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Internet-Draft Editor: R. Harrison
Intended Category: Draft Standard Novell, Inc.
Document: draft-ietf-ldapbis-authmeth-05.txt March 2003
Obsoletes: RFC 2829, RFC 2830
LDAP: Authentication Methods
and
Connection Level Security Mechanisms
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
This document is intended to be, after appropriate review and
revision, submitted to the RFC Editor as a Standard Track document.
Distribution of this memo is unlimited. Technical discussion of
this document will take place on the IETF LDAP Extension Working
Group mailing list <ietf-ldapbis@OpenLDAP.org>. Please send
editorial comments directly to the author
<roger_harrison@novell.com>.
Internet-Drafts are working documents 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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-
Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document describes LDAPv3 (Lightweight Directory Access
Protocol v3) authentication methods and connection level security
mechanisms that are required of all conforming LDAPv3 server
implementations and makes recommendations for combinations of these
mechanisms to be used in various deployment circumstances.
Among the mechanisms described are
- various forms of authentication including anonymous
authentication, password-based authentication, and certificate
based authentication
- the use of SASL mechanisms with LDAPv3
- the use of TLS (Transport Layer Security) with LDAPv3
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Authentication Methods for LDAPv3
- the various authentication and authorization states through
which a connection to an LDAP server may pass and the actions
that trigger these state changes.
1. Conventions Used in this Document
1.1. Glossary of Terms
The following terms are used in this document. To aid the reader,
these terms are defined here.
- "user" represents any application which is an LDAP client using
the directory to retrieve or store information.
- "LDAP association" is used to distinguish the LDAP-level
connection from any underlying TLS-level connection that may or
may not exist.
1.2. Security Terms and Concepts
In general, security terms in this document are used consistently
with the definitions provided in [RFC2828]. In addition, several
terms and concepts relating to security, authentication, and
authorization are presented in Appendix B of this document. While
the formal definition of these terms and concepts is outside the
scope of this document, an understanding of them is prerequisite to
understanding much of the material in this document. Readers who are
unfamiliar with security-related concepts are encouraged to review
Appendix B before reading the remainder of this document.
1.3. Keywords
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 RFC 2119 [RFC2119].
2. Introduction
This document is an integral part of the LDAP Technical
Specification [ROADMAP]. This document replaces RFC 2829 and
portions of RFC 2830. Changes to RFC 2829 are summarized in Appendix
C and changes to RFC 2830 are summarized in Appendix D.
LDAPv3 is a powerful access protocol for directories. It offers
means of searching, retrieving and manipulating directory content,
and ways to access a rich set of security functions.
It is vital that these security functions be interoperable among all
LDAP clients and servers on the Internet; therefore there has to be
a minimum subset of security functions that is common to all
implementations that claim LDAPv3 conformance.
Basic threats to an LDAP directory service include:
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(1) Unauthorized access to directory data via data-retrieval
operations,
(2) Unauthorized access to reusable client authentication
information by monitoring others' access,
(3) Unauthorized access to directory data by monitoring others'
access,
(4) Unauthorized modification of directory data,
(5) Unauthorized modification of configuration information,
(6) Unauthorized or excessive use of resources (denial of service),
and
(7) Spoofing of directory: Tricking a client into believing that
information came from the directory when in fact it did not,
either by modifying data in transit or misdirecting the client's
connection.
Threats (1), (4), (5) and (6) are due to hostile clients. Threats
(2), (3) and (7) are due to hostile agents on the path between
client and server or hostile agents posing as a server.
The LDAP protocol suite can be protected with the following security
mechanisms:
(1) Client authentication by means of the SASL [RFC2222] mechanism
set, possibly backed by the TLS [RFC2246] credentials exchange
mechanism,
(2) Client authorization by means of access control based on the
requestor's authenticated identity,
(3) Data integrity protection by means of the TLS protocol or SASL
mechanisms that provide data integrity services,
(4) Data confidentiality protection against snooping by means of the
TLS protocol or SASL mechanisms that provide data
confidentiality services,
(5) Server resource usage limitation by means of administrative
service limits configured on the server, and
(6) Server authentication by means of the TLS protocol or SASL
mechanism.
At the moment, imposition of access controls is done by means
outside the scope of the LDAPv3 protocol.
3. Rationale for LDAPv3 Security Mechanisms
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It seems clear that allowing any implementation, faced with the
above requirements, to simply pick and choose among the possible
alternatives is not a strategy that is likely to lead to
interoperability. In the absence of mandates, clients will be
written that do not support any security function supported by the
server, or worse, they will support only mechanisms like the LDAPv3
simple bind using clear text passwords that provide inadequate
security for most circumstances.
Given the presence of the Directory, there is a strong desire to see
mechanisms where identities take the form of an LDAP distinguished
name [LDAPDN] and authentication data can be stored in the
directory. This means that this data must be updated outside the
protocol or only updated in sessions well protected against
snooping. It is also desirable to allow authentication methods to
carry authorization identities based on existing--non-LDAP DN--forms
of user identities for backwards compatibility with non-LDAP-based
authentication services.
The set of security mechanisms provided in LDAPv3 and described in
this document is intended to meet the security needs for a wide
range of deployment scenarios and still provide a high degree of
interoperability among various LDAPv3 implementations and
deployments. Appendix A contains example deployment scenarios that
list the mechanisms that might be used to achieve a reasonable level
of security in various circumstances.
4. Bind Operation
The Bind operation defined in section 4.2 of [Protocol] allows
authentication information to be exchanged between the client and
server.
4.1. Unbound Connection Treated as Anonymous ("Implied Anonymous Bind")
Unlike LDAP version 2, the client need not send a Bind Request in
the first PDU of the connection. The client may send any operation
request prior to binding, and the server MUST treat it as if it had
been performed after an anonymous bind operation. If the server
requires that the client bind before browsing or modifying the
directory, the server MAY reject a request other than binding,
unbinding or an extended request with the "operationsError" result.
4.2. Simple Authentication
The simple authentication option provides minimal authentication
facilities, with the contents of the authentication field consisting
only of a cleartext password. Note that the use of cleartext
passwords is strongly discouraged over open networks when the
underlying transport service cannot guarantee confidentiality (see
section 8).
4.3. SASL Authentication
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The sasl authentication option allows for any mechanism defined for
use with SASL [RFC2222] not specifically prohibited by this document
(see section 4.3.1).
Clients sending a bind request with the sasl choice selected SHOULD
NOT send a value in the name field. Servers receiving a bind request
with the sasl choice selected SHALL ignore any value in the name
field.
The mechanism field in SaslCredentials contains the name of the
mechanism. The credentials field contains the arbitrary data used
for authentication, inside an OCTET STRING wrapper. Note that unlike
some Internet application protocols where SASL is used, LDAP is not
text-based, thus no Base64 transformations are performed on the
credentials.
If any SASL-based integrity or confidentiality services are enabled,
they take effect following the transmission by the server and
reception by the client of the final BindResponse with a resultCode
of success.
If a SASL security layer is negotiated, the client MUST discard all
information about the server fetched prior to the initiation of the
SASL negotiation. If the client is configured to support multiple
SASL mechanisms, it SHOULD fetch the supportedSASLmechanisms list
both before and after the SASL security layer is negotiated. This
allows the client to detect active attacks that remove supported
SASL mechanisms from the supportedSASLMechanisms list and allows the
client to ensure that it is using the best mechanism supported by
both client and server. (This requirement is a SHOULD to allow for
environments where the supportedSASLMechanisms list is provided to
the client through a different trusted source, e.g. as part of a
digitally signed object.)
The client can request that the server use authentication
information from a lower layer protocol by using the SASL EXTERNAL
mechanism (see section 5.2.2.).
4.3.1. Use of ANONYMOUS and PLAIN SASL Mechanisms
As LDAP includes native anonymous and plaintext authentication
methods, the "ANONYMOUS" and "PLAIN" SASL mechanisms are not used
with LDAP. If an authorization identity of a form different from a
DN is requested by the client, a data confidentiality mechanism that
protects the password in transit should be used.
4.3.2. Use of EXTERNAL SASL Mechanism
The "EXTERNAL" SASL mechanism can be used to request the LDAP server
make use of security credentials exchanged by a lower layer. If a
TLS session has not been established between the client and server
prior to making the SASL EXTERNAL Bind request and there is no other
external source of authentication credentials (e.g. IP-level
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security [RFC2401]), or if during the process of establishing the
TLS session, the server did not request the client's authentication
credentials, the SASL EXTERNAL bind MUST fail with a resultCode of
inappropriateAuthentication. Any client authentication and
authorization state of the LDAP association is lost, so the LDAP
association is in an anonymous state after the failure (see
[Protocol] section 4.2.1).
4.3.3. Other SASL Mechanisms
Other SASL mechanisms may be used with LDAP, but their usage is not
considered in this document.
4.4. SASL Authorization Identity
The authorization identity is carried as part of the SaslCredentials
credentials field in the Bind request and response.
When the "EXTERNAL" SASL mechanism is being negotiated, if the
credentials field is present, it contains an authorization identity
of the authzId form described below.
Other mechanisms define the location of the authorization identity
in the credentials field.
4.4.1. Authorization Identity Syntax
The authorization identity is a string in the UTF-8 character set,
corresponding to the following ABNF grammar [RFC2234]:
; Specific predefined authorization (authz) id schemes are
; defined below -- new schemes may be defined in the future.
authzId = dnAuthzId / uAuthzId
DNCOLON = %x64 %x6e %x3a ; "dn:"
UCOLON = %x75 %x3a ; "u:"
; distinguished-name-based authz id.
dnAuthzId = DNCOLON dn
dn = utf8string ; with syntax defined in [LDAPDN] section 3.
; unspecified authorization id, UTF-8 encoded.
uAuthzId = UCOLON userid
userid = utf8string ; syntax unspecified
The dnAuthzId choice allows client applications to assert
authorization identities in the form of a distinguished name. The
decision to allow or disallow an authentication identity to have
access to the requested authorization identity is a matter of local
policy ([SASL] section 4.2). For this reason there is no requirement
that the asserted dn be that of an entry in directory.
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The uAuthzId choice allows for compatibility with client
applications that wish to assert an authorization identity to a
local directory but do not have that identity in distinguished name
form. The format of utf8string is defined as only a sequence of UTF-
8 encoded ISO 10646 characters, and further interpretation is
subject to prior agreement between the client and server.
For example, the userid could identify a user of a specific
directory service, or be a login name or the local-part of an RFC
822 email address. In general, a uAuthzId MUST NOT be assumed to be
globally unique.
Additional authorization identity schemes MAY be defined in future
versions of this document.
4.5. SASL Service Name for LDAP
For use with SASL [RFC2222], a protocol must specify a service name
to be used with various SASL mechanisms, such as GSSAPI. For LDAP,
the service name is "ldap", which has been registered with the IANA
as a GSSAPI service name.
4.6. SASL Integrity and Privacy Protections
Any negotiated SASL integrity and privacy protections SHALL start on
the first octet of the first LDAP PDU following successful
completion of the SASL bind operation. If lower level security layer
is negotiated, such as TLS, any SASL security services SHALL be
layered on top of such security layers regardless of the order of
their negotiation.
5. Start TLS Operation
The Start Transport Layer Security (StartTLS) operation defined in
section 4.13 of [Protocol] provides the ability to establish
Transport Layer Security [RFC2246] on an LDAP association.
5.1. 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 5.5.
5.1.1. 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:
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- 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 [Protocol] section 14.3.2.2.
In particular, there is no requirement that the client have or have
not already performed a Bind operation before sending a Start TLS
operation request. 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 by sending a resultCode of
confidentialityRequired or strongAuthRequired. In response, the
client MAY send a Start TLS extended request, or it MAY choose to
close the connection.
5.1.2. 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 in [Protocol] section 4.13.2.2) if it
is unable to do so.
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 [RFC2246].
5.1.3. TLS Version Negotiation
Negotiating the version of TLS or SSL to be used is a part of the
TLS Handshake Protocol, as documented in [RFC2246]. Please refer to
that document for details.
5.1.4. 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.
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 [Protocol] section 4.13.3.1 and section 5.2.3 below).
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If the client decides to continue, it MAY attempt to Start TLS
again, it MAY send an unbind request, or it MAY send any other LDAP
request.
5.1.5. Assertion of Client's Authorization Identity
The client MAY, upon receipt of a Start TLS response indicating
success, assert that a specific authorization identity be utilized
in determining the client's authorization status. The client
accomplishes this via an LDAP Bind request specifying a SASL
mechanism of "EXTERNAL" [RFC2222] (see section 5.5.1.2 below).
5.1.6. Server Identity Check
The client MUST check its understanding of the server's hostname
against the server's identity as presented in the server's
Certificate message, in order to prevent man-in-the-middle attacks.
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 as
expressed in the server's certificate. The client MUST NOT use
the any other derived form of name including the server's
canonical DNS 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. If present, it applies
only to the left-most name component.
For example, *.bar.com would match a.bar.com and b.bar.com, but it
would not match a.x.bar.com nor would it match bar.com. If more
than one identity of a given type is present in the certificate
(e.g. more than one dNSName name), a match in any one of the set is
considered acceptable.
If the hostname does not match the dNSName-based identity in the
certificate 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 terminate the
connection and indicate that the server's identity is suspect.
Automated clients SHOULD close the connection, returning and/or
logging an error indicating that the server's identity is suspect.
Beyond the server identity checks described in this section, clients
SHOULD be prepared to do further checking to ensure that the server
is authorized to provide the service it is observed to provide. The
client MAY need to make use of local policy information.
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5.1.7. Refresh of Server Capabilities Information
Upon TLS session establishment, the client MUST discard all
information about the server fetched prior to the initiation of the
TLS negotiation and MUST refresh any cached server capabilities
information (e.g. from the server's root DSE; see section 3.4 of
[Protocol]). This is necessary to protect against active-
intermediary attacks that may have altered any server capabilities
information retrieved prior to TLS establishment.
The server MAY advertise different capabilities after TLS
establishment. In particular, the value of supportedSASLMechanisms
MAY be different after TLS has been negotiated (specifically, the
EXTERNAL mechanism or the proposed PLAIN mechanism are likely to
only be listed after a TLS negotiation has been performed).
5.2. Effects of TLS on a Client's Authorization Identity
This section describes the effects on a client's authorization
identity brought about by establishing TLS on an LDAP association.
The default effects are described first, and next the facilities for
client assertion of authorization identity are discussed including
error conditions. Finally, the effects of closing the TLS connection
are described.
Authorization identities and related concepts are described in
Appendix B.
5.2.1. Default Effects
Upon establishment of the TLS session 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 --
e.g. requests the client to supply its certificate during TLS
negotiation (see [RFC2246]).
5.2.2. Client Assertion of Authorization Identity
A client MAY either implicitly request that its LDAP authorization
identity be derived from its authenticated TLS credentials or it MAY
explicitly provide an authorization identity and assert that it be
used in combination with its authenticated TLS credentials. The
former is known as an implicit assertion, and the latter as an
explicit assertion.
5.2.2.1. Implicit Assertion
An implicit authorization identity assertion is accomplished after
TLS establishment by invoking a Bind request of the SASL form using
the "EXTERNAL" mechanism name [RFC2222] [Protocol] that SHALL NOT
include the optional credentials octet string (found within the
SaslCredentials sequence in the Bind Request). The server will
derive the client's authorization identity from the authentication
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Authentication Methods for LDAPv3
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.
5.2.2.2. 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 [RFC2222] [Protocol] that SHALL
include the credentials octet string. This string MUST be
constructed as documented in section 4.4.1.
5.2.2.3. Error Conditions
For either form of assertion, the server MUST verify that the
client's authentication identity as supplied in its TLS credentials
is permitted to be mapped to the asserted authorization identity.
The server MUST reject the Bind operation with an invalidCredentials
resultCode in the Bind response if the client is not so authorized.
Additionally, with either form of assertion, if a TLS session has
not been established between the client and server prior to making
the SASL EXTERNAL Bind request and there is no other external source
of authentication credentials (e.g. IP-level security [RFC2401]), or
if during the process of establishing the TLS session, the server
did not request the client's authentication credentials, the SASL
EXTERNAL bind MUST fail with a result code of
inappropriateAuthentication.
After the above Bind operation failures, any client authentication
and authorization state of the LDAP association is lost (see
[Protocol] section 4.2.1), so the LDAP association is in an
anonymous state after the failure. The TLS session state is
unaffected, though a server MAY end the TLS session, via a TLS
close_notify message, based on the Bind failure (as it MAY at any
time).
5.2.3. TLS Connection Closure Effects
Closure of the TLS session 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 session establishment.
6. LDAP Association State Transition Tables
To comprehensively diagram the various authentication and TLS states
through which an LDAP association may pass, this section provides a
state transition table to represent a state diagram for the various
states through which an LDAP association may pass during the course
of its existence and the actions that cause these changes in state.
6.1. LDAP Association States
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The following table lists the valid LDAP association states and
provides a description of each state. The ID for each state is used
in the state transition table in section 6.4.
ID State Description
-- --------------------------------------------------------------
S1 no Auth ID
no AuthZ ID
[TLS: no Creds, OFF]
S2 no Auth ID
no AuthZ ID
[TLS: no Creds, ON]
S3 no Auth ID
no AuthZ ID
[TLS: Creds Auth ID "I", ON]
S4 Auth ID = Xn
AuthZ ID= Y
[TLS: no Creds, OFF]
S5 Auth ID = Xn
AuthZ ID= Yn
[TLS: no Creds, ON]
S6 Auth ID = Xn
AuthZ ID= Yn
[TLS: Creds Auth ID "I", ON]
S7 Auth ID = I
AuthZ ID= J
[TLS: Creds Auth ID "I", ON]
S8 Auth ID = I
AuthZ ID= K
[TLS: Creds Auth ID "I", ON]
6.2. Actions that Affect LDAP Association State
The following table lists the actions that can affect the state of
an LDAP association. The ID for each action is used in the state
transition table in section 6.4.
ID Action
-- ------------------------------------------------
A1 Client binds anonymously
A2 Inappropriate authentication: client attempts an anonymous
bind or a bind without supplying credentials to a server that
requires the client to provide some form of credentials.
A3 Client Start TLS request
Server: client auth NOT required
A4 Client: Start TLS request
Server: client creds requested
Client: [TLS creds: Auth ID "I"]
A5 Client or Server: send TLS closure alert ([Protocol] section
X)
A6 Client: Bind w/simple password or SASL mechanism (e.g. DIGEST-
MD5 password, Kerberos, etc. -<2D> except EXTERNAL [Auth ID "X"
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maps to AuthZ ID "Y"]
A7 Client Binds SASL EXTERNAL with credentials: AuthZ ID "J"
[Explicit Assertion (section 5.2.1.2.2)]
A8 Client Bind SASL EXTERNAL without credentials [Implicit
Assertion (section 5.2 .1.2.1)]
6.3. Decisions Used in Making LDAP Association State Changes
Certain changes in the state of an LDAP association are only allowed
if the server can affirmatively answer a question. These questions
are applied as part of the criteria for allowing or disallowing a
state change in the state transition table in section 6.4.
ID Decision Question
-- --------------------------------------------------------------
D1 Can TLS Credentials Auth ID "I" be mapped to AuthZ ID "J"?
D2 Can a valid AuthZ ID "K" be derived from TLS Credentials Auth
ID "I"?
6.4. LDAP Association State Transition Table
The LDAP Association table below lists the valid states for an LDAP
association and the actions that could affect them. For any given
row in the table, the Current State column gives the state of an
LDAP association, the Action column gives an action that could
affect the state of an LDAP assocation, and the Next State column
gives the resulting state of an LDAP association after the action
occurs.
The initial state for the state machine described in this table is
S1.
Current Next
State Action State Comment
------- ------------- ----- -----------------------------------
S1 A1 S1
S1 A2 S1 Error: Inappropriate authentication
S1 A3 S2
S1 A4 S3
S1 A6 S4
S1 A7 ? identity could be provided by
another underlying mechanism such
as IPSec.
S1 A8 ? identity could be provided by
another underlying mechanism such
as IPSec.
S2 A1 S2
S2 A2 S2 Error: Inappropriate authentication
S2 A5 S1
S2 A6 S5
S2 A7 ? identity could be provided by
another underlying mechanism such
as IPSec.
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S2 A8 ? identity could be provided by
another underlying mechanism such
as IPSec.
S3 A1 S3
S3 A2 S3 Error: Inappropriate authentication
S3 A5 S1
S3 A6 S6
S3 A7 and D1=NO S3 Error: InvalidCredentials
S3 A7 and D1=YES S7
S3 A8 and D2=NO S3 Error: InvalidCredentials
S3 A8 and D2=YES S8
S4 A1 S1
S4 A2 S4 Error: Inappropriate Authentication
S4 A3 S5
S4 A4 S6
S4 A5 S1
S4 A6 S4
S4 A7 ? identity could be provided by
another underlying mechanism such
as IPSec.
S4 A8 ? identity could be provided by
another underlying mechanism such
as IPSec.
S5 A1 S2
S5 A2 S5 Error: Inappropriate Authentication
S5 A5 S1
S5 A6 S5
S5 A7 ? identity could be provided by
another underlying mechanism such
as IPSec.
S5 A8 ? identity could be provided by
another underlying mechanism such
as IPSec.
S6 A1 S3
S6 A2 S6 Error: Inappropriate Authentication
S6 A5 S1
S6 A6 S6
S6 A7 and D1=NO S6 Error: InvalidCredentials
S6 A7 and D1=YES S7
S6 A8 and D2=NO S6 Error: InvalidCredentials
S6 A8 and D2=YES S8
S7 A1 S3
S7 A2 S7 Error: Inappropriate Authentication
S7 A5 S1
S7 A6 S6
S7 A7 S7
S7 A8 and D2=NO S3 Error: InvalidCredentials
S7 A8 and D2=YES S8
S8 A1 S3
S8 A2 S8 Error: Inappropriate Authentication
S8 A5 S1
S8 A6 S6
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S8 A7 and D1=NO S6 Error: InvalidCredentials
S8 A7 and D1=YES S7
S8 A8 S8
7. Anonymous Authentication
Directory operations that modify entries or access protected
attributes or entries generally require client authentication.
Clients that do not intend to perform any of these operations
typically use anonymous authentication. Servers SHOULD NOT allow
clients with anonymous authentication to modify directory entries or
access sensitive information in directory entries.
LDAP implementations MUST support anonymous authentication, as
defined in section 7.1.
LDAP implementations MAY support anonymous authentication with TLS,
as defined in section 7.2.
While there MAY be access control restrictions to prevent access to
directory entries, an LDAP server SHOULD allow an anonymously-bound
client to retrieve the supportedSASLMechanisms attribute of the root
DSE.
An LDAP server MAY use other information about the client provided
by the lower layers or external means to grant or deny access even
to anonymously authenticated clients.
7.1. Anonymous Authentication Procedure
An LDAPv3 client that has not successfully completed a bind
operation on a connection is anonymously authenticated. See section
4.3.3.
An LDAP client MAY also choose to explicitly bind anonymously. A
client that wishes to do so MUST choose the simple authentication
option in the Bind Request (see section 4.1) and set the password to
be of zero length. (This is often done by LDAPv2 clients.) Typically
the name is also of zero length.
7.2. Anonymous Authentication and TLS
An LDAP client MAY use the Start TLS operation (section 5) to
negotiate the use of TLS security [RFC2246]. If the client has not
bound beforehand, then until the client uses the EXTERNAL SASL
mechanism to negotiate the recognition of the client's certificate,
the client is anonymously authenticated.
Recommendations on TLS ciphersuites are given in section 10.
An LDAP server which requests that clients provide their certificate
during TLS negotiation MAY use a local security policy to determine
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whether to successfully complete TLS negotiation if the client did
not present a certificate which could be validated.
8. Password-based Authentication
This section discusses various options for performing password-based
authentication to LDAPv3 compliant servers and the environments
suitable for their use.
8.1. Simple Authentication
The LDAP "simple" authentication choice is not suitable for
authentication in environments where there is no network or
transport layer confidentiality. LDAP implementations SHOULD support
authentication with the "simple" authentication choice when the
connection is protected against eavesdropping using TLS, as defined
in section 5. LDAP implementations SHOULD NOT support authentication
with the "simple" authentication choice unless the data on the
connection is protected using TLS or other data confidentiality and
data integrity protection.
8.2. Digest Authentication
LDAP servers that implement any password-based authentication method
MUST support authentication with a password using the DIGEST-MD5
SASL mechanism for password protection.
An LDAP client MAY determine whether the server supports this
mechanism by performing a search request on the root DSE, requesting
the supportedSASLMechanisms attribute, and checking whether the
string "DIGEST-MD5" is present as a value of this attribute.
In the first stage of authentication, when the client is performing
an "initial authentication" as defined in section 2.1 of [RFC2831],
the client sends a bind request in which the version number is 3,
the authentication choice is sasl, the sasl mechanism name is
"DIGEST-MD5", and the credentials are absent. The client then waits
for a response from the server to this request.
The server will respond with a bind response in which the resultCode
is saslBindInProgress, and the serverSaslCreds field is present. The
contents of this field is a string defined by "digest-challenge" in
section 2.1.1 of [RFC2831]. The server SHOULD include a realm
indication and MUST indicate support for UTF-8.
The client will send a bind request with a distinct message id, in
which the version number is 3, the authentication choice is sasl,
the sasl mechanism name is "DIGEST-MD5", and the credentials contain
the string defined by "digest-response" in section 2.1.2 of
[RFC2831]. The serv-type is "ldap".
The server will respond with a bind response in which the resultCode
is either success, or an error indication. If the authentication is
successful and the server does not support subsequent
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authentication, then the credentials field is absent. If the
authentication is successful and the server supports subsequent
authentication, then the credentials field contains the string
defined by "response-auth" in section 2.1.3 of [RFC2831]. Support
for subsequent authentication is OPTIONAL in clients and servers.
8.3. "simple" authentication choice under TLS encryption
Following the negotiation of an appropriate TLS ciphersuite
providing connection confidentiality [RFC2246], a client MAY
authenticate to a directory that supports the simple authentication
choice by performing a simple bind operation.
The client will use the Start TLS operation [Protocol] to negotiate
the use of TLS security [RFC2246] on the connection to the LDAP
server. The client need not have bound to the directory beforehand.
For this authentication procedure to be successful, the client and
server MUST negotiate a ciphersuite which contains a bulk encryption
algorithm of appropriate strength. Recommendations on cipher suites
are given in section 10.
Following the successful completion of TLS negotiation, the client
MUST send an LDAP bind request with the version number of 3, the
name field containing a DN, and the "simple" authentication choice,
containing a password.
8.3.1. "simple" Authentication Choice
DSAs that map the DN sent in the bind request to a directory entry
with an associated set of one or more passwords will compare the
presented password to the set of passwords associated with that
entry. If there is a match, then the server will respond with
resultCode success, otherwise the server will respond with
resultCode invalidCredentials.
8.4. Other authentication choices with TLS
It is also possible, following the negotiation of TLS, to perform a
SASL authentication that does not involve the exchange of plaintext
reusable passwords. In this case the client and server need not
negotiate a ciphersuite that provides confidentiality if the only
service required is data integrity.
9. Certificate-based authentication
LDAP server implementations SHOULD support authentication via a
client certificate in TLS, as defined in section 5.2.2.
9.1. Certificate-based authentication with TLS
A user who has a public/private key pair in which the public key has
been signed by a Certification Authority may use this key pair to
authenticate to the directory server if the user's certificate is
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requested by the server. The user's certificate subject field SHOULD
be the name of the user's directory entry, and the Certification
Authority that issued the user's certificate must be sufficiently
trusted by the directory server in order for the server to process
the certificate. The means by which servers validate certificate
paths is outside the scope of this document.
A server MAY support mappings for certificates in which the subject
field name is different from the name of the user's directory entry.
A server which supports mappings of names MUST be capable of being
configured to support certificates for which no mapping is required.
The client will use the Start TLS operation [Protocol] to negotiate
the use of TLS security [RFC2246] on the connection to the LDAP
server. The client need not have bound to the directory beforehand.
In the TLS negotiation, the server MUST request a certificate. The
client will provide its certificate to the server, and the server
MUST perform a private key-based encryption, proving it has the
private key associated with the certificate.
In deployments that require protection of sensitive data in transit,
the client and server MUST negotiate a ciphersuite that contains a
bulk encryption algorithm of appropriate strength. Recommendations
of cipher suites are given in section 10.
The server MUST verify that the client's certificate is valid. The
server will normally check that the certificate is issued by a known
certification authority (CA), and that none of the certificates on
the client's certificate chain are invalid or revoked. There are
several procedures by which the server can perform these checks.
Following the successful completion of TLS negotiation, the client
will send an LDAP bind request with the SASL "EXTERNAL" mechanism.
10. TLS Ciphersuites
The following ciphersuites defined in [RFC2246] MUST NOT be used for
confidentiality protection of passwords or data:
TLS_NULL_WITH_NULL_NULL
TLS_RSA_WITH_NULL_MD5
TLS_RSA_WITH_NULL_SHA
The following ciphersuites defined in [RFC2246] can be cracked
easily (less than a day of CPU time on a standard CPU in 2000).
These ciphersuites are NOT RECOMMENDED for use in confidentiality
protection of passwords or data. Client and server implementers
SHOULD carefully consider the value of the password or data being
protected before using these ciphersuites:
TLS_RSA_EXPORT_WITH_RC4_40_MD5
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
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TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA
TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
The following ciphersuites are vulnerable to man-in-the-middle
attacks, and SHOULD NOT be used to protect passwords or sensitive
data, unless the network configuration is such that the danger of a
man-in-the-middle attack is tolerable:
TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
TLS_DH_anon_WITH_RC4_128_MD5
TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
TLS_DH_anon_WITH_DES_CBC_SHA
TLS_DH_anon_WITH_3DES_EDE_CBC_SHA
A client or server that supports TLS MUST support
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA and MAY support other ciphersuites
offering equivalent or better protection.
11. Security Considerations
Security issues are discussed throughout this memo; the
(unsurprising) conclusion is that mandatory security is important
and that session confidentiality protection is required when
snooping is a problem.
Servers are encouraged to prevent modifications by anonymous users.
Servers may also wish to minimize denial of service attacks by
timing out idle connections, and returning the unwillingToPerform
result code rather than performing computationally expensive
operations requested by unauthorized clients.
Operational experience shows that clients can misuse unauthenticated
access (simple bind with name but no password). For this reason,
servers SHOULD by default reject authentication requests that have a
DN with an empty password with an error of invalidCredentials.
Access control SHOULD be applied when reading sensitive information
or updating directory information.
A connection on which the client has not performed the Start TLS
operation or negotiated a suitable SASL mechanism for connection
integrity and encryption services is subject to man-in-the-middle
attacks to view and modify information in transit.
11.1. Start TLS Security Considerations
The goals of using the TLS protocol with LDAP are to ensure
connection confidentiality and integrity, and to optionally provide
for authentication. TLS expressly provides these capabilities, as
described in [RFC2246].
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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.
Once established, TLS only provides for and ensures confidentiality
and integrity of the operations and data in transit over the LDAP
association--and only if the implementations on the client and
server support and negotiate it. 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. Nor does it secure the data from
inspection by the server administrators.
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. Additionally, an active-
intermediary attacker can remove the Start TLS extended operation
from the supportedExtension attribute of the root DSE. Therefore,
both parties SHOULD independently ascertain and consent to the
security level achieved once TLS is established and before beginning
use of the TLS connection. For example, the security level of the
TLS connection might have been negotiated down to plaintext.
Clients SHOULD either warn the user when the security level achieved
does not provide confidentiality and/or integrity protection, or be
configurable to refuse to proceed without an acceptable level of
security.
Client and server implementors SHOULD take measures to ensure proper
protection of credentials and other confidential data where such
measures are not otherwise provided by the TLS implementation.
Server implementors SHOULD allow for server administrators to elect
whether and when connection confidentiality and/or integrity is
required, as well as elect whether and when client authentication
via TLS is required.
Additional security considerations relating to the EXTERNAL
mechanism to negotiate TLS can be found in [RFC2222] and [RFC2246].
12. Acknowledgements
This document combines information originally contained in RFC 2829
and RFC 2830. The author acknowledges the work of Harald Tveit
Alvestrand, Jeff Hodges, Tim Howes, Steve Kille, RL "Bob" Morgan ,
and Mark Wahl, each of whom authored one or more of these documents.
RFC 2829 and RFC 2830 were products of the IETF LDAPEXT Working
Group. RFC 2251 was a product of the ASID Working Group.
This document is based upon input of the IETF LDAP Revision working
group. The contributions of its members is greatly appreciated.
13. Normative References
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[RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2222] Myers, J., "Simple Authentication and Security Layer
(SASL)", draft-myers-saslrev-xx.txt, a work in progress.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2246] Dierks, T. and C. Allen. "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC2831] Leach, P. and C. Newman, "Using Digest Authentication as
a SASL Mechanism", RFC 2831, May 2000.
[LDAPDN] Zeilenga, Kurt D. (editor), "LDAP: String Representation of
Distinguished Names", draft-ietf-ldapbis-dn-xx.txt, a work in
progress.
[Protocol] Sermersheim, J., "LDAP: The Protocol", draft-ietf-
ldapbis-protocol-xx.txt, a work in progress.
[ROADMAP] K. Zeilenga, "LDAP: Technical Specification Road Map",
draft-ietf-ldapbis-roadmap-xx.txt, a work in progress.
14. Informative References
[RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828, May
2000.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
15. Author's Address
Roger Harrison
Novell, Inc.
1800 S. Novell Place
Provo, UT 84606
+1 801 861 2642
roger_harrison@novell.com
16. Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
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document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Appendix A. Example Deployment Scenarios
The following scenarios are typical for LDAP directories on the
Internet, and have different security requirements. (In the
following discussion, "sensitive data" refers to information whose
disclosure, alteration, destruction, or loss would adversely affect
the interests or business of its owner or user. Also note that there
may be data that is protected but not sensitive.) This is not
intended to be a comprehensive list; other scenarios are possible,
especially on physically protected networks.
(1) A read-only directory, containing no sensitive data, accessible
to "anyone", and TCP connection hijacking or IP spoofing is not
a problem. Anonymous authentication, described in section 7, is
suitable for this type of deployment, and requires no additional
security functions except administrative service limits.
(2) A read-only directory containing no sensitive data; read access
is granted based on identity. TCP connection hijacking is not
currently a problem. This scenario requires data confidentiality
for sensitive authentication information AND data integrity for
all authentication information.
(3) A read-only directory containing no sensitive data; and the
client needs to ensure the identity of the directory server and
that the directory data is not modified while being returned
from the server. A data origin authentication service AND data
integrity service are required.
(4) A read-write directory, containing no sensitive data; read
access is available to "anyone", update access to properly
authorized persons. TCP connection hijacking is not currently a
problem. This scenario requires data confidentiality for
sensitive authentication information AND data integrity for all
authentication information.
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(5) A directory containing sensitive data. This scenario requires
data confidentiality protection AND secure authentication.
Appendix B. Authentication and Authorization: Definitions and Concepts
This appendix defines basic terms, concepts, and interrelationships
regarding authentication, authorization, credentials, and identity.
These concepts are used in describing how various security
approaches are utilized in client authentication and authorization.
B.1. Access Control Policy
An access control policy is a set of rules defining the protection
of resources, generally in terms of the capabilities of persons or
other entities accessing those resources. A common expression of an
access control policy is an access control list. Security objects
and mechanisms, such as those described here, enable the expression
of access control policies and their enforcement. Access control
policies are typically expressed in terms of access control
attributes as described below.
B.2. Access Control Factors
A request, when it is being processed by a server, may be associated
with a wide variety of security-related factors (section 4.2 of
[Protocol]). The server uses these factors to determine whether and
how to process the request. These are called access control factors
(ACFs). They might include source IP address, encryption strength,
the type of operation being requested, time of day, etc. Some
factors may be specific to the request itself, others may be
associated with the connection via which the request is transmitted,
others (e.g. time of day) may be "environmental".
Access control policies are expressed in terms of access control
factors. E.g., a request having ACFs i,j,k can perform operation Y
on resource Z. The set of ACFs that a server makes available for
such expressions is implementation-specific.
B.3. Authentication, Credentials, Identity
Authentication credentials are the evidence supplied by one party to
another, asserting the identity of the supplying party (e.g. 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 and thus the identity
they assert. An authentication identity 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.
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B.4. Authorization Identity
An authorization identity is one kind of access control factor. It
is the name of the user or other entity that requests that
operations be performed. Access control policies are often expressed
in terms of authorization identities; e.g., entity X can perform
operation Y on resource Z.
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 asserted by the
client's credentials. 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 [RFC2222].
Also, the form of authentication identity supplied by a service like
TLS may not correspond to the authorization identities used to
express a server's access control policy, requiring a server-
specific mapping to be done. The method by which a server composes
and validates an authorization identity from the authentication
credentials supplied by a client is implementation-specific.
Appendix C. RFC 2829 Change History
This appendix lists the changes made to the text of RFC 2829 in
preparing this document.
C.0. General Editorial Changes
Version -00
- Changed other instances of the term LDAP to LDAPv3 where v3 of
the protocol is implied. Also made all references to LDAPv3 use
the same wording.
- Miscellaneous grammatical changes to improve readability.
- Made capitalization in section headings consistent.
Version -01
- Changed title to reflect inclusion of material from RFC 2830 and
2251.
C.1. Changes to Section 1
Version -01
- Moved conventions used in document to a separate section.
C.2. Changes to Section 2
Version -01
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- Moved section to an appendix.
C.3. Changes to Section 3
Version -01
- Moved section to an appendix.
C.4 Changes to Section 4
Version -00
- Changed "Distinguished Name" to "LDAP distinguished name".
C.5. Changes to Section 5
Version -00
- Added the following sentence: "Servers SHOULD NOT allow clients
with anonymous authentication to modify directory entries or
access sensitive information in directory entries."
C.5.1. Changes to Section 5.1
Version -00
- Replaced the text describing the procedure for performing an
anonymous bind (protocol) with a reference to section 4.2 of RFC
2251 (the protocol spec).
Version -01
- Brought text describing procedure for performing an anonymous
bind from section 4.2 of RFC 2251 bis. This text will be
removed from the draft standard version of that document.
C.6. Changes to Section 6.
Version -00
Reorganized text in section 6.1 as follows:
1. Added a new section (6.1) titled "Simple Authentication" and
moved one of two introductory paragraphs for section 6 into
section 6.1. Added sentences to the paragraph indicating:
a. simple authentication is not suitable for environments where
confidentiality is not available.
b. LDAP implementations SHOULD NOT support simple
authentication unless confidentiality and data integrity
mechanisms are in force.
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2. Moved first paragraph of section 6 (beginning with "LDAP
implementations MUST support authentication with a password<72>")
to section on Digest Authentication (Now section 6.2).
C.6.1. Changes to Section 6.1.
Version -00 Renamed section to 6.2
- Added sentence from original section 6 indicating that the
DIGEST-MD5 SASL mechanism is required for all conforming LDAPv3
implementations
C.6.2. Changes to Section 6.2
Version -00
- Renamed section to 6.3
- Reworded first paragraph to remove reference to user and the
userPassword password attribute Made the first paragraph more
general by simply saying that if a directory supports simple
authentication that the simple bind operation MAY performed
following negotiation of a TLS ciphersuite that supports
confidentiality.
- Replaced "the name of the user's entry" with "a DN" since not
all bind operations are performed on behalf of a "user."
- Added Section 6.3.1 heading just prior to paragraph 5.
- Paragraph 5: replaced "The server" with "DSAs that map the DN
sent in the bind request to a directory entry with a
userPassword attribute."
C.6.3. Changes to section 6.3.
Version -00
- Renamed to section 6.4.
C.7. Changes to section 7.
none
C.7.1. Changes to section 7.1.
Version -00
- Clarified the entity issuing a certificate by moving the phrase
"to have issued the certificate" immediately after
"Certification Authority."
C.8. Changes to section 8.
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Version -00
- Removed the first paragraph because simple authentication is
covered explicitly in section 6.
- Added section 8.1. heading just prior to second paragraph.
- Added section 8.2. heading just prior to third paragraph.
- Added section 8.3. heading just prior to fourth paragraph.
Version -01
- Moved entire section 8 of RFC 2829 into section 3.4 (Using SASL
for Other Security Services) to bring material on SASL
mechanisms together into one location.
C.9. Changes to section 9.
Version -00
- Paragraph 2: changed "EXTERNAL mechanism" to "EXTERNAL SASL
mechanism."
- Added section 9.1. heading.
- Modified a comment in the ABNF from "unspecified userid" to
"unspecified authz id".
- Deleted sentence, "A utf8string is defined to be the UTF-8
encoding of one or more ISO 10646 characters," because it is
redundant.
- Added section 9.1.1. heading.
- Added section 9.1.2. heading.
Version -01
- Moved entire section 9 to become section 3.5 so that it would be
with other SASL material.
C.10. Changes to Section 10.
Version -00
- Updated reference to cracking from a week of CPU time in 1997 to
be a day of CPU time in 2000.
- Added text: "These ciphersuites are NOT RECOMMENDED for use...
and server implementers SHOULD" to sentence just prior the
second list of ciphersuites.
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- Added text: "and MAY support other ciphersuites offering
equivalent or better protection," to the last paragraph of the
section.
C.11. Changes to Section 11.
Version -01
- Moved to section 3.6 to be with other SASL material.
C.12. Changes to Section 12.
Version -00
- Inserted new section 12 that specifies when SASL protections
begin following SASL negotiation, etc. The original section 12
is renumbered to become section 13.
Version -01
- Moved to section 3.7 to be with other SASL material.
C.13. Changes to Section 13 (original section 12).
None
Appendix D. RFC 2830 Change History
This appendix lists the changes made to the text of RFC 2830 in
preparing this document.
D.0. General Editorial Changes
- Material showing the PDUs for the Start TLS response was broken
out into a new section.
- The wording of the definition of the Start TLS request and Start
TLS response was changed to make them parallel. NO changes were
made to the ASN.1 definition or the associated values of the
parameters.
- A separate section heading for graceful TLS closure was added
for parallelism with section on abrupt TLS closure.
Appendix E. RFC 2251 Change History
This appendix lists the changes made to the text of RFC 2251 in
preparing this document.
E.0. General Editorial Changes
- All material from section 4.2 of RFC 2251 was moved into this
document.
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- A new section was created for the Bind Request
- Section 4.2.1 of RFC 2251 (Sequencing Bind Request) was moved
after the section on the Bind Response for parallelism with the
presentation of the Start TLS operations. The section was also
subdivided to explicitly call out the various effects being
described within it.
- All SASL profile information from RFC 2829 was brought within
the discussion of the Bind operation (primarily sections 4.4 -
4.7).
Appendix F. Change History to Combined Document
F.1. Changes for draft-ldap-bis-authmeth-02
General
- Added references to other LDAP standard documents, to sections
within the document, and fixed broken references.
- General editorial changes<65>punctuation, spelling, formatting,
etc.
Section 1.
- Added glossary of terms and added sub-section headings
Section 2.
- Clarified security mechanisms 3, 4, & 5 and brought language in
line with IETF security glossary.
Section 3.
- Brought language in requirement (3) in line with security
glossary.
- Clarified that information fetched prior to initiation of TLS
negotiation must be discarded
-Clarified that information fetched prior to initiation of SASL
negotiation must be discarded
- Rewrote paragraph on SASL negotiation requirements to clarify
intent
Section 4.4.
- Added stipulation that sasl choice allows for any SASL mechanism
not prohibited by this document. (Resolved conflict between this
statement and one that prohibited use of ANONYMOUS and PLAIN
SASL mechanisms.)
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Section 5.3.6
- Added a.x.bar.com to wildcard matching example on hostname
check.
Section 6
- Added LDAP Association State Transition Tables to show the
various states through which an LDAP association may pass along
with the actions and decisions required to traverse from state
to state.
Appendix A
- Brought security terminology in line with IETF security glossary
throughout the appendix.
F.2. Changes for draft-ldap-bis-authmeth-03
General
- Added introductory notes and changed title of document and
references to conform to WG chair suggestions for the overall
technical specification.
- Several issues--G.13, G.14, G.16, G.17--were resolved without
requiring changes to the document.
Section 3
- Removed reference to /etc/passwd file and associated text.
Section 4
- Removed sections 4.1, 4.2 and parts of section 4.3. This
information was being duplicated in the protocol specification
and will now reside there permanently.
Section 4.2
- changed words, "not recommended" to "strongly discouraged"
Section 4.3
- Based on ldapbis WG discussion at IETF52 two sentences were
added indicating that clients SHOULD NOT send a DN value when
binding with the sasl choice and servers SHALL ignore any value
received in this circumstance.
-
Section 8.3.1
- Generalized the language of this section to not refer to any
specific password attribute or to refer to the directory entry
as a "user" entry.
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Section 11
- Added security consideration regarding misuse of unauthenticated
access.
- Added security consideration requiring access control to be
applied only to authenticated users and recommending it be
applied when reading sensitive information or updating directory
information.
F.3. Changes for draft-ldap-bis-authmeth-04
General
- Changed references to use [RFCnnnn] format wherever possible.
(References to works in progress still use [name] format.)
- Various edits to correct typos and bring field names, etc. in
line with specification in [Protocol] draft.
- Several issues--G.13, G.14, G.16, G.17--were resolved without
requiring changes to the document.
Section 4.4.1.
- Changed ABNF grammar to use productions that are like those in
the model draft.
Section 5
- Removed sections 5.1, 5.2, and 5.4 that will be added to
[Protocol]. Renumbered sections to accommodate this change.
-
Section 6
- Reviewed LDAP Association State table for completeness and
accuracy. Renumbered actions A3, A4, and A5 to be A5, A3, and A4
respectively. Re-ordered several lines in the table to ensure
that actions are in ascending order (makes analyzing the table
much more logical). Added action A2 to several states where it
was missing and valid. Added actions A7 and A8 placeholders to
states S1, S2, S4 and S5 pending resolution of issue G.28.
Section 11
- Modified security consideration (originally added in -03)
requiring access control to be applied only to authenticated
users. This seems nonsensical because anonymous users may have
access control applied to limit permissible actions.
-
Section 13
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- Verified all normative references and moved informative
references to a new section 14.
F.4. Changes for draft-ldap-bis-authmeth-05
General
- General editory changes to fix punctuation, spelling, line
length issues, etc.
- Verified and updated intra- and inter-document references
throughout.
- Document-wide review for proper usage of RFC 2119 keywords with
several changes to correct improper usage.
Abstract
- Updated to match current contents of documents. This was needed
due to movement of material on Bind and Start TLS operations to
[Protocol] in this revision.
Section 3.
- Renamed section to "Rationale for LDAPv3 Security Mechanisms"
and removed text that did not support this theme. Part of the
motivation for this change was to remove the implication of the
previous section title, "Required Security Mechanisms", and
other text found in the section that everything in the section
was a requirement
- Information from several removed paragraphs that describe
deployment scenarios will be added Appendix A in the next
revision of the draft.
- Paragraph beginning, " If TLS is negotiated, the client MUST
discard all information..." was moved to section 5.1.7 and
integrated with related material there.
- Paragraph beginning, "If a SASL security layer is negotiated..."
was moved to section 4.2
Section 4.l.
- Changed wording of first paragraph to clarify meaning.
Section 4.2.
- Added paragraph from section 3 of -04 beginning, "If a SASL
security layer is negotiated..."
Section 4.3.3.
- Renamed to "Other SASL Mechanisms" and completely rewrote the
section (one sentence) to generalize the treatment of SASL
mechanisms not explicitly mentioned in this document.
Section 4.4.1.
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- Added paragraph beginning, "The dnAuthzID choice allows client
applications..." to clarify whether DN form authorization
identities have to also have a corresponding directory entry.
This change was based on editor's perception of WG consensus.
- Made minor clarifying edits in the paragraph beginning, "The
uAuthzID choice allows for compatibility..."
Section 5.1.1.
- Made minor clarifying edits in the last paragraph of the
section.
Section 5.1.7.
- Wording from section 3 paragraph beginning " If TLS is
negotiated, the client MUST discard all information..." was
moved to this section and integrated with existing text.
Section 5.2.
- Changed usage of "TLS connection" to "TLS session" throughout.
- Removed empty section 5.2.1 and renumbered sections it had
previously contained.
Section 8.
- Added introductory paragraph at beginning of section.
Section 8.1.
- Changed term "data privacy" to "data confidentiality" to be
consistent with usage in rest of document.
Section 8.2.
- Changed first paragraph to require implementations that
implement *password-based* authentication to implement and
support DIGEST-MD5 SASL authentication.
Section 11.
- First paragraph: changed "session encryption" to "session
confidentiality protection" to be consistent with usage in rest
of document.
Appendix A.
- Began changes to incorporate information on deployment scenarios
removed from section 3.
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Appendix G. Issues to be Resolved
This appendix lists open questions and issues that need to be
resolved before work on this document is deemed complete.
G.1.
Section 1 lists 6 security mechanisms that can be used by LDAP
servers. I'm not sure what mechanism 5, "Resource limitation by
means of administrative limits on service controls" means.
Status: resolved. Changed wording to "administrative service limits"
to clarify meaning.
G.2.
Section 2 paragraph 1 defines the term, "sensitive." Do we want to
bring this term and other security-related terms in alignment with
usage with the IETF security glossary (RFC 2828)?
Status: resolved. WG input at IETF 51 was that we should do this, so
the appropriate changes have been made.
G.3.
Section 2, deployment scenario 2: What is meant by the term "secure
authentication function?"
Status: resolved. Based on the idea that a "secure authentication
function" could be provided by TLS, I changed the wording to require
data confidentiality for sensitive authentication information and
data integrity for all authentication information.
G.4.
Section 3, deployment scenario 3: What is meant by the phrase,
"directory data is authenticated by the server?"
Status: resolved. I interpreted this to mean the ability to ensure
the identity of the directory server and the integrity of the data
sent from that server to the client, and explictly stated such.
G.5.
Section 4 paragraph 3: What is meant by the phrase, "this means that
either this data is useless for faking authentication (like the Unix
"/etc/passwd" file format used to be)?"
Status: resolved. Discussion at IETF 52 along with discussions with
the original authors of this material have convinced us that this
reference is simply too arcane to be left in place. In -03 the text
has been modified to focus on the need to either update password
information in a protected fashion outside of the protocol or to
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update it in session well protected against snooping, and the
reference to /etc/passwd has been removed.
G.6.
Section 4 paragraph 7 begins: "For a directory needing session
protection..." Is this referring to data confidentiality or data
integrity or both?
Status: resolved. Changed wording to say, "For a directory needing
data security (both data integrity and data confidentiality)..."
G.7.
Section 4 paragraph 8 indicates that "information about the server
fetched fetched prior to the TLS negotiation" must be discarded. Do
we want to explicitly state that this applies to information fetched
prior to the *completion* of the TLS negotiation or is this going
too far?
Status: resolved. Based on comments in the IETF 51 LDAPBIS WG
meeting, this has been changed to explicitly state, "fetched prior
to the initiation of the TLS negotiation..."
G.8.
Section 4 paragraph 9 indicates that clients SHOULD check the
supportedSASLMechanisms list both before and after a SASL security
layer is negotiated to ensure that they are using the best available
security mechanism supported mutually by the client and server. A
note at the end of the paragraph indicates that this is a SHOULD
since there are environments where the client might get a list of
supported SASL mechanisms from a different trusted source.
I wonder if the intent of this could be restated more plainly using
one of these two approaches (I've paraphrased for the sake of
brevity):
Approach 1: Clients SHOULD check the supportedSASLMechanisms
list both before and after SASL negotiation or clients SHOULD
use a different trusted source to determine available supported
SASL mechanisms.
Approach 2: Clients MUST check the supportedSASLMechanisms list
both before and after SASL negotiation UNLESS they use a
different trusted source to determine available supported SASL
mechanisms.
Status: resolved. WG input at IETF 51 was that Approach 1 was
probably best. I ended up keeping the basic structure similar to the
original to meet this intent.
G.9.
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Section 6.3.1 states: "DSAs that map the DN sent in the bind request
to a directory entry with a userPassword attribute will... compare
[each value in the named user's entry]... with the presented
password." This implies that this applies only to user entries with
userPassword attributes. What about other types of entries that
might allow passwords and might store in the password information in
other attributes? Do we want to make this text more general?
Status: resolved in -03 draft by generalizing section 8.3.1 to not
refer to any specific password attribute and by removing the term
"user" in referring to the directory entry specified by the DN in
the bind request.
G.10 userPassword and simple bind
We need to be sure that we don't require userPassword to be the only
attribute used for authenticating via simple bind. (See 2251 sec 4.2
and authmeth 6.3.1. Work with Jim Sermersheim on resolution to this.
On publication state something like: "This is the specific
implementation of what we discussed in our general reorg
conversation on the list." (Source: Kurt Zeilenga)
Status: resolved in -03 draft by generalizing section 8.3.1 to not
refer to any specific password attribute and by removing the term
"user" in referring to the directory entry specified by the DN in
the bind request.
G.11. Meaning of LDAP Association
The original RFC 2830 uses the term "LDAP association" in describing
a connection between an LDAP client and server regardless of the
state of TLS on that connection. This term needs to be defined or
possibly changed.
Status: resolved. at IETF 51 Bob Morgan indicated that the term
"LDAP association" was intended to distinguish the LDAP-level
connection from the TLS-level connection. This still needs to be
clarified somewhere in the draft. Added "LDAP association" to a
glossary in section 1.
G.12. Is DIGEST-MD5 mandatory for all implementations?
Reading 2829bis I think DIGEST-MD5 is mandatory ONLY IF your server
supports password based authentication...but the following makes it
sound mandatory to provide BOTH password authentication AND DIGEST-
MD5:
"6.2. Digest authentication
LDAP implementations MUST support authentication with a password
using the DIGEST-MD5 SASL mechanism for password protection, as
defined in section 6.1."
The thing is for acl it would be nice (though not critical) to be
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able to default the required authentication level for a subject to a
single "fairly secure" mechanism--if there is no such mandatory
authentication scheme then you cannot do that. (Source: Rob Byrne)
Status: resolved. -00 version of the draft added a sentence at the
beginning of section 8.2 stating that LDAP server implementations
must support this method.
G.13. Ordering of authentication levels requested
Again on the subject of authentication level, is it possible to
define an ordering on authentication levels which defines their
relative "strengths" ? This would be useful in acl as you could say
things like"a given aci grants access to a given subject at this
authentication level AND ABOVE". David Chadwick raised this before
in the context of denying access to a subject at a given
authentication level, in which case he wanted to express "deny
access to this subject at this authentication level AND TO ALL
IDENTITIES AUTHENTICATED BELOW THAT LEVEL". (Source: Rob Byrne)
Status: out of scope. This is outside the scope of this document and
will not be addressed.
G.14. Document vulnerabilities of various mechanisms
While I'm here...in 2829, I think it would be good to have some
comments or explicit reference to a place where the security
properties of the particular mandatory authentication schemes are
outlined. When I say "security properties" I mean stuff like "This
scheme is vulnerable to such and such attacks, is only safe if the
key size is > 50, this hash is widely considered the best, etc...".
I think an LDAP implementor is likely to be interested in that
information, without having to wade through the security RFCs.
(Source: Rob Byrne)
Status: out of scope. This is outside the scope of this document and
will not be addressed.
G.15. Include a StartTLS state transition table
The pictoral representation it is nominally based on is here (URL
possibly folded):
http://www.stanford.edu/~hodges/doc/LDAPAssociationStateDiagram-
1999-12-14.html
(Source: Jeff Hodges)
Status: In Process. Table provided in -03. Review of content for
accuracy in -04. Additional review is needed, plus comments from WG
members indicate that additional description of each state's meaning
would be helpful.
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G.16. Empty sasl credentials question
I spent some more time looking microscopically at ldap-auth-methods
and ldap-ext-tls drafts. The drafts say that the credential must
have the form dn:xxx or u:xxx or be absent, and although they don't
say what to do in the case of an empty octet string I would say that
we could send protocolError (claim it is a bad PDU).
There is still the question of what to do if the credential is 'dn:'
(or 'u:') followed by the empty string. (Source: ariel@columbia.edu
via Jeff Hodges)
Status: resolved. Kurt Zeilenga indicated during ldapbis WG
discussion at IETF 52 that SASL AuthzID credentials empty and absent
are equivalent in the latest SASL ID. This resolves the issue.
G.17. Hostname check from MUST to SHOULD?
I am uneasy about the hostname check. My experience from PKI with
HTTP probably is a contributing factor; we have people using the
short hostname to get to a server which naturally has the FQDN in
the certificate, no end of problems. I have a certificate on my
laptop which has the FQDN for the casse when the system is on our
Columbia network with a fixed IP; when I dial in however, I have
some horrible dialup name, and using the local https server becomes
annoying. Issuing a certificate in the name 'localhost' is not a
solution! Wildcard match does not solve this problem. For these
reasons I am inclined to argue for 'SHOULD' instead of
'MUST' in paragraph...
Also, The hostname check against the name in the certificate is a
very weak means of preventing man-in-the-middle attacks; the proper
solution is not here yet (SecureDNS or some equivalent). Faking out
DNS is not so hard, and we see this sort of thing in the press on a
pretty regular basis, where site A hijacks the DNS server for site B
and gets all their requests. Some mention of this should be made in
the draft. (Source: ariel@columbia.edu via Jeff Hodges)
Status: resolved. Based on discussion at IETF 52 ldapbis WG meeting,
this text will stand as it is. The check is a MUST, but the behavior
afterward is a SHOULD. This gives server implementations the room to
maneuver as needed.
G.18. Must SASL DN exist in the directory?
If the 'dn:' form of sasl creds is used, is it the intention of the
draft(ers) that this DN must exist in the directory and the client
will have the privileges associated with that entry, or can the
server map the sasl DN to perhaps some other DN in the directory,
in an implementation-dependent fashion?
We already know that if *no* sasl credentials are presented, the DN
or altname in the client certificate may be mapped to a DN in an
implementation-dependent fashion, or indeed to something not in the
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directory at all. (Right?) (Source: ariel@columbia.edu via Jeff
Hodges)
Status: resolved. (11/12/02)Based on my research I propose that the
DN MUST exist in the directory when the DN form of sasl creds is
used. I have made this proposal to the ldapbis mailing list.
(11/21/02) Feedback from mailing list has proposed removing this
paragraph entirely because (1) explicit assertion of authorization
identity should only be done when proxying (2) mapping of the
asserted authorization identity is implementation specific and
policy driven [SASL] section 4.2, and (3) keeping this paragraph is
not required for interoperability.
G.19. DN used in conjunction with SASL mechanism
We need to specify whether the DN field in Bind operation can/cannot
be used when SASL mechanism is specified. (source: RL Bob)
Status: resolved. (-03) Based on ldapbis WG discussion at IETF52 two
sentences were added to section 4.3 indicating that clients SHOULD
NOT send a DN value when binding with the sasl choice and servers
SHALL ignore any value received in this circumstance. During edits
for -04 version of draft it was noted that [Protocol] section 4.2
conflicts with this draft. The editor of [Protocol] has been
notified of the discrepancy, and they have been handled.
G.20. Bind states
Differences between unauthenticated and anonymous. There are four
states you can get into. One is completely undefined (this is now
explicitly called out in [Protocol]). This text needs to be moved
from [Protocol] to this draft. (source: Jim Sermersheim)
Status: Resolved. There are four states: (1) no name, no password
(anon); (2) name, no password (anon); (3) no name, password
(invalid); (4) name, password (simple bind). States 1, 2, and 4 are
called out in [AuthMeth]. State 3 is called out in [Protocol]; this
seems appropriate based on review of alternatives.
G.21. Misuse of unauthenticated access
Add a security consideration that operational experience shows that
clients can misuse unauthenticated access (simple bind with name but
no password). Servers SHOULD by default reject authentication
requests that have a DN with an empty password with an error of
invalidCredentials. (Source: Kurt Zeilenga and Chris Newman (Sun))
Status: Resolved. Added to security considerations in <20>03.
G.22. Need to move StartTLS protocol information to [Protocol]
Status: Resolved. Removed Sections 5.1, 5.2, and 5.4 for -04 and
they are [Protocol] -11.
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G.23. Split Normative and Non-normative references into separate
sections.
Status: Resolved. Changes made in -04
G.24. What is the authentication state if a Bind operation is
abandoned?
Status: In process. (11/12/02) This text was suggested to be added
to [Protocol] -11 to cover what happens if a bind operation is
abandoned:
"If a server receives an Abandon request for a Bind operation, the
server SHOULD leave the connection in the anonymous state. Clients
that abandon a Bind operation MUST rebind after abandoning the Bind
request in order to have a known authentication state on the
connection."
(11/21/02) Jim Sermersheim prposed the following wording on the
ldapbis mail list: "Authentication from earlier binds are
subsequently ignored. A failed or abandoned Bind Operation has the
effect of leaving the connection in an anonymous state. Clients MUST
rebind after abandoning a bind operation in order to determine a
known authentication state."
Once this is resolved in [Protocol] the state table in section 6 of
[AuthMeth] will need to be updated to reflect the consensus wording.
G.25. Difference between checking server hostname and server's
canonical DNS name in Server Identity Check?
Section 5.1.6: I now understand the intent of the check (prevent
man-in-the-middle attacks). But what is the subtle difference
between the "server hostname" and the "server's canonical DNS name"?
(Source: Tim Hahn)
Status: In Process. (11/12/02) Sent suggested wording change to this
paragraph to the ldapbis mail list and also asked for opinion as to
whether we should discuss the distinction between server DNS
hostname and server canonical DNS hostname in [AuthMeth].
(11/21/02): RL Bob Morgan will provide wording that allows
derivations of the name that are provided securely.
6.26. Server Identity Check using servers located via SRV records
Section 5.1.6: What should be done if the server was found using SRV
records based on the "locate" draft/RFC? (Source: Tim Hahn).
Status: Resolved. Section 5 of draft-ietf-ldapext-locate-08
specifically calls out how the server identity should be performed
if the server is located using the method defined in that draft.
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This is the right location for this information, and the coverage
appears to be adequate.
G.27 Inconsistency in effect of TLS closure on LDAP association.
Section 5.4.1 of authmeth -03 (section 4.1 of RFC2830) states that
TLS closure alert will leave the LDAP association intact. Contrast
this with Section 5.5.2 (section 5.2 of RFC2830) that says that the
closure of the TLS connection MUST cause the LDAP association to
move to an anonymous authentication.
Status: in process. (11/12/02) This is actually a [Protocol] issue
because these sections have now been moved to [Protocol] -11. I have
proposed the following text for Section 5.4.1 of [AuthMeth] -03
(section 4.13.3.1 of [Protocol]) to resolve this apparent
discrepancy:
"Either the client or server MAY terminate the TLS connection on an
LDAP association by sending a TLS closure alert. The LDAP
connection remains open for further communication after TLS closure
occurs although the authentication state of the LDAP connection is
affected (see [AuthMeth] section 5.2.2).
(11/21/02): resolution to this is expected in [Protocol] -12
G.28 Ordering of external sources of authorization identities
Section 4.3.2 implies that external sources of authorization
identities other than TLS are permitted. What is the behavior when
two external sources of authentication credentials are available
(e.g. TLS and IPsec are both present (is this possible?)) and a SASL
EXTERNAL Bind operation is performed?
Status: resolved. 11/20/02: Resolved by Section 4.2 of [SASL] which
states that the decision to allow or disallow the asserted identity
is based on an implementation defined policy.
G.29 Rewrite of Section 10, TLS Ciphersuites
This section contains anachronistic references and needs to be
updated/rewritten in a way that provides useful guidance for future
readers in a way that will transcend the passage of time.
G.30 Update to Appendix A, Example Deployment Scenarios
This section needs to be updated to indicate which security
mechanisms and/or combinations of security mechanisms described
elsewhere in the document can provide the types of protections
suggested in this appendix.
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