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Lightweight Directory Access Protocol (v3):
Extension for Transport Layer Security
<draft-ietf-ldapext-ldapv3-tls-00.txt>
<draft-ietf-ldapext-ldapv3-tls-01.txt>
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Comments and suggestions on this document are encouraged. Comments on
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This document expires in September 1998. January 1999.
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", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [ReqsKeywords].
3. The Start TLS Operation 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.
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
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.
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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 Refer to transfer LDAP requests on
section 4, below, for details.
3.3. Response other than "success"
If the con-
nection, MUST either begin standardResponse field contains 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 resultCode other than success,
this indicates that the TLS connection server is established, both parties MUST individually
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decide whether unwilling or not unable to continue based on the privacy level achieved.
Ascertaining negotiate TLS.
If the Start TLS connection's privacy level is implementation depen-
dent, and accomplished by communicating with one's respective local TLS
implementation.
If extended request was not successful, the client 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 decides that the level of authentication doesn't do TLS, try this one)
unavailable (e.g. some major problem with TLS, 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.
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 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
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
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4. Sequencing
including discovery of resultant security level and assertion of the
client's authorization identity.
Note that the precise effects, on a client's authorzation identity, of
establishing TLS on an LDAP association are described in detail in sec-
tion 7.
4.1. Requesting to Start TLS Operation 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 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
4.2. Starting TLS Connection
5.1. Graceful Closure
Either the client or
The server MAY terminate the TLS connection on an LDAP
association by sending a TLS closure alert. This will leave return an extended response with the LDAP
association intact.
Before closing standardResponse
field containing a TLS connection, the client MUST either wait for any
outstanding LDAP operations to complete, or explicitly abandon them
[LDAPv3].
After the initiator resultCode of a close has sent a closure alert, it MUST discard
any TLS messages until success if it has received an alert from the other party. is willing and able to
negotiate TLS. It will cease to send TLS Record Protocol PDUs, and following the
reciept of the alert, MAY send and receive LDAP PDUs.
The return other party, resultCodes, documented above, if
it receives a closure alert, is unable.
In the successful case, the client, which has ceased to transfer LDAP
requests on the connection, MUST immediately
transmit either begin a TLS closure alert. It negotiation or close
the connection. The client will subequently cease to send PDUs in the TLS Record Protocol PDUs, and MAY send and receive LDAP PDUs.
5.2. Abrupt Closure
Either
directly over the underlying transport connection to the client or server MAY abruptly close to ini-
tiate TLS negotiation [TLS].
4.3. TLS Version Negotiation
Negotiating the entire LDAP associa-
tion and any version of TLS connection established on it by dropping or SSL to be used is a part of the underlying TLS
Handshake Protocol, as documented in [TLS]. Please refer to that docu-
ment for details.
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TCP connection. A server MAY beforehand send the client a Notice of
Disconnection [LDAPv3] in this case.
6. Authentication and Authorization: Definitions and Concepts
This section defines basic terms, concepts, and interrelationships
regarding authentication, authorization, credentials, and identity.
These concepts are used in describing the use
4.4. Discovery of Resultant Security Level
After a TLS in client authenti-
cation and authorization in section 7.
6.1. Access Control Policy
An access control policy connection is a set of rules defining established on an LDAP association, both par-
ties MUST individually decide whether or not to continue based on the protection of
resources, generally in terms of
privacy level achieved. Ascertaining the capabilities of persons or other
entities accessing those resources. A common expression of an access
control policy TLS connection's privacy level
is an access control list. Security objects implementation dependent, and mechan-
isms, such as those described here, enable the expression of access con-
trol policies and their enforcement. Access control policies are typi-
cally expressed in terms of access control attributes as described
below.
6.2. Access Control Factors
A request, when it is being processed accomplished by a server, may be associated communicating with a wide variety of security-related factors (see [LDAPv3] section
4.2). The
one's respective local TLS implementation.
If the client or server uses these factors decides that the level of authentication or
privacy is not high enough for it to determine whether continue, it SHOULD gracefully
close the TLS connection immediately after the TLS negotiation has com-
pleted (see sections 5 and how 7.2, below).
The client MAY attempt to pro-
cess the Start TLS again, or MAY send an unbind
request, or send any other LDAP request. These are called access control factors (ACFs). They
might include source IP address, encryption strength, the type
4.5. Assertion of opera-
tion being requested, time Client's Authorization Identity
The client MAY, upon receipt of day, etc. Some factors may be a Start TLS extended response indicating
success, assert that a specific to
the request itself, others may authorization identity be associated with utilized in
determining the connection client's authorization status. The client accomplishes
this via
which the an LDAP Bind request is transmitted, others (e.g. time of day) may be
"environmental".
Access control policies are expressed in terms of access control fac-
tors. E.g., specifying a request having ACFs i,j,k can perform operation Y on
resource Z. The set SASL mechanism of ACFs that a server makes available for such
expressions is implementation-specific.
6.3. Authentication, Credentials, "EXTERNAL"
[SASL]. See section 7, below.
4.6. Server Identity
Authentication credentials are Check
The client SHOULD check its understanding of the evidence supplied by one party to
another, asserting server's hostname
against the server's identity of as presented in the supplying party (typically a
user) who is attempting server's Certificate
message, in order to establish an association with the other party
(typically prevent man-in-the-middle attacks.
If a server). Authentication subjectAltName extension of type dNSName is present, it SHOULD be
used as the process source of generating,
transmitting, and verifying these credentials and thus the identity they
assert. An authentication identity server's identity.
Matching is performed according to these rules:
- The client MUST use the server hostname it used to open
the LDAP connection as the value to compare against the
server name presented as expressed in a creden-
tial.
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The client MUST NOT use the server's canonical DNS name or
any other derived form of name.
- If a subjectAltName extension of type dNSName is present
in the certificate, it SHOULD be used as the source of the
server's identity.
- Matching is case-insensitive.
- The "*" wildcard character is allowed.
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There are many forms of authentication credentials -- the form used
depends upon the particular authentication mechanism negotiated by
- If present, it applies only to the
parties. For example: X.509 certificates, Kerberos tickets, simple left-most name component.
E.g. *.bar.com would match a.bar.com, b.bar.com, etc. but not bar.com.
If more than one identity and password pairs. Note that an authentication mechanism may
constrain the form of authentication identities used with it.
6.4. Authorization Identity
An authorization identity a given type is present in the certificate
(e.g. more than one dNSName name), a match in any one kind of access control factor. It the set is con-
sidered acceptable.
If the name of hostname does not match the dNSName-based identity in the certi-
ficate per the above check, user-oriented clients SHOULD either notify
the user (clients MAY give the user the opportunity to continue with the
connection in any case) or other entity that requests terminate the connection and indicate that operations be
performed. Access control policies are often expressed in terms of
authorization identities; e.g., user X can perform operation Y on
resource Z.
The authorization
the server's identity bound to an association is often exactly suspect. Automated clients SHOULD close the
same as
connection, returning and/or logging an error indicating hat the authentication
server's identity presented is suspect.
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 client, but it may
be different. SASL allows clients LDAP
association intact.
Before closing a TLS connection, the client MUST either wait for any
outstanding LDAP operations to specify 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 authorization identity
distinct alert from the authentication identity asserted by the client's
credentials. This permits agents such as proxy servers other party.
It will cease to authenticate
using their own credentials, yet request send TLS Record Protocol PDUs, and following the access privileges
reciept of the
identity for which they are proxying [SASL]. Also, 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 form of authen-
tication identity supplied by client a service like Notice of
Disconnection [LDAPv3] in this case.
6. Effects of TLS may not correspond to
the authorization identities used to express on a server's access control
policy, requiring Client's Authorization Identity
This section describes the effects on a server-specific mapping to be done. The method client's authorization identity
brought about by
which a server composes and validates establishing TLS on an LDAP association. The default
effects are described first, and next the facilities for client
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assertion of authorization identity from are discussed including error condi-
tions. Lastly, the
authentication credentials supplied by a client is implementation-
specific.
7. Effects effects of TLS on closing the Client's TLS connection are described.
Authorization Identity
7.1. Session identities and related concepts are defined in [AuthMeth].
6.1. TLS Connection Establishment Effects
6.1.1. Default Effects
Upon establishment of the TLS connection onto the LDAP association, any
previously established authentication and authorization identities MUST
remain in force, including anonymous state. This holds even in the case
where the server requests client authentication via TLS (i.e. -- e.g. requests
the client to supply its certificate during TLS negotiation). negotiation (see [TLS]).
6.1.2. Client Assertion of Authorization Identity
A client MAY explicitly either implicitly request that its LDAP authorization iden-
tity be derived from its authenticated TLS credentials or it MAY expli-
citly provide an authorization identity and assert that it be used to establish in
combination with its LDAP authenticated TLS credentials. The former is known
as an implicit assertion, and the latter as an explicit assertion.
6.1.2.1. Implicit Assertion
An implicit authorization identity. This identity assertion is accom-
plished accomplished after TLS
establishment by invoking a Bind request of the SASL form using the
"EXTERNAL" mechanism name [SASL].
The [SASL, LDAPv3] that SHALL NOT include the
optional credentials field (within octet string (found within the SaslCredentials
sequence in the Bind
Request) MAY contain an Request). The server will derive the client's
authorization identity, or it MAY identity from the authentication identity supplied in the
client's TLS credentials (typically a public key certificate) according
to local policy. The underlying mechanics of how this is accomplished
are implementation specific.
6.1.2.2. Explicit Assertion
An explicit authorization identity assertion is accomplished after TLS
establishment by invoking a Bind request of the SASL form using the
"EXTERNAL" mechanism name [SASL, LDAPv3] that SHALL include the creden-
tials octet string. This string MUST be empty. If
it does contain an identity, constructed as documented in
section 11 of [AuthMeth].
6.1.2.3. Error Conditions
For either form of assertion, the server MUST verify that the client's
authenticated
authentication identity as supplied in its TLS credentials are is permitted
to use that be mapped to the asserted authorization identity. The server MUST reject the Bind operation with an
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invalidAuthorizationId
reject the Bind operation with an invalidCredentials resultCode in the
Bind response if the client is not so authorized. If the credentials field is empty, the server bases
the client's authorization identity on the The LDAP association's
authentication identity sup-
plied and authorization identity (if any) which were
in the client's effect after TLS credentials (typically a public-key certifi-
cate).
If establishment but prior to making the Bind request,
MUST remain in force.
Additionally, with either form of assertion, if a TLS session has not
been established between the client and server
(and prior to making the SASL
EXTERNAL Bind request and there is no other external source of authentication credentials), authenti-
cation credentials (e.g. IP-level security RFC 1825), or if, during the
process of establishing the TLS session, the server did not request the
client's authentication credentials, the SASL EXTER-
NAL EXTERNAL bind MUST fail, fail
with a result code of inappropriateAuthentication.
7.2. Session Any authentication
identity and authorization identity, as well as TLS connection, which
were in effect prior to making the Bind request, MUST remain in force.
6.2. TLS Connection 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.
8. invalidAuthorizationId Error Code
A value of the resultCode field of the LDAPResult construct is defined:
invalidAuthorizationId (55)
- invalidAuthorizationId: the authorization identity requested
is invalid or is not consistent with the supplied
authentication credentials.
9. Conformance Requirements
The TLS standard [TLS] does not mandate that the client must have a cer-
tificate -- i.e. client-side authentication is optional within the
bounds of the TLS specification. However, clients conformant to this
specification MUST have the capability to supply a client side certifi-
cate to the server. Additionally, they MUST implement the mandatory
cipher suite specified in [TLS].
10.
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.
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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
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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.
11.
8. Acknowledgements
The authors thank Tim Howes, Paul Hoffman, John Kristian, and Harald
Alvestrand for their contributions to this document.
12.
9. References
[ABNF] D. Crocker, Ed., P. Overell. "Augmented BNF for Syntax
Specifications: ABNF". RFC 2234.
[AuthMeth] M. Wahl, H. Alvestrand, J. Hodges, R. Morgan. "Authenti-
cation Methods for LDAP". INTERNET-DRAFT, Work In Pro-
gress. draft-ietf-ldapext-authmeth-02.txt
[LDAPv3] M. Wahl, S. Kille and T. Howes, Howes. "Lightweight Directory
Access Pro-
tocol (v3)", Protocol (v3)". RFC 2251.
[ReqsKeywords] Scott Bradner, Bradner. "Key Words for use in RFCs to Indicate
Requirement
Levels", Levels". RFC 2119.
[SASL]J. Myers,
[SASL] J. Myers. "Simple Authentication and Security Layer (SASL)",
(SASL)". RFC 2222.
[TLS]Tim
[TLS] Tim Dierks, C. Allen, Allen. "The TLS Protocol Version 1.0", RFC 22??.
13. 1.0".
INTERNET-DRAFT, Work In Progress. draft-ietf-tls-
protocol-05.txt
10. Authors' Addresses
Jeff Hodges
Computing & Communication Services
Stanford University
Pine Hall
241 Panama Street
Stanford, CA 94305-4122
USA
Phone: +1-650-723-2452
EMail: Jeff.Hodges@Stanford.edu
RL "Bob" Morgan
Hodges, Morgan, Wahl [Page 8] 9]
I-D LDAPv3: Extension for Transport Layer Security March June 1998
Stanford, CA 94305-4122
USA
Phone: +1-650-723-2452
EMail: Jeff.Hodges@Stanford.edu
RL "Bob" Morgan
Computing & Communication Services
Stanford University
Pine Hall
241 Panama Street
Stanford, CA 94305-4122
USA
Phone: +1-650-723-9711
EMail: Bob.Morgan@Stanford.edu
Mark Wahl
Critical Angle
Innosoft International, Inc.
4815 W. Braker Lane #502-385
8911 Capital of Texas Hwy, Suite 4140
Austin, TX 78759
USA
Phone: +1 626 919 3600
EMail: M.Wahl@critical-angle.com Mark.Wahl@innosoft.com
-----------------------------------
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Hodges, Morgan, Wahl [Page 10]
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