicate  Requirement
     Levels", Internet Draft, RFC 2119.

     M. Wahl, S. Kille and T. Howes, "Lightweight Directory Access Pro-
     tocol (v3)", Internet  Draft, Draft (work in progress), February, 1997.
     Available as draft-ietf-asid-ldapv3-protocol-06.txt.

     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-

[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

[SASL]J. Myers,  "Simple  Authentication  and  Security  Layer  (SASL)",
     Internet  Draft,  April  1997.  Available as draft-myers-auth-sasl-
     10.txt draft-ietf-tls-

10.  Author's Address

   Jeff Hodges
   Computing & Communication Services
   Stanford University
   Pine Hall
   241 Panama Street
   Stanford, CA 94305-4122

   Phone: +1-415-723-2452

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

   Phone: +1-415-723-9711

   Mark Wahl
   Critical Angle Inc.
   4815 W. Braker Lane #502-385
   Austin, TX 78759