One document matched: draft-simon-emu-rfc2716bis-05.txt
Differences from draft-simon-emu-rfc2716bis-04.txt
Network Working Group Dan Simon
INTERNET-DRAFT Bernard Aboba
Category: Proposed Standard Microsoft
<draft-simon-emu-rfc2716bis-05.txt>
7 November 2006
The EAP TLS Authentication Protocol
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Copyright Notice
Copyright (C) The IETF Trust (2006). All rights reserved.
Abstract
The Extensible Authentication Protocol (EAP), defined in RFC 3748,
provides support for multiple authentication methods. Transport
Level Security (TLS) provides for mutual authentication, integrity-
protected ciphersuite negotiation and key exchange between two
endpoints. This document defines EAP-TLS, which includes support for
certificate-based mutual authentication and key derivation.
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Table of Contents
1. Introduction.............................................. 3
1.1 Requirements Language ........................... 3
1.2 Terminology ..................................... 3
2. Protocol Overview ........................................ 4
2.1 Overview of the EAP-TLS Conversation ............ 4
2.2 Retry Behavior .................................. 8
2.3 Fragmentation ................................... 8
2.4 Identity Verification ........................... 9
2.5 Key Hierarchy ................................... 10
2.6 Ciphersuite and Compression Negotiation ......... 13
2.7 Privacy ......................................... 13
3. Detailed Description of the EAP-TLS Protocol ............. 14
3.1 EAP TLS Packet Format .......................... 14
3.2 EAP TLS Request Packet ......................... 16
3.3 EAP TLS Response Packet ........................ 17
4. Security Considerations .................................. 19
4.1 Security Claims ................................ 19
4.2 Certificate Usage .............................. 20
4.3 Certificate Revocation ......................... 21
4.4 Separation of EAP Authenticator and Server ..... 21
4.5 Lower Layer Security Mechanisms ................ 22
4.6 Packet Modification Attacks .................... 22
5. References ............................................... 23
5.1 Normative references ....... .................... 23
5.2 Informative references .......................... 23
Acknowledgments .............................................. 25
Authors' Addresses ........................................... 26
Appendix A - Changes from RFC 2716 ........................... 27
Appendix B - Examples ........................................ 28
Intellectual Property Statement .............................. 34
Disclaimer of Validity ....................................... 34
Copyright Statement .......................................... 35
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1. Introduction
The Extensible Authentication Protocol (EAP), described in [RFC3748],
provides a standard mechanism for support of multiple authentication
methods. Through the use of EAP, support for a number of
authentication schemes may be added, including smart cards, Kerberos,
Public Key, One Time Passwords, and others.
While the EAP methods defined in [RFC3748] did not support mutual
authentication, the use of EAP with wireless technologies such as
[IEEE-802.11i] has resulted in development of a new set of
requirements. As described in "EAP Method Requirements for Wireless
LANs" [RFC4017], it is desirable for EAP methods used for wireless
LAN authentication to support mutual authentication and key
derivation. Since PPP encryption protocols such as DESE-bis
[RFC2419], 3DESE [RFC2420], and MPPE [RFC3078] assume existence of a
session key, it is useful to have a mechanism for session key
establishment. Since design of secure key management protocols is
non-trivial, it is desirable to avoid creating new mechanisms for
this. The EAP protocol described in this document allows a EAP peer
to take advantage of the protected ciphersuite negotiation, mutual
authentication and key management capabilities of the TLS protocol,
described in "The Transport Layer Security (TLS) Protocol Version
1.1" [RFC4346].
1.1. Requirements
In this document, several words are used to signify the requirements
of the specification. 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
"Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].
1.2. Terminology
This document frequently uses the following terms:
authenticator
The end of the link initiating EAP authentication. The term
authenticator is used in [IEEE-802.1X], and has the same meaning in
this document.
peer The end of the link that responds to the authenticator. In
[IEEE-802.1X], this end is known as the Supplicant.
backend authentication server
A backend authentication server is an entity that provides an
authentication service to an authenticator. When used, this server
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typically executes EAP methods for the authenticator. This
terminology is also used in [IEEE-802.1X].
EAP server
The entity that terminates the EAP authentication method with the
peer. In the case where no backend authentication server is used,
the EAP server is part of the authenticator. In the case where the
authenticator operates in pass-through mode, the EAP server is
located on the backend authentication server.
Master Session Key (MSK)
Keying material that is derived between the EAP peer and server and
exported by the EAP method. The MSK is at least 64 octets in
length.
Extended Master Session Key (EMSK)
Additional keying material derived between the EAP client and
server that is exported by the EAP method. The EMSK is at least 64
octets in length.
2. Protocol Overview
2.1. Overview of the EAP-TLS Conversation
As described in [RFC3748], the EAP-TLS conversation will typically
begin with the authenticator and the peer negotiating EAP. The
authenticator will then typically send an EAP-Request/Identity packet
to the peer, and the peer will respond with an EAP-Response/Identity
packet to the authenticator, containing the peer's userId.
From this point forward, while nominally the EAP conversation occurs
between the EAP authenticator and the peer, the authenticator MAY act
as a passthrough device, with the EAP packets received from the peer
being encapsulated for transmission to a backend security server. In
the discussion that follows, we will use the term "EAP server" to
denote the ultimate endpoint conversing with the peer.
Once having received the peer's Identity, the EAP server MUST respond
with an EAP-TLS/Start packet, which is an EAP-Request packet with
EAP-Type=EAP-TLS, the Start (S) bit set, and no data. The EAP-TLS
conversation will then begin, with the peer sending an EAP-Response
packet with EAP-Type=EAP-TLS. The data field of that packet will
encapsulate one or more TLS records in TLS record layer format,
containing a TLS client_hello handshake message. The current cipher
spec for the TLS records will be TLS_NULL_WITH_NULL_NULL and null
compression. This current cipher spec remains the same until the
change_cipher_spec message signals that subsequent records will have
the negotiated attributes for the remainder of the handshake.
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The client_hello message contains the client's TLS version number, a
sessionId, a random number, and a set of ciphersuites supported by
the client. The version offered by the client MUST correspond to TLS
v1.0 or later.
The EAP server will then respond with an EAP-Request packet with EAP-
Type=EAP-TLS. The data field of this packet will encapsulate one or
more TLS records. These will contain a TLS server_hello handshake
message, possibly followed by TLS certificate, server_key_exchange,
certificate_request, server_hello_done and/or finished handshake
messages, and/or a TLS change_cipher_spec message. The server_hello
handshake message contains a TLS version number, another random
number, a sessionId, and a ciphersuite. The version offered by the
server MUST correspond to TLS v1.0 or later.
If the client's sessionId is null or unrecognized by the server, the
server MUST choose the sessionId to establish a new session;
otherwise, the sessionId will match that offered by the client,
indicating a resumption of the previously established session with
that sessionID. The server will also choose a ciphersuite from those
offered by the client; if the session matches the client's, then the
ciphersuite MUST match the one negotiated during the handshake
protocol execution that established the session.
The purpose of the sessionId within the TLS protocol is to allow for
improved efficiency in the case where a client repeatedly attempts to
authenticate to an EAP server within a short period of time. While
this model was developed for use with HTTP authentication, it also
can be used to provide "fast reconnect" functionality as defined in
[RFC3748] Section 7.2.1.
It is left up to the peer whether to attempt to continue a previous
session, thus shortening the TLS conversation. Typically the peer's
decision will be made based on the time elapsed since the previous
authentication attempt to that EAP server. Based on the sessionId
chosen by the peer, and the time elapsed since the previous
authentication, the EAP server will decide whether to allow the
continuation, or whether to choose a new session.
In the case where the EAP server and authenticator reside on the same
device, then client will only be able to continue sessions when
connecting to the same NAS or tunnel server. Should these devices be
set up in a rotary or round-robin then it may not be possible for the
peer to know in advance the authenticator it will be connecting to,
and therefore which sessionId to attempt to reuse. As a result, it is
likely that the continuation attempt will fail. In the case where
the EAP authentication is remoted then continuation is much more
likely to be successful, since multiple NAS devices and tunnel
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servers will remote their EAP authentications to the same backend
authentication server.
If the EAP server is resuming a previously established session, then
it MUST include only a TLS change_cipher_spec message and a TLS
finished handshake message after the server_hello message. The
finished message contains the EAP server's authentication response to
the peer. If the EAP server is not resuming a previously established
session, then it MUST include a TLS server_certificate handshake
message, and a server_hello_done handshake message MUST be the last
handshake message encapsulated in this EAP-Request packet.
The certificate message contains a public key certificate chain for
either a key exchange public key (such as an RSA or Diffie-Hellman
key exchange public key) or a signature public key (such as an RSA or
DSS signature public key). In the latter case, a TLS
server_key_exchange handshake message MUST also be included to allow
the key exchange to take place.
The certificate_request message is included when the server desires
the client to authenticate itself via public key. While the EAP
server SHOULD require client authentication, this is not a
requirement, since it may be possible that the server will require
that the peer authenticate via some other means.
If the peer supports EAP-TLS and is configured to use it, it MUST
respond to the EAP-Request with an EAP-Response packet of EAP-
Type=EAP-TLS. The data field of this packet will encapsulate one or
more TLS records containing a TLS change_cipher_spec message and
finished handshake message, and possibly certificate,
certificate_verify and/or client_key_exchange handshake messages. If
the preceding server_hello message sent by the EAP server in the
preceding EAP-Request packet indicated the resumption of a previous
session, then the peer MUST send only the change_cipher_spec and
finished handshake messages. The finished message contains the
peer's authentication response to the EAP server.
If the preceding server_hello message sent by the EAP server in the
preceeding EAP-Request packet did not indicate the resumption of a
previous session, then the peer MUST send, in addition to the
change_cipher_spec and finished messages, a client_key_exchange
message, which completes the exchange of a shared master secret
between the peer and the EAP server. If the EAP server sent a
certificate_request message in the preceding EAP-Request packet, then
unless the peer is configured for privacy (see Section 2.7) the peer
MUST send, in addition, certificate and certificate_verify handshake
messages. The former contains a certificate for the peer's signature
public key, while the latter contains the peer's signed
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authentication response to the EAP server. After receiving this
packet, the EAP server will verify the peer's certificate and digital
signature, if requested.
If the peer's authentication is unsuccessful, the EAP server SHOULD
send an EAP-Request packet with EAP-Type=EAP-TLS, encapsulating a TLS
record containing the appropriate TLS alert message. The EAP server
SHOULD send a TLS alert message rather immediately terminating the
conversation so as to allow the peer to inform the user of the cause
of the failure and possibly allow for a restart of the conversation.
To ensure that the peer receives the TLS alert message, the EAP
server MUST wait for the peer to reply with an EAP-Response packet.
The EAP-Response packet sent by the peer MAY encapsulate a TLS
client_hello handshake message, in which case the EAP server MAY
allow the EAP-TLS conversation to be restarted, or it MAY contain an
EAP-Response packet with EAP-Type=EAP-TLS and no data, in which case
the EAP-Server MUST send an EAP-Failure packet, and terminate the
conversation. It is up to the EAP server whether to allow restarts,
and if so, how many times the conversation can be restarted. An EAP
Server implementing restart capability SHOULD impose a limit on the
number of restarts, so as to protect against denial of service
attacks.
If the peers authenticates successfully, the EAP server MUST respond
with an EAP-Request packet with EAP-Type=EAP-TLS, which includes, in
the case of a new TLS session, one or more TLS records containing TLS
change_cipher_spec and finished handshake messages. The latter
contains the EAP server's authentication response to the peer. The
peer will then verify the hash in order to authenticate the EAP
server.
If the EAP server authenticates unsuccessfully, the peer MAY send an
EAP-Response packet of EAP-Type=EAP-TLS containing a TLS Alert
message identifying the reason for the failed authentication. The
peer MAY send a TLS alert message rather than immediately terminating
the conversation so as to allow the EAP server to log the cause of
the error for examination by the system administrator.
To ensure that the EAP Server receives the TLS alert message, the
peer MUST wait for the EAP-Server to reply before terminating the
conversation. The EAP Server MUST reply with an EAP-Failure packet
since server authentication failure is a terminal condition.
If the EAP server authenticates successfully, the peer MUST send an
EAP-Response packet of EAP-Type=EAP-TLS, and no data. The EAP-Server
then MUST respond with an EAP-Success message.
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2.2. Retry Behavior
As with other EAP protocols, the EAP authenticator is responsible for
retry behavior. This means that if the EAP authenticator does not
receive a reply from the peer, it MUST resend the EAP-Request for
which it has not yet received an EAP-Response. However, the peer
MUST NOT resend EAP- Response packets without first being prompted by
the EAP authenticator.
For example, if the initial EAP-TLS start packet sent by the EAP
authenticator were to be lost, then the peer would not receive this
packet, and would not respond to it. As a result, the EAP-TLS start
packet would be resent by the EAP authenticator. Once the peer
received the EAP-TLS start packet, it would send an EAP-Response
encapsulating the client_hello message. If the EAP-Response were to
be lost, then the EAP authenticator would resend the initial EAP-TLS
start, and the peer would resend the EAP-Response.
As a result, it is possible that a peer will receive duplicate EAP-
Request messages, and may send duplicate EAP-Responses. Both the
peer and the EAP server should be engineered to handle this
possibility.
2.3. Fragmentation
A single TLS record may be up to 16384 octets in length, but a TLS
message may span multiple TLS records, and a TLS certificate message
may in principle be as long as 16MB. The group of EAP-TLS messages
sent in a single round may thus be larger than the MTU size or the
maximum RADIUS packet size of 4096 octets. As a result, an EAP-TLS
implementation MUST provide its own support for fragmentation and
reassembly. However, in order to ensure interoperability with
existing implementations, TLS handshake messages SHOULD NOT be
fragmented into multiple TLS records if they fit within a single TLS
record.
In order to protect against reassembly lockup and denial of service
attacks, it may be desirable for an implementation to set a maximum
size for one such group of TLS messages. Since a single certificate
is rarely longer than a few thousand octets, and no other field is
likely to be anywhere near as long, a reasonable choice of maximum
acceptable message length might be 64 KB.
Since EAP is a simple ACK-NAK protocol, fragmentation support can be
added in a simple manner. In EAP, fragments that are lost or damaged
in transit will be retransmitted, and since sequencing information is
provided by the Identifier field in EAP, there is no need for a
fragment offset field as is provided in IPv4.
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EAP-TLS fragmentation support is provided through addition of a flags
octet within the EAP-Response and EAP-Request packets, as well as a
TLS Message Length field of four octets. Flags include the Length
included (L), More fragments (M), and EAP-TLS Start (S) bits. The L
flag is set to indicate the presence of the four octet TLS Message
Length field, and MUST be set for the first fragment of a fragmented
TLS message or set of messages. The M flag is set on all but the last
fragment. The S flag is set only within the EAP-TLS start message
sent from the EAP server to the peer. The TLS Message Length field is
four octets, and provides the total length of the TLS message or set
of messages that is being fragmented; this simplifies buffer
allocation.
When an EAP-TLS peer receives an EAP-Request packet with the M bit
set, it MUST respond with an EAP-Response with EAP-Type=EAP-TLS and
no data. This serves as a fragment ACK. The EAP server MUST wait
until it receives the EAP-Response before sending another fragment.
In order to prevent errors in processing of fragments, the EAP server
MUST increment the Identifier field for each fragment contained
within an EAP-Request, and the peer MUST include this Identifier
value in the fragment ACK contained within the EAP-Response.
Retransmitted fragments will contain the same Identifier value.
Similarly, when the EAP server receives an EAP-Response with the M
bit set, it MUST respond with an EAP-Request with EAP-Type=EAP-TLS
and no data. This serves as a fragment ACK. The EAP peer MUST wait
until it receives the EAP-Request before sending another fragment.
In order to prevent errors in the processing of fragments, the EAP
server MUST increment the Identifier value for each fragment ACK
contained within an EAP-Request, and the peer MUST include this
Identifier value in the subsequent fragment contained within an EAP-
Response.
2.4. Identity Verification
As noted in [RFC3748] Section 5.1:
It is RECOMMENDED that the Identity Response be used primarily for
routing purposes and selecting which EAP method to use. EAP
Methods SHOULD include a method-specific mechanism for obtaining
the identity, so that they do not have to rely on the Identity
Response.
As part of the TLS negotiation, the server presents a certificate to
the peer, and if mutual authentication is requested, the peer
presents a certificate to the server. EAP-TLS therefore provides a
mechanism for determining both the peer identity (Peer-Id in
[KEYFRAME]) and server identity (Server-Id in [KEYFRAME]). For
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details, see Section 4.2.
Since the identity presented in the Identity Response need not be
related to the identity presented in the peer certificate, EAP-TLS
implementations SHOULD NOT require that they be identical, and SHOULD
NOT use the identity presented in the Identity Response for access
control or accounting purposes.
The peer MUST verify the validity of the EAP server certificate, and
SHOULD also examine the Server-id in order to determine whether the
EAP server can be trusted. For example, just because a server
certificate can chain to a trust anchor does not necessarily imply
that it is valid for connection to a particular network. As a
result, the peer may also want to test whether the EAP server
certificate is signed by a CA controlling the destination network and
whether the Server-Id matches the format expected for that network.
For example, an EAP peer connecting to the "EXAMPLE" SSID may wish to
check whether the Server-Id matches the regular expression
"*.example.com", in addition to checking whether the server
certificate chains to the example.com CA.
2.5. Key Hierarchy
Figure 1 illustrates the TEK key hierarchy for EAP-TLS which is based
on the TLS key hierarchy described in [RFC4346]. The TLS-negotiated
ciphersuite is used to set up a protected channel for use in
protecting the EAP conversation, keyed by the derived TEKs. The TEK
derivation proceeds as follows:
master_secret = TLS-PRF-48(pre_master_secret, "master secret",
client.random || server.random)
TEK = TLS-PRF-X(master_secret, "key expansion",
server.random || client.random)
Where:
TLS-PRF-X = TLS pseudo-random function defined in [RFC4346],
computed to X octets.
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| | pre_master_secret |
server| | | client
Random| V | Random
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
+---->| master_secret |<----+
| | (TMS) | |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
V V V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Key Block (TEKs) |
| label == "key expansion" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | | | |
| client | server | client | server | client | server
| MAC | MAC | write | write | IV | IV
| | | | | |
V V V V V V
Figure 1 - TLS [RFC4346] Key Hierarchy
In EAP-TLS, the MSK, EMSK and IV are derived from the TLS master
secret via a one-way function. This ensures that the TLS master
secret cannot be derived from the MSK, EMSK or IV unless the one-way
function (TLS PRF) is broken. Since the MSK and EMSK are derived
from the TLS master secret, if the TLS master secret is compromised
then the MSK and EMSK are also compromised.
The MSK is divided into two halves, corresponding to the "Peer to
Authenticator Encryption Key" (Enc- RECV-Key, 32 octets) and
"Authenticator to Peer Encryption Key" (Enc- SEND-Key, 32 octets).
The IV is a 64 octet quantity that is a known value; octets 0-31 are
known as the "Peer to Authenticator IV" or RECV-IV, and Octets 32-63
are known as the "Authenticator to Peer IV", or SEND-IV.
EAP-TLS derives exported keying material and parameters as follows:
MSK(0,63) = TLS-PRF-64(TMS, "client EAP encryption",
client.random || server.random)
EMSK(0,63) = second 64 octets of:
TLS-PRF-128(TMS, "client EAP encryption",
client.random || server.random)
IV(0,63) = TLS-PRF-64("", "client EAP encryption",
client.random || server.random)
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Enc-RECV-Key = MSK(0,31) = Peer to Authenticator Encryption Key
(MS-MPPE-Recv-Key in [RFC2548]). Also known as the
PMK in [IEEE-802.11i].
Enc-SEND-Key = MSK(32,63) = Authenticator to Peer Encryption Key
(MS-MPPE-Send-Key in [RFC2548])
RECV-IV = IV(0,31) = Peer to Authenticator Initialization Vector
SEND-IV = IV(32,63)= Authenticator to Peer Initialization Vector
Session-Id = 0x0C || client.random || server.random
Where:
IV(W,Z) = Octets W through Z inclusive of the IV.
MSK(W,Z) = Octets W through Z inclusive of the MSK.
EMSK(W,Z) = Octets W through Z inclusive of the EMSK.
TMS = TLS master_secret
TLS-PRF-X = TLS PRF function computed to X octets
client.random = Nonce generated by the TLS client.
server.random = Nonce generated by the TLS server.
| | pre_master_secret |
server| | | client
Random| V | Random
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
+---->| master_secret |<----+
| | (TMS) | |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
V V V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MSK, EMSK |
| label == "client EAP encryption" |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
| MSK(0,31) | MSK(32,63) | EMSK(0,63)
| | |
| | |
V V V
Figure 2 - EAP-TLS Key Hierarchy
The use of these keys is specific to the lower layer, as described in
[KEYFRAME] Section 2.1.
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2.6. Ciphersuite and Compression Negotiation
EAP-TLS implementations need not necessarily support all TLS
ciphersuites listed in [RFC4346]. Not all TLS ciphersuites are
supported by available TLS tool kits and licenses may be required in
some cases.
To ensure interoperability, EAP-TLS peers and servers MUST support
the TLS [RFC4346] mandatory-to-implement ciphersuite:
TLS_RSA_WITH_3DES_EDE_CBC_SHA.
In addition, EAP-TLS servers SHOULD support and be able to negotiate
all of the following TLS ciphersuites:
TLS_RSA_WITH_RC4_128_MD5
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_AES_128_CBC_SHA
In addition, EAP-TLS peers SHOULD support the following TLS
ciphersuites [RFC3268]:
TLS_RSA_WITH_AES_128_CBC_SHA
TLS_RSA_WITH_RC4_128_SHA
Since TLS supports ciphersuite negotiation, peers completing the TLS
negotiation will also have selected a ciphersuite, which includes
encryption and hashing methods. Since the ciphersuite negotiated
within EAP-TLS applies only to the EAP conversation, TLS ciphersuite
negotiation SHOULD NOT be used to negotiate the ciphersuites used to
secure data.
TLS also supports compression as well as ciphersuite negotiation.
However, during the EAP-TLS conversation the EAP peer and server MUST
NOT request or negotiate compression.
2.7. Privacy
EAP-TLS peer and server implementations MAY support privacy.
Disclosure of the username is avoided by utilizing a privacy Network
Access Identifier (NAI) [RFC4282] in the EAP-Response/Identity, and
transmitting the client certificate within a TLS session providing
confidentiality.
In order to avoid disclosing the peer username, an EAP-TLS peer
configured for privacy MUST negotiate a TLS ciphersuite supporting
confidentiality and MUST provide a client certificate list containing
no entries in response to the initial certificate_request from the
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EAP-TLS server.
An EAP-TLS server supporting privacy MUST NOT treat a certificate
list containing no entries as a terminal condition; instead it MUST
bring up the TLS session and then send a server_hello followed by a
certificate_request. An EAP-TLS peer supporting privacy MUST provide
a certificate list containing at least one entry in response to this
subsequent certificate_request. If the EAP-TLS server supporting
privacy does not receive a client certificate in response to the
subsequent certificate_request, then it MUST abort the session.
EAP-TLS privacy support is designed to allow EAP-TLS peers that do
not support privacy to interoperate with EAP-TLS servers supporting
privacy. EAP-TLS servers supporting privacy MUST request a client
certificate, and MUST accept a client certificate offered by the EAP-
TLS peer, in order to preserve interoperability with EAP-TLS peers
that do not support privacy.
However, an EAP-TLS peer configured for privacy typically will not be
able to successfully authenticate with an EAP-TLS server that does
not support privacy, since such a server will typically treat the
refusal to provide a client certificate as a terminal error. As a
result, unless authentication failure is considered preferable to
disclosure of the username, EAP-TLS peers should only be configured
for privacy on networks known to support it.
This is most easily achieved with EAP lower layers that support
network advertisement, so that the network and appropriate privacy
configuration can be determined. In order to determine the privacy
configuration on link layers (such as IEEE 802 wired networks) which
do not support network advertisement, it may be desirable to utilize
information provided in the server certificate or within identity
selection hints [RFC4284] to determine the appropriate configuration.
3. Detailed description of the EAP-TLS protocol
3.1. EAP TLS Packet Format
A summary of the EAP TLS Request/Response packet format is shown
below. The fields are transmitted from left to right.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
1 - Request
2 - Response
Identifier
The Identifier field is one octet and aids in matching responses
with requests.
Length
The Length field is two octets and indicates the length of the EAP
packet including the Code, Identifier, Length, Type, and Data
fields. Octets outside the range of the Length field should be
treated as Data Link Layer padding and MUST be ignored on
reception.
Type
13 - EAP TLS
Data
The format of the Data field is determined by the Code field.
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3.2. EAP TLS Request Packet
A summary of the EAP TLS Request packet format is shown below. The
fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Flags | TLS Message Length
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLS Message Length | TLS Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
1
Identifier
The Identifier field is one octet and aids in matching responses
with requests. The Identifier field MUST be changed on each
Request packet.
Length
The Length field is two octets and indicates the length of the EAP
packet including the Code, Identifier, Length, Type, and TLS
Response fields.
Type
13 - EAP TLS
Flags
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
|L M S R R R R R|
+-+-+-+-+-+-+-+-+
L = Length included
M = More fragments
S = EAP-TLS start
R = Reserved
The L bit (length included) is set to indicate the presence of the
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four octet TLS Message Length field, and MUST be set for the first
fragment of a fragmented TLS message or set of messages. The M bit
(more fragments) is set on all but the last fragment. The S bit
(EAP-TLS start) is set in an EAP-TLS Start message. This
differentiates the EAP-TLS Start message from a fragment
acknowledgment. Implementations of this specification MUST set
the reserved bits to zero, and MUST ignore them on reception.
TLS Message Length
The TLS Message Length field is four octets, and is present only
if the L bit is set. This field provides the total length of the
TLS message or set of messages that is being fragmented.
TLS data
The TLS data consists of the encapsulated TLS packet in TLS record
format.
3.3. EAP TLS Response Packet
A summary of the EAP TLS Response packet format is shown below. The
fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Flags | TLS Message Length
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLS Message Length | TLS Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
2
Identifier
The Identifier field is one octet and MUST match the Identifier
field from the corresponding request.
Length
The Length field is two octets and indicates the length of the EAP
packet including the Code, Identifier, Length, Type, and TLS data
fields.
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Type
13 - EAP TLS
Flags
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
|L M S R R R R R|
+-+-+-+-+-+-+-+-+
L = Length included
M = More fragments
S = EAP-TLS start
R = Reserved
The L bit (length included) is set to indicate the presence of the
four octet TLS Message Length field, and MUST be set for the first
fragment of a fragmented TLS message or set of messages. The M
bit (more fragments) is set on all but the last fragment. The S
bit (EAP-TLS start) is set in an EAP-TLS Start message. This
differentiates the EAP-TLS Start message from a fragment
acknowledgment. Implementations of this specification MUST set
the reserved bits to zero, and MUST ignore them on reception.
TLS Message Length
The TLS Message Length field is four octets, and is present only
if the L bit is set. This field provides the total length of the
TLS message or set of messages that is being fragmented.
TLS data
The TLS data consists of the encapsulated TLS packet in TLS record
format.
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4. Security Considerations
4.1. Security Claims
EAP security claims are defined in [RFC3748] Section 7.2.1. The
security claims for EAP-TLS are as follows:
Auth. mechanism: Certificates
Ciphersuite negotiation: Yes [1]
Mutual authentication: Yes [1]
Integrity protection: Yes [1]
Replay protection: Yes [1]
Confidentiality: Yes [2]
Key derivation: Yes
Key strength: [3]
Dictionary attack prot.: Yes
Fast reconnect: Yes
Crypt. binding: N/A
Session independence: Yes [1]
Fragmentation: Yes
Channel binding: No
Notes
-----
[1] A formal proof of the security of EAP-TLS when used with
[IEEE-802.11i] is provided in [He]. This proof relies on the
assumption that the private key pairs used by the EAP peer and server
are not shared with other parties or applications. For example, a
backend authentication server supporting EAP-TLS SHOULD NOT utilize
the same certificate with https.
[2] Privacy is an optional feature described in Section 2.7.
[3] 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:
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Attack Resistance RSA or DH Modulus DSA subgroup
(bits) size (bits) size (bits)
----------------- ----------------- ------------
70 947 128
80 1228 145
90 1553 153
100 1926 184
150 4575 279
200 8719 373
250 14596 475
4.2. Certificate Usage
The EAP-TLS peer name (Peer-Id) represents the Network Access
Identifier (NAI) [RFC4282] to be used for access control and
accounting purposes. The Peer-Id and Server-Id are determined from
the subject or altSubjectName fields in the peer and server
certificates. As noted in [RFC3280] Section 4.1.2.6:
The subject field identifies the entity associated with the public
key stored in the subject public key field. The subject name MAY
be carried in the subject field and/or the subjectAltName
extension... If subject naming information is present only in the
subjectAltName extension (e.g., a key bound only to an email
address or URI), then the subject name MUST be an empty sequence
and the subjectAltName extension MUST be critical.
Where it is non-empty, the subject field MUST contain an X.500
distinguished name (DN).
Where the subject field is not empty, the Peer-Id and Server-Id are
obtained from the Common Name (CN) field of the DN. Where subject
naming information is present only in the subjectAltName extension,
the Peer-Id and Server-Id are obtained from the subjectAltName.
A valid EAP-TLS client certificate SHOULD contain an extendedKeyUsage
value indicating support for Client Authentication
(1.3.6.1.5.5.7.3.2). A valid EAP-TLS server certificate SHOULD
contain an extendedKeyUsage value indicating support for Server
Authentication (1.3.6.1.5.5.7.3.1).
As discussed in [He], the security of EAP-TLS can be compromised if
the same credentials are used for authentication within multiple
applications. Certificate extensions for use with EAP-TLS are
discussed in "Certificate Extensions and Attributes Supporting
Authentication in Point-to-Point Protocol (PPP) and Wireless Local
Area Networks (WLAN)" [RFC4334]. These extensions enable certificate
usage to be restricted to use with lower layers such as PPP or IEEE
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802.11. An EAP-TLS implementation MAY make these and other
certificate fields available to the lower layer.
4.3. Certificate revocation
Since the EAP server is on the Internet during the EAP conversation,
the server is capable of following a certificate chain or verifying
whether the peer's certificate has been revoked. In contrast, the
peer may or may not have Internet connectivity, and thus while it can
validate the EAP server's certificate based on a pre-configured set
of CAs, it may not be able to follow a certificate chain or verify
whether the EAP server's certificate has been revoked.
In the case where the peer is initiating a voluntary Layer 2 tunnel
using PPTP [RFC2637] or L2TP [RFC2661], the peer will typically
already have a PPP interface and Internet connectivity established at
the time of tunnel initiation. As a result, during the EAP
conversation it is capable of checking for certificate revocation.
However, in the case where the peer is initiating an initial PPP
conversation, it will not have Internet connectivity and is therefore
not capable of checking for certificate revocation until after NCP
negotiation completes and the peer has access to the Internet. In
this case, the peer SHOULD check for certificate revocation after
connecting to the Internet.
4.4. Separation of the EAP Authenticator and Server
As a result of the EAP-TLS conversation, the EAP peer and server
endpoints will mutually authenticate and derive the MSK and EMSK.
Subsequently the EAP peer and authenticator may negotiate a
ciphersuite for protection of data and derive a session key for
subsequent use. Since the peer and EAP client reside on the same
machine, it is necessary for the EAP client module to pass the
required keying material to the lower layer, as described in
[KEYFRAME].
The situation may be more complex on the EAP authenticator, which may
or may not reside on the same machine as the EAP server. In the case
where the EAP server and authenticator reside on different machines,
there are several implications for security. Firstly, the mutual
authentication defined in EAP-TLS will occur between the EAP peer and
server, not between the peer and the authenticator. This means that
as a result of the EAP-TLS conversation, it is not possible for the
EAP peer to validate the identity of the NAS or tunnel server that it
is speaking to.
The second issue is that the EAP keying material derived between the
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peer and EAP server will need to be transported to the authenticator.
The implications of this are described in more detail in [KEYFRAME];
however the specification of this transport mechanism is outside the
scope of this document.
4.5. Lower Layer Security Mechanisms
EAP-TLS has been deployed for use with a variety of lower layers,
including PPP, Layer 2 tunneling protocols such as PPTP and L2TP,
IEEE 802 wired networks [IEEE-802.1X] and wireless technologies such
as IEEE 802.11 [IEEE-802.11i] and IEEE 802.16 [IEEE-802.16e].
In compulsory layer 2 tunneling, a PPP peer makes a connection to a
NAS or router which tunnels the PPP packets to a tunnel server.
Since with compulsory tunneling a PPP peer cannot tell whether its
packets are being tunneled, let alone whether the network device is
securing the tunnel, if security is required then the client must
make its own arrangements. In the case where all endpoints cannot be
relied upon to implement IPSEC, TLS, or another suitable security
protocol, PPP encryption provides a convenient means to ensure the
privacy of packets transiting between the client and the tunnel
server.
4.6. Packet Modification Attacks
The integrity protection of EAP-TLS packets does not extend to the
EAP header fields (Code, Identifier, Length) or the Type or Flags
fields. As a result, these fields may be modified by an attacker.
In most cases modification of the Code or Identifier fields will only
result in a denial of service attack. However, it may be possible
for an attacker to add additional data to an EAP-TLS packet so as to
cause it to be longer than implied by the Length field. EAP peers,
authenticators or servers that do not check for this could be
vulnerable to a buffer overrun.
It is also possible for an attacker to modify the Type or Flags
fields. By modifying the Type field, an attacker could cause one
TLS-based EAP method to be negotiated instead of another. For
example, the EAP-TLS Type field (13) could be changed to indicate
another TLS-based EAP method. Unless the alternative TLS-based EAP
method utilizes a different key derivation formula, it is possible
that an EAP method conversation altered by a man-in-the-middle could
run all the way to completion without detection. Unless the
ciphersuite selection policies are identical for all TLS-based EAP
methods utilizing the same key derivation formula, it may be possible
for an attacker to mount a successful downgrade attack, causing the
peer to utilize an inferior ciphersuite or TLS-based EAP method.
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5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3268] Chown, P., "Advanced Encryption Standard (AES)
Ciphersuites for Transport Layer Security (TLS)", RFC
3268, June 2002.
[RFC3280] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H.
Lefkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC4282] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The
Network Access Identifier", RFC 4282, December 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The TLS Protocol Version
1.1", RFC 4346, April 2006.
5.2. Informative References
[FIPS] National Bureau of Standards, "Data Encryption Standard",
FIPS PUB 46 (January 1977).
[IEEE-802.11] Institute of Electrical and Electronics Engineers,
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific Requirements Part
11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications", IEEE Standard
802.11-2003, 2003.
[IEEE-802.1X] Institute of Electrical and Electronics Engineers, "Local
and Metropolitan Area Networks: Port-Based Network Access
Control", IEEE Standard 802.1X-2004, December 2004.
[IEEE-802.11i] Institute of Electrical and Electronics Engineers,
"Supplement to STANDARD FOR Telecommunications and
Information Exchange between Systems - LAN/MAN Specific
Requirements - Part 11: Wireless Medium Access Control
(MAC) and physical layer (PHY) specifications:
Simon & Aboba Proposed Standard [Page 23]
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Specification for Enhanced Security", IEEE 802.11i,
December 2004.
[IEEE-802.16e] Institute of Electrical and Electronics Engineers, "IEEE
Standard for Local and Metropolitan Area Networks: Part
16: Air Interface for Fixed and Mobile Broadband Wireless
Access Systems: Amendment for Physical and Medium Access
Control Layers for Combined Fixed and Mobile Operations
in Licensed Bands" IEEE 802.16e, August 2005.
[He] He, C., Sundararajan, M., Datta, A., Derek, A. and J.
Mitchell, "A Modular Correctness Proof of IEEE 802.11i
and TLS", CCS '05, November 7-11, 2005, Alexandria,
Virginia, USA
[KEYFRAME] Aboba, B., Simon, D., Eronen, P. and H. Levkowetz,
"Extensible Authentication Protocol (EAP) Key Management
Framework", Internet Draft (work in progress), draft-
ietf-eap-keying-15.txt, October 2006.
[RFC1321] Rivest, R. and S. Dusse, "The MD5 Message-Digest
Algorithm", RFC 1321, April 1992.
[RFC1570] Simpson, W., Editor, "PPP LCP Extensions", RFC 1570,
January 1994.
[RFC1661] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)",
STD 51, RFC 1661, July 1994.
[RFC1962] D. Rand, "The PPP Compression Control Protocol", RFC
1962, Novell, June 1996.
[RFC1968] Meyer, G., "The PPP Encryption Protocol (ECP)", RFC 1968,
June 1996.
[RFC1990] Sklower, K., Lloyd, B., McGregor, G., Carr, D. and T.
Coradetti, "The PPP Multilink Protocol (MP)", RFC 1990,
August 1996.
[RFC2419] Sklower, K. and G. Meyer, "The PPP DES Encryption
Protocol, Version 2 (DESE-bis)", RFC 2419, September
1998.
[RFC2420] Hummert, K., "The PPP Triple-DES Encryption Protocol
(3DESE)", RFC 2420, September 1998.
[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes",
RFC 2548, March 1999.
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[RFC2637] Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little,
W., and G. Zorn, "Point-to-Point Tunneling Protocol", RFC
2637, July 1999.
[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, August 1999.
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication
Protocol", RFC 2716, October 1999.
[RFC3078] Pall, G. and G. Zorn, "Microsoft Point-to-Point
Encryption (MPPE) Protocol", RFC 3078, March 2001.
[RFC3766] Orman. H. and P. Hoffman, "Determining Strengths for
Public Keys Used for Exchanging Symmetric Keys", RFC
3766, April 2004.
[RFC4017] Stanley, D., Walker, J. and B. Aboba, "Extensible
Authentication Protocol (EAP) Method Requirements for
Wireless LANs", RFC 4017, March 2005.
[RFC4284] Adrangi, F., Lortz, V., Bari, F. and P. Eronen, "Identity
Selection Hints for the Extensible Authentication
Protocol (EAP)", RFC 4284, January 2006.
[RFC4334] Housley, R. and T. Moore, "Certificate Extensions and
Attributes Supporting Authentication in Point-to-Point
Protocol (PPP) and Wireless Local Area Networks (WLAN)",
RFC 4334, February 2006.
[SP800-57] National Institute of Standards and Technology,
"Recommendation for Key Management", Special Publication
800-57, May 2006.
Acknowledgments
Thanks to Terence Spies, Glen Zorn and Narendra Gidwani of Microsoft
for useful discussions of this problem space.
Simon & Aboba Proposed Standard [Page 25]
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Authors' Addresses
Dan Simon
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: +1 425 706 6711
EMail: dansimon@microsoft.com
Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: +1 425 706 6605
EMail: bernarda@microsoft.com
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Appendix A - Changes from RFC 2716
This Appendix lists the major changes between [RFC2716] and this
document. Minor changes, including style, grammar, spelling, and
editorial changes are not mentioned here.
o As EAP is now in use with a variety of lower layers, not just
PPP for which it was first designed, mention of PPP is restricted
to situations relating to PPP-specific behavior and reference is
made to other lower layers such as IEEE 802.11, IEEE 802.16, etc.
o The terminology section has been updated to reflect definitions
from [RFC3748] (Section 1.2).
o The responsibility for retry is clarified to reside with the EAP
authenticator, not the EAP server (Section 2.2).
o The recommendation that the identity presented in the EAP-
Response/Identity correspond to the identity provided in the peer
certificate has been removed. The Peer-Id and Server-Id are
defined. Recommendations on EAP server certificate validation are
provided (Section 2.4).
o The EAP-TLS key hierarchy is defined, using terminology from
[RFC3748]. This includes formulas for the computation of TEKs as
well as the MSK, EMSK, IV and Session-Id (Section 2.5).
o Mandatory and recommended TLS ciphersuites are provided. The
use of TLS ciphersuite negotiation for determining the lower layer
ciphersuite is not recommended (Section 2.6).
o Privacy is supported as an optional feature (Section 2.7).
o A section on security claims has been added and advice on key
strength is provided (Section 4.1).
o Advice on certificate usage is provided (Section 4.2).
o Packet modification attacks are described (Section 4.6).
o The examples have been updated to reflect typical messages sent
in the described scenarios. For example, where mutual
authentication is performed, the EAP-TLS server is shown to
request a client certificate and the client is shown to provide a
certificate_verify message. A privacy example is provided, and
two faulty examples of session resume failure were removed
(Appendix B).
Simon & Aboba Proposed Standard [Page 27]
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Appendix B - Examples
1. In the case where the EAP-TLS mutual authentication is
successful, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS Start)
EAP-Response/
EAP-Type=EAP-TLS
(TLS client_hello)->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
TLS certificate_request,
TLS server_hello_done)
EAP-Response/
EAP-Type=EAP-TLS
(TLS certificate,
TLS client_key_exchange,
TLS certificate_verify,
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=EAP-TLS ->
<- EAP-Success
2. In the case where the peer and server support privacy and
mutual authentication, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (AnonymousNAI) ->
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<- EAP-Request/
EAP-Type=EAP-TLS
(TLS Start)
EAP-Response/
EAP-Type=EAP-TLS
(TLS client_hello)->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
TLS certificate_request,
TLS server_hello_done)
EAP-Response/
EAP-Type=EAP-TLS
(TLS certificate (no cert),
TLS client_key_exchange,
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=EAP-TLS
(TLS client_hello)->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS server_hello,
[TLS certificate,]
[TLS server_key_exchange,]
TLS certificate_request,
TLS server_hello_done)
EAP-Response/
EAP-Type=EAP-TLS
(TLS certificate,
TLS client_key_exchange,
TLS certificate_verify,
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=EAP-TLS ->
<- EAP-Success
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3. In the case where the EAP-TLS mutual authentication is
successful, and fragmentation is required, the conversation will
appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS Start, S bit set)
EAP-Response/
EAP-Type=EAP-TLS
(TLS client_hello)->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
TLS certificate_request,
TLS server_hello_done)
(Fragment 1: L, M bits set)
EAP-Response/
EAP-Type=EAP-TLS ->
<- EAP-Request/
EAP-Type=EAP-TLS
(Fragment 2: M bit set)
EAP-Response/
EAP-Type=EAP-TLS ->
<- EAP-Request/
EAP-Type=EAP-TLS
(Fragment 3)
EAP-Response/
EAP-Type=EAP-TLS
(TLS certificate,
TLS client_key_exchange,
TLS certificate_verify,
TLS change_cipher_spec,
TLS finished)(Fragment 1:
L, M bits set)->
<- EAP-Request/
EAP-Type=EAP-TLS
EAP-Response/
EAP-Type=EAP-TLS
(Fragment 2)->
<- EAP-Request/
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EAP-Type=EAP-TLS
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=EAP-TLS ->
<- EAP-Success
4. In the case where the server authenticates to the client
successfully, but the client fails to authenticate to the server,
the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS Start)
EAP-Response/
EAP-Type=EAP-TLS
(TLS client_hello)->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
TLS certificate_request,
TLS server_hello_done)
EAP-Response/
EAP-Type=EAP-TLS
(TLS certificate,
TLS client_key_exchange,
TLS certificate_verify,
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=EAP-TLS ->
<- EAP-Request
EAP-Type=EAP-TLS
(TLS Alert message)
EAP-Response/
EAP-Type=EAP-TLS ->
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<- EAP-Failure
(User Disconnected)
5. In the case where server authentication is unsuccessful, the
conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS Start)
EAP-Response/
EAP-Type=EAP-TLS
(TLS client_hello)->
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
TLS certificate_request,
TLS server_hello_done)
EAP-Response/
EAP-Type=EAP-TLS
(TLS Alert message) ->
<- EAP-Failure
(User Disconnected)
6. In the case where a previously established session is being
resumed, and both sides authenticate successfully, the
conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Request/
EAP-Type=EAP-TLS
(TLS Start)
EAP-Response/
EAP-Type=EAP-TLS
(TLS client_hello)->
Simon & Aboba Proposed Standard [Page 32]
INTERNET-DRAFT EAP TLS Authentication Protocol 7 November 2006
<- EAP-Request/
EAP-Type=EAP-TLS
(TLS server_hello,
TLS change_cipher_spec
TLS finished)
EAP-Response/
EAP-Type=EAP-TLS
(TLS change_cipher_spec,
TLS finished) ->
<- EAP-Success
Simon & Aboba Proposed Standard [Page 33]
INTERNET-DRAFT EAP TLS Authentication Protocol 7 November 2006
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Simon & Aboba Proposed Standard [Page 34]
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