Internet-Draft Dynamic Provisioning using EAP-FAST January 2007
Network Working Group N. Cam-Winget
Internet Draft D. McGrew
Category: Informational J. Salowey
Expires: July 11, 2007 H. Zhou
Cisco Systems
January 11, 2007
Dynamic Provisioning using EAP-FAST
draft-cam-winget-eap-fast-provisioning-03.txt
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Copyright (C) The Internet Society (2007). All Rights Reserved.
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Abstract
EAP-FAST is an flexible EAP method that enables secure
communication between a client and a server by using the Transport
Layer Security (TLS) to establish a mutually authenticated tunnel.
EAP-FAST also enables the provisioning credentials or other
information thru this protected tunnel. This document describes the
use of EAP-FAST for dynamic provisioning.
Table of Contents
1. Introduction...................................................3
1.1. Specification Requirements.............................3
1.2. Terminology............................................3
2. EAP-FAST Provisioning Modes....................................4
3. Dynamic Provisioning using EAP-FAST Conversation...............5
3.1 Network Access after EAP-FAST Provisioning.................7
3.2 Authenticating Using EAP-MSCHAPv2..........................8
3.3 Use of other Inner EAP Methods for EAP-FAST Provisioning...9
3.4 Key Derivations Used in the EAP-FAST Provisioning Exchange10
3.5 Peer-Id, Server-Id and Session-Id.........................11
3.6 Provisioning or Refreshment of a PAC......................11
4. Information Provisioned in EAP-FAST...........................12
4.1 Protected Access Credential...............................12
4.2 Provisioning PACs through PAC TLV.........................13
4.2.1 Formats for PAC TLV Attributes ......................14
4.2.2 PAC-Key .............................................15
4.2.3 PAC-Opaque ..........................................16
4.2.4 PAC-Info ............................................17
4.2.5 PAC-Acknowledgement TLV..............................19
4.2.6 PAC-Type TLV.........................................20
4.3 Server Trusted Root Certificate...........................20
4.3.1 Server-Trusted-Root TLV .............................21
4.3.2 PKCS #7 TLV .........................................22
5. Security Considerations.......................................24
5.1 User Identity Protection and Validation...................24
5.2 Mitigation of Dictionary Attacks..........................24
5.3 Mitigation of Man-in-the-middle (MitM) attacks in server-
unauthenticated provisioning mode.............................26
5.4 Mitigation of Man-in-the-middle (MitM) attacks in server-
authenticated provisioning mode...............................27
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5.5 Generation of Diffie-Hellman Groups.......................27
5.6 PAC Storage Considerations................................28
5.7 Security Claims...........................................29
6. IANA Considerations...........................................31
7. References....................................................31
7.1 Normative.................................................31
7.2 Informative...............................................32
8. Acknowledgments...............................................32
9. Author's Addresses............................................32
10. Appendix: Examples...........................................33
10.1 Example 1: Successful Tunnel PAC Provisioning............33
10.2 Example 2: Failed Provisioning...........................35
10.3 Example 3: Provisioning a Authentication Server's Trusted
Root Certificate..............................................37
11. Intellectual Property Statement..............................39
12. Disclaimer of Validity.......................................39
13. Copyright Statement..........................................39
14. Expiration Date..............................................40
1.
Introduction
[EAP-FAST] is an EAP method that can be used to mutually authenticate
peer and server. However, to mutually authenticate with EAP-FAST,
credentials such as a preshared key, trusted anchor or a Protected
Access Credential (PAC) MUST be provisioned to the peer before it can
establish a secure communication channel with the server. In some
cases, the provisioning of such information present deployment
hurdles. Through the use of the protected tunnel, EAP-FAST can also
be used to enable the means for dynamic in-band provisioning to
address such deployment obstacles.
1.1. Specification Requirements
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 [RFC2119].
1.2. Terminology
Much of the terminology in this document comes from [RFC3748].
Additional terms are defined below:
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Man in the Middle (MitM)
An adversary that can successfully inject itself between a peer and
EAP server. The MitM succeeds by impersonating itself as a valid
peer, authenticator or authentication server.
Provisioning
Providing peer with a trust anchor, shared secret or other
appropriate information based on which a security association can
be established.
Protected Access Credential (PAC)
Credentials distributed to a peer for future optimized network
authentication. The PAC consists of at most three components: a
shared secret, an opaque element and optionally other information.
The shared secret part contains the pre-shared key between the peer
and authentication server. The opaque part is provided to the peer
and is presented to the authentication server when the peer wishes
to obtain access to network resources. Finally, a PAC may
optionally include other information that may be useful to the
peer.
Tunnel PAC
A set of credentials stored by the peer and consumed by both the
peer and the server to establish a TLS tunnel.
2.
EAP-FAST Provisioning Modes
EAP-FAST supports two modes for provisioning:
1) Server-Authenticated Mode: Provisioning inside a server-
authenticated TLS tunnel.
2) Server-Unauthenticated Mode: Provisioning inside a server-
unauthenticated TLS tunnel.
In the Server-Authenticated Provisioning mode, the peer has
successfully authenticated the EAP server as part of EAP-FAST Phase 1
(i.e. TLS tunnel establishment). Additional exchanges MAY be needed
inside the tunnel for the EAP Server to authenticate the peer before
any information can be provisioned.
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In the Server-Unauthenticated Provisioning mode, an unauthenticated
TLS tunnel is established in the EAP-FAST Phase 1 where the server is
not authenticated. This provisioning mode is defined to enable
bootstrapping or initial configuration of peers where the peer lacks
strong credentials (if any) to mutually authenticate with the server
and configuration of such credentials through out-of-band mechanisms
are prohibitive.
In the Server-Unauthenticated Provisioning mode, the peer and server
do not achieve mutual authentication during EAP-FAST Phase 1. It is
expected that the peer negotiates TLS_DH_anon based cipher suites to
signal that it can not provide proof of authenticity. While other
cipher suites such as those requiring the use of server certificates
may be used, the peer may lack the necessary trust anchors to
validate the certificate and authenticate the server.
Since the server is not authenticated in the Server-Unauthenticated
Provisioning mode, it is possible that the TLS tunnel may be
terminated by an attacker. It is strongly recommended that an inner
EAP method be used to provide some authenticity assurances and MitM
detection and warning outlined in Section 5 MUST be applied.
The EAP-FAST Phase 2 conversation is unchanged in either Provisioning
mode. However, if the server is not authenticated in Phase 1 the
peer MUST negotiate an EAP method supporting mutual authentication
and key derivation that is compatible with its initial or
bootstrapping credentials (such as a password-based EAP method). The
peer then uses the Crypto-Binding TLV to validate that the same
server terminates both the TLS tunnel and the inner EAP method,
thereby verifying that the exchange was not subject to a man-in-the-
middle attack. Assuming that the Crypto-Binding TLV exchange is
successful, the server will subsequently provide the information such
as a shared key or the trusted root(s) of server
certificate using a PAC TLV or a Server-Trusted-Root TLV
respectively.
Once the EAP-FAST Provisioning conversation completes, the peer is
expected to use the provisioned credentials in subsequent EAP-FAST
authentications.
3.
Dynamic Provisioning using EAP-FAST Conversation
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The provisioning EAP-FAST exchange uses same sequence as the EAP-FAST
Authentication Phase 1 to establish a protected TLS tunnel. Once a
tunnel is secured between the two parties, the client and server can
then negotiate and execute an EAP authentication method by which both
parties can achieve mutual authentication.
Provisioning in EAP-FAST is negotiated by the client in the first
communication exchange when EAP-FAST is requested from the server.
If the client does not have a Protected Access Credential (PAC) or
requires provisioning of other information (such as the server's
Trusted Root certificate), it can request to initiate a provisioning
EAP-FAST exchange and dynamically obtain a PAC or other information
from the server.
The EAP-FAST provisioning conversation will typically occur between
the peer and an authentication server; more specifically, the server
that can provision the peer with the requested information.
The conversation between a peer and authentication server commences
as a normal EAP-FAST exchange as defined in [EAP-FAST]. On receipt of
the EAP-FAST Start message, the peer determines it must be
provisioned with a new PAC or server's trusted root certificate.
This version of the EAP-FAST provisioning mode implementation MUST
support the following TLS ciphersuites:
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_AES_128_CBC_SHA
TLS_DH_anon_WITH_AES_128_CBC_SHA [RFC 3268]
TLS_DHE_RSA_WITH_AES_128_CBC_SHA [RFC 3268]
Other TLS ciphersuites MAY be supported. To provide best security
practices, it is highly recommended that the peer obtain the server's
public key or trust anchor to enable server-side authentication.
However, as the provisioning of the public key or trust anchor must
also be secured to ensure the public key is to be trusted, some
deployments may be willing to trade off the security risks for ease
of deployment and thus use TLS_DH_anon_WITH_AES_128_CBC_SHA that is
allowed for EAP-FAST provisioning mode only.
With a successful EAP-FAST Phase 1 tunnel established, subsequent
messages exchanged between peer and authentication server are
protected using the negotiated TLS cipher suites as defined by both
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[RFC 2246], [RFC4346] and [RFC 3268] to provide message
confidentiality and integrity respectively.
With a protected tunnel, the peer must authenticate itself to the
server before the server can provision it with information such as a
PAC.
Following a successful authentication exchange and successful
Intermediate Result TLV and Crypto-Binding TLV exchange, the server
can then provision the peer with a unique PAC. The provisioning is
invoked through the a PAC-TLV exchange that is executed following the
successful authentication exchange including the Intermediate Result
TLV and Crypto-Binding TLV exchange, with the server distributing the
information such as a PAC in a corresponding PAC TLV to the peer and
the peer confirming its receipt in a final PAC TLV Acknowledgement
message.
3.1
Network Access after EAP-FAST Provisioning
Depending on server policy, network access can be granted or denied
based on the EAP-FAST Provisioning mode, the credential(s) or other
information that have been provisioned, and the inner EAP methods
used. For example, in the Server-Authenticated Provisioning Mode,
access can be granted after the EAP server has authenticated the peer
and provisioned the peer with a Tunnel PAC (e.g. a PAC used to
mutually authenticate and establish the EAP-FAST tunnel).
Additionally, peer policy may also be used to disconnect the current
provisioning connection and initiate a new EAP-FAST exchange for
authentication utilizing the newly provisioned information and ensure
the inner methods are conducted with the trusted server. The peer
policy may be required as the peer determines whether it can
authenticate the EAP Server. In the case where a peer lacks the
trust anchors to validate the server's certificate, the peer SHOULD
negotiate using one of the TLS_DH_anon based cipher suites to signal
the EAP server that it lacks the trust anchors to authenticate the
server.
At the end of the Server-Unauthenticated Provisioning Mode, network
access SHOULD NOT be granted. EAP server SHOULD conclude with an EAP
Failure to acknowledge that this conversation was intended for
provisioning only and thus no network access is authorized. Upon
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completion of the exchange, the EAP Server SHALL NOT grant network
access or distribute any session keys to the NAS as this phase is not
intended to provide network access. Even though provisioning mode
completes with a successful inner termination (e.g. successful Result
TLV), server policy defines whether the peer gains network access or
not. Thus, it is feasible for the server, while providing a
successful Result TLV may conclude with an EAP Failure.
The EAP-FAST server, when denying network access after EAP-FAST
Provisioning, may choose to instead, immediately invoke another EAP-
FAST Start and thus initiate the EAP-FAST Phase 1 conversation. This
server based implementation policy may be chosen to avoid
applications such as wireless devices from being disrupted (e.g. in
802.11 devices, an EAP Failure may trigger a full 802.11
disassociation) and allow them to smoothly transition to the
subsequent EAP-FAST authentications to enable network access. As an
alternative, both the peer and server can initiate TLS renegotiation,
where the newly provisioned credentials can be used to establish a
server authenticated or mutually authenticated TLS tunnel for
authentication. Upon completion of the TLS negotiation and subsequent
authentication, normal network access policy on EAP-FAST
authentication can be applied.
Similarly, if Server-Authenticated Provisioning Mode is used and the
server policy is to disallow network access, the EAP Server SHALL NOT
grant network access or distribute any session keys to the NAS as
this phase is not intended to provide network access. Even though
provisioning mode completes with a successful inner termination (e.g.
successful Result TLV), the EAP-FAST Server-Authenticated
Provisioning Mode MUST conclude with an EAP Failure to acknowledge
that this conversation was intended for provisioning only and thus no
network access is authorized. The EAP-FAST server may choose to
instead, immediately invoke another EAP authentication transaction.
3.2
Authenticating Using EAP-MSCHAPv2
This version of the EAP-FAST provisioning mode implementation MUST
support EAP-MSCHAPv2 as the inner authentication method for enabling
Server-Unauthenticated Provisioning Mode. While other authentication
methods are allowed and exist to achieve mutual authentication, when
using an anonymous or unauthenticated TLS tunnel, MSCHAPv2 was chosen
for several reasons:
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* Provide the ability of slowing an active attack by obscuring the
password through some hash
* Especially in the Server-Unauthenticated EAP-FAST Provisioning
conversation, MSCHAPv2 provides the ability to detect, based on the
challenge responses, whether there is a possible attack.
* It is understood that a large deployed base is already able to
support MSCHAPv2
* Allow support for password change during the EAP-FAST
Provisioning mode.
The MSCHAPv2 exchange forces the server to provide a valid
ServerChallengeResponse which must be a function of the server
challenge, client challenge and password as part of its response.
This reduces the window of vulnerability in the EAP-FAST for in-band
provisioning mode to force the man-in-the-middle, acting as the
server, to successfully break the password within the client's
challenge response time limit.
EAP-FAST for provisioning MUST support EAP-MSCHAPv2 as the inner
method when using an anonymous DH key agreement. However, with
support of signed DH key agreement, the provisioning protocol of EAP-
FAST may support other methods such as EAP-GTC to enable peers (using
other password databases such as LDAP and OTP) to be provisioned in-
band as well. However, the replacement may only be achieved when
used with cipher suites that enable server side authentication (for
example, using TLS_DHE_RSA_WITH_AES_128_CBC_SHA) to ensure no loss in
security.
When using an anonymous DH key agreement and MSCHAPv2, a binding
between the tunnel and the MSCHAPv2 exchanges is formed by using
keying material generated during the EAP-FAST tunnel establishment as
the MSCHAPv2 challenges. A detailed description of the challenge
generation is described in Section 3.4.
3.3
Use of other Inner EAP Methods for EAP-FAST Provisioning
Once a protected tunnel is established, the peer must authenticate
itself to the server before the server can provision the peer. When
using TLS_DH_anon_WITH_AES_128_CBC_SHA cipher suite in the EAP-FAST
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Phase 1 conversation, an EAP method providing both mutual
authentication and keying material MUST be employed.
With the use of additional TLS cipher suites, especially when server
authenticity is verified as part of the TLS tunnel establishment,
other inner EAP methods with weaker protection than EAP-MSCHAPv2 can
be used safely inside tunnel. Hence, in addition to EAP-MSCHAPV2 as
the inner method, EAP-GTC MAY be used in Server-Authenticated
Provisioning Mode. This will enable peers using other user databases
such as LDAP and OTP to be provisioned in-band as well. However, the
replacement may only be achieved when used with the TLS cipher suites
that ensure server authentication, such as
TLS_DHE_RSA_WITH_AES_128_CBC_SHA, to ensure no loss in security.
This version of the EAP-FAST provisioning mode implementation MUST
support both EAP-GTC and EAP-MS-CHAPv2 within the tunnel in Server-
Authenticated Provisioning Mode.
It should be noted that Server-Authenticated Provisioning Mode
provides significant security advantages over Server-Unauthenticated
Provisioning even when EAP-MSCHAPv2 is being used as inner method. It
protects the EAP-MSCHAPv2 exchanges from potential MitM attacks by
verifying server's authenticity before exchanging MSCHAPv2. Thus
Server-Authenticated Provisioning Mode is the preferred provisioning
mode. The EAP-FAST peer MUST use the Server-Authenticated
Provisioning Mode whenever a certificate or (server's) public key is
available to authenticate the server, in order to ensure best
security practices.
3.4
Key Derivations Used in the EAP-FAST Provisioning Exchange
When generating keys in the EAP-FAST Provisioning conversation, the
DH computation is used as the pre_master_secret and is converted into
the master_secret as specified by [RFC 2246].
The TLS tunnel key is calculated similar to the TLS key calculation
with an extra 72 octets generated. Portions of the extra 72 octets
are used for the EAP-FAST provisioning exchange session key seed and
as the random challenges in the MSCHAPv2 exchange.
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To generate the key material, compute
key_block = PRF(master_secret,
"key expansion",
server_random +
client_random);
until enough output has been generated. Then the key_block is
partitioned as follows:
client_write_MAC_secret[hash_size]
server_write_MAC_secret[hash_size]
client_write_key[Key_material_length]
server_write_key[key_material_length]
client_write_IV[IV_size]
server_write_IV[IV_size]
session_key_seed[seed_size= 40]
MSCHAPv2 ServerChallenge[16]
MSCHAPv2 ClientChallenge[16]
The extra key material, session_key_seed is used for the Crypto-
Binding while the ServerChallenge and ClientChallenge correspond to
the authentication server's MSCHAPv2 challenge and the peer's
MSCHAPv2 challenge respectively. The ServerChallenge and
ClientChallenge are only used for the MSCHAPv2 exchange when DH
anonymous key agreement is used in the EAP-FAST tunnel establishment.
3.5
Peer-Id, Server-Id and Session-Id
The provisioning modes of EAP-FAST does not change the general EAP-
FAST protocol and thus how the Peer-Id, Server-Id and Session-Id are
determined is based on the [EAP-FAST] techniques.
[EAP-FAST] Section 3.4 describes how the Peer-Id and Server-Id are
determined; Section 3.5 describes how the Session-Id is generated.
3.6
Provisioning or Refreshment of a PAC
The server may provision or refresh information by use of the
Protected Access Credential (PAC) after a successful user
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authentication. A PAC TLV is defined to facilitate the distribution
and refreshing of information and is defined in Section 4.2. A fresh
PAC may be distributed after a successful Intermediate Result TLV and
Crypto-Binding TLV exchange, if the server detects that the PAC is
expiring soon. A successful EAP-FAST inner method authentication,
including a successful Crypto-Binding exchange must ensue before an
EAP-FAST server can distribute a fresh PAC. A PAC TLV should not be
accepted if it is not TLS tunnel-encapsulated.
N.B. In-band PAC refreshing is enforced by server policy. The
server, based on the PAC-Opaque information, may determine not to
refresh a peer's PAC through the PAC TLV mechanism even if the PAC-
Key has expired.
4.
Information Provisioned in EAP-FAST
In addition to the Tunnel PAC (the one used to establish the EAP-FAST
Phase 1 TLS tunnel), other types of credentials and information can
also be provisioned in EAP-FAST. They may include trusted root
certificates for the server certificates, application specific PACs,
and user identities to name a few. Typically, provisioning is invoked
after both peer and server validate their authenticities and after a
successful Crypto-Binding TLV exchange. However, depending on the
information being provisioned, mutual authentication MAY not be
needed.
At minimum, at least one entity (peer or server) must prove
authenticity before credentials are provisioned to ensure that
information is not freely provisioned to or by adversaries. For
example, the EAP server MAY not need to authenticate the peer to
provision the peer with trusted root certificates. However, the peer
MUST authenticate the server before it can accept a trusted server
root certificate.
4.1
Protected Access Credential
A Protected Access Credential (PAC) is a security credential provided
by the Authentication Server (AS) that holds application specific
information. The server distributes all PAC information through the
use of a PAC TLV. Each type of PAC information is typed through a
PAC Type and PAC TLV Attribute defined in this section.
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For instance, a Tunnel PAC holds a shared secret mutually and
uniquely shared between the peer and AS and is used to secure an EAP-
FAST (TLS) tunnel. EAP-FAST uses the Tunnel PAC to facilitate the
storage of secure information between a peer and a server on the peer
and minimize the per user state management on the AS.
The Tunnel PAC is distributed by the server to the peer and used to
establish a secure EAP-FAST TLS tunnel and convey the server policy
of what must and can occur in the tunnel. The server policy can
include EAP methods, TLV exchanges and identities allowed in the
tunnel. It is up to the server policy to include what's necessary in
a PAC to enforce the policy in subsequent authentications that use
the PAC. For example, user identity, I-ID, can be included as the
part of the server policy. This I-ID information limits the inner
EAP methods to be carried only on the specified user identity. Other
types of information can also be included, such as which EAP
method(s) and which cipher suite is allowed. If the server policy is
not included in a PAC, then there is no validation or limitation on
the inner EAP methods or user identities inside the tunnel
established by the use of that PAC.
To request provisioning of a Tunnel PAC, a peer MUST send a PAC TLV
with a PAC-Type PAC TLV with its TLVs field and '1' (Tunnel PAC
Type). The request may be issued after the peer has determined that
it has successfully authenticated the EAP Server and the tunnel and
inner EAP methods were between the same peer and EAP Server by
validating the Crypto-Binding TLV. This would differentiate the
Tunnel PAC request from other types of PAC provisioning requests. If
anonymous DH is negotiated and the peer does not send any PAC-TLV to
request provisioning, then Tunnel PAC is provisioned automatically
by the server. PAC-Acknowledge TLV MUST be used for peer to
acknowledge the receipt of the Tunnel PAC.
Please see Section 10.1 for an example of packet exchanges to
provision a Tunnel PAC.
4.2
Provisioning PACs through PAC TLV
The PAC TLV is defined to enable the provisioning of PAC information.
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Additionally, the PAC-Type in PAC TLV MAY be used by the peer to
request provisioning for specific types of information. Conversely,
the PAC TLV is used by the server to provision the requested
information to a peer.
The PAC TLV provides support for Protected Access Credential (PAC)
defined within [EAP-FAST]. A consistent PAC format will allow it to
be used by multiple applications beyond EAP-FAST. A general PAC TLV
format is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PAC Attributes...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
0 - Non-mandatory TLV
1 - Mandatory TLV
R
Reserved, set to zero (0)
TLV Type
11
Length
The length of the PAC Attributes field in octets.
PAC Attributes
A list of PAC attributes in the TLV format.
4.2.1 Formats for PAC TLV Attributes
A common encapsulating format is used to convey the different fields
that comprise a PAC attribute. The common encapsulation is defined
as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The type field is two octets, denoting the attribute type.
Allocated Types include:
1 - PAC-Key
2 - PAC-Opaque
3 - PAC-Lifetime
4 - A-ID
5 - I-ID
6 - Reserved
7 - A-ID-Info
8 - PAC-Acknowledgement
9 - PAC-Info
10 - PAC-Type
Length
The Length filed is two octets, which contains the length of
the Value field in octets.
Value
The value of the PAC Attribute.
4.2.2 PAC-Key
The PAC-Key is distributed as an attribute of type PAC-Key (Type=1).
The key is a randomly generated octet string. The key is represented
as an octet string whose length is determined by the length field.
The generator of this key is the issuer of the credential, identified
by the A-ID.
0 1 2 3
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Key ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1 - PAC-Key
Length
The Length filed is two octets. For this version of EAP-FAST,
PAC-Key is 32 octets.
Key
The Key field contains the key used to establish the TLS
tunnel.
4.2.3 PAC-Opaque
The PAC-Opaque contains data that is opaque to the recipient, the
peer is not the intended consumer of PAC-Opaque and thus should not
attempt to interpret it. A peer that has been issued a PAC-Opaque by
a server MUST store that data, and present it back to the server as
is, in the ClientHello SessionTicket extension field [RFC4507]. If a
client has opaque data issued to it by multiple servers, then it MUST
store the data issued by each server separately according to A-ID.
This requirement allows the client to maintain and use each opaque
data as an independent PAC pairing, with a PAC-Key mapping to a PAC-
Opaque identified by the A-ID. As there is a one to one
correspondence between PAC-Key and PAC-Opaque, the peer must
determine the PAC-Key and corresponding PAC-Opaque based on the A-ID
provided in the EAP-FAST/Start message and the A-ID provided in the
PAC-Info when it was provisioned with a PAC-Opaque.
As the PAC-Opaque is server specific, its contents and definition are
specific to the issuer of the PAC, e.g. the PAC server.
The PAC-Opaque field is embedded as part of the PAC TLV when the
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server has determined that the PAC must be provisioned or refreshed.
The PAC-Opaque field format is summarized as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
2 - PAC-Opaque
Length
The Length filed is two octets, which contains the length of
the value field in octets.
Value
The Value field contains the actual data for PAC-Opaque.
The PAC-Opaque field is also passed from the peer to the server
during the EAP-FAST Authentication Phase 1 conversation to enable
the server to validate and recreate the PAC-Key. When it is passed
from the peer, it is encapsulated as defined above in the
ClientHello SessionTicket Extension [RFC4507].
4.2.4 PAC-Info
PAC-Info is comprised of a set of PAC attributes. At minimum, the
A-ID, A-ID-Info, and PAC-Type attribute is required to convey the
issuing identity to the peer. Other optional fields may be included
in the PAC to provide more information to the peer. It is a container
attribute for various types of information each of which is encoded
in conformance to the PAC TLV attribute field format as defined in
Section 4.2.
0 1 2 3
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attributes...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
9 - PAC-Info
Length
The Length filed is two octets, which contains the length of
the Attributes field in octets.
Attributes
The Attributes field contains a list of PAC Attributes.
Each mandatory and optional field type is defined as follows:
PAC-LIFETIME (type 3)
This is a 4 octet quantity representing the expiration time
of the credential in UNIX UTC time. This is a mandatory
field contained in the PAC-Opaque field to enable the server
to validate the PAC. This field may also be optionally
provided to the peer as part of PAC-Info.
A- ID (type 4)
Authority identifier is the name of the authority that
issued the PAC. The A-ID is intended to be unique across
all issuing servers to avoid namespace collisions. Server
implementations should use measures to ensure the A-ID used
is globally unique to avoid name collisions. The A-ID is
used by the peer to determine which PAC to employ.
Similarly, the server uses the A-ID to both authenticate the
PAC-Opaque and determine which master key was used to issue
the PAC. This field is mandatory and included in both the
PAC-Opaque and PAC-Info.
I-ID (type 5)
Initiator identifier (I-ID) is the peer identity associated
with the credential. The server employs the I-ID in the EAP-
FAST Phase 2 conversation to validate that the same peer
identity used to execute EAP-FAST Phase 1 is also used in at
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minimum one inner EAP method in EAP-FAST Phase 2. This
field is a mandatory field in PAC-Opaque and may optionally
be included in the PAC-Info. If the AS is enforcing the I-ID
validation on inner EAP method, then I-ID is mandatory in
PAC-Info, to enable the client to also enforce a unique PAC
for each unique user. If I-ID is missing from the PAC-Info,
it is assumed that the Tunnel PAC can be used for multiple
users and client will not enforce the unique Tunnel PAC per
user policy.
A-ID-Info (type 7)
Authority Identifier Information is a mandatory TLV intended
to provide a user-friendly name for the A-ID. It may contain
the enterprise name and server name in a more human-readable
format. This TLV serves as an aid to the peer to better
inform the end-user about the A-ID. This field is a
mandatory field in the PAC-Info.
PAC-Type (type 10)
PAC-Type is a mandatory TLV intended to provide the type of
PAC. This field is a mandatory field in the PAC-Info. For
legacy implementations, if PAC-Type is not present, then it
defaults to a Tunnel PAC (Type 1).
4.2.5 PAC-Acknowledgement TLV
The PAC-Acknowledgement TLV is used to acknowledge the receipt of the
Tunnel PAC by the peer. Peer sends this TLV in response to the PAC
TLV to indicate the result of the retrieving and storing of the new
Tunnel PAC. This TLV is only used when Tunnel PAC is provisioned.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Result |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
8 - PAC-Acknowledgement
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Length
The length of this field is two octets and value must be 2.
Result
The resulting value must be one of the following:
1 - Success
2 - Failure
4.2.6 PAC-Type TLV
The PAC-Type TLV is a TLV intended to specify the PAC type. Its
format is described below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PAC Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
10 - PAC-Type
Length
The length of this field is two octets and value must be 2.
PAC Type
This two octet field defined the type of PAC being requested or
provisioned. Its value must be one of the following:
1 - Tunnel PAC
4.3
Server Trusted Root Certificate
It is desirable to provision the peer with the server's trusted root
certificates (or CA certificates), which can later be used for
enabling PKI based cipher suites. Server-Trusted-Root TLV is
introduced to facilitate the request for and delivery of server
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trusted root certificates. Within the EAP-FAST Phase 2 conversation,
a peer MAY request for a server's trusted root certificate using a
Server-Trusted-Root TLV, and the EAP server MAY respond with a
Server-Trusted-Root TLV containing the trusted root certificate in
the PCKS#7 TLV to the peer. The Server-Trusted-Root TLV can be
exchanged in regular EAP-FAST Authentication mode or Provisioning
mode.
After the peer has determined that it has successfully authenticated
the EAP server and determined that the tunnel and inner EAP methods
were between the same peer and EAP Server by validating the Crypto-
Binding TLV, it MAY send one or more Server-Trusted-Root TLVs
(marked as optional) to request for the certificate trust anchors of
the server certificate from the EAP server. The EAP server will send
the trusted root(s) of server certificate after its internal policy
has been satisfied; or it may ignore the request or request
additional authentications based on its policy. The peer may receive
a trusted root of server certificate, but is not required to use it.
Please see Section 10.3 for an example of a server provisioning a
server trusted root certificate.
4.3.1 Server-Trusted-Root TLV
The Server-Trusted-Root TLV allows the peer to send a request to the
EAP server for a trusted root in PKCS#7 [RFC2315]format.
The Server-Trusted-Root TLV is always marked as optional, and cannot
be responded to with a NAK TLV.
The Server-Trusted-Root TLV can only be sent as an inner TLV (inside
the protection of the tunnel).
The peer MUST NOT request, or accept the trusted root sent inside the
Server-Trusted-Root-TLV by the EAP server until it has completed
authentication of the EAP server, and validated the Crypto-Binding
TLV. The peer may receive a trusted root, but is not required to use
the trusted root sent from the EAP server.
If the EAP server sets credential-format to PKCS#7-Server-
Certificate-Root, then the Server-Trusted-Root TLV MUST contain the
root of the certificate chain of the certificate issued to the EAP
server packaged in a PKCS#7 TLV. If the Server certificate is a
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self-signed certificate, then the root is the self-signed
certificate.
If the Server-Trusted-Root TLV credential format does not contain one
of the known values, then the EAP-server MUST ignore the TLV.
The Server-Trusted-Root TLV is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credential-Format | TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
M
0 - Optional TLV
R
Reserved, set to zero (0)
TLV Type
18
Length
>=2
Credential-Format
The Credential-Format field is two octets. Values include:
1 - PKCS#7-Server-Certificate-Root.
TLVs
This field is of indefinite length. It contains TLVs
associated with the certificate request and response.
4.3.2 PKCS #7 TLV
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The PKCS#7 TLV is sent by the EAP server to the peer inside the
Server-Trusted-Root TLV. It contains the PKCS #7 [RFC2315] wrapped
X.509 certificate. This field contains a certificate or certificate
chain in PKCS#7 format requested by the peer as defined in [RFC2315].
The PKCS#7 TLV is always marked as optional, which cannot be
responded to with a NAK TLV. EAP-FAST server implementations that
claim to support dynamic provisioning MUST support this TLV. EAP-
FAST peer implementations MAY not support this TLV.
If the PKCS#7 TLV contains a certificate or certificate chain that is
not acceptable to the peer, then peer MUST ignore the TLV.
The PKCS#7 TLV is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PKCS #7 Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
M
0 - Optional TLV
R
Reserved, set to zero (0)
TLV Type
20 (for PKCS #7 TLV)
Length
The length of the PKCS #7 Data field
PKCS #7 Data
This field contains the PKCS #7 wrapped X.509 certificate or
certificate chain in the PKCS #7 format.
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5.
Security Considerations
The Dynamic Provisioning EAP-FAST protocol shares the same security
considerations outlined in [EAP-FAST]. Additionally, it also has its
unique security considerations described below:
5.1
User Identity Protection and Validation
EAP-FAST for provisioning employs the TLS key agreement (as defined
in the TLS protocol) to establish a protected tunnel; the initial
EAP-Identity request/response may be omitted as it must be
transmitted in the clear and thus subject to snooping and forgery.
Alternately, an
anonymous identity may be used in the EAP-Identity response to
prevent disclosure of the peer's true identity.
As the provisioning EAP-FAST exchange is used for provisioning a PAC
to a specific identity, e.g. I-ID, it is expected that the server
will assign the I-ID based on the identity provided in the protected
inner EAP authentication method. Thus, the protected identity may
not be identical to the cleartext identity presented in the initial
EAP identity exchange messages. In order to shield the user identity
from snooping, the cleartext Identity may only provide enough
information to enable routing of the authentication request to the
correct realm. For example, the peer may initially claim the identity
of "anonymous@example.com" in order to route the authentication
request to the example.com EAP server. Subsequently, once the EAP-
FAST session has been negotiated, in the inner authentication method,
the peer may claim the identity of "user1@example.com". Thus, the
EAP-FAST protocol for provisioning can provide protection for the
user's identity, though not necessarily the destination realm, unless
the provisioning EAP-FAST conversation terminates at the local
authentication server.
5.2
Mitigation of Dictionary Attacks
When EAP-FAST is invoked for provisioning, the peer specifies the
means for securing the communications for the provisioning. As such,
it can invoke the TLS key agreement in one of two ways: anonymously
or server-authenticated. With a server-authenticated TLS key
agreement, the server must provide its certificate and be validated
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by the peer, whereas in an anonymous TLS key agreement, there is no
ability to authenticate the server.
In a server authenticated TLS key agreement, the protected
communications is assured that the AS is authentic as the peer must
have been pre-provisioned with the AS's certificate or public (RSA)
key prior to the negotiation. In this instance, the AS provides
proof of identity through an identity and (certificate) credential,
preventing an adversary from posing as an AS to mount a dictionary
attack. An EAP-FAST compliant implementation must assure that
provisioning of the AS public key, certificate or root certificate to
the peer must be achieved through a secure mechanism. Only through a
secure mechanism can server-authenticated DH key agreement provide
resistance to dictionary attacks. While this option affords best
security practices, it presents deployment issues as, especially for
wireless clients where there is little means to provide secure
configuration, peers must be configured with a means to validate the
server's credential (e.g. public key).
In an anonymous DH key agreement, an adversary may attempt to
impersonate a client and enable EAP-FAST for provisioning. However,
it must successfully authenticate inside the DH tunnel to succeed and
gain a PAC credential from a server. Thus, peer impersonation is
mitigated through the enabling of peer authentication inside a
protected tunnel. However, an adversary may impersonate as a valid
AS and obtains the MSCHAPv2 exchanges in order to gain peer's
identity and credentials. While the adversary must successfully
gain contact with a peer that is willing to negotiate EAP-FAST for
provisioning and provide a valid A-ID that a client accepts, this
occurrence is feasible and enables an adversary to mount a dictionary
attack. For this reason, an EAP-FAST compliant implementation must
support an MSCHAPv2 or stronger EAP method for peer authentication
when an anonymous DH key agreement is used for the tunnel
establishment.
With MSCHAPv2, a peer may detect it is under attack when the AS that
has provided an acceptable Authority ID (A-ID) fails to provide a
successful MSCHAPv2 server challenge response. By employing the
ServerChallenge and ClientChallenge derived during tunnel
establishment; detection of a MitM is feasible during the MSCHAPv2
exchange.
The peer MAY choose to use a more secure out-of-band mechanism for
PAC provisioning that affords better security than the anonymous DH
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key agreement. Similarly, the peer MAY find a means of pre-
provisioning the server's public key securely to invoke the server-
authenticated DH key agreement.
The anonymous DH key agreement is presented as a viable option as
there may be deployments that can physically confine devices during
the provisioning or are willing to accept the risk of an active
dictionary attack. Further, it is the only option that enables zero
out-of-band provisioning and facilitates simpler deployments
requiring little to no peer configuration.
5.3
Mitigation of Man-in-the-middle (MitM) attacks in server-
unauthenticated provisioning mode
EAP-FAST invocation of provisioning addresses MitM attacks in server-
unauthenticated provisioning mode in the following way:
* Generating MSCHAPv2 server and client challenges as a function
of the DH key agreement: in enforcing the dependence of the MSCHAP
challenges on the DH exchange, a MitM is prevented from
successfully establishing a secure tunnel with both the peer and
legitimate server and succeed in obtaining the PAC credential.
* Cryptographic binding of EAP-FAST Phase 1 and the Phase 2
authentication method: by cryptographically binding key material
generated in all phases, both peer and AS are assured that they
were the sole participants of all transpired phases.
The binding of the MSCHAPv2 random challenge derivations to the DH
key agreement protocol enables early detection of a MitM attack.
This is required to guard from adversaries who may otherwise reflect
the inner EAP authentication messages between the true peer and AS
and enforces that the adversary successfully respond with a valid
challenge response.
The cryptographic binding is another reassurance that indeed the true
peer and AS were the two parties ensuing both the tunnel
establishment and inner EAP authentication conversations. While it
would be sufficient to only support the cryptographic binding to
mitigate the MitM; the extra precaution of binding the MSCHAP
challenge to the DH key agreement affords the client earlier
detection of a MitM and further guards the peer from having to
respond to the success or failure of the adversary's attempt to
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respond with a challenge response (e.g. indication of whether the
adversary succeeded in breaking the peer's identity and password).
A failure in either step, results in no PAC provisioning.
EAP-FAST invocation of provisioning using an unauthenticated tunnel
can invoke certain procedures to guard implementations for potential
MitM attacks. Detectors can be devised to warn the user when the
peer encounters error conditions that warrant the likelihood of a
MitM. For example, when the MSCHAPv2 server challenge response is
never received or fails, the peer implementation can impose policy
decisions to warn the user and respond to the likelihood that the
failure was due to a MitM attack.
Similarly, to guard against attacks in the EAP-FAST Authentication
that may force a peer to invoke in-band provisioning, guards and
detectors can and should be implemented as part of the EAP-FAST
Authentication protocols.
5.4
Mitigation of Man-in-the-middle (MitM) attacks in server-
authenticated provisioning mode
EAP-FAST provisioning in server-authenticated mode addresses MitM
attacks by enforcing the server to present a valid certificate as
part of the TLS negotiation. To ensure the authenticity of the
server and address MitM attacks, the peer MUST verify the validity of
the EAP server certificate to guarantee it is not subject to a MitM
attack.
The cryptographic binding is another reassurance that indeed the true
peer and AS were the two parties communicating in both the tunnel
establishment and inner EAP authentication conversations.
5.5
Generation of Diffie-Hellman Groups
The security of the DH key exchange is based on the difficulty of
solving the Discrete Logarithm Problem (DLP). As algorithms and
adversaries become more efficient in their abilities to precompute
values for a given fixed group, it becomes more important for a
server to generate new groups as a means to allay this threat. The
server could, for instance, constantly compute new groups in the
background. Such an example is cited in [SECSH-DH].
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Thus, the server can maintain a list of safe primes and corresponding
generators to choose from. A prime p is safe, if:
p = 2q + 1 and q is prime
New primes may be generated in the background.
Initial implementations of the EAP-FAST provisioning exchange limit
the generator to be 2 as it both improves the multiplication
efficiency and still covers half of the space of possible residues.
Furthermore, as the server defines the group used for the DH exchange,
it may restrict the prime size to be 1024 bits.
Additionally, since the EAP-FAST provisioning exchange employs DH per
[RFC 3268] to generate AES keys, the DH keys must provide enough
entropy to ensure that a strong 128bit results from the DH key
agreement.
EAP-FAST employs the 2048 bit DH groups defined in [RFC 3526].
5.6
PAC Storage Considerations
The main premise behind EAP-FAST is to protect the authentication
stream over the media link. However, physical security is still an
issue. Some care should be taken to protect the PAC on both the peer
and server. The peer must store securely both the PAC-Key and PAC-
Opaque, while the server must secure storage of its security
association context used to consume the PAC-Opaque. Additionally, if
manual provisioning is employed, the transportation mechanism used to
distribute the PAC must also be secured.
Most of the attacks described here would require some level of
effort to execute; conceivably greater than their value. The main
focus therefore, should be to ensure that proper protections are
used on both the client and server. There are a number of
potential attacks which can be considered against secure key
storage such as:
* weak passphrases
On the peer side, keys are usually protected by a passphrase. On
some environments, this passphrase may be associated with the
user's password. In either case, if an attacker can obtain the
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encrypted key for a range of users, he may be able to successfully
attack a weak passphrase. The tools are already in place today to
allow an attacker to easily attack all email users in an enterprise
environment. Most viruses or worms of this sort attract attention
to themselves by their action, but that need not be the case. A
simple, genuine appearing email could surreptitiously access keys
from known locations and email them directly to the attacker,
attracting little notice.
* key finding attacks
Key finding attacks are usually mentioned in reference to web
servers, where the private SSL key may be stored securely, but at
some point it must be decrypted and stored in system memory. An
attacker with access to system memory can actually find the key by
identifying their mathematical properties. To date, this attack
appears to be purely theoretical and primarily acts to argue
strongly for secure access controls on the server itself to prevent
such unauthorized code from executing.
* key duplication , key substitution, key modification
Once keys are accessible to an attacker on either the client or
server, they fall under three forms of attack: key duplication, key
substitution and key modification. The first option would be the
most common, allowing the attacker to masquerade as the user in
question. The second option could have some use if an attacker
could implement it on the server. Alternatively, an attacker could
use one of the latter two attacks on either the peer or server to
force a PAC re-key, and take advantage of the MitM/dictionary
attack weakness of the EAP-FAST provisioning protocol.
Another consideration is the use of secure mechanisms afforded by the
particular device. For instance, some laptops enable secure key
storage through a special chip. It would be worthwhile for
implementations to explore the use of such a mechanism.
5.7
Security Claims
This section provides needed security claim requirement for EAP
[RFC3748].
Auth. mechanism: Certificate based, shared secret based
and various tunneled authentication
mechanisms.
Ciphersuite negotiation: Yes
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Mutual authentication: Yes
Integrity protection: Yes, Any method executed within the EAP-
FAST tunnel is integrity protected. The
cleartext EAP headers outside the tunnel
are not integrity protected.
Replay protection: Yes
Confidentiality: Yes
Key derivation: Yes
Key strength: [1]
Dictionary attack prot.: Yes
Fast reconnect: Yes
Cryptographic binding: Yes
Session independence: Yes
Fragmentation: Yes
Key Hierarchy: Yes
Channel binding: No, but TLVs could be defined for this.
Notes
1. BCP 86 [RFC3766] offers advice on appropriate key sizes. The
National Institute for Standards and Technology (NIST) also
offers advice on appropriate key sizes in [SP800-57].
[RFC3766]
Section 5 advises use of the following required RSA or DH
module
and DSA subgroup size in bits, for a given level of attack
resistance in bits. Based on the table below, a 2048-bit RSA
key
is required to provide 128-bit equivalent key strength:
Attack Resistance RSA or DH Modulus DSA subgroup
(bits) size (bits) size (bits)
----------------- ----------------- ------------
70 947 129
80 1228 148
90 1553 167
100 1926 186
150 4575 284
200 8719 383
250 14596 482
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6.
IANA Considerations
This section explains the criteria to be used by the IANA for
assignment of Type value in PAC TLV attribute, PAC Type value in PAC-
Type TLV, Credential-Format value in Server-Trusted-Root TLV. The
"Specification Required" policy is used here with the meaning defined
in BCP 26 [RFC2434].
7.
References
7.1
Normative
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC4346] Dierks, T. and E. Rescorla, "The TLS Protocol Version
1.1", RFC 4346, April 2006.
[EAP] Blunk, L., et. al., "Extensible Authentication Protocol
(EAP)", RFC 3748, June 2004.
[RFC3268] Chown, P., "Advanced Encryption Standard (AES)
Ciphersuites for Transport Layer Security (TLS)", RFC
3268, June 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to indicate
Requirement Levels", RFC 2119, March 1997.
[RFC3546] Blake-Wilson, S., et al., "Transport Layer Security (TLS)
Extensions", RFC 3546, June 2003.
[EAP-FAST] Cam-Winget, N., et al., "EAP Flexible Authentication via
Secure Tunneling (EAP-FAST) ", draft-cam-winget-eap-fast-
07 (work in progress), January 2007.
[RFC4507] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption
without Server-Side State", RFC 4507, May 2006.
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[MSCHAPv2] Zorn, G., "Microsoft PPP CHAP Extensions, Version 2", RFC
2759, January 2000.
[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
Version 1.5", RFC 2315, March 1998.
7.2
Informative
[RFC2434] Narten, T., and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 2434, October
1998.
[RFC2631] Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC
2631, January 1999.
[RFC3526] Kivinen, T., "More Modular Exponential (MODP) Diffie-
Hellman groups for Internet Key Exchange (IKE)", RFC
3526, May 2003
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys", BCP 86,
RFC 3766, April 2004.
[MITM] Puthenkulam, J., "The Compound Authentication Binding
Problem", draft-puthenkulam-eap-binding-04 (expired),
October 2003.
8.
Acknowledgments
The EAP-FAST design and protocol specification is based on the ideas
and contributions from Pad Jakkahalli, Mark Krischer, Doug Smith,
Ilan Frenkel and Jeremy Steiglitz.
9.
Author's Addresses
Nancy Cam-Winget
Cisco Systems
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190 W Tasman Drive
San Jose, CA 95134
US
Phone: +1 408 853 0532
E-mail: ncamwing@cisco.com
David McGrew
Cisco Systems
San Jose, CA 95134
US
E-mail: mcgrew@cisco.com
Joseph Salowey
Cisco Systems
2901 3rd Ave
Seattle, WA 98121
US
Phone: +1 206 256 3380
E-mail: jsalowey@cisco.com
Hao Zhou
Cisco Systems
4125 Highlander Parkway
Richfield, OH 44286
US
Phone : +1 330 523 2132
E-mail: hzhou@cisco.com
10.
Appendix: Examples
10.1
Example 1: Successful Tunnel PAC Provisioning
The following exchanges show anonymous DH with a successful EAP-
MSCHAPv2 exchange within Phase 2 to provision a Tunnel PAC, the
conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
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(EAP-FAST Start, S bit set, A-ID)
EAP-Response/
EAP-Type=EAP-FAST, V=1
(TLS client_hello without
PAC-Opaque extension)->
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(TLS server_hello,
TLS Server Key Exchange
TLS Server Hello Done)
EAP-Response/
EAP-Type=EAP-FAST, V=1 ->
(TLS Client Key Exchange
TLS change_cipher_spec,
TLS finished)
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(TLS change_cipher_spec
TLS finished)
EAP-Response/
EAP-Type=EAP-FAST, V=1 ->
(Acknowledgement)
TLS channel established
(messages sent within the TLS channel)
<- EAP Payload TLV,
EAP-Request/
EAP Identity Request
EAP Payload TLV, EAP-Response/
EAP Identity Response ->
<- EAP Payload TLV,
EAP-Request,
EAP-MSCHAPV2, Challenge
EAP Payload TLV, EAP-Response,
EAP-MSCHAPV2, Response) ->
<- EAP Payload TLV,
EAP-Request, EAP-MSCHAPV2, Success)
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EAP Payload TLV, EAP-Response,
EAP-MSCHAPV2, Success) ->
<- Intermediate Result TLV (Success)
Crypto-Binding-TLV=(Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC)
Intermediate Result TLV (Success)
Crypto-Binding-TLV=(Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC)
<- Result TLV (Success)
PAC TLV
Result TLV (Success)
PAC Acknowledgment ->
TLS channel torn down
(messages sent in cleartext)
<- EAP-Failure
10.2
Example 2: Failed Provisioning
The following exchanges show a failed EAP-MSCHAPV2 exchange
within Phase 2, where the peer failed to authenticate the Server.
The conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(EAP-FAST Start, S bit set, A-ID)
EAP-Response/
EAP-Type=EAP-FAST, V=1
(TLS client_hello without
Ticket extension)->
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<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(TLS Server Key Exchange
TLS Server Hello Done)
EAP-Response/
EAP-Type=EAP-FAST, V=1 ->
(TLS Client Key Exchange
TLS change_cipher_spec,
TLS finished)
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(TLS change_cipher_spec
TLS finished)
EAP-Response/
EAP-Type=EAP-FAST, V=1 ->
(Acknowledgement)
TLS channel established
(messages sent within the TLS channel)
<- EAP Payload TLV
EAP-Request/EAP Identity Request
EAP Payload TLV
EAP-Response/
EAP Identity Response ->
<- EAP Payload TLV, EAP-Request,
EAP-MSCHAPV2, Challenge
EAP Payload TLV, EAP-Response,
EAP-MSCHAPV2, Response ->
<- EAP Payload TLV, EAP-Request,
EAP-MSCHAPV2, Success)
// peer failed to verify server MSCHAPv2 response
EAP Payload TLV, EAP-Response,
EAP-MSCHAPV2, Failure) ->
<- Result TLV (Failure)
Result TLV (Failure) ->
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TLS channel torn down
(messages sent in cleartext)
<- EAP-Failure
10.3
Example 3: Provisioning a Authentication Server's Trusted Root
Certificate
The following exchanges show a successful provisioning of a server
trusted root certificate using anonymous DH and EAP-MSCHAPV2 exchange
within Phase 2, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(EAP-FAST Start, S bit set, A-ID)
EAP-Response/
EAP-Type=EAP-FAST, V=1
(TLS client_hello without
Ticket extension)->
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(TLS server_hello,
(TLS Server Key Exchange
TLS Server Hello Done)
EAP-Response/
EAP-Type=EAP-FAST, V=1 ->
(TLS Client Key Exchange
TLS change_cipher_spec,
TLS finished)
<- EAP-Request/
EAP-Type=EAP-FAST, V=1
(TLS change_cipher_spec
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TLS finished)
EAP-Payload-TLV[
EAP-Request/Identity])
// TLS channel established
(messages sent within the TLS channel)
// First EAP Payload TLV is piggybacked to the TLS Finished as
Application Data and protected by the TLS tunnel
EAP-Payload TLV/
[EAP Identity Response] ->
<- EAP Payload TLV, EAP-Request,
[EAP-MSCHAPV2, Challenge]
EAP Payload TLV, EAP-Response,
[EAP-MSCHAPV2, Response] ->
<- EAP Payload TLV, EAP-Request,
[EAP-MSCHAPV2, Success Request]
EAP Payload TLV, EAP-Response,
[EAP-MSCHAPV2, Success Response] ->
<- Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Crypto-Binding TLV (Version=1
EAP-FAST Version=1, Nonce,
CompoundMAC)
Server-Trusted-Root TLV
[Type = PKCS#7 ] ->
<- Result TLV (Success)
Server-Trusted-Root TLV
[PKCS#7 TLV]
Result TLV (Success) ->
// TLS channel torn down
(messages sent in cleartext)
<- EAP-Failure
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11.
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this standard. Please address the information to the IETF at
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12.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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13.
Copyright Statement
Copyright (C) The Internet Society (2007). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
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14.
Expiration Date
This memo is filed as <draft-cam-winget-eap-fast-provisioning-
03.txt>, and expires July 11, 2007.
Cam-Winget, et al. Expires July 11, 2007 [Page 40]