Internet DRAFT - draft-funk-tls-inner-application-extension
draft-funk-tls-inner-application-extension
TLS Working Group P. Funk
Internet-Draft Funk Software, Inc.
Expires: December 27, 2006 S. Blake-Wilson
Basic Commerce & Industries,
Inc.
N. Smith
Intel Corporation
H. Tschofenig
Siemens
T. Hardjono
Verisign Inc
June 25, 2006
TLS Inner Application Extension (TLS/IA)
draft-funk-tls-inner-application-extension-03.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
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This document defines a new TLS extension called "Inner Application".
When TLS is used with the Inner Application extension (TLS/IA),
additional messages are exchanged after completion of the TLS
handshake, in effect providing an extended handshake prior to the
start of upper layer data communications. Each TLS/IA message
contains an encrypted sequence of Attribute-Value-Pairs (AVPs) from
the RADIUS/Diameter namespace. Hence, the AVPs defined in RADIUS and
Diameter have the same meaning in TLS/AI; that is, each attribute
code point refers to the same logical attribute in any of these
protocols. Arbitrary "applications" may be implemented using the AVP
exchange. Possible applications include EAP or other forms of user
authentication, client integrity checking, provisioning of additional
tunnels, and the like. Use of the RADIUS/Diameter namespace provides
natural compatibility between TLS/IA applications and widely deployed
AAA infrastructures.
It is anticipated that TLS/IA will be used with and without
subsequent protected data communication within the tunnel established
by the handshake. For example, TLS/IA may be used to secure an HTTP
data connection, allowing more robust password-based user
authentication to occur than would otherwise be possible using
mechanisms available in HTTP. TLS/IA may also be used for its
handshake portion alone; for example, EAP-TTLSv1 encapsulates a
TLS/IA handshake in EAP as a means to mutually authenticate a client
and server and establish keys for a separate data connection.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. A bit of History . . . . . . . . . . . . . . . . . . . . . 5
1.2. TLS With or Without Upper Layer Data Communications . . . 6
2. The Inner Application Extension to TLS . . . . . . . . . . . . 7
2.1. TLS/IA Overview . . . . . . . . . . . . . . . . . . . . . 8
2.2. Message Exchange . . . . . . . . . . . . . . . . . . . . . 9
2.3. Inner Secret . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.1. Application Session Key Material . . . . . . . . . . . 11
2.4. Session Resumption . . . . . . . . . . . . . . . . . . . . 13
2.5. Error Termination . . . . . . . . . . . . . . . . . . . . 13
2.6. Negotiating the Inner Application Extension . . . . . . . 13
2.7. InnerApplication Protocol . . . . . . . . . . . . . . . . 14
2.7.1. InnerApplicationExtension . . . . . . . . . . . . . . 14
2.7.2. InnerApplication Message . . . . . . . . . . . . . . . 15
2.7.3. IntermediatePhaseFinished and FinalPhaseFinished
Messages . . . . . . . . . . . . . . . . . . . . . . . 15
2.7.4. The ApplicationPayload Message . . . . . . . . . . . . 16
2.8. Alerts . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3. Encapsulation of AVPs within ApplicationPayload Messages . . . 18
3.1. AVP Format . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2. AVP Sequences . . . . . . . . . . . . . . . . . . . . . . 19
3.3. Guidelines for Maximum Compatibility with AAA Servers . . 20
4. Tunneled Authentication within Application Phases . . . . . . 21
4.1. Implicit challenge . . . . . . . . . . . . . . . . . . . . 21
4.2. Tunneled Authentication Protocols . . . . . . . . . . . . 22
4.2.1. EAP . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.2.2. CHAP . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2.3. MS-CHAP . . . . . . . . . . . . . . . . . . . . . . . 23
4.2.4. MS-CHAP-V2 . . . . . . . . . . . . . . . . . . . . . . 24
4.2.5. PAP . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.3. Performing Multiple Authentications . . . . . . . . . . . 26
5. Example Message Sequences . . . . . . . . . . . . . . . . . . 27
5.1. Full Initial Handshake with Intermediate and Final
Application Phasess . . . . . . . . . . . . . . . . . . . 27
5.2. Resumed Session with Single Application Phase . . . . . . 29
5.3. Resumed Session with No Application Phase . . . . . . . . 29
6. Security Considerations . . . . . . . . . . . . . . . . . . . 31
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.1. Normative References . . . . . . . . . . . . . . . . . . . 34
7.2. Informative References . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
Intellectual Property and Copyright Statements . . . . . . . . . . 37
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1. Introduction
This specification defines the TLS "Inner Application" extension.
The term "TLS/IA" refers to the TLS protocol when used with the Inner
Application extension.
In TLS/IA, the setup portion of TLS is extended to allow an arbitrary
exchange of information between client and server within a protected
tunnel established during the TLS handshake and prior to the start of
upper layer TLS data communications. The TLS handshake itself is
unchanged; the subsequent Inner Application exchange is conducted
under the confidentiality and integrity protection that is afforded
by the TLS handshake.
The primary motivation for providing this facility is to allow robust
user authentication to occur as part of an "extended" handshake, in
particular, user authentication that is based on password
credentials, which is best conducted under the protection of an
encrypted tunnel to preclude dictionary attack by eavesdroppers. For
example, the Extensible Authentication Protocol (EAP) may be used for
authentication using any of a wide variety of methods as part of this
extended handshake. The multi-layer approach of TLS/IA, in which a
strong authentication, typically based on a server certificate, is
used to protected a password-based authentication, distinguishes it
from other TLS variants that rely entirely on a pre-shared key or
password for security (such as [I-D.ietf-tls-psk]).
The protected exchange accommodates any type of client-server
application, not just authentication, though authentication may often
be the prerequisite for other applications to proceed. For example,
TLS/IA may be used to set up HTTP connections, establish IPsec
security associations (as an alternative to IKE), obtain credentials
for single sign-on, provide client integrity verification, and so on.
The new messages that are exchanged between client and server are
encoded as sequences of Attribute-Value-Pairs (AVPs) from the RADIUS/
Diameter namespace. Use of the RADIUS/Diameter namespace provides
natural compatibility between TLS/IA applications and widely deployed
AAA infrastructures. This namespace is extensible, allowing new AVPs
and, thus, new applications to be defined as needed, either by
standards bodies or by vendors wishing to define proprietary
applications.
The TLS/IA exchange comprises one or more "phases", each of which
consists of an arbitrary number of AVP exchanges followed by a
confirmation exchange. Authentications occurring in any phase must
be confirmed prior to continuing to the next phase. This allows
applications to implement security dependencies in which particular
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assurances are required prior to the exchange of additional
information.
1.1. A bit of History
The TLS protocol has its roots in the Netscape SSL protocol, which
was originally intended to protect HTTP traffic. It provides either
one-way or mutual certificate-based authentication of client and
server. In its most typical use in HTTP, the client authenticates
the server based on the server's certificate and establishes a tunnel
through which HTTP traffic is passed.
For the server to authenticate the client within the TLS handshake,
the client must have its own certificate. In cases where the client
must be authenticated without a certificate, HTTP, not TLS,
mechanisms would have to be employed. For example, HTTP headers have
been defined to perform user authentications. However, these
mechanisms are primitive compared to other mechanisms, most notably
EAP, that have been defined for contexts other than HTTP.
Furthermore, any mechanisms defined for HTTP cannot be utilized when
TLS is used to protect non-HTTP traffic.
The TLS protocol has also found an important use in authentication
for network access, originally within PPP for dial-up access and
later for wireless and wired 802.1X access. Several EAP types have
been defined that utilize TLS to perform mutual client-server
authentication. The first to appear, EAP-TLS, uses the TLS handshake
to authenticate both client and server based on their certificates.
Subsequently proposed protocols, such EAP-TTLSv0 and EAP-PEAP,
utilize the TLS handshake to allow the client to authenticate the
server based on the latter's certificate, and then use the protected
channel established by the TLS handshake to perform user
authentication, typically based on a password. Such protocols are
called "tunneled" EAP protocols. The authentication mechanism used
inside the tunnel may itself be EAP, and the tunnel may also be used
to convey additional information between client and server.
While tunneled authentication would be useful in other contexts
besides EAP, the tunneled protocols mentioned above cannot be
employed in a more general use of TLS, since the outermost protocol
is EAP, not TLS. Furthermore, these protocols use the TLS tunnel to
carry authentication exchanges, and thus preclude use of the TLS
tunnel for other purposes such as carrying HTTP traffic.
TLS/IA provides a means to perform user authentication and other
message exchanges between client and server strictly within TLS.
TLS/IA can thus be used both for flexible user authentication within
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a TLS session and as a basis for tunneled authentication within EAP.
The TLS/IA approach is to insert an additional message exchange
between the TLS handshake and the subsequent data communications
phase. This message exchange is carried in a new record type, which
is distinct from the record type that carries upper layer data.
Thus, the data portion of the TLS exchange becomes available for HTTP
or another protocol that needs to be secured.
1.2. TLS With or Without Upper Layer Data Communications
It is anticipated that TLS/IA will be used with and without
subsequent protected data communication within the tunnel established
by the handshake.
For example, TLS/IA may be used to protect an HTTP connection,
allowing more robust password-based user authentication to occur
within the TLS/IA extended handshake than would otherwise be possible
using mechanisms available in HTTP.
TLS/IA may also be used for its handshake portion alone. For
example, EAP-TTLSv1 encapsulates a TLS/IA extended handshake in EAP
as a means to mutually authenticate a client and server and establish
keys for a separate data connection; no subsequent TLS data portion
is required. Another example might be the use of TLS/IA directly
over TCP in order to provide a user with credentials for single
sign-on.
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2. The Inner Application Extension to TLS
The Inner Application extension to TLS follows the guidelines of
[RFC3546].
A new extension type is defined for negotiating use of TLS/IA:
The InnerApplicationExtension extension type. The client proposes
use of this extension by including a InnerApplicationExtension
message in its ClientHello handshake message, and the server
confirms its use by including a InnerApplicationExtension message
in its ServerHello handshake message.
A new record type (ContentType) is defined for use in TLS/IA:
The InnerApplication record type. This record type carries all
messages that are exchanged after the TLS handshake and prior to
exchange of data.
A new message type is defined for use within the InnerApplication
record type:
The InnerApplication message. This message may encapsulate any of
the three following subtypes:
The ApplicationPayload message. This message is used to carry
AVP (Attribute-Value Pair) sequences within the TLS/IA extended
handshake, in support of client-server applications such as
authentication.
The IntermediatePhaseFinished message. This message confirms
session keys established during the current TLS/IA phase, and
indicates that at least one additional phase is to follow.
The FinalPhaseFinished message. This message confirms session
keys established during the current TLS/IA phase, and indicates
that no further phases are to follow.
Two new alert codes are defined for use in TLS/IA:
The InnerApplicationFailure alert. This error alert allows either
party to terminate the TLS/IA extended handshake due to a failure
in an application implemented via AVP sequences carried in
ApplicationPayload messages.
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The InnerApplicationVerification alert. This error alert allows
either party to terminate the TLS/IA extended handshake due to
incorrect verification data in a received
IntermediatePhaseFinished or FinalPhaseFinished message.
The following new assigned numbers are used in TLS/IA:
"InnerApplicationExtension" extension type: 37703
"InnerApplication" record type: 24
"InnerApplicationFailure" alert code: 208
"InnerApplicationVerification" alert code: 209
[Editor's note: I have not checked these types yet against types
defined in RFCs or drafts. The TLS RFC specifies that new record
types use the next number after ones already defined; hence I used
24, though I don't know if that is already taken.]
2.1. TLS/IA Overview
In TLS/IA, zero or more "application phases are inserted after the
TLS handshake and prior to ordinary data exchange. The last such
application phase is called the "final phase"; any application phases
prior to the final phase are called "intermediate phases".
Intermediate phases are only necessary if interim confirmation of
session keys generated during an application phase is desired.
Each application phase consists of ApplicationPayload handshake
messages exchanged by client and server to implement applications
such as authentication, plus concluding messages for cryptographic
confirmation. These messages are encapsulated in records with
ContentType of InnerApplication. All application phases prior to the
final phase use IntermediatePhaseFinished rather than
FinalPhaseFinished as the concluding message. The final phase
concludes with the FinalPhaseFinished message.
Application phases may be omitted entirely only when session
resumption is used, provided both client and server agree that no
application phase is required. The client indicates in its
ClientHello whether it is willing to omit application phases in a
resumed session, and the server indicates in its ServerHello whether
any application phases are to ensue.
In each application phase, the client sends the first
ApplicationPayload message. ApplicationPayload messages are then
traded one at a time between client and server, until the server
concludes the phase by sending, in response to an ApplicationPayload
message from the client, an IntermediatePhaseFinished sequence to
conclude an intermediate phase, or a FinalPhaseFinished sequence to
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conclude the final phase. The client then responds with its own
IntermediatePhaseFinished or FinalPhaseFinished message.
Note that the server MUST NOT send an IntermediatePhaseFinished or
FinalPhaseFinished message immediately after sending an
ApplicationPayload message. It must allow the client to send an
ApplicationPayload message prior to concluding the phase. Thus,
within any application phase, there will be one more
ApplicationPayload message sent by the client than sent by the
server.
The server determines which type of concluding message is used,
either IntermediatePhaseFinished or FinalPhaseFinished, and the
client MUST echo the same type of concluding message. Each
IntermediatePhaseFinished or FinalPhaseFinished message provides
cryptographic confirmation of any session keys generated during the
current and any prior applications phases.
Each ApplicationPayload message contains opaque data interpreted as
an AVP (Attribute-Value Pair) sequence. Each AVP in the sequence
contains a typed data element. The exchanged AVPs allow client and
server to implement "applications" within a secure tunnel. An
application may be any procedure that someone may usefully define. A
typical application might be authentication; for example, the server
may authenticate the client based on password credentials using EAP.
Other possible applications include distribution of keys, validating
client integrity, setting up IPsec parameters, setting up SSL VPNs,
and so on.
An "inner secret" is computed during each application phase that
cryptographically combines the TLS master secret with any session
keys that have been generated during the current and any previous
application phases. At the conclusion of each application phase, a
new inner secret is computed a nd is used to create verification data
that is exchanged via the IntermediatePhaseFinished or
FinalPhaseFinished messages. By mixing session keys of inner
authentications with the TLS master secret, certain man-in-the-middle
attacks are thwarted [MITM].
2.2. Message Exchange
Each intermediate application phase consists of ApplicationPayload
messages sent alternately by client and server, and a concluding
exchange of IntermediatePhaseFinished messages. The first and last
ApplicationPayload message in each intermediate phase is sent by the
client; the first IntermediatePhaseFinished message is sent by the
server. Thus the client begins the exchange with an
ApplicationPayload message and the server determines when to conclude
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it by sending IntermediatePhaseFinished. When it receives the
server's IntermediatePhaseFinished message, the client sends its own
IntermediatePhaseFinished message, followed by an ApplicationPayload
message to begin the next handshake phase.
The final application proceeds in the same manner as the intermediate
phase, except that the FinalPhaseFinished message is sent by the
server and echoed by the client, and the client does not send an
ApplicationPayload message for the next phase because there is no
next phase.
At the start of each application phase, the server MUST wait for the
client's opening ApplicationPayload message before it sends its own
ApplicationPayload message to the client. The client MUST NOT
initiate conclusion of an application phase by sending the first
IntermediatePhaseFinished or FinalPhaseFinished message; it MUST
allow the server to initiate the conclusion of the phase.
Note that it is perfectly acceptable for either client or server to
send an ApplicationPayload message containing no AVPs. The client,
for example, may have no AVPs to send in its first or last
ApplicationPayload message during an application phase.
2.3. Inner Secret
The inner secret is a 48-octet value used to confirm that the
endpoints of the TLS handshake are the same entities as the endpoints
of the inner authentications that may have been performed during each
application phase.
The inner secret is initialized to the master secret at the
conclusion of the TLS handshake. At the conclusion of each
application phase, prior to computing verification data for inclusion
in the IntermediatePhaseFinished or FinalPhaseFinished message, each
party permutes the inner secret using a PRF that includes session
keys produced during the current application phase. The value that
results replaces the current inner secret and is used to compute the
verification data.
inner_secret = PRF(inner_secret,
"inner secret permutation",
SecurityParameters.server_random +
SecurityParameters.client_random +
session_key_material) [0..48];
session_key_material is the concatenation of session_key vectors,
one for each session key generated during the current phase, where:
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opaque session_key<1..2^16-1>;
In other words, each session key is prefixed by a 2-octet length to
produce the session_key vector.
Since multiple session keys may be produced during a single
application phase, the following method is used to determine the
order of concatenation: Each session key is treated as an unsigned
big-endian numeric value, and the set of session keys is ordered from
lowest to highest. The session keys are then converted to
session_key vectors and concatenated in the determined order to form
session_key_material.
If no session keys were generated during the current phase,
session_key_material will be null.
Note that session_key_material itself is not a vector and therefore
not prefixed with the length of the entire collection of session_key
vectors. Note that, within TLS itself, the inner secret is used for
verification only, not for encryption. However, the inner secret
resulting from the final application phase may be exported for use as
a key from which additional session keys may be derived for arbitrary
purposes, including encryption of data communications separate from
TLS.
An exported inner secret should not be used directly for any
cryptographic purpose. Instead, additional keys should be derived
from the inner secret, for example by using a PRF. This ensures
cryptographic separation between use of the inner secret for session
key confirmation and additional use of the inner secret outside
TLS/IA.
2.3.1. Application Session Key Material
Many authentication protocols used today generate session keys that
are bound to the authentication. Such keying material is normally
intended for use in a subsequent data connection for encryption and
validation. For example, EAP-TLS, MS-CHAP-V2, and EAP-MS-CHAP-V2
generate session keys.
Any session keys generated during an application phase MUST be used
to permute the TLS/IA inner secret between one phase and the next,
and MUST NOT be used for any other purpose.
Each authentication protocol may define how the session key it
generates is mapped to an octet sequence of some length for the
purpose of TLS/IA mixing. However, for protocols which do not
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specify this (including the multitude of protocols that pre-date
TLS/IA) the following rules are defined. The first rule that applies
SHALL be the method for determining the session key.
If the authentication protocol produces an MSK (as defined in
[RFC3784]), the MSK is used as the session key. Note that an MSK
is 64 octets.
If the authentication protocol maps its keying material to the
RADIUS attributes MS-MPPE-Recv-Key and MS-MPPE-Send-Key
[RFC2548]], then the keying material for those attributes are
concatenated, with MS-MPPE-Recv-Key first (Note that this rule
applies to MS-CHAP-V2 and EAP-MS-CHAP-V2.)
If the authentication protocol uses a pseudo-random function to
generate keying material, that function is used to generate 64
octets for use as keying material.
Providing verification of the binding of session keys to the TLS
master secret is necessary to preclude man-in-the-middle attacks
against tunneled authentication protocols, as described in [MITM].
In such an attack, an unsuspecting client is induced to perform an
untunneled authentication with an attacker posing as a server; the
attacker then introduces the authentication protocol into a tunneled
authentication protocol, fooling an authentic server into believing
that the attacker is the authentic user.
By mixing both the TLS master secret and session keys generated
during application phase authentication into the inner secret used
for application phase verification, such attacks are thwarted, as it
guarantees that the same client acted as the endpoint for both the
TLS handshake and the application phase authentication. Note that
the session keys generated during authentication must be
cryptographically bound to the authentication and not derivable from
data exchanged during authentication in order for the keying material
to be useful in thwarting such attacks.
In addition, the fact that the inner secret cryptographically
incorporates session keys from application phase authentications
provides additional protection when the inner secret is exported for
the purpose of generating additional keys for use outside of the TLS
exchange. If such an exported secret did not include keying material
from inner authentications, an eavesdropper who somehow knew the
server's private key could, in an RSA-based handshake, determine the
exported secret and hence would be able to compute the additional
keys that are based on it. When inner authentication keying
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material, unknown to the attacker, is incorporated into the exported
secret, such an attack becomes infeasible.
2.4. Session Resumption
A TLS/IA initial handshake phase may be resumed using standard
mechanisms defined in [RFC2246]. When the TLS session is resumed,
client and server may not deem it necessary to exchange AVPs in one
or more additional application phases, as the resumption itself may
provide the necessary security.
The client indicates within the InnerApplicationExtension message in
ClientHello whether it requires AVP exchange when session resumption
occurs. If it indicates that it does not, then the server may at its
option omit application phases and the two parties proceed to upper
layer data communications immediately upon completion of the TLS
handshake. The server indicates whether application phases are to
follow the TLS handshake in its InnerApplication extension message in
ServerHello.
Note that [RFC3546] specifically states that when session resumption
is used, the server MUST ignore any extensions in the ClientHello.
However, it is not possible to comply with this requirement for the
Inner Application extension, since even in a resumed session it may
be necessary to include application phases, and whether they must be
included is negotiated in the extension message itself. Therefore,
the [RFC3546] provision is explicitly overridden for the single case
of the Inner Application extension, which is considered an exception
to this rule.
A TLS/IA session MAY NOT be resumed if an application phase resulted
in failure, even though the TLS handshake itself succeeded. Both
client and server MUST NOT save session state for possible future
resumption unless the TLS handshake and all subsequent application
phases have been successfully executed.
2.5. Error Termination
The TLS/IA handshake may be terminated by either party sending a
fatal alert, following standard TLS procedures.
2.6. Negotiating the Inner Application Extension
Use of the InnerApplication extension follows [RFC3546]. The client
proposes use of this extension by including the
InnerApplicationExtension message in the client_hello_extension_list
of the extended ClientHello. If this message is included in the
ClientHello, the server MAY accept the proposal by including the
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InnerApplicationExtension message in the server_hello_extension_list
of the extended ServerHello. If use of this extension is either not
proposed by the client or not confirmed by the server, the
InnerApplication record type MUST NOT be used.
2.7. InnerApplication Protocol
All specifications of TLS/IA messages follow the usage defined in
[RFC2246].
2.7.1. InnerApplicationExtension
enum {
no(0), yes(1), (255)
} AppPhaseOnResumption;
struct {
AppPhaseOnResumption app_phase_on_resumption;
} InnerApplicationExtension;
If the client wishes to propose use of the Inner Application
extension, it must include the InnerApplicationExtension message in
the extension_data vector in the Extension structure in its extended
ClientHello message.
If the server wishes to confirm use of the Inner Application
extension that has been proposed by the client, it must include the
InnerApplicationExtension message in the extension_data vector in the
Extension structure in its extended ServerHello message. The
AppPhaseOnResumption enumeration allow client and server to negotiate
an abbreviated, single-phase handshake when session resumption is
employed. If the client sets app_phase_on_resumption to "no", and if
the server resumes the previous session, then the server MAY set
app_phase_on_resumption to "no" in the InnerApplication message it
sends to the client. If the server sets app_phase_on_resumption to
"no", no application phases occur and the TLS connection proceeds to
upper layer data exchange immediately upon conclusion of the TLS
handshake.
The server MUST set app_phase_on_resumption to "yes" if the client
set app_phase_on_resumption to "yes" or if the server does not resume
the session. The server MAY set app_phase_on_resumption to "yes" for
a resumed session even if the client set app_phase_on_resumption to
"no", as the server may have reason to proceed with one or more
application phases.
If the server sets app_phase_on_resumption to "yes" for a resumed
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session, then the client MUST initiate an application phase at the
conclusion of the TLS handshake.
The value of app_phase_on_resumption applies to the current handshake
only; that is, it is possible for app_phase_on_resumption to have
different values in two handshakes that are both resumed from the
same original TLS session.
2.7.2. InnerApplication Message
enum {
application_payload(0), intermediate_phase_finished(1),
final_phase_finished(2), (255)
} InnerApplicationType;
struct {
InnerApplicationType msg_type;
uint24 length;
select (InnerApplicationType) {
case application_payload: ApplicationPayload;
case intermediate_phase_finished:
IntermediatePhaseFinished;
case final_phase_finished: FinalPhaseFinished;
} body;
} InnerApplication;
The InnerApplication message carries any of the message types defined
for the InnerApplication protocol.
2.7.3. IntermediatePhaseFinished and FinalPhaseFinished Messages
struct {
opaque verify_data[12];
} PhaseFinished;
PhaseFinished IntermediatePhaseFinished;
PhaseFinished FinalPhaseFinished;
verify_data
PRF(inner_secret, finished_label) [0..11];
finished_label
when sent by the client, the string "client phase finished"
when sent by the server, the string "server phase finished"
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The IntermediatePhaseFinished and FinalPhaseFinished messages have
the same structure and include verification data based on the current
inner secret. IntermediatePhaseFinished is sent by the server and
echoed by the client to conclude an intermediate application phase,
and FinalPhaseFinished is used in the same manner to conclude the
final application phase.
2.7.4. The ApplicationPayload Message
The ApplicationPayload message carries an AVP sequence during an
application handshake phase. It is defined as follows:
struct {
opaque avps[InnerApplication.length];
} ApplicationPayload;
avps
The AVP sequence, treated as an opaque sequence of octets.
InnerApplication.length
The length field in the encapsulating InnerApplication
message.
Note that the "avps" element has its length defined in square bracket
rather than angle bracket notation, implying a fixed rather than
variable length vector. This avoids having the length of the AVP
sequence specified redundantly both in the encapsulating
InnerApplication message and as a length prefix in the avps element
itself.
2.8. Alerts
Two new alert codes are defined for use during an application phase.
The AlertLevel for either of these alert codes MUST be set to
"fatal".
InnerApplicationFailure: An InnerApplicationFailure error alert may
be sent by either party during an application phase. This indicates
that the sending party considers the negotiation to have failed due
to an application carried in the AVP sequences, for example, a failed
authentication.
InnerApplicationVerification: An InnerApplicationVerification error
alert is sent by either party during an application phase to indicate
that the received IntermediatePhaseFinished or FinalPhaseFinished is
invalid.
Note that other alerts are possible during an application phase; for
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example, decrypt_error. The InnerApplicationFailure alert relates
specifically to the failure of an application implemented via AVP
sequences; for example, failure of an EAP or other authentication
method, or information passed within the AVP sequence that is found
unsatisfactory.
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3. Encapsulation of AVPs within ApplicationPayload Messages
During application phases of the TLS handshake, information is
exchanged between client and server through the use of attribute-
value pairs (AVPs). This data is encrypted using the current cipher
state.
The AVP format chosen for TLS/IA is compatible with the Diameter AVP
format. This does not in any way represent a requirement that
Diameter be supported by any of the devices or servers participating
in the TLS/IA conversation, whether directly as client or server or
indirectly as a backend authenticator. Use of this format is merely
a convenience. Diameter is a superset of RADIUS and includes the
RADIUS attribute namespace by definition, though it does not limit
the size of an AVP as does RADIUS. RADIUS, in turn, is a widely
deployed AAA protocol and attribute definitions exist for the
encapsulation of EAP as well as all commonly used non-EAP password
authentication protocols.
Thus, Diameter is not considered normative except as specified in
this document. Specifically, the AVP Codes used in TLS/IA are
semantically equivalent to those defined for Diameter, and, by
extension, RADIUS.
Use of the RADIUS/Diameter namespace allows a TLS/IA server to
translate between AVPs it uses to communicate with clients and the
protocol requirements of AAA servers that are widely deployed.
Additionally, it provides a well-understood mechanism to allow
vendors to extend that namespace for their particular requirements.
3.1. AVP Format
The format of an AVP is shown below. All items are in network, or
big-endian, order; that is, they have most significant octet first.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V M r r r r r r| AVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-ID (opt) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
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AVP Code
The AVP Code is four octets and, combined with the Vendor-ID field
if present, identifies the attribute uniquely. The first 256 AVP
numbers represent attributes defined in RADIUS. AVP numbers 256
and above are defined in Diameter.
AVP Flags
The AVP Flags field is one octet, and provides the receiver with
information necessary to interpret the AVP.
The 'V' (Vendor-Specific) bit indicates whether the optional
Vendor-ID field is present. When set to 1, the Vendor-ID field is
present and the AVP Code is interpreted according to the namespace
defined by the vendor indicated in the Vendor-ID field.
The 'M' (Mandatory) bit indicates whether support of the AVP is
required. When set to 0, this indicates that the AVP may be
safely ignored if the receiving party does not understand or
support it. When set to 1, if the receiving party does not
understand or support the AVP it MUST fail the negotiation by
sending an InnerApplicationFailure error alert. The 'r'
(reserved) bits are unused and must be set to 0.
AVP Length
The AVP Length field is three octets, and indicates the length of
this AVP including the AVP Code, AVP Length, AVP Flags, Vendor-ID
(if present) and Data.
Vendor-ID
The Vendor-ID field is present if and only if the 'V' bit is set
in the AVP Flags field. It is four octets, and contains the
vendor's IANA-assigned "SMI Network Management Private Enterprise
Codes" [RFC1700] value. Vendors defining their own AVPs must
maintain a consistent namespace for use of those AVPs within
RADIUS, Diameter and TLS/IA. A Vendor-ID value of zero is
semantically equivalent to absence of the Vendor-ID field
altogether.
3.2. AVP Sequences
Data encapsulated within the TLS Record Layer must consist entirely
of a sequence of zero or more AVPs. Each AVP must begin on a 4-octet
boundary relative to the first AVP in the sequence. If an AVP is not
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a multiple of 4 octets, it must be padded with 0s to the next 4-octet
boundary. Note that the AVP Length does not include the padding.
3.3. Guidelines for Maximum Compatibility with AAA Servers
When maximum compatibility with AAA servers is desired, the following
guidelines for AVP usage are suggested:
Non-vendor-specific AVPs should be selected from the set of
attributes defined for RADIUS; that is, attributes with codes less
than 256. This provides compatibility with both RADIUS and
Diameter.
Vendor-specific AVPs should be defined in terms of RADIUS.
Vendor-specific RADIUS attributes translate to Diameter
automatically; the reverse is not true. RADIUS vendor-specific
attributes use RADIUS attribute 26 and include vendor ID, vendor-
specific attribute code and length; see[RFC2865] for details.
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4. Tunneled Authentication within Application Phases
TLS/IA permits user authentication information to be tunneled within
an application phase between client and server, protecting the
authentication information against active and passive attack.
Any type of authentication method may be tunneled. Also, multiple
tunneled authentications may be performed. Normally, tunneled
authentication is used when the TLS handshake provides only one-way
authentication of the server to the client; however, in certain cases
it may be desirable to perform certificate authentication of the
client during the initial handshake phase as well as tunneled user
authentication in a subsequent application phase.
This section establishes rules for using well known authentication
mechanisms within TLS/IA. Any new authentication mechanism should,
in general, be covered by these rules if it is defined as an EAP
type. Authentication mechanisms whose use within TLS/IA is not
covered within this specification may require separate
standardization, preferably within the standard that describes the
authentication mechanism in question.
4.1. Implicit challenge
Certain authentication protocols that use a challenge/response
mechanism rely on challenge material that is not generated by the
authentication server, and therefore require special handling.
In PPP protocols such CHAP, MS-CHAP and MS-CHAP-V2, for example, the
Network Access Server (NAS) issues a challenge to the client, the
client then hashes the challenge with the password and forwards the
response to the NAS. The NAS then forwards both challenge and
response to a AAA server. But because the AAA server did not itself
generate the challenge, such protocols are susceptible to replay
attack.
Since within TLS/IA the client also plays the role of NAS, the replay
problem is exacerbated. If the client were able to create both
challenge and response, anyone able to observe a CHAP or MS-CHAP
exchange could pose as that user by replaying that challenge and
response into a TLS/IA conversation.
To make these protocols secure in TLS/IA, it is necessary to provide
a mechanism that produces a challenge that the client cannot control
or predict. When a challenge-based authentication mechanism is used,
both client and server use the TLS PRF function to generate as many
octets as are required for the challenge, using the constant string
"inner application challenge", based on the master secret and random
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values established during the TLS handshake, as follows.
IA_challenge = PRF(SecurityParameters.master_secret,
"inner application challenge",
SecurityParameters.server_random +
SecurityParameters.client_random);
4.2. Tunneled Authentication Protocols
This section describes the rules for tunneling specific
authentication protocols within TLS/IA. For each protocol, the
RADIUS RFC that defines the relevant attribute formats is cited.
Note that these attributes are encapsulated as described in section
3.1; that is, as Diameter attributes, not as RADIUS attributes. In
other words, the AVP Code, Length, Flags and optional Vendor-ID are
formatted as described in section 3.1, while the Data is formatted as
described by the cited RADIUS RFC.
All tunneled authentication protocols except EAP must be initiated by
the client in the first ApplicationPayload message of an application
phase. EAP may be initiated by the client in the first
ApplicationPayload message of an application phase; it may also be
initiated by the server in any ApplicationPayload message.
The authentication protocols described below may be performed
directly by the TLS/IA server or may be forwarded to a backend AAA
server. For authentication protocols that generate session keys, the
backend server must return those session keys to the TLS/IA server in
order to allow the protocol to succeed within TLS/IA. RADIUS or
Diameter servers are suitable backend AAA servers for this purpose.
RADIUS servers typically return session keys in MS-MPPE-Recv-Key and
MS-MPPE-Send-Key attributes [RFC2548]; Diameter servers return
session keys in the EAP-Master-Session-Key AVP [I-D.ietf-aaa-eap].
4.2.1. EAP
EAP is described in [RFC3784]; RADIUS attribute formats are described
in [RFC3579]. When EAP is the tunneled authentication protocol, each
tunneled EAP packet between the client and server is encapsulated in
an EAP-Message AVP. Either the client or the server may initiate
EAP.
The client is the first to transmit within any application phase, and
it may include an EAP-Response/Identity AVP in its ApplicationPayload
message to begin an EAP conversation. Alternatively, if the client
does not initiate EAP the server may, by including an EAP-Request/
Identity AVP in its ApplicationPayload message. The client's EAP-
Response/Identity provides the username, which MUST be a Network
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Access Identifier (NAI) [RFC2486]; that is, it MUST be in the
following format: username@realm
The @realm portion is optional, and is used to allow the server to
forward the EAP message sequence to the appropriate server in the AAA
infrastructure when necessary.
The EAP authentication between client and server proceeds normally,
as described in [RFC3784]. However, upon completion the server does
not send an EAP-Success or EAP-Failure AVP. Instead, the server
signals success when it concludes the application phase by issuing a
Finished or PhaseFinished message, or it signals failure by issuing
an InnerApplicationFailure alert.
Note that the client may also issue an InnerApplicationFailure alert,
for example, when authentication of the server fails in a method
providing mutual authentication.
4.2.2. CHAP
The CHAP algorithm is described in [RFC1994]; RADIUS attribute
formats are described in [RFC2865].
Both client and server generate 17 octets of challenge material,
using the constant string "inner application challenge" as described
above. These octets are used as follows:
CHAP-Challenge [16 octets]
CHAP Identifier [1 octet]
The client initiates CHAP by including User-Name, CHAP-Challenge and
CHAP-Password AVPs in the first ApplicationPayload message in any
application phase. The CHAP-Challenge value is taken from the
challenge material. The CHAP-Password consists of CHAP Identifier,
taken from the challenge material; and CHAP response, computed
according to the CHAP algorithm.
Upon receipt of these AVPs from the client, the server must verify
that the value of the CHAP-Challenge AVP and the value of the CHAP
Identifier in the CHAP-Password AVP are equal to the values generated
as challenge material. If either item does not match, the server
must reject the client. Otherwise, it validates the CHAP-Challenge
to determine the result of the authentication.
4.2.3. MS-CHAP
The MS-CHAP algorithm is described in [RFC2433]; RADIUS attribute
formats are described in [RFC2548].
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Both client and server generate 9 octets of challenge material, using
the constant string "inner application challenge" as described above.
These octets are used as follows:
MS-CHAP-Challenge [8 octets]
Ident [1 octet]
The client initiates MS-CHAP by including User-Name, MS-CHAP-
Challenge and MS-CHAP-Response AVPs in the first ApplicationPayload
message in any application phase. The MS-CHAP-Challenge value is
taken from the challenge material. The MS-CHAP-Response consists of
Ident, taken from the challenge material; Flags, set according the
client preferences; and LM-Response and NT-Response, computed
according to the MS-CHAP algorithm.
Upon receipt of these AVPs from the client, the server must verify
that the value of the MS-CHAP-Challenge AVP and the value of the
Ident in the client's MS-CHAP-Response AVP are equal to the values
generated as challenge material. If either item does not match
exactly, the server must reject the client. Otherwise, it validates
the MS-CHAP-Challenge to determine the result of the authentication.
4.2.4. MS-CHAP-V2
The MS-CHAP-V2 algorithm is described in [RFC2759]; RADIUS attribute
formats are described in [RFC2548].
Both client and server generate 17 octets of challenge material,
using the constant string "inner application challenge" as described
above. These octets are used as follows:
MS-CHAP-Challenge [16 octets]
Ident [1 octet]
The client initiates MS-CHAP-V2 by including User-Name, MS-CHAP-
Challenge and MS-CHAP2-Response AVPs in the first ApplicationPayload
message in any application phase. The MS-CHAP-Challenge value is
taken from the challenge material. The MS-CHAP2-Response consists of
Ident, taken from the challenge material; Flags, set to 0; Peer-
Challenge, set to a random value; and Response, computed according to
the MS-CHAP-V2 algorithm.
Upon receipt of these AVPs from the client, the server must verify
that the value of the MS-CHAP-Challenge AVP and the value of the
Ident in the client's MS-CHAP2-Response AVP are equal to the values
generated as challenge material. If either item does not match
exactly, the server must reject the client. Otherwise, it validates
the MS-CHAP2-Challenge.
If the MS-CHAP2-Challenge received from the client is correct, the
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server tunnels the MS-CHAP2-Success AVP to the client.
Upon receipt of the MS-CHAP2-Success AVP, the client is able to
authenticate the server. In its next InnerApplicationPayload message
to the server, the client does not include any MS-CHAP-V2 AVPs.
(This may result in an empty InnerApplicationPayload if no other AVPs
need to be sent.)
If the MS-CHAP2-Challenge received from the client is not correct,
the server tunnels an MS-CHAP2-Error AVP to the client. This AVP
contains a new Ident and a string with additional information such as
error reason and whether a retry is allowed. If the error reason is
an expired password and a retry is allowed, the client may proceed to
change the user's password. If the error reason is not an expired
password or if the client does not wish to change the user's
password, it issues an InnerApplicationFailure alert.
If the client does wish to change the password, it tunnels MS-CHAP-
NT-Enc-PW, MS-CHAP2-CPW, and MS-CHAP-Challenge AVPs to the server.
The MS-CHAP2-CPW AVP is derived from the new Ident and Challenge
received in the MS-CHAP2-Error AVP. The MS-CHAP-Challenge AVP simply
echoes the new Challenge.
Upon receipt of these AVPs from the client, the server must verify
that the value of the MS-CHAP-Challenge AVP and the value of the
Ident in the client's MS-CHAP2-CPW AVP match the values it sent in
the MS-CHAP2-Error AVP. If either item does not match exactly, the
server must reject the client. Otherwise, it validates the MS-CHAP2-
CPW AVP.
If the MS-CHAP2-CPW AVP received from the client is correct, and the
server is able to change the user's password, the server tunnels the
MS-CHAP2-Success AVP to the client and the negotiation proceeds as
described above.
Note that additional AVPs associated with MS-CHAP-V2 may be sent by
the server; for example, MS-CHAP-Domain. The server must tunnel such
authentication-related AVPs along with the MS-CHAP2-Success.
4.2.5. PAP
PAP RADIUS attribute formats are described in [RFC2865].
The client initiates PAP by including User-Name and User-Password
AVPs in the first ApplicationPayload message in any application
phase.
In RADIUS, User-Password is padded with nulls to a multiple of 16
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octets, then encrypted using a shared secret and other packet
information.
A TLS/IA, however, does not RADIUS-encrypt the password since all
application phase data is already encrypted. The client SHOULD,
however, null-pad the password to a multiple of 16 octets, to
obfuscate its length.
Upon receipt of these AVPs from the client, the server may be able to
decide whether to authenticate the client immediately, or it may need
to challenge the client for more information.
If the server wishes to issue a challenge to the client, it MUST
tunnel the Reply-Message AVP to the client; this AVP normally
contains a challenge prompt of some kind. It may also tunnel
additional AVPs if necessary, such the Prompt AVP. Upon receipt of
the Reply-Message AVPs, the client tunnels User-Name and User-
Password AVPs again, with the User-Password AVP containing new
information in response to the challenge. This process continues
until the server determines the authentication has succeeded or
failed.
4.3. Performing Multiple Authentications
In some cases, it is desirable to perform multiple user
authentications. For example, a server may want first to
authenticate the user by password, then by a hardware token.
The server may perform any number of additional user authentications
using EAP, simply by issuing a EAP-Request with a new protocol type
once the previous authentication has completed.
For example, a server wishing to perform MD5-Challenge followed by
Generic Token Card would first issue an EAP-Request/MD5-Challenge AVP
and receive a response. If the response is satisfactory, it would
then issue EAP-Request/Generic Token Card AVP and receive a response.
If that response were also satisfactory, it would consider the user
authenticated.
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5. Example Message Sequences
This section presents a variety of possible TLS/IA message sequences.
These examples are not meant to exhaustively depict all possible
scenarios.
Parentheses indicate optional TLS messages. Brackets indicate
optional message exchanges. An ellipsis (. . .) indicates optional
repetition of preceding messages.
5.1. Full Initial Handshake with Intermediate and Final Application
Phasess
The diagram below depicts a full initial handshake phase followed by
two application phases.
Note that the client concludes the intermediate phase and starts the
final phase in an uninterrupted sequence of three messages:
ChangeCipherSpec and PhaseFinished belong to the intermediate phase,
and ApplicationPayload belongs to the final phase.
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Client Server
------ ------
*** TLS Handshake:
ClientHello -------->
ServerHello
(Certificate)
ServerKeyExchange
(CertificateRequest)
<-------- ServerHelloDone
(Certificate)
ClientKeyExchange
(CertificateVerify)
ChangeCipherSpec
Finished -------->
ChangeCipherSpec
<-------- Finished
*** Intermediate Phase:
ApplicationPayload -------->
[
<-------- ApplicationPayload
ApplicationPayload -------->
...
]
<-------- IntermediatePhaseFinished
IntermediatePhaseFinished
*** Final Phase:
ApplicationPayload -------->
[
<-------- ApplicationPayload
ApplicationPayload -------->
...
]
<-------- FinalPhaseFinished
FinalPhaseFinished -------->
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5.2. Resumed Session with Single Application Phase
The diagram below depicts a resumed session followed by a single
application phase.
Note that the client concludes the initial phase and starts the final
phase in an uninterrupted sequence of three messages:
ChangeCipherSpec and PhaseFinished belong to the initial phase, and
ApplicationPayload belongs to the final phase.
Client Server
------ ------
*** TLS Handshake:
ClientHello -------->
ServerHello
ChangeCipherSpec
<-------- Finished
ChangeCipherSpec
Finished
*** Final Phase:
ApplicationPayload -------->
[
<-------- ApplicationPayload
ApplicationPayload -------->
...
]
<-------- FinalPhaseFinished
FinalPhaseFinished -------->
5.3. Resumed Session with No Application Phase
The diagram below depicts a resumed session without any subsequent
application phase. This will occur if the client indicates in its
ClientInnerApplication message that no application phase is required
and the server concurs. Note that this message sequence is identical
to that of a standard TLS resumed session.
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Client Server
------ ------
*** TLS Handshake:
ClientHello -------->
ServerHello
ChangeCipherSpec
<-------- Finished
ChangeCipherSpec
Finished -------->
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6. Security Considerations
This document introduces a new TLS extension called "Inner
Application". When TLS is used with the Inner Application extension
(TLS/IA), additional messages are exchanged during the TLS handshake.
Hence a number of security issues need to be taken into
consideration. Since the security heavily depends on the information
(called "applications") which are exchanged between the TLS client
and the TLS server as part of the TLS/IA extension we try to classify
them into two categories: The first category considers the case where
the exchange results in the generation of keying material. This is,
for example, the case with certain EAP methods. EAP is one of the
envisioned main "applications". The second category focuses on cases
where no session key is generated. The security treatment of the
latter category is discouraged since it is subject to man-in-the-
middle attacks if the two sessions cannot be bound to each other as
suggested in [MITM].
In the following, we investigate a number of security issues:
Architecture and Trust Model
For many of the use cases in this document we assume that three
functional entities participate in the protocol exchange: TLS
client, TLS server and a AAA infrastructure (typically consisting
of a AAA server and possibly a AAA broker). The protocol exchange
described in this document takes place between the TLS client and
the TLS server. The interaction between the AAA client (which
corresponds to the TLS server) and the AAA server is described in
the respective AAA protocol documents and therefore outside the
scope of this document. The trust model behind this architecture
with respect to the authentication, authorization, session key
establishment and key transport within the AAA infrastructure is
discussed in [I-D.ietf-eap-keying].
Authentication
This document assumes that the TLS server is authenticated to the
TLS client as part of the authentication procedure of the initial
TLS Handshake. This approach is similar to the one chosen with
the EAP support in IKEv2 (see [RFC4306]. Typically, public key
based server authentication is used for this purpose. More
interesting is the client authentication property whereby
information exchanged as part of the Inner Application is used to
authenticate (or authorize) the client. For example, if EAP is
used as an inner application then EAP methods are used to perform
authentication and key agreement between the EAP peer (most likely
the TLS client) and the EAP server (i.e., AAA server).
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Authorization
Throughout this document it is assumed that the TLS server can be
authorized by the TLS client as a legitimate server as part of the
authentication procedure of the initial TLS Handshake. The entity
acting as TLS client can be authorized either by the TLS server or
by the AAA server (if the authorization decision is offloaded).
Typically, the authenticated identity is used to compute the
authorization decision but credential-based authorization
mechanisms may be used as well.
Man-in-the-Middle Attack
Man-in-the-middle attacks have become a concern with tunneled
authentication protocols because of the discovered vulnerabilities
(see [MITM]) of a missing cryptographic binding between the
independent protocol sessions. This document also proposes a
tunneling protocol, namely individual inner application sessions
are tunneled within a previously executed session. The first
protocol session in this exchange is the initial TLS Handshake.
To avoid man-in-the-middle attacks a number of sections address
how to establish such a cryptographic binding (see Section 2.3).
User Identity Confidentiality
The TLS/IA extension allows splitting the authentication of the
TLS server from the TLS client into two separate sessions. As one
of the advantages, this provides active user identity
confidentiality since the TLS client is able to authenticate the
TLS server and to establish a unilateral authenticated and
confidentiality-protected channel prior to starting the client-
side authentication.
Session Key Establishment
TLS [RFC2246] defines how session key material produced during the
TLS Handshake is generated with the help of a pseudo-random
function to expand it to keying material of the desired length for
later usage in the TLS Record Layer. Section 2.3 gives some
guidelines with regard to the master key generation. Since the
TLS/IA extension supports multiple exchanges whereby each phase
concludes with a generated keying material. In addition to the
keying material established as part of TLS itself, most inner
applications will produce their keying material. For example,
keying material established as part of an EAP method must be
carried from the AAA server to the AAA client. Details are
subject to the specific AAA protocol (for example, EAP usage in
Diameter [I-D.ietf-aaa-eap]).
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Denial of Service Attacks
This document does not modify the initial TLS Handshake and as
such, does not introduce new vulnerabilities with regard to DoS
attacks. Since the TLS/IA extension allows to postpone the
client-side authentication to a later stage in the protocol phase.
As such, it allows malicious TLS clients to initiate a number of
exchanges while remaining anonymous. As a consequence, state at
the server is allocated and computational efforts are required at
the server side. Since the TLS client cannot be stateless this is
not strictly a DoS attack.
Confidentiality Protection and Dictionary Attack Resistance
Similar to the user identity confidentiality property the usage of
the TLS/IA extension allows to establish a unilateral
authenticated tunnel which is confidentiality protected. This
tunnel protects the inner application information elements to be
protected against active adversaries and therefore provides
resistance against dictionary attacks when password-based
authentication protocols are used inside the tunnel. In general,
information exchanged inside the tunnel experiences
confidentiality protection.
Downgrading Attacks
This document defines a new extension. The TLS client and the TLS
server indicate the capability to support the TLS/IA extension as
part of the client_hello_extension_list and the
server_hello_extension_list payload. More details can be found in
Section 2.6. To avoid downgrading attacks whereby an adversary
removes a capability from the list is avoided by the usage of the
Finish or PhaseFinished message.
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7. References
7.1. Normative References
[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
October 1994.
[RFC1994] Simpson, W., "PPP Challenge Handshake Authentication
Protocol (CHAP)", RFC 1994, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC2433] Zorn, G. and S. Cobb, "Microsoft PPP CHAP Extensions",
RFC 2433, October 1998.
[RFC2486] Aboba, B. and M. Beadles, "The Network Access Identifier",
RFC 2486, January 1999.
[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes",
RFC 2548, March 1999.
[RFC2759] Zorn, G., "Microsoft PPP CHAP Extensions, Version 2",
RFC 2759, January 2000.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3546] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 3546, June 2003.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE)",
RFC 3784, June 2004.
Funk, et al. Expires December 27, 2006 [Page 34]
Internet-Draft TLS inner Application June 2006
7.2. Informative References
[I-D.ietf-aaa-eap]
Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application",
draft-ietf-aaa-eap-10 (work in progress), November 2004.
[I-D.ietf-eap-keying]
Aboba, B., "Extensible Authentication Protocol (EAP) Key
Management Framework", draft-ietf-eap-keying-13 (work in
progress), May 2006.
[I-D.ietf-pppext-eap-ttls]
Funk, P. and S. Blake-Wilson, "EAP Tunneled TLS
Authentication Protocol (EAP-TTLS)",
draft-ietf-pppext-eap-ttls-05 (work in progress),
July 2004.
[I-D.ietf-tls-psk]
Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
for Transport Layer Security (TLS)", draft-ietf-tls-psk-09
(work in progress), June 2005.
[I-D.josefsson-pppext-eap-tls-eap]
Josefsson, S., Palekar, A., Simon, D., and G. Zorn,
"Protected EAP Protocol (PEAP) Version 2",
draft-josefsson-pppext-eap-tls-eap-10 (work in progress),
October 2004.
[MITM] Asokan, N., Niemi, V., Nyberg, K., and W. Dixon, "Man-in-
the-Middle in Tunneled Authentication", October 2002.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[ieee] "IEEE Standards for Local and Metropolitan Area Networks:
Port based Network Access Control", E Std 802.1X-2001,
June 2001.
Funk, et al. Expires December 27, 2006 [Page 35]
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Authors' Addresses
Paul Funk
Funk Software, Inc.
222 Third Street
Cambridge, MA 02142
USA
Phone: +1 617 497-6339
Email: paul@funk.com
Simon Blake-Wilson
Basic Commerce & Industries, Inc.
96 Spadina Ave, Unit 606
Toronto, Ontario M5V 2J6
Canada
Phone: +1 416 214-5961
Email: sblakewilson@bcisse.com
Ned Smith
Intel Corporation.
2111 N.E. 25th Ave.
Hillsboro, OR 97124
USA
Phone: +1 503 264-2692
Email: ned.smith@intel.com
Hannes Tschofenig
Siemens
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: Hannes.Tschofenig@siemens.com
URI: http://www.tschofenig.com
Thomas Hardjono
Verisign Inc
Email: thomas@signacert.com
Funk, et al. Expires December 27, 2006 [Page 36]
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Funk, et al. Expires December 27, 2006 [Page 37]
