INTERNET-DRAFT Editor: R. Harrison
draft-ietf-ldapbis-authmeth-10.txt Novell, Inc.
Obsoletes: 2829, 2830 10 February 2003
Intended Category: Draft Standard
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.
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes authentication methods and connection level
security mechanisms of the Lightweight Directory Access Protocol
(LDAP).
This document also details establishment of TLS (Transport Layer
Security) using the Start TLS operation.
This document also details the simple Bind authentication method
including anonymous, unauthenticated, and plain-text password
methods and the SASL (Simple Authentication and Security Layer) Bind
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authentication method including the use of DIGEST-MD5 and EXTERNAL
mechanisms.
This document describes various authentication and authorization
states through which a connection to an LDAP server may pass and the
actions that trigger these state changes.
Table of Contents
1. Introduction................................................3
1.1. Relationship to Other Documents...........................5
2. Conventions Used in this Document...........................5
2.1. Glossary of Terms.........................................5
2.2. Security Terms and Concepts...............................5
2.3. Keywords..................................................6
3. Start TLS Operation.........................................6
3.1. Sequencing of the Start TLS Operation ....................6
3.1.1. Start TLS Request.......................................6
3.1.2. Start TLS Response......................................7
3.1.3. TLS Version Negotiation.................................7
3.1.4. Discovery of Resultant Security Level...................7
3.1.5. Server Identity Check...................................7
3.1.6. Refresh of Server Capabilities Information..............8
3.2. Effects of TLS on a Client's Authorization Identity.......8
3.2.1. TLS Connection Establishment Effects....................9
3.2.2. Client Assertion of Authorization Identity..............9
3.2.3. TLS Connection Closure Effects..........................9
4. Bind Operation..............................................9
4.1. Simple Authentication.....................................9
4.2. SASL Authentication.......................................9
5. Anonymous LDAP Association on Unbound Connections......... 10
6. Anonymous Authentication ................................. 10
7. Simple Authentication..................................... 10
8. SASL Authentication Profile............................... 11
8.1. SASL Service Name for LDAP.............................. 11
8.2. SASL Authentication Initiation and Protocol Exchange.... 11
8.3. Octet Where Negotiated Security Mechanisms Take Effect.. 12
8.4. Determination of Supported SASL Mechanisms.............. 12
8.5. Rules for Using SASL Security Layers.................... 13
9. SASL EXTERNAL Mechanism................................... 13
9.1. Implicit Assertion...................................... 13
9.2. Explicit Assertion...................................... 14
9.3. SASL Authorization Identity............................. 14
9.4 Authorization Identity Syntax............................ 14
10. SASL DIGEST-MD5 Mechanism................................ 15
11. General Requirements for Password-based Authentication .. 15
12. Invalidated Associations................................. 16
13. TLS Ciphersuites......................................... 16
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13.1. TLS Ciphersuites Recommendations....................... 17
14. Security Considerations ................................. 18
14.1. Start TLS Security Considerations...................... 18
15. IANA Considerations...................................... 19
Acknowledgements............................................. 19
Normative References......................................... 19
Informative References....................................... 21
Author's Address............................................. 21
Appendix A. LDAP Association State Transition Tables......... 21
A.1. LDAP Association States................................. 21
A.2. Actions that Affect LDAP Association State.............. 22
A.3. Decisions Used in Making LDAP Association State Changes. 22
A.4. LDAP Association State Transition Table................. 22
Appendix B. Example Deployment Scenarios..................... 23
Appendix C. Authentication and Authorization Concepts........ 24
C.1. Access Control Policy................................... 24
C.2. Access Control Factors ................................. 24
C.3. Authentication, Credentials, Identity .................. 25
C.4. Authorization Identity ................................. 25
Appendix D. RFC 2829 Change History ......................... 25
Appendix E. RFC 2830 Change History ......................... 29
Appendix F. RFC 2251 Change History ......................... 30
Appendix G. Change History to Combined Document.............. 30
Appendix H. Issues to be Resolved............................ 41
1. Introduction
The Lightweight Directory Access Protocol (LDAP) [Protocol] 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 LDAP conformance.
Basic threats to an LDAP directory service include:
(1) Unauthorized access to directory data via data-retrieval
operations,
(2) Unauthorized access to directory data by monitoring others'
access,
(3) Unauthorized access to reusable client authentication
information by monitoring others' access,
(4) Unauthorized modification of directory data,
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(5) Unauthorized modification of configuration information,
(6) Denial of Service: Use of resources (commonly in excess) in a
manner intended to deny service to others. and
(7) Spoofing: Tricking a user or 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. Tricking a user or client into sending privileged
information to a hostile entity that appears to be the directory
server but is not. Tricking a directory server into believing
that information came from a particular client when in fact it
came from a hostile entity.
(8) Hijacking of prototocol sessions.
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, e.g. IP
spoofing.
LDAP offers the following security mechanisms:
(1) Authentication by means of the Bind operation. The Bind
operation provides a simple method which supports anonymous,
unauthenticated, and authenticated with password mechanisms, and
the Secure Authentication and Security Layer (SASL) method which
supports a wide variety of authentication mechanisms and which
may be extended to support additional methods of authentication.
(2) Client authorization by means of access control based on the
requestor's authenticated identity,
(3) Data integrity protection by means of TLS or SASL mechanisms
with security layers 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 LDAP.
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
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server, or worse, they will support only 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 identities not represented as LDAP DNs that are familiar to
the user or that are used in other systems.
The set of security mechanisms provided in LDAP 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 LDAP implementations and deployments.
Appendix B contains example deployment scenarios that list the
mechanisms that might be used to achieve a reasonable level of
security in various circumstances.
1.1. Relationship to Other Documents
This document is an integral part of the LDAP Technical
Specification [Roadmap].
This document obsoletes RFC 2829.
Sections 2 and 4 of RFC 2830 are obsoleted by [Protocol]. The
remainder of RFC 2830 is obsoleted by this document.
2. Conventions Used in this Document
2.1. Glossary of Terms
The following terms are used in this document. To aid the reader,
these terms are defined here.
- "user" represents any human or application entity which is
accessing the directory using a directory client. A directory
client (or client) is also known as a directory user agent
(DUA).
- "connection" and "LDAP connection" both refer to the underlying
transport protocol connection between two protocol peers.
- "TLS connection" refers to a TLS-protected [TLS] LDAP
connection.
- "association" and "LDAP association" both refer to the
association of the LDAP connection and its current
authentication and authorization state.
2.2. Security Terms and Concepts
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In general, security terms in this document are used consistently
with the definitions provided in [Glossary]. In addition, several
terms and concepts relating to security, authentication, and
authorization are presented in Appendix C 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 C before reading the remainder of this document.
2.3. 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 [Keyword].
3. Start TLS Operation
The Start Transport Layer Security (Start TLS) operation defined in
section 4.13 of [Protocol] provides the ability to establish [TLS]
on an LDAP connection.
3.1. 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 connection are described in detail in
section 3.2.
3.1.1. Start TLS Request
A client may send the Start TLS extended request at any time after
establishing an LDAP connection, except:
- when TLS is currently established on the connection,
- when a multi-stage SASL negotiation is in progress on the
connection, or
- when there are outstanding LDAP operations on the connection.
The result of violating any of these requirements is a resultCode of
operationsError, as described in [Protocol] section 4.13.2.2. Client
implementers should note that it is possible to receive a resultCode
of success for a Start TLS operation that is sent on a connection
with outstanding LDAP operations if the server has sufficient time
to process them prior to its receiving the Start TLS request.
Implementors of clients should ensure that they do not inadvertently
depend upon this race condition.
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There is no requirement that the client have or have not already
performed a Bind operation (section 4) before sending a Start TLS
operation request.
If the client did not establish a TLS connection before sending some
other request, and the server requires the client to establish a TLS
connection before performing that request, the server MUST reject
that request by sending a resultCode of confidentialityRequired or
strongAuthRequired.
An LDAP server which requests that clients provide their certificate
during TLS negotiation MAY use a local security policy to determine
whether to successfully complete TLS negotiation if the client did
not present a certificate which could be validated.
3.1.2. Start TLS Response
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 resultCode values (documented in [Protocol] section 4.13.2.2)
if it is unwilling or 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.
3.1.3. TLS Version Negotiation
Negotiating the version of TLS to be used is a part of the TLS
Handshake Protocol [TLS]. Please refer to that document for details.
3.1.4. Discovery of Resultant Security Level
After a TLS connection is established on an LDAP connection, both
parties must individually decide whether or not to continue based on
the security level achieved. Ascertaining the TLS connection's
security 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
security 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 3.2.3 below).
If the client decides to continue, it may gracefully close the TLS
connection and attempt to Start TLS again, it may send an unbind
request, or it may send any other LDAP request.
3.1.5. 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.
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Matching is performed according to these rules:
- The client MUST use the server provided by the user (or other
trusted entity) as the value to compare against the server name
as expressed in the server's certificate. A hostname derived
from the user input is to be considered provided by the user
only if derived in a secure fashion (e.g., DNSSEC).
- 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 in making
this determination.
3.1.6. Refresh of Server Capabilities Information
Upon TLS session establishment, the client SHOULD discard or refresh
all information about the server it obtained prior to the initiation
of the TLS negotiation and not obtained through secure mechanisms.
This protects 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 and PLAIN [PLAIN] mechanisms are likely to be listed only
after a TLS negotiation has been performed).
3.2. Effects of TLS on a Client's Authorization Identity
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This section describes the effects on a client's authorization
identity brought about by establishing TLS on an LDAP connection.
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 C.
3.2.1. TLS Connection Establishment Effects
The decision to keep or invalidate the established authentication
and authorization identities in place after TLS closure is a matter
of local server policy.
3.2.2. Client Assertion of Authorization Identity
After successfully establishing a TLS session, a client may request
that its credentials exchanged during the TLS establishment be
utilized to authenticate the LDAP association and thus determine the
client's authorization status. The client accomplishes this via an
LDAP Bind request specifying a SASL mechanism of EXTERNAL [SASL]
(section 9). LDAP server implementations SHOULD support this
authentication method.
3.2.3. TLS Connection Closure Effects
The decision to keep or invalidate the established authentication
and authorization identities in place after TLS closure is a matter
of local server policy.
4. Bind Operation
The Bind operation defined in section 4.2 of [Protocol] allows
authentication information to be exchanged between the client and
server to establish a new LDAP association.
Upon receipt of a Bind request, the LDAP association is moved to an
anonymous state and only upon successful completion of the
authentication exchange (and the Bind operation) is the association
moved to an authenticated state.
4.1. Simple Authentication
The simple authentication choice of the Bind Operation provides
minimal facilities for establishing an anonymous association
(section 6) or for establishing an LDAP association based upon
credentials consisting of a name (in the form of an LDAP
distinguished name [LDAPDN]) and a password (section 7).
4.2. SASL Authentication
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The sasl authentication choice of the Bind Operation provides
facilities for authenticating via SASL mechanisms (sections 8-10).
5. Anonymous LDAP Association on Unbound Connections
Prior to the successful completion of a Bind operation and during
any subsequent authentication exchange, the session has an anonymous
LDAP association. Among other things this implies that 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. This authentication state on an LDAP association is
sometimes referred to as an implied anonymous bind.
6. 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.
An LDAP client may explicitly establish an anonymous association by
sending a Bind Request with the simple authentication choice
containing a value--construed as the password--of zero length. A
bind request where both the name and password are of zero length is
said to be an anonymous bind. A bind request where the name, a DN,
is of non-zero length, and the password is of zero length is said to
be an unauthenticated bind. Both variations produce an anonymous
association.
Unauthenticated binds can have significant security issues (see
section 14). Servers SHOULD by default reject unauthenticated bind
requests with a resultCode of invalidCredentials, and clients may
need to actively detect situations where they would make an
unauthenticated bind request.
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.
LDAP implementations MUST support anonymous authentication.
7. Simple Authentication
An LDAP client may establish an LDAP association by sending a Bind
Request with a name value consisting of an LDAP distinguished name
[LDAPDN] and specifying the simple authentication choice with a
password value.
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 the presented password matches any member of that set,
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then the server will respond with a success resultCode, otherwise
the server will respond with an invalidCredentials resultCode.
The 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 4.
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. SASL Authentication Profile
LDAP allows authentication via any SASL mechanism [SASL]. As LDAP
includes native anonymous and plaintext authentication methods, the
ANONYMOUS [ANONYMOUS] and PLAIN [PLAIN] SASL mechanisms are
typically not used with LDAP.
Each protocol that utilizes SASL services is required to supply
certain information profiling the way they are exposed through the
protocol ([SASL] section 5). This section explains how each of these
profiling requirements are met by LDAP.
8.1. SASL Service Name for LDAP
The SASL service name for LDAP is "ldap", which has been registered
with the IANA as a GSSAPI service name.
8.2. SASL Authentication Initiation and Protocol Exchange
SASL authentication is initiated via an LDAP bind request
([Protocol] section 4.2) with the following parameters:
- The version is 3.
- The AuthenticationChoice is sasl.
- The mechanism element of the SaslCredentials sequence contains
the value of the desired SASL mechanism.
- The optional credentials field of the SaslCredentials sequence
may be used to provide an initial client response for
mechanisms that are defined to have the client send data first
(see [SASL] sections 5 and 5.1).
In general, a SASL authentication protocol exchange consists of a
series of server challenges and client responses, the contents of
which are specific to and defined by the SASL mechanism. Thus for
some SASL authentication mechanisms, it may be necessary for the
client to respond to one or more server challenges by invoking the
BindRequest multiple times. A challenge is indicated by the server
sending a BindResponse with the resultCode set to
saslBindInProgress. This indicates that the server requires the
client to send a new bind request with the same sasl mechanism to
continue the authentication process.
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To the encapsulating protocol, these challenges and responses are
opaque binary tokens of arbitrary length. LDAP servers use the
serverSaslCreds field, an OCTET STRING, in a bind response message
to transmit each challenge. LDAP clients use the credentials field,
an OCTET STRING, in the SaslCredentials sequence of a bind request
message to transmit each response. Note that unlike some Internet
protocols where SASL is used, LDAP is not text-based, thus no Base64
transformations are performed on these challenge and response
values.
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.
A client may abort a SASL bind negotiation by sending a BindRequest
with a different value in the mechanism field of SaslCredentials, or
an AuthenticationChoice other than sasl.
If the client sends a BindRequest with the sasl mechanism field as
an empty string, the server MUST return a BindResponse with
authMethodNotSupported as the resultCode. This will allow clients to
abort a negotiation if it wishes to try again with the same SASL
mechanism.
The server indicates completion of the SASL challenge-response
exchange by responding with a bind response in which the resultCode
is either success, or an error indication.
The serverSaslCreds field in the bind response can be used to
include an optional challenge with a success notification for
mechanisms which are defined to have the server send additional data
along with the indication of successful completion.
8.3. Octet Where Negotiated Security Mechanisms Take Effect
SASL security layers take effect following the transmission by the
server and reception by the client of the final successful
BindResponse in the exchange.
Once a SASL security layer providing integrity or confidentiality
services takes effect, the layer remains in effect until a new layer
is installed (i.e. at the first octet following the final
BindResponse of the bind operation that caused the new layer to take
effect).
8.4. Determination of Supported SASL Mechanisms
Clients may determine the SASL mechanisms a server supports by
reading the 'supportedSASLMechanisms ' attribute from the root DSE
(DSA-Specific Entry) ([Models] section 5.1). The values of this
attribute, if any, list the mechanisms the server supports in the
current LDAP session state.
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LDAP servers SHOULD allow an anonymously-bound client to retrieve
the supportedSASLMechanisms attribute of the root DSE.
8.5. Rules for Using SASL Security Layers
If a SASL security layer is negotiated, the client SHOULD discard
information about the server it obtained prior to the initiation of
the SASL negotiation and not obtained through secure mechanisms.
If a lower level security layer (such as TLS) is negotiated, any
SASL security services SHALL be layered on top of such security
layers regardless of the order of their negotiation. In all other
respects, SASL security services and other security layers act
independently, e.g. if both TLS and SASL security service are in
effect removing the SASL security service does not affect the
continuing service of TLS and vice versa.
Because SASL mechanisms provide critical security functions, clients
and servers should allow the user to specify what mechanisms are
acceptable and allow only those mechanisms to be used.
9. SASL EXTERNAL Mechanism
A client can use the EXTERNAL SASL [SASL] mechanism to request the
LDAP server to make use of security credentials exchanged by a lower
security layer (such as by TLS authentication or IP-level security
[SecArch]).
If the client's authentication credentials have not been established
at a lower security layer, 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). In such a situation, the
state of any established security layer is unaffected.
A client may either implicitly request that its LDAP authorization
identity be derived from a lower layer 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.
9.1. Implicit Assertion
An implicit authorization identity assertion is performed by
invoking a Bind request of the SASL form using the EXTERNAL
mechanism name that does 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 identity supplied by the security layer
(e.g., a public key certificate used during TLS establishment)
according to local policy. The underlying mechanics of how this is
accomplished are implementation specific.
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9.2. Explicit Assertion
An explicit authorization identity assertion is performed by
invoking a Bind request of the SASL form using the EXTERNAL
mechanism name that includes the credentials octet string. This
string MUST be constructed as documented in section 3.4.1.
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.
9.3. SASL Authorization Identity
When the EXTERNAL SASL mechanism is being negotiated, if the
SaslCredentials credentials field is present, it contains an
authorization identity. Other mechanisms define the location of the
authorization identity in the credentials field. In either case, the
authorization identity is represented in the authzId form described
below.
9.4 Authorization Identity Syntax
The authorization identity is a string of [UTF-8] encoded [Unicode]
characters corresponding to the following [ABNF] grammar:
authzId = dnAuthzId / uAuthzId
DNCOLON = %x64 %x6e %x3a ; "dn:"
UCOLON = %x75 %x3a ; "u:"
; distinguished-name-based authz id.
dnAuthzId = DNCOLON distinguishedName
; unspecified authorization id, UTF-8 encoded.
uAuthzId = UCOLON userid
userid = *UTF8 ; syntax unspecified
where the <distinguishedName> production is defined in section 3 of
[LDAPDN] and <UTF8> production is defined in section 1.3 of
[Models].
In order to support additional specific authorization identity
forms, future updates to this specification may add new choices
supporting other forms may be added to the authzId production.
The dnAuthzId choice allows clients to assert authorization
identities in the form of a distinguished name to be matched in
accordance with the distinguishedNameMatch matching rule [Syntaxes].
The decision to allow or disallow an authentication identity to have
access to the requested authorization identity is a matter of local
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policy ([SASL] section 4.2). For this reason there is no requirement
that the asserted dn be that of an entry in directory.
The uAuthzId choice allows for compatibility with clients that wish
to assert an authorization identity to a local directory but do not
have that identity in distinguished name form. The value contained
within a uAuthzId MUST be prepared using [SASLPrep] before being
compared octet-wise. The format of userid is defined as only a
sequence of [UTF-8] encoded [Unicode] 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. A uAuthzId SHOULD NOT be assumed to be globally
unique.
10. SASL DIGEST-MD5 Mechanism
LDAP servers that implement any authentication method or mechanism
other than simple anonymous bind MUST implement the SASL
DIGEST-MD5 mechanism [DIGEST-MD5]. This provides client
authentication with protection against passive eavesdropping attacks
but does not provide protection against active intermediary attacks.
DIGEST-MD5 also provides data integrity and data confidentiality
capabilities.
Support for subsequent authentication ([DIGEST-MD5] section 2.2) is
OPTIONAL in clients and servers.
Implementers must take care to ensure that they maintain the
semantics of the DIGEST-MD5 specification even when handling data
that has different semantics in the LDAP protocol.
For example, the SASL DIGEST-MD5 authentication mechanism utilizes
realm and username values ([DIGEST-MD5] section 2.1) which are
syntactically simple strings and semantically simple realm and
username values. These values are not LDAP DNs, and there is no
requirement that they be represented or treated as such. Username
and realm values that look like LDAP DNs in form, e.g. <cn=bob,
dc=example,dc=com>, are syntactically allowed, however DIGEST-MD5
treats them as simple strings for comparison purposes. To illustrate
further, the two DNs <cn=Bob,dc=example,dc=com> (upper case "B") and
<cn=bob,dc=example,dc=com> (lower case "b") are equivalent when
being compared semantically as LDAP DNs because the cn attribute is
defined to be case insensitive, however the two values are not
equivalent if they represent username values in DIGEST-MD5 because
[SASLPrep] semantics are used by DIGEST-MD5.
11. General Requirements for Password-based Authentication
The transmission of passwords in the clear--typically for
authentication or modification--poses a significant security risk.
This risk can be avoided by using SASL authentication [SASL]
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mechanisms that do not transmit passwords in the clear or by
negotiating transport or session layer confidentiality services
before transmitting password values.
To mitigate the security risks associated with the use of passwords,
a server implementation MUST implement a configuration that at the
time of authentication or password modification, requires:
1) A Start TLS encryption layer has been successfully negotiated.
OR
2) Some other confidentiality mechanism that protects the password
value from snooping has been provided.
OR
3) The server returns a resultCode of confidentialityRequired for
the operation (i.e. simple bind with password value, SASL bind
transmitting a password value in the clear, add or modify
including a userPassword value, etc.), even if the password
value is correct.
12. Invalidated Associations
The server may, at any time, invalidate the association, e.g. if the
established security association between the client and server has
unexpectedly failed or been compromised. The association remains
invalidated until the next successful bind request. While the
association is invalidated, the server may reject any operation
request other than Bind, Unbind, and Start TLS by responding with a
resultCode of strongAuthRequired to indicate that the client needs
to bind to reestablish its authentication state before performing
the requested operation.
13. TLS Ciphersuites
A client or server that supports TLS MUST support
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA. Servers SHOULD NOT support
weaker ciphersuites unless other data integrity and
confidentiality protection (such as a SASL security layer) is
in place
Several issues should be considered when selecting TLS ciphersuites
that are appropriate for use in a given circumstance. These issues
include the following:
- The ciphersuite's ability to provide adequate confidentiality
protection for passwords and other data sent over the LDAP
connection. Client and server implementers should recognize that
some TLS ciphersuites provide no confidentiality protection
while other ciphersuites that do provide confidentiality
protection may be vulnerable to being cracked using brute force
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methods, especially in light of ever-increasing CPU speeds that
reduce the time needed to successfully mount such attacks.
Client and server implementers SHOULD carefully consider the
value of the password or data being protected versus the level
of confidentially protection provided by the ciphersuite to
ensure that the level of protection afforded by the ciphersuite
is appropriate.
- The ciphersuite's vulnerability (or lack thereof) to man-in-the-
middle attacks. Ciphersuites vulnerable to man-in-the-middle
attacks 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.
13.1. TLS Ciphersuites Recommendations
As of the writing of this document, the following recommendations
regarding TLS ciphersuites are applicable. Because circumstances are
constantly changing, this list must not be considered exhaustive,
but is hoped that it will serve as a useful starting point for
implementers.
The following ciphersuites defined in [TLS] 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 [TLS] can be cracked easily
(less than a day of CPU time on a standard CPU in 2000) and are NOT
RECOMMENDED for use in confidentiality protection of passwords or
data.
TLS_RSA_EXPORT_WITH_RC4_40_MD5
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
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:
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
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14. 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 can minimize denial of service attacks by timing out idle
connections, and returning the unwillingToPerform resultCode rather
than performing computationally expensive operations requested by
unauthorized clients.
The use of cleartext passwords and other unprotected authentication
credentials is strongly discouraged over open networks when the
underlying transport service cannot guarantee confidentiality.
Operational experience shows that clients can (and frequently do)
misuse unauthenticated bind (see section 5.1). For example, a
client program might make a decision to grant access to non-
directory information on the basis of completing a successful bind
operation. Some LDAP server implementations will return a success
response to an unauthenticated bind thus leaving the client with the
impression that the server has successfully authenticated the
identity represented by the user name, when in effect, an anonymous
LDAP association has been created. Clients that use the results from
a simple bind operation to make authorization decisions should
actively detect unauthenticated bind requests (via the empty
password value) and react appropriately.
Access control SHOULD always be applied when reading sensitive
information or updating directory information.
A connection on which the client has not established connection
integrity and privacy services (e.g via Start TLS, IPSec or a
suitable SASL mechanism) is subject to man-in-the-middle attacks to
view and modify information in transit.
14.1. 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.
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
connection--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
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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 supported 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 data 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 [SASL] and [TLS].
15. IANA Considerations
The following IANA considerations apply to this document:
Please update the GSSAPI service name registry to point to [Roadmap]
and this document.
[To be completed]
Acknowledgements
This document combines information originally contained in RFC 2829
and RFC 2830. The editor 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.
This document is based upon input of the IETF LDAP Revision working
group. The contributions and suggestions made by its members in
shaping the contents and technical accuracy of this document is
greatly appreciated.
Normative References
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[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, November 1997.
[DIGEST-MD5] Leach, P. C. Newman, and A. Melnikov, "Using Digest
Authentication as a SASL Mechanism", draft-ietf-sasl-
rfc2831bis-xx.txt, a work in progress.
[Keyword] Bradner, S., "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[LDAPDN] Zeilenga, Kurt D. (editor), "LDAP: String
Representation of Distinguished Names", draft-ietf-
ldapbis-dn-xx.txt, a work in progress.
[Models] Zeilenga, Kurt D. (editor), "LDAP: Directory
Information Models", draft-ietf-ldapbis-models-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.
[SASL] Melnikov, A. (editor), "Simple Authentication and
Security Layer (SASL)", draft-ietf-sasl-rfc2222bis-
xx.txt, a work in progress.
[SASLPrep] Zeilenga, K., "Stringprep profile for user names and
passwords", draft-ietf-sasl-saslprep-xx.txt, (a work in
progress).
[StringPrep] Hoffman P. and M. Blanchet, "Preparation of
Internationalized Strings ('stringprep')", draft-
hoffman-rfc3454bis-xx.txt, a work in progress.
[Syntaxes] Legg, S. (editor), "LDAP: Syntaxes and Matching Rules",
draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress.
[TLS] Dierks, T. and C. Allen. "The TLS Protocol Version
1.1", draft-ietf-tls-rfc2246-bis-xx.txt, a work in
progress.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 3629, STD 63, November 2003.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
3.2.0" is defined by "The Unicode Standard, Version
3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-
61633-5), as amended by the "Unicode Standard Annex
#27: Unicode 3.1"
(http://www.unicode.org/reports/tr27/) and by the
"Unicode Standard Annex #28: Unicode 3.2"
(http://www.unicode.org/reports/tr28/).
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Informative References
[ANONYMOUS] Zeilenga, K.,"Anonymous SASL Mechanism", draft-
zeilenga-sasl-anon-xx.txt, a work in progress.
[Glossary] Shirey, R., "Internet Security Glossary", RFC 2828, May
2000.
[PLAIN] Zeilenga, K.,"Plain SASL Mechanism", draft-zeilenga-
sasl-plain-xx.txt, a work in progress.
[SecArch] Kent, S. and R. Atkinson, "Security Architecture for
the Internet Protocol", RFC 2401, November 1998.
Author's Address
Roger Harrison
Novell, Inc.
1800 S. Novell Place
Provo, UT 84606
USA
+1 801 861 2642
roger_harrison@novell.com
Appendix A. LDAP Association State Transition Tables
This section provides a state transition table to represent a state
diagram for the various authentication and TLS states through which
an LDAP association may pass during the course of its existence and
the actions that cause these changes in state.
This section is based entirely on information found in this document
and other documents that are part of the LDAP Technical
Specification [Roadmap]. As such, it is strictly informational in
nature.
A.1. LDAP Association States
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 A.4.
ID State Description
-- --------------------------------------------------------------
S1 Anonymous
no Authentication ID is associated with the LDAP connection
no Authorization ID is in force
S2 Authenticated
Authentication ID = I
Authorization ID = X
S3 Authenticated SASL EXTERNAL, implicit authorization ID
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Authentication ID = J
Authorization ID = Y
S4 Authenticated SASL EXTERNAL, explicit authorization ID
Authentication ID = J
Authorization ID = Z
A.2. Actions that Affect LDAP Association State
The following table lists the actions that can affect the
authentication and authorization state of an LDAP association. The
ID for each action is used in the state transition table in section
A.4.
ID Action
-- --------------------------------------------------------------
A1 Client bind request fails
A2 Client successfully performs anonymous simple bind
A3 Client successfully performs unauthenticated simple bind
A4 Client successfully performs simple bind with name and
password OR SASL bind with any mechanism except EXTERNAL using
an authentication ID = I that maps to authorization ID X
A5 Client Binds SASL EXTERNAL with implicit assertion of
authorization ID (section 3.3.6.1)]. The current
authentication ID maps to authorization ID = Y.
A6 Client Binds SASL EXTERNAL with explicit assertion of
authorization ID = Z (section 3.3.6.2)]
A7 Client abandons a bind operation, and server processes the
abandon
A8 Client abandons a bind operation, and server does not process
the abandon
A9 Client Start TLS request fails
A10 Client Start TLS request succeeds
A11 Client or Server: graceful TLS closure ([Protocol] section
4.13.3.1.)
A.3. Decisions Used in Making LDAP Association State Changes
Certain changes in the authentication and authorization 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 transition in the state
transition table in section A.4.
ID Decision Question
-- --------------------------------------------------------------
D1 Are lower-layer credentials available?
D2 Can lower-layer credentials for Auth ID "K" be mapped to
asserted AuthZID "L"?
A.4. LDAP Association State Transition Table
The LDAP Association table below lists the valid authentication and
authorization states for an LDAP association and the actions that
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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.
S1, the initial state for the state machine described in this table,
is the authentication state when an LDAP connection is initially
established.
Current Next
State Action State Comment
------- ------- ----- ---------------------------------------
Any A1 S1 [Protocol] section 4.2.1
Any A2 S1 Section 6
Any A3 S1 Section 6
Any A4 S2 Sections 6.1, 6.2
Any A5, S1 Failed bind, section 3.3.6
D1=no
Any A5, S3
D1=yes
Any A6, S1 failed bind, section 3.3.6
D1=no
Any A6, S1 failed bind, section 3.3.6.2
D1=yes,
D2=no
Any A6, S4
D1=yes,
D2=yes
Any A7 S1 [Protocol] section 4.2.1. Clients
cannot detect this state.
Any A8 no [Protocol] section 4.2.1. Clients
change cannot detect this state.
Any A9 no [Protocol] section 4.13.2.2
change
Any A10 no Section 4.2.1
change
Any A11 S1 Section 4.2.3
Appendix B. 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
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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.
(5) A directory containing sensitive data. This scenario requires
data confidentiality protection AND secure authentication.
Appendix C. Authentication and Authorization 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.
C.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. Security objects and
mechanisms, such as those described here, enable the expression of
access control policies and their enforcement.
C.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
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on resource Z. The set of ACFs that a server makes available for
such expressions is implementation-specific.
C.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.
C.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 [SASL]. 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 D. RFC 2829 Change History
This appendix lists the changes made to the text of RFC 2829 in
preparing this document.
D.0. General Editorial Changes
Version -00
- Changed other instances of the term LDAP to LDAP where v3 of the
protocol is implied. Also made all references to LDAP use the
same wording.
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- 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.
D.1. Changes to Section 1
Version -01
- Moved conventions used in document to a separate section.
D.2. Changes to Section 2
Version -01
- Moved section to an appendix.
D.3. Changes to Section 3
Version -01
- Moved section to an appendix.
D.4 Changes to Section 4
Version -00
- Changed "Distinguished Name" to "LDAP distinguished name".
D.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."
D.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.
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D.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.
2. Moved first paragraph of section 6 (beginning with "LDAP
implementations MUST support authentication with a password...")
to section on Digest Authentication (Now section 6.2).
D.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 LDAP
implementations
D.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."
D.6.3. Changes to section 6.3.
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Version -00
- Renamed to section 6.4.
D.7. Changes to section 7.
none
D.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."
D.8. Changes to section 8.
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.
D.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.
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Version -01
- Moved entire section 9 to become section 3.5 so that it would be
with other SASL material.
D.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.
- Added text: "and MAY support other ciphersuites offering
equivalent or better protection," to the last paragraph of the
section.
D.11. Changes to Section 11.
Version -01
- Moved to section 3.6 to be with other SASL material.
D.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.
D.13. Changes to Section 13 (original section 12).
None
Appendix E. RFC 2830 Change History
This appendix lists the changes made to the text of RFC 2830 in
preparing this document.
E.0. General Editorial Changes
- Material showing the PDUs for the Start TLS response was broken
out into a new section.
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- 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 F. RFC 2251 Change History
This appendix lists the changes made to the text of RFC 2251 in
preparing this document.
F.0. General Editorial Changes
- All material from section 4.2 of RFC 2251 was moved into this
document.
- 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 G. Change History to Combined Document
G.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--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.
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- 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.)
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.
G.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--H.13, H.14, H.16, H.17--were resolved without
requiring changes to the document.
Section 3
- Removed reference to /etc/passwd file and associated text.
Section 4
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- 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.
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.
G.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--H.13, H.14, H.16, H.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.
-
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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 H.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
- Verified all normative references and moved informative
references to a new section 14.
G.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 LDAP 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.
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- 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.
- 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.
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- 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 B.
- Began changes to incorporate information on deployment scenarios
removed from section 3.
G.5. Changes for draft-ldap-bis-authmeth-06
General
- Combined Section 2 (Introduction) and Section 3 (Motivation) and
moved Introduction to section 1. All following sections numbers
were decremented by one as result.
- Edits to fix typos, I-D nits, etc.
- Opened several new issues in Appendix G based on feedback from
WG. Some of these have been resolved. Others require further
discussion.
Section 1
- Added additional example of spoofing under threat (7).
Section 2.1
- Changed definition of "LDAP association" and added terms,
"connection" and "TLS connection" to bring usage in line with
[Protocol].
Section 4.1.6
- Clarified sentence stating that the client MUST NOT use derived
forms of DNS names.
Section 5.1
- Began edits to LDAP Association state table to clarify meaning
of various states and actions.
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- Added action A9 to cover abandoned bind operation and added
appropriate transitions to the state transition table to
accommodate it.
Section 7.2
- Replaced first paragraph to clarify that the "DIGEST-MD5" SASL
mechanism is required to implement.
Section 9
- Rewrote the section to make the advice more applicable over the
long term, i.e. more "timeless." The intent of content in the
original section was preserved.
Section 10
- Added a clarifying example to the consideration regarding misuse
of unauthenticated access.
G.6. Changes for draft-ldap-bis-authmeth-07
General
- Updated external and internal references to accommodate changes
in recent drafts.
- Opened several new issues in Appendix G based on feedback from
WG. Some of these have been resolved. Others require further
discussion.
Section 3
- Rewrote much of section 3.3 to meet the SASL profile
requirements of draft-ietf-sasl-rfc2222bis-xx.txt section 5.
- Changed treatement of SASL ANONYMOUS and PLAIN mechanisms to
bring in line with WG consensus.
Section 4
- Note to implementers in section 4.1.1 based on operational
experience.
- Clarification on client continuing by performing a Start TLS
with TLS already established in section 4.1.4.
- Moved verification of mapping of client's authentication ID to
asserted authorization ID to apply only to explicit assertion.
The local policy in place for implicit assertion is adequate.
Section 7
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- Removed most of section 7.2 as the information is now covered
adequately via the new SASL profile in section 3.3. Added note
to implementors regarding the treatment of username and realm
values in DIGEST-MD5.
- Section 7.3. Minor clarifications in wording.
- Section 7.3.1. Clarification that a match of the presented value
to any member of the set of stored passwords constitutes a
successful authentication.
G.7. Changes for draft-ldap-bis-authmeth-08
General
- Changed usage from LDAPv3 to LDAP for usage consistency across
LDAP technical specification.
- Fixed a number of usage nits for consistency and to bring doc in
conformance with publication guidelines.
Abstract
- Significant cleanup and rewording of abstract based on WG
feedback.
Section 2.1
- New definition of user.
Section 3
- Added 1.5 sentences at end of introductory paragraph indicating
the effect of the Bind op on the LDAP association.
Section 3.1
- Retitled section and clarified wording
Section 3.2
- Clarified that simple authentication choice provides three types
of authentication: anonymous, unauthenticated, and simple
password.
Section 3.3.3
- New wording clarifying when negotiated security mechanisms take
effect.
Section 3.3.5
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- Changed requirement to discard information about server fetched
prior to SASL negotiation from MUST to SHOULD to allow for
information obtained through secure mechanisms.
Section 3.3.6
- Simplified wording of first paragraph based on suggestion from
WG.
Section 3.4
- Minor clarifications in wording.
Section 3.4.1
- Minor clarifications in wording in first sentence.
- Explicitly called out that the DN value in the dnAuthzID form is
to be matched using DN matching rules.
- Called out that the uAuthzID MUST be prepared using SASLprep
rules before being compared.
- Clarified requirement on assuming global uniqueness by changing
a "generally... MUST" wording to "SHOULD".
Section 4.1.1
- Simplified wording describing conditions when Start TLS cannot
be sent.
- Simplified wording in note to implementers regarding race
condition with outstanding LDAP operations on connection.
Section 4.1.5
- Removed section and moved relevant text to section 4.2.2.
Section 4.1.6
- Renumbered to 4.1.5.
- Updated server identity check rules for server's name based on
WG list discussion.
Section 4.1.7
- Renumbered to 4.1.6
- Changed requirement to discard information about server fetched
prior to TLS negotion from MUST to SHOULD to allow for
information obtained through secure mechanisms.
Section 6.1
- Clarified wording.
- Added definition of anonymous and unauthenticated binds.
Section 10
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- Added security consideration (moved from elsewhere) discouraging
use of cleartext passwords on unprotected communication
channels.
Section 11
- Added an IANA consideration to update GSSAPI service name
registry to point to [Roadmap] and [Authmeth]
G.8. Changes for draft-ldap-bis-authmeth-09
General
- Updated section references within document
- Changed reference tags to match other docs in LDAP TS
- Used non-quoted names for all SAL mechanisms
Abstract
- Inspected keyword usage and removed several improper usages.
- Removed sentence saying DIGEST-MD5 is LDAP's mandatory-to-
implement mechanism. This is covered elsewhere in document.
- Moved section 5, authentication state table, of -08 draft to
section 8 of -09 and completely rewrote it.
Section 1
- Reworded sentence beginning, "It is also desireable to allow
authentication methods to carry identities based on existingù
non-LDAP DN-forms..."
- Clarified relationship of this document to other documents in
the LDAP TS.
Section 3.3.5
- Removed paragraph beginning,"If the client is configured to
support multiple SASL mechanisms..." because the actions
specified in the paragraph do not provide the protections
indicated. Added a new paragraph indicating that clients and
server should allow specification of acceptable mechanisms and
only allow those mechanisms to be used.
- Clarified independent behavior when TLS and SASL security layers
are both in force (e.g. one being removed doesn't affect the
other).
Section 3.3.6
- Moved most of section 4.2.2, Client Assertion of Authorization
Identity, to sections 3.3.6, 3.3.6.1, and 3.3.6.2.
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Section 3.3.6.4
- Moved some normative comments into text body.
Section 4.1.2
- Non success resultCode values are valid if server is *unwilling*
or unable to negotiate TLS.
Section 4.2.1
- Rewrote entire section based on WG feedback.
Section 4.2.2
- Moved most of this section to 3.3.6 for better document flow.
Section 4.2.3
- Rewrote entire section based on WG feedback.
Section 5.1
- Moved imperative language regarding unauthenticated access from
security considerations to here.
Section 6
- Added several paragraphs regarding the risks of transmitting
passwords in the clear and requiring server implementations to
provide a specific configuration that reduces these risks.
Section 6.2
- Added sentence describing protections provided by DIGEST-MD5
method.
- Changed DNs in exmple to be dc=example,dc=com.
Section 10
- Updated consideration on use of cleartext passwords to include
other unprotected authentication credentials
- Substantial rework of consideration on misuse of unauthenticated
bind.
G.9. Changes for draft-ldap-bis-authmeth-10
- Reorganized content of sections 3-9 to improve document flow and
reduce redundancy.
- Resolved issue of effect of Start TLS and TLS closure on LDAP
association state.
- Made numerous minor wording changes based on WG feedback.
- Updated list of threats for Section 1.
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- Recommendation that servers should not support weaker TLS
ciphersuites unless other protection is in place.
- Moved authentication state table to appendix and relettered
appendices.
Appendix H. Issues to be Resolved
This appendix lists open questions and issues that need to be
resolved before work on this document is deemed complete.
H.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.
H.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.
H.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.
H.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.
H.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)?"
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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
update it in session well protected against snooping, and the
reference to /etc/passwd has been removed.
H.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)..."
H.7.
Section 4 paragraph 8 indicates that "information about the server
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..."
H.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.
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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.
H.9.
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.
H.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.
H.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.
H.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
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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
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.
H.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.
H.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.
H.15. Include a Start TLS 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)
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Status: Resolved.
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.
Did a significant revision of state transition table in -09. Changes
were based on suggestions from WG and greatly simplified overall
table.
H.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.
H.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.
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H.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
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.
H.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.
H.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.
H.21. Misuse of unauthenticated access
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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 -03.
H.22. Need to move Start TLS protocol information to [Protocol]
Status: Resolved. Removed Sections 5.1, 5.2, and 5.4 for -04 and
they are [Protocol] -11.
H.23. Split Normative and Non-normative references into separate
sections.
Status: Resolved. Changes made in -04
H.24. What is the authentication state if a Bind operation is
abandoned?
Status: Resolved.
(3/24/03) This following text appears in section 4.2.1 of [Protocol]
revision -13 to cover what happens if a bind operation is abandoned:
A failed or abandoned Bind Operation has the effect of leaving the
connection in an anonymous state. To arrive at a known
authentication state after abandoning a bind operation, clients may
unbind, rebind, or make use of the BindResponse.
(6/28/03): The state table in section 6 of [AuthMeth] has been
updated to reflect this wording.
H.25. Difference between checking server hostname and server's
canonical DNS name in Server Identity Check?
Section 4.1.6: 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: Resolved.
(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.
(6/28/03): posted to the WG list asking Bob or any other WG member
who is knowledgeable about the issues involved to help me with
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wording or other information I can use to make this change and close
the work item.
(10/08/03): Based on WG list feedback, I've updated this text to
read what I judge to be the WG consensus, "The client MUST use the
server provided by the user (or other trusted entity) as the value
to compare against the server name as expressed in the server's
certificate. A hostname derived from the user input is to be
considered provided by the user only if derived in a secure fashion
(e.g., DNSSEC)."
H.26. Server Identity Check using servers located via SRV records
Section 4.1.6: 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.
This is the right location for this information, and the coverage
appears to be adequate.
H.27 Inconsistency in effect of TLS closure on LDAP association.
Section 4.4.1 of authmeth -03 (section 4.1 of RFC2830) states that
TLS closure alert will leave the LDAP association intact. Contrast
this with Section 4.5.2 (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: Resolved. (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 4.4.1 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 4.2.2).
(11/21/02): resolution to this is expected in [Protocol] -12
(06/28/03): [Protocol]-15 clarifies that a TLS closure alert
terminates the TLS connection while leaving the LDAP connection
intact. The authentication state table in [AuthMeth] specifies the
effect on the LDAP association.
H.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
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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.
H.29 Rewrite of Section 9, 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.
Status: Resolved. (6/28/03): Rewrote the section to cover the
general issues and considerations involved in selecting TLS
ciphersuites.
H.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.
H.31 Use of PLAIN SASL Mechanism
At least one LDAP server implementer has found the SASL "PLAIN"
mechanism useful in authenticating to legacy systems that do not
represent authentication identities as DNs. Section 3.3.1 appears to
implicitly disallow the use of the SASL "PLAIN" mechanism with LDAP.
Should we allow the use of this mechanism? I.e. is this "SASL"
"PLAIN" MUST NOT be used with LDAP, or is it simply that LDAP
doesn't define bindings for these mechanism. If SASL "PLAIN" is
allowed, the following adjustments will be needed to section 3.3.1:
(a) change section heading, (b) remove reference to "PLAIN" in the
section, (c) ensure wording of last sentence regarding non-DN
AuthZIDs is consistent with rest of the section.
Status: Resolved.
(6/28/03): email to WG list stating issue and asking if we should
remove the reference to SASL "PLAIN".
For -07 draft I've generalized the SASL profile in section 3.3 to
allow any SASL mechanism.
H.32 Clarification on use of SASL mechanisms
Section 3.3.1: BTW, what _are_ the "ANONYMOUS" and "PLAIN" SASL
mechanisms? They are not defined in RFC2222. If you refer to other
SASL mechanisms than those in rfc2222, Maybe you should only list
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which mechanisms _are_used, instead of which ones are _not. (Source:
Hallvard Furuseth)
I (Kurt Zeilenga) note[s] as well that the ANONYMOUS/PLAIN section
(4.2) should
be deleted. ANONYMOUS and PLAIN, like in other mechanism,
can be used in LDAP if a) supported and b) enabled. I note
that they each offer capabilities not found in their simple
bind equivalents (and hence are used in some deployments).
For example, PLAIN (over TLS) is quite useful when interacting
with legacy authentication subsystems. (Source: Kurt Zeilenga)
Status: Resolved.
For -07 draft I've generalized the SASL profile in section 3.3 to
allow any SASL mechanism.
H.33 Clarification on use of password protection based on AuthZID form
Section 3.3.1: "If an authorization identity of a form different
from a DN is requested by the client, a mechanism that protects the
password in transit SHOULD be used." What has that to do with DNs?
A mechanism that protects the password in transit should be used in
any case, shouldn't it?
Status: Resolved.
In -08 draft this text was removed. There is already a general
security consideration that covers this issue.
H.34 Clarification on use of matching rules in Server Identity Check
The text in section 4.1.6 isn't explicit on whether all rules apply
to both CN and dNSName values. The text should be clear as to which
rules apply to which values.... in particular, the wildcard
rules. (Source: Kurt Zeilenga)
H.35 Requested Additions to Security Considerations
Requested to mention hostile servers which the user might have been
fooled to into contacting. Which mechanisms that are standardized by
the LDAP standard do/do not disclose the user's password to the
server? (Or to servers doing man-in-the-middle attack? Or is that a
stupid question?)
Requested to mention denial of service attacks.
Requested list of methods that need/don't need the server to know
the user's plaintext password. (I say 'know' instead of 'store'
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because it could still store the password encrypted, but in a way
which it knows how to decrypt.)
(Source: Hallvard Furuseth)
H.36 Add reference to definition of DIGEST-MD5
Need a reference to the definition of DIGEST-MD5 SASL mechanism in
section 7.2 (Source: Hallvard Furuseth)
Status: Resolved. A reference to to the DIGEST-MD5 SASL mechanism,
[DigestAuth], is included in the -07 revision.
H.37 Clarification on procedure for certificate-based authentication
8.1. Certificate-based authentication with TLS states: "Following
the successful completion of TLS negotiation, the client will send
an LDAP bind request with the SASL "EXTERNAL" mechanism." Is this
immediately following, or just some time later? Should the wording,
"the client will send..." actually read, "the client MUST send..."?
Status: Resolved. In -10 this text has been absorbed into the SASL
EXTERNAL mechanism section.
H.38 Effect of Start TLS on authentication state
Should the server drop all knowledge of connection, i.e. return to
anonymous state, if it gets a Start TLS request on a connection that
has successfully bound using the simple method?
Status: Resolved. In -09 the effect on an LDAP association by a
Start TLS operation is made a matter of local policy. This is based
on editorÆs perception of WG consensus gaged by conversations at
IETF 58 and subsequent discussion on the WG mail list.
H.39 Be sure that there is a consideration in [SCHEMA] that discusses
multiple password values in userPassword
Allowing multiple values obviously does raise a number of security
considerations and these need to be discussed in the document.
Certainly applications which intend to replace the userPassword with
new value(s) should use modify/replaceValues (or
modify/deleteAttribute+addAttribute). Additionally, server
implementations should be encouraged to provide administrative
controls which, if enabled, restrict userPassword to one value.
H.40. Clarify need to verify mapping between authentication identity
and resulting authorization identity on implicit assertion of AuthZID.
4.2.2.3. Error Conditions
"For either form of assertion, the server MUST verify that the
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client's authentication identity as supplied in its TLS credentials
is permitted to be mapped to the asserted authorization identity."
This makes sense for the explicit assertion case, but seems to be
ambiguous for the implicit case.
IMHO, the mapping can be done as two steps:
a). deriving LDAP authentication identity from TLS credentials; If t
this steps fails, EXTERNAL mechanism returns failure.
b). verify that the authorization identity is allowed for the
derived authentication identity. This is always "noop" for the
implicit case.
I am not sure that the text is saying this.
(Source: Alexey Melnikov email 8/1/2003 5:30:43 PM)
Status: Resolved in -07. After reading the comments and the text of
the draft, I believe that this should be clarified. The local policy
used to map the AuthNID to the AuthZID in the implicit case is
sufficient and that no additional verification is useful or needed.
This text has been moved to apply only to the explicit assertion
case.
H.41. Section 7.2 contains unnecessary and misleading detail.
" I am not sure why this section is required in the document.
DIGEST-MD5 is defined in a separate document and there should be
nothing magical about its usage in LDAP. If DIGEST-MD5 description
creates confusion for LDAP implementors, let's fix the DIGEST-MD5
document! Also, this section tries to redefine DIGEST-MD5 behavior,
which is explicitly prohibited by the SASL specification."
(Source: Alexey Melnikov: email 8/1/2003 5:30:43 PM)
Status: Resolved.
After reading the comments and the text of the draft plus the
related text in draft-ietf-sasl-rfc2831bis-02.txt plus
http://www.ietf.org/internet-drafts/draft-ietf-sasl-rfc2222bis-
02.txt, I am inclined to agree with Alexey. In -07 I rewrote section
3.3 (SASL mechanisms) to match the profiling requirements
rfc2831bis. I then dramatically reduced the material in section 7.2
to a bare minimum and let the SASL profile stand on its own.
H.42. Does change for H.41 cause interoperability issue?
There is one issue with the way the authmeth draft is currently
written that changes the SASL DIGEST-MD5 behavior on the way the
server responds with the subsequent authentication information .
This has been documented in this fashion since RFC 2829 (section
6.1) was originally published and may cause an interoperability
issue at this point if it changed to follow the DIGEST-MD5 spec (as
it was in -07 of AuthMeth). Take this issue to the list.
Status: Resolved
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(10/08/03) This item was discussed on the WG list between 5/2/03 and
5/9/03. Consensus apppears to support the notion that RFC 2829 was
in error and that the semantics of RFC 2831 are correct and should
be reflected in authmeth. This is already the case as of the -07
draft.
H.43. DIGEST-MD5 Realms recommendations for LDAP
From http://www.ietf.org/internet-drafts/draft-ietf-sasl-rfc2222bis-
02.txt: A protocol profile SHOULD provide a guidance how realms are
to be constructed and used in the protocol and MAY further restrict
its syntax and protocol-specific semantics."
I don't believe that any such guidance exists within the LDAP TS.
The most likely place for this to reside is in the authmeth draft.
Related email from Alexey Melnikov (8/4/2003 1:08:40 PM):
"The problem I have with the document is that it references realm
without explaining what it is (or at least some examples of valid
values). For LDAP, some recommendations should be given. For
example:
1). Use a hardcoded string as the realm (one of the implementations
I worked on was doing that)
2). Use hostname (realm==host) or domain/cluster name (realm
includes multiple hosts).
3). Use a node in DIT above user entry, for example for "cn=Barbara
Jensen, ou=Accounting, o=Ace Industry, c=US"
and "cn=John Doe, ou=Accounting, o=Ace Industry, c=US" realm can be
"ou=Accounting, o=Ace Industry, c=US"
(or "o=Ace Industry, c=US"); for "cn=Gern Jensen, ou=Product
Testing,o=Ace Industry, c=US" realm can be "ou=Product Testing,
o=Ace Industry, c=US".
Of course other choices are possible.
Alexey
To summarize: I'd like authmeth to define a realm name for use with
Digest-MD5 that corresponds to LDAP DNs known to this server.
Authzid is okay, but perhaps could be better put into context.
John McMeeking (5/12/2003)
Status: Resolved.
draft-ietf-sasl-rfc2222bis-03.txt no longer requires this
information in a SASL protocol. In addition, the ldapbis WG chairs
have ruled this work out of scope. Individuals are welcome to make
submissions to provide guidance on the use of realm and realm values
in LDAP.
H.44. Use of DNs in usernames and realms in DIGEST-MD5
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In reading the discussion on the mailing list, I reach the following
conclusions:
DIGEST-MD5 username and realm are simple strings. The syntax of
these strings allows strings that look like DNs in form, however,
DIGEST-MD5 treats them a simple strings for comparision purposes.
For example, the DNs cn=roger, o=US and cn=roger,o=us are equivalent
when being compared semantically as DNs, however, these would be
considered two different username values in DIGEST-MD5 because
simple octet-wise semantics (rather than DN semantics) are used to
compare username values in DIGEST-MD5. Ditto for realm values.
Status: Resolved.
In -07 revision I added notes to implementors expressing this issue
in section 7.2.
H.45: Open Issue: Is Simple+TLS mandatory to implement?
Going forward, it would be much better to clarify that simple
+TLS is to be used for DN/password credentials and DIGEST-MD5
(or PLAIN+TLS) be used for username/password credentials. (Kurt
Zeilenga, 5/12/2003)
I don't believe you can mandate simple/TLS! At the time RFC 2829 was
debated, a large number on the WG wanted this. They did not get
their way because of the complexity of the solution. It was argued
that a password-based method would be better. I think they believed
it would still be DN/password, though. (Ron Ramsay, 5/12/2003)
This was officially opened as an issue by WG co-chair Kurt Zeilenga
on 5/12/03. Little direct discussion has occurred since, however
there has been significant discussion on the use of DN values as the
username for DIGEST-MD5.
Status: Resolved.
Based on WG list discussion, Kurt Zeilenga has gaged a lack of WG
consensus that Simple+TLS should be mandatory to implement. No
further discussion is necessary.
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