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Network Working Group V. Fajardo, Ed.
Request for Comments: 5609 Telcordia Technologies
Category: Informational Y. Ohba
Toshiba
R. Marin-Lopez
Univ. of Murcia
August 2009
State Machines for
the Protocol for Carrying Authentication for Network Access (PANA)
Abstract
This document defines the conceptual state machines for the Protocol
for Carrying Authentication for Network Access (PANA). The state
machines consist of the PANA Client (PaC) state machine and the PANA
Authentication Agent (PAA) state machine. The two state machines
show how PANA can interface with the Extensible Authentication
Protocol (EAP) state machines. The state machines and associated
models are informative only. Implementations may achieve the same
results using different methods.
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Fajardo, et al. Informational [Page 1]
RFC 5609 PANA State Machines August 2009
Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Interface between PANA and EAP ..................................3
4. Document Authority ..............................................5
5. Notations .......................................................5
6. Common Rules ....................................................6
6.1. Common Procedures ..........................................6
6.2. Common Variables ...........................................9
6.3. Configurable Values .......................................10
6.4. Common Message Initialization Rules .......................10
6.5. Common Retransmission Rules ...............................10
6.6. Common State Transitions ..................................11
7. PaC State Machine ..............................................12
7.1. Interface between PaC and EAP Peer ........................12
7.1.1. Delivering EAP Messages from PaC to EAP Peer .......12
7.1.2. Delivering EAP Messages from EAP Peer to PaC .......12
7.1.3. EAP Restart Notification from PaC to EAP Peer ......13
7.1.4. EAP Authentication Result Notification from
EAP Peer to PaC ....................................13
7.1.5. Alternate Failure Notification from PaC to
EAP Peer ...........................................13
7.2. Configurable Values .......................................13
7.3. Variables .................................................14
7.4. Procedures ................................................15
7.5. PaC State Transition Table ................................15
8. PAA State Machine ..............................................21
8.1. Interface between PAA and EAP Authenticator ...............21
8.1.1. EAP Restart Notification from PAA to EAP
Authenticator ......................................21
8.1.2. Delivering EAP Responses from PAA to EAP
Authenticator ......................................22
8.1.3. Delivering EAP Messages from EAP
Authenticator to PAA ...............................22
8.1.4. EAP Authentication Result Notification from
EAP Authenticator to PAA ...........................22
8.2. Variables .................................................23
8.3. Procedures ................................................24
8.4. PAA State Transition Table ................................24
9. Implementation Considerations ..................................29
9.1. PAA and PaC Interface to Service Management Entity ........29
10. Security Considerations .......................................29
11. Acknowledgments ...............................................29
12. References ....................................................29
12.1. Normative References .....................................29
12.2. Informative References ...................................30
Fajardo, et al. Informational [Page 2]
RFC 5609 PANA State Machines August 2009
1. Introduction
This document defines the state machines for the Protocol for
Carrying Authentication for Network Access (PANA) [RFC5191]. There
are state machines for the PANA Client (PaC) and for the PANA
Authentication Agent (PAA). Each state machine is specified through
a set of variables, procedures, and a state transition table. The
state machines and associated models described in this document are
informative only. Implementations may achieve similar results using
different models and/or methods.
A PANA protocol execution consists of several exchanges to carry
authentication information. Specifically, EAP PDUs are transported
inside PANA PDUs between PaC and PAA; that is, PANA represents a
lower layer for EAP. Thus, a PANA state machine bases its execution
on an EAP state machine execution and vice versa. Thus, this
document also shows for each of PaC and PAA an interface between an
EAP state machine and a PANA state machine and how this interface
allows to exchange information between them. Thanks to this
interface, a PANA state machine can be informed about several events
generated in an EAP state machine and make its execution conditional
to its events.
The details of EAP state machines are out of the scope of this
document. Additional information can be found in [RFC4137].
Nevertheless, PANA state machines presented here have been
coordinated with state machines shown by [RFC4137].
This document, apart from defining PaC and PAA state machines and
their interfaces to EAP state machines (running on top of PANA),
provides some implementation considerations, taking into account that
it is not a specification but an implementation guideline.
2. Terminology
This document reuses the terminology used in [RFC5191].
3. Interface between PANA and EAP
PANA carries EAP messages exchanged between an EAP peer and an EAP
authenticator (see Figure 1). Thus, a PANA state machine interacts
with an EAP state machine.
Two state machines are defined in this document: the PaC state
machine (see Section 7) and the PAA state machine (see Section 8).
The definition of each state machine consists of a set of variables,
procedures, and a state transition table. A subset of these
variables and procedures defines the interface between a PANA state
Fajardo, et al. Informational [Page 3]
RFC 5609 PANA State Machines August 2009
machine and an EAP state machine, and the state transition table
defines the PANA state machine behavior based on results obtained
through them.
On the one hand, the PaC state machine interacts with an EAP peer
state machine in order to carry out the PANA protocol on the PaC
side. On the other hand, the PAA state machine interacts with an EAP
authenticator state machine to run the PANA protocol on the PAA side.
Peer |EAP Auth
EAP <---------|------------> EAP
^ | | ^ |
| | | EAP-Message | | EAP-Message
EAP-Message | |EAP-Message | | |
| v |PANA | v
PaC <---------|------------> PAA
Figure 1: Interface between PANA and EAP
Thus, two interfaces are needed between PANA state machines and EAP
state machines, namely:
o Interface between the PaC state machine and the EAP peer state
machine
o Interface between the PAA state machine and the EAP authenticator
state machine
In general, the PaC and PAA state machines present EAP messages to
the EAP peer and authenticator state machines through the interface,
respectively. The EAP peer and authenticator state machines process
these messages and send EAP messages through the PaC and PAA state
machines that are responsible for actually transmitting this message,
respectively.
For example, [RFC4137] specifies four interfaces to lower layers: (i)
an interface between the EAP peer state machine and a lower layer,
(ii) an interface between the EAP standalone authenticator state
machine and a lower layer, (iii) an interface between the EAP full
authenticator state machine and a lower layer, and (iv) an interface
between the EAP backend authenticator state machine and a lower
layer. In this document, the PANA protocol is the lower layer of EAP
and only the first three interfaces are of interest to PANA. The
second and third interfaces are the same. In this regard, the EAP
standalone authenticator or the EAP full authenticator and its state
machine in [RFC4137] are referred to as the EAP authenticator and the
EAP authenticator state machine, respectively, in this document. If
an EAP peer and an EAP authenticator follow the state machines
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RFC 5609 PANA State Machines August 2009
defined in [RFC4137], the interfaces between PANA and EAP could be
based on that document. Detailed definition of interfaces between
PANA and EAP are described in the subsequent sections.
4. Document Authority
This document is intended to comply with the technical contents of
any of the related documents ([RFC5191] and [RFC4137]). When there
is a discrepancy, the related documents are considered authoritative
and they take precedence over this document.
5. Notations
The following state transition tables are completed mostly based on
the conventions specified in [RFC4137]. The complete text is
described below.
State transition tables are used to represent the operation of the
protocol by a number of cooperating state machines each comprising a
group of connected, mutually exclusive states. Only one state of
each machine can be active at any given time.
All permissible transitions from a given state to other states and
associated actions performed when the transitions occur are
represented by using triplets of (exit condition, exit action, exit
state). All conditions are expressions that evaluate to TRUE or
FALSE; if a condition evaluates to TRUE, then the condition is met.
A state "ANY" is a wildcard state that matches any state in each
state machine except those explicitly enumerated as exception states.
The exit conditions of a wildcard state are evaluated after all other
exit conditions specific to the current state are met.
On exit from a state, the exit actions defined for the state and the
exit condition are executed exactly once, in the order that they
appear. (Note that the procedures defined in [RFC4137] are executed
on entry to a state, which is one major difference from this
document.) Each exit action is deemed to be atomic; i.e., execution
of an exit action completes before the next sequential exit action
starts to execute. No exit action executes outside of a state block.
The exit actions in only one state block execute at a time even if
the conditions for execution of state blocks in different state
machines are satisfied. All exit actions in an executing state block
complete execution before the transition to and execution of any
other state blocks. The execution of any state block appears to be
atomic with respect to the execution of any other state block, and
the transition condition to that state from the previous state is
TRUE when execution commences. The order of execution of state
blocks in different state machines is undefined except as constrained
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RFC 5609 PANA State Machines August 2009
by their transition conditions. A variable that is set to a
particular value in a state block retains this value until a
subsequent state block executes an exit action that modifies the
value.
On completion of the transition from the previous state to the
current state, all exit conditions occurring during the current state
(including exit conditions defined for the wildcard state) are
evaluated until an exit condition for that state is met.
Any event variable is set to TRUE when the corresponding event occurs
and set to FALSE immediately after completion of the action
associated with the current state and the event.
The interpretation of the special symbols and operators used is
defined in [RFC4137].
6. Common Rules
There are following procedures, variables, message initializing
rules, and state transitions that are common to both the PaC and PAA
state machines.
Throughout this document, the character string "PANA_MESSAGE_NAME"
matches any one of the abbreviated PANA message names, i.e., "PCI",
"PAR", "PAN", "PTR", "PTA", "PNR", "PNA".
6.1. Common Procedures
void None()
A null procedure, i.e., nothing is done.
void Disconnect()
A procedure to delete the PANA session as well as the
corresponding EAP session and authorization state.
boolean Authorize()
A procedure to create or modify authorization state. It returns
TRUE if authorization is successful. Otherwise, it returns FALSE.
It is assumed that Authorize() procedure of PaC state machine
always returns TRUE. In the case that a non-key-generating EAP
method is used but a PANA SA is required after successful
authentication (generate_pana_sa() returns TRUE), Authorize()
procedure must return FALSE.
Fajardo, et al. Informational [Page 6]
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void Tx:PANA_MESSAGE_NAME[flag](AVPs)
A procedure to send a PANA message to its peering PANA entity.
The "flag" argument contains one or more flags (e.g., Tx:PAR[C])
to be set to the message, except for 'R' (Request) flag. The
"AVPs" contains a list of names of optional AVPs to be inserted in
the message, except for AUTH AVP.
This procedure includes the following action before actual
transmission:
if (flag==S)
PANA_MESSAGE_NAME.S_flag=Set;
if (flag==C)
PANA_MESSAGE_NAME.C_flag=Set;
if (flag==A)
PANA_MESSAGE_NAME.A_flag=Set;
if (flag==P)
PANA_MESSAGE_NAME.P_flag=Set;
PANA_MESSAGE_NAME.insert_avp(AVPs);
if (key_available())
PANA_MESSAGE_NANE.insert_avp("AUTH");
void TxEAP()
A procedure to send an EAP message to the EAP state machine to
which it interfaces.
void RtxTimerStart()
A procedure to start the retransmission timer, reset RTX_COUNTER
variable to zero, and set an appropriate value to RTX_MAX_NUM
variable. Note that RTX_MAX_NUM is assumed to be set to the same
default value for all messages. However, implementations may also
reset RTX_MAX_NUM in this procedure and its value may vary
depending on the message that was sent.
void RtxTimerStop()
A procedure to stop the retransmission timer.
void SessionTimerReStart(TIMEOUT)
A procedure to (re)start the PANA session timer. TIMEOUT
specifies the expiration time associated with the session timer.
Expiration of TIMEOUT will trigger a SESS_TIMEOUT event.
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void SessionTimerStop()
A procedure to stop the current PANA session timer.
void Retransmit()
A procedure to retransmit a PANA message and increment RTX_COUNTER
by one(1).
void EAP_Restart()
A procedure to (re)start an EAP conversation resulting in the re-
initialization of an existing EAP session.
void PANA_MESSAGE_NAME.insert_avp("AVP_NAME1", "AVP_NAME2",...)
A procedure to insert AVPs for each specified AVP name in the list
of AVP names in the PANA message. When an AVP name ends with "*",
zero, one, or more AVPs are inserted; otherwise, one AVP is
inserted.
boolean PANA_MESSAGE_NAME.exist_avp("AVP_NAME")
A procedure that checks whether an AVP of the specified AVP name
exists in the specified PANA message and returns TRUE if the
specified AVP is found, otherwise returns FALSE.
boolean generate_pana_sa()
A procedure to check whether the EAP method being used generates
keys and that a PANA SA will be established on successful
authentication. For the PaC, the procedure is also used to check
and match the PRF and Integrity algorithm AVPs advertised by the
PAA in PAR[S] message. For the PAA, it is used to indicate
whether a PRF and Integrity algorithm AVPs will be sent in the
PAR[S]. This procedure will return TRUE if a PANA SA will be
generated. Otherwise, it returns FALSE.
boolean key_available()
A procedure to check whether the PANA session has a PANA_AUTH_KEY.
If the state machine already has a PANA_AUTH_KEY, it returns TRUE.
If the state machine does not have a PANA_AUTH_KEY, it tries to
retrieve a Master Session Key (MSK) from the EAP entity. If an
MSK is retrieved, it computes a PANA_AUTH_KEY from the MSK and
returns TRUE. Otherwise, it returns FALSE.
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6.2. Common Variables
PAR.RESULT_CODE
This variable contains the Result-Code AVP value in the PANA-Auth-
Request message in process. When this variable carries
PANA_SUCCESS, it is assumed that the PAR message always contains
an EAP-Payload AVP that carries an EAP-Success message.
NONCE_SENT
This variable is set to TRUE to indicate that a Nonce-AVP has
already been sent. Otherwise, it is set to FALSE.
RTX_COUNTER
This variable contains the current number of retransmissions of
the outstanding PANA message.
Rx:PANA_MESSAGE_NAME[flag]
This event variable is set to TRUE when the specified PANA message
is received from its peering PANA entity. The "flag" contains a
flag (e.g., Rx:PAR[C]), except for 'R' (Request) flag.
RTX_TIMEOUT
This event variable is set to TRUE when the retransmission timer
is expired.
REAUTH
This event variable is set to TRUE when an initiation of re-
authentication phase is triggered. This event variable can only
be set while in the OPEN state.
TERMINATE
This event variable is set to TRUE when initiation of PANA session
termination is triggered. This event variable can only be set
while in the OPEN state.
PANA_PING
This event variable is set to TRUE when initiation of liveness
test based on PANA-Notification exchange is triggered. This event
variable can only be set while in the OPEN state.
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SESS_TIMEOUT
This event is variable is set to TRUE when the session timer has
expired.
LIFETIME_SESS_TIMEOUT
Configurable value used by the PaC and PAA to close or disconnect
an established session in the access phase. This variable
indicates the expiration of the session and is set to the value of
Session-Lifetime AVP if present in the last PANA-Auth-Request
message in the case of the PaC. Otherwise, it is assumed that the
value is infinite and therefore has no expiration. Expiration of
LIFETIME_SESS_TIMEOUT will cause the event variable SESS_TIMEOUT
to be set.
ANY
This event variable is set to TRUE when any event occurs.
6.3. Configurable Values
RTX_MAX_NUM
Configurable maximum for how many retransmissions should be
attempted before aborting.
6.4. Common Message Initialization Rules
When a message is prepared for sending, it is initialized as follows:
o For a request message, R-flag of the header is set. Otherwise,
R-flag is not set.
o Other message header flags are not set. They are set explicitly
by specific state machine actions.
o AVPs that are mandatory to be included in a message are inserted
with appropriate values set.
6.5. Common Retransmission Rules
The state machines defined in this document assume that the PaC and
the PAA cache the last transmitted answer message. This scheme is
described in Section 5.2 of [RFC5191]. When the PaC or PAA receives
a retransmitted or duplicate request, it would be able to resend the
corresponding answer without any aid from the EAP layer. However, to
simplify the state machine description, this caching scheme is
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RFC 5609 PANA State Machines August 2009
omitted in the state machines below. In the case that there is not a
corresponding answer to a retransmitted request, the request will be
handled by the corresponding state machine.
6.6. Common State Transitions
The following transitions can occur at any state with exemptions
explicitly noted.
----------
State: ANY
----------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - (Re-transmissions)- - - - - - - - - -
RTX_TIMEOUT && Retransmit(); (no change)
RTX_COUNTER<
RTX_MAX_NUM
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - (Reach maximum number of transmissions)- - - - - -
(RTX_TIMEOUT && Disconnect(); CLOSED
RTX_COUNTER>=
RTX_MAX_NUM) ||
SESS_TIMEOUT
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-------------------------
State: ANY except INITIAL
-------------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - (liveness test initiated by peer)- - - - - -
Rx:PNR[P] Tx:PNA[P](); (no change)
-------------------------------
State: ANY except WAIT_PNA_PING
-------------------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - (liveness test response) - - - - - - - -
Rx:PNA[P] None(); (no change)
The following transitions can occur on any exit condition within the
specified state.
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RFC 5609 PANA State Machines August 2009
-------------
State: CLOSED
-------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - -(Catch all event on closed state) - - - - - - - -
ANY None(); CLOSED
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
7. PaC State Machine
7.1. Interface between PaC and EAP Peer
This interface defines the interactions between a PaC and an EAP
peer. The interface serves as a mechanism to deliver EAP messages
for the EAP peer. It allows the EAP peer to receive EAP requests and
send EAP responses via the PaC. It also provides a mechanism to
notify the EAP peer of PaC events and a mechanism to receive
notification of EAP peer events. The EAP message delivery mechanism
as well as the event notification mechanism in this interface have
direct correlation with the PaC state transition table entries.
These message delivery and event notifications mechanisms occur only
within the context of their associated states or exit actions.
7.1.1. Delivering EAP Messages from PaC to EAP Peer
TxEAP() procedure in the PaC state machine serves as the mechanism to
deliver EAP messages contained in PANA-Auth-Request messages to the
EAP peer. This procedure is enabled only after an EAP restart event
is notified to the EAP peer and before any event resulting in a
termination of the EAP peer session. In the case where the EAP peer
follows the EAP peer state machine defined in [RFC4137], TxEAP()
procedure sets eapReq variable of the EAP peer state machine and puts
the EAP request in eapReqData variable of the EAP peer state machine.
7.1.2. Delivering EAP Messages from EAP Peer to PaC
An EAP message is delivered from the EAP peer to the PaC via
EAP_RESPONSE event variable. The event variable is set when the EAP
peer passes the EAP message to its lower layer. In the case where
the EAP peer follows the EAP peer state machine defined in [RFC4137],
EAP_RESPONSE event variable refers to eapResp variable of the EAP
peer state machine and the EAP message is contained in eapRespData
variable of the EAP peer state machine.
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7.1.3. EAP Restart Notification from PaC to EAP Peer
The EAP peer state machine defined in [RFC4137] has an initialization
procedure before receiving an EAP message. To initialize the EAP
state machine, the PaC state machine defines an event notification
mechanism to send an EAP (re)start event to the EAP peer. The event
notification is done via EAP_Restart() procedure in the
initialization action of the PaC state machine.
7.1.4. EAP Authentication Result Notification from EAP Peer to PaC
In order for the EAP peer to notify the PaC of an EAP authentication
result, EAP_SUCCESS and EAP_FAILURE event variables are defined. In
the case where the EAP peer follows the EAP peer state machine
defined in [RFC4137], EAP_SUCCESS and EAP_FAILURE event variables
refer to eapSuccess and eapFail variables of the EAP peer state
machine, respectively. In this case, if EAP_SUCCESS event variable
is set to TRUE and an MSK is generated by the EAP authentication
method in use, eapKeyAvailable variable is set to TRUE and eapKeyData
variable contains the MSK. Note that EAP_SUCCESS and EAP_FAILURE
event variables may be set to TRUE even before the PaC receives a PAR
with a 'Complete' flag set from the PAA.
7.1.5. Alternate Failure Notification from PaC to EAP Peer
alt_reject() procedure in the PaC state machine serves as the
mechanism to deliver an authentication failure event to the EAP peer
without accompanying an EAP message. In the case where the EAP peer
follows the EAP peer state machine defined in [RFC4137], alt_reject()
procedure sets altReject variable of the EAP peer state machine.
Note that the EAP peer state machine in [RFC4137] also defines
altAccept variable; however, it is never used in PANA in which EAP-
Success messages are reliably delivered by the last PANA-Auth
exchange.
7.2. Configurable Values
FAILED_SESS_TIMEOUT
This is a configurable value that allows the PaC to determine
whether a PaC authentication and authorization phase has stalled
without an explicit EAP success or failure notification.
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7.3. Variables
AUTH_USER
This event variable is set to TRUE when initiation of EAP-based
(re-)authentication is triggered by the application.
EAP_SUCCESS
This event variable is set to TRUE when the EAP peer determines
that an EAP conversation completes with success.
EAP_FAILURE
This event variable is set to TRUE when the EAP peer determines
that an EAP conversation completes with failure.
EAP_RESPONSE
This event variable is set to TRUE when the EAP peer delivers an
EAP message to the PaC. This event accompanies an EAP message
received from the EAP peer.
EAP_RESP_TIMEOUT
This event variable is set to TRUE when the PaC that has passed an
EAP message to the EAP layer does not receive a subsequent EAP
message from the EAP layer in a given period. This provides a
time limit for certain EAP methods where user interaction may be
required.
EAP_DISCARD
This event variable is set to TRUE when the EAP peer indicates
that it has silently discarded the last received EAP-Request.
This event does not accompany any EAP message. In the case where
the EAP peer follows the EAP peer state machine defined in
[RFC4137], this event variable refers to eapNoResp. Note that
this specification does not support silently discarding EAP
messages. They are treated as fatal errors instead. This may
have an impact on denial-of-service resistance.
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7.4. Procedures
boolean eap_piggyback()
This procedure returns TRUE to indicate whether the next EAP
response will be carried in the pending PAN message for
optimization.
void alt_reject()
This procedure informs the EAP peer of an authentication failure
event without accompanying an EAP message.
void EAP_RespTimerStart()
This is a procedure to start a timer to receive an EAP-Response
from the EAP peer.
void EAP_RespTimerStop()
This is a procedure to stop a timer to receive an EAP-Response
from the EAP peer.
7.5. PaC State Transition Table
------------------------------
State: INITIAL (Initial State)
------------------------------
Initialization Action:
NONCE_SENT=Unset;
RTX_COUNTER=0;
RtxTimerStop();
Exit Condition Exit Action Exit State
------------------------+--------------------------+-----------
- - - - - - - - - - (PaC-initiated Handshake) - - - - - - - - -
AUTH_USER Tx:PCI[](); INITIAL
RtxTimerStart();
SessionTimerReStart
(FAILED_SESS_TIMEOUT);
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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- - - - - - -(PAA-initiated Handshake, not optimized) - - - - -
Rx:PAR[S] && EAP_Restart(); WAIT_PAA
!PAR.exist_avp SessionTimerReStart
("EAP-Payload") (FAILED_SESS_TIMEOUT);
if (generate_pana_sa())
Tx:PAN[S]("PRF-Algorithm",
"Integrity-Algorithm");
else
Tx:PAN[S]();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - -(PAA-initiated Handshake, optimized) - - - - - -
Rx:PAR[S] && EAP_Restart(); INITIAL
PAR.exist_avp TxEAP();
("EAP-Payload") && SessionTimerReStart
eap_piggyback() (FAILED_SESS_TIMEOUT);
Rx:PAR[S] && EAP_Restart(); WAIT_EAP_MSG
PAR.exist_avp TxEAP();
("EAP-Payload") && SessionTimerReStart
!eap_piggyback() (FAILED_SESS_TIMEOUT);
if (generate_pana_sa())
Tx:PAN[S]("PRF-Algorithm",
"Integrity-Algorithm");
else
Tx:PAN[S]();
EAP_RESPONSE if (generate_pana_sa()) WAIT_PAA
Tx:PAN[S]("EAP-Payload",
"PRF-Algorithm",
"Integrity-Algorithm");
else
Tx:PAN[S]("EAP-Payload");
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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RFC 5609 PANA State Machines August 2009
---------------
State: WAIT_PAA
---------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - - -(PAR-PAN exchange) - - - - - - - -
Rx:PAR[] && RtxTimerStop(); WAIT_EAP_MSG
!eap_piggyback() TxEAP();
EAP_RespTimerStart();
if (NONCE_SENT==Unset) {
NONCE_SENT=Set;
Tx:PAN[]("Nonce");
}
else
Tx:PAN[]();
Rx:PAR[] && RtxTimerStop(); WAIT_EAP_MSG
eap_piggyback() TxEAP();
EAP_RespTimerStart();
Rx:PAN[] RtxTimerStop(); WAIT_PAA
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - -(PANA result) - - - - - - - - - -
Rx:PAR[C] && TxEAP(); WAIT_EAP_RESULT
PAR.RESULT_CODE==
PANA_SUCCESS
Rx:PAR[C] && if (PAR.exist_avp WAIT_EAP_RESULT_
PAR.RESULT_CODE!= ("EAP-Payload")) CLOSE
PANA_SUCCESS TxEAP();
else
alt_reject();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Fajardo, et al. Informational [Page 17]
RFC 5609 PANA State Machines August 2009
-------------------
State: WAIT_EAP_MSG
-------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - (Return PAN/PAR from EAP) - - - - - - - - -
EAP_RESPONSE && EAP_RespTimerStop() WAIT_PAA
eap_piggyback() if (NONCE_SENT==Unset) {
Tx:PAN[]("EAP-Payload",
"Nonce");
NONCE_SENT=Set;
}
else
Tx:PAN[]("EAP-Payload");
EAP_RESPONSE && EAP_RespTimerStop() WAIT_PAA
!eap_piggyback() Tx:PAR[]("EAP-Payload");
RtxTimerStart();
EAP_RESP_TIMEOUT && Tx:PAN[](); WAIT_PAA
eap_piggyback()
EAP_DISCARD && Tx:PAN[](); CLOSED
eap_piggyback() SessionTimerStop();
Disconnect();
EAP_FAILURE || SessionTimerStop(); CLOSED
(EAP_DISCARD && Disconnect();
!eap_piggyback())
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
----------------------
State: WAIT_EAP_RESULT
----------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - (EAP Result) - - - - - - - - - - - - -
EAP_SUCCESS if (PAR.exist_avp OPEN
("Key-Id"))
Tx:PAN[C]("Key-Id");
else
Tx:PAN[C]();
Authorize();
SessionTimerReStart
(LIFETIME_SESS_TIMEOUT);
Fajardo, et al. Informational [Page 18]
RFC 5609 PANA State Machines August 2009
EAP_FAILURE Tx:PAN[C](); CLOSED
SessionTimerStop();
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
----------------------------
State: WAIT_EAP_RESULT_CLOSE
----------------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - (EAP Result) - - - - - - - - - - - - -
EAP_SUCCESS || if (EAP_SUCCESS && CLOSED
EAP_FAILURE PAR.exist_avp("Key-Id"))
Tx:PAN[C]("Key-Id");
else
Tx:PAN[C]();
SessionTimerStop();
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-----------
State: OPEN
-----------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - (liveness test initiated by PaC)- - - - - -
PANA_PING Tx:PNR[P](); WAIT_PNA_PING
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - (re-authentication initiated by PaC)- - - - - -
REAUTH NONCE_SENT=Unset; WAIT_PNA_REAUTH
Tx:PNR[A]();
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Fajardo, et al. Informational [Page 19]
RFC 5609 PANA State Machines August 2009
- - - - - - - - - (re-authentication initiated by PAA)- - - - - -
Rx:PAR[] EAP_RespTimerStart(); WAIT_EAP_MSG
TxEAP();
if (!eap_piggyback())
Tx:PAN[]("Nonce");
else
NONCE_SENT=Unset;
SessionTimerReStart
(FAILED_SESS_TIMEOUT);
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - -(Session termination initiated by PAA) - - - - - -
Rx:PTR[] Tx:PTA[](); CLOSED
SessionTimerStop();
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - -(Session termination initiated by PaC) - - - - - -
TERMINATE Tx:PTR[](); SESS_TERM
RtxTimerStart();
SessionTimerStop();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
----------------------
State: WAIT_PNA_REAUTH
----------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - -(re-authentication initiated by PaC) - - - - -
Rx:PNA[A] RtxTimerStop(); WAIT_PAA
SessionTimerReStart
(FAILED_SESS_TIMEOUT);
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - -(Session termination initiated by PAA) - - - - - -
Rx:PTR[] RtxTimerStop(); CLOSED
Tx:PTA[]();
SessionTimerStop();
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
--------------------
State: WAIT_PNA_PING
--------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - -(liveness test initiated by PaC) - - - - - - -
Rx:PNA[P] RtxTimerStop(); OPEN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Fajardo, et al. Informational [Page 20]
RFC 5609 PANA State Machines August 2009
- - - - - - - - - (re-authentication initiated by PAA)- - - - -
Rx:PAR[] RtxTimerStop(); WAIT_EAP_MSG
EAP_RespTimerStart();
TxEAP();
if (!eap_piggyback())
Tx:PAN[]("Nonce");
else
NONCE_SENT=Unset;
SessionTimerReStart
(FAILED_SESS_TIMEOUT);
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - -(Session termination initiated by PAA) - - - - - -
Rx:PTR[] RtxTimerStop(); CLOSED
Tx:PTA[]();
SessionTimerStop();
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
----------------
State: SESS_TERM
----------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - -(Session termination initiated by PaC) - - - - -
Rx:PTA[] Disconnect(); CLOSED
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
8. PAA State Machine
8.1. Interface between PAA and EAP Authenticator
The interface between a PAA and an EAP authenticator provides a
mechanism to deliver EAP messages for the EAP authenticator as well
as a mechanism to notify the EAP authenticator of PAA events and to
receive notification of EAP authenticator events. These message
delivery and event notification mechanisms occur only within context
of their associated states or exit actions.
8.1.1. EAP Restart Notification from PAA to EAP Authenticator
An EAP authenticator state machine defined in [RFC4137] has an
initialization procedure before sending the first EAP request. To
initialize the EAP state machine, the PAA state machine defines an
event notification mechanism to send an EAP (re)start event to the
EAP authenticator. The event notification is done via EAP_Restart()
procedure in the initialization action of the PAA state machine.
Fajardo, et al. Informational [Page 21]
RFC 5609 PANA State Machines August 2009
8.1.2. Delivering EAP Responses from PAA to EAP Authenticator
TxEAP() procedure in the PAA state machine serves as the mechanism to
deliver EAP-Responses contained in PANA-Auth-Answer messages to the
EAP authenticator. This procedure is enabled only after an EAP
restart event is notified to the EAP authenticator and before any
event resulting in a termination of the EAP authenticator session.
In the case where the EAP authenticator follows the EAP authenticator
state machines defined in [RFC4137], TxEAP() procedure sets eapResp
variable of the EAP authenticator state machine and puts the EAP
response in eapRespData variable of the EAP authenticator state
machine.
8.1.3. Delivering EAP Messages from EAP Authenticator to PAA
An EAP request is delivered from the EAP authenticator to the PAA via
EAP_REQUEST event variable. The event variable is set when the EAP
authenticator passes the EAP request to its lower layer. In the case
where the EAP authenticator follows the EAP authenticator state
machines defined in [RFC4137], EAP_REQUEST event variable refers to
eapReq variable of the EAP authenticator state machine and the EAP
request is contained in eapReqData variable of the EAP authenticator
state machine.
8.1.4. EAP Authentication Result Notification from EAP Authenticator to
PAA
In order for the EAP authenticator to notify the PAA of the EAP
authentication result, EAP_SUCCESS, EAP_FAILURE, and EAP_TIMEOUT
event variables are defined. In the case where the EAP authenticator
follows the EAP authenticator state machines defined in [RFC4137],
EAP_SUCCESS, EAP_FAILURE, and EAP_TIMEOUT event variables refer to
eapSuccess, eapFail, and eapTimeout variables of the EAP
authenticator state machine, respectively. In this case, if
EAP_SUCCESS event variable is set to TRUE, an EAP-Success message is
contained in eapReqData variable of the EAP authenticator state
machine, and additionally, eapKeyAvailable variable is set to TRUE
and eapKeyData variable contains an MSK if the MSK is generated as a
result of successful authentication by the EAP authentication method
in use. Similarly, if EAP_FAILURE event variable is set to TRUE, an
EAP-Failure message is contained in eapReqData variable of the EAP
authenticator state machine. The PAA uses EAP_SUCCESS and
EAP_FAILURE event variables as a trigger to send a PAR message to the
PaC.
Fajardo, et al. Informational [Page 22]
RFC 5609 PANA State Machines August 2009
8.2. Variables
OPTIMIZED_INIT
This variable indicates whether the PAA is able to piggyback an
EAP-Request in the initial PANA-Auth-Request. Otherwise, it is
set to FALSE.
PAC_FOUND
This variable is set to TRUE as a result of a PAA-initiated
handshake.
REAUTH_TIMEOUT
This event variable is set to TRUE to indicate that the PAA
initiates a re-authentication with the PaC. The re-authentication
timeout should be set to a value less than the session timeout
carried in the Session-Lifetime AVP if present.
EAP_SUCCESS
This event variable is set to TRUE when an EAP conversation
completes with success. This event accompanies an EAP-Success
message passed from the EAP authenticator.
EAP_FAILURE
This event variable is set to TRUE when an EAP conversation
completes with failure. This event accompanies an EAP-Failure
message passed from the EAP authenticator.
EAP_REQUEST
This event variable is set to TRUE when the EAP authenticator
delivers an EAP Request to the PAA. This event accompanies an
EAP-Request message received from the EAP authenticator.
EAP_TIMEOUT
This event variable is set to TRUE when an EAP conversation times
out without generating an EAP-Success or an EAP-Failure message.
This event does not accompany any EAP message.
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RFC 5609 PANA State Machines August 2009
EAP_DISCARD
This event variable is set to TRUE when the EAP authenticator
indicates that it has silently discarded the last received EAP-
Response message. This event does not accompany any EAP message.
In the case where the EAP authenticator follows the EAP
authenticator state machines defined in [RFC4137], this event
variable refers to eapNoReq.
8.3. Procedures
boolean new_key_available()
This is a procedure to check whether the PANA session has a new
PANA_AUTH_KEY. If the state machine already has a PANA_AUTH_KEY,
it returns FALSE. If the state machine does not have a
PANA_AUTH_KEY, it tries to retrieve an MSK from the EAP entity.
If an MSK has been retrieved, it computes a PANA_AUTH_KEY from the
MSK and returns TRUE. Otherwise, it returns FALSE.
8.4. PAA State Transition Table
------------------------------
State: INITIAL (Initial State)
------------------------------
Initialization Action:
OPTIMIZED_INIT=Set|Unset;
NONCE_SENT=Unset;
RTX_COUNTER=0;
RtxTimerStop();
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - (PCI and PAA initiated PANA) - - - - - - - - -
(Rx:PCI[] || if (OPTIMIZED_INIT == INITIAL
PAC_FOUND) Set) {
EAP_Restart();
SessionTimerReStart
(FAILED_SESS_TIMEOUT);
}
else {
if (generate_pana_sa())
Tx:PAR[S]("PRF-Algorithm",
"Integrity-Algorithm");
else
Tx:PAR[S]();
Fajardo, et al. Informational [Page 24]
RFC 5609 PANA State Machines August 2009
}
EAP_REQUEST if (generate_pana_sa()) INITIAL
Tx:PAR[S]("EAP-Payload",
"PRF-Algorithm",
"Integrity-Algorithm");
else
Tx:PAR[S]("EAP-Payload");
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - (PAN Handling) - - - - - - - - - -
Rx:PAN[S] && if (PAN.exist_avp WAIT_EAP_MSG
((OPTIMIZED_INIT == ("EAP-Payload"))
Unset) || TxEAP();
PAN.exist_avp else {
("EAP-Payload")) EAP_Restart();
SessionTimerReStart
(FAILED_SESS_TIMEOUT);
}
Rx:PAN[S] && None(); WAIT_PAN_OR_PAR
(OPTIMIZED_INIT ==
Set) &&
! PAN.exist_avp
("EAP-Payload")
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-------------------
State: WAIT_EAP_MSG
-------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - -(Receiving EAP-Request)- - - - - - - - -
EAP_REQUEST if (NONCE_SENT==Unset) { WAIT_PAN_OR_PAR
Tx:PAR[]("Nonce",
"EAP-Payload");
NONCE_SENT=Set;
}
else
Tx:PAR[]("EAP-Payload");
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - -(Receiving EAP-Success/Failure) - - - - -
EAP_FAILURE PAR.RESULT_CODE = WAIT_FAIL_PAN
PANA_AUTHENTICATION_
Fajardo, et al. Informational [Page 25]
RFC 5609 PANA State Machines August 2009
REJECTED;
Tx:PAR[C]("EAP-Payload");
RtxTimerStart();
SessionTimerStop();
EAP_SUCCESS && PAR.RESULT_CODE = WAIT_SUCC_PAN
Authorize() PANA_SUCCESS;
if (new_key_available())
Tx:PAR[C]("EAP-Payload",
"Key-Id");
else
Tx:PAR[C]("EAP-Payload");
RtxTimerStart();
EAP_SUCCESS && PAR.RESULT_CODE = WAIT_FAIL_PAN
!Authorize() PANA_AUTHORIZATION_
REJECTED;
if (new_key_available())
Tx:PAR[C]("EAP-Payload",
"Key-Id");
else
Tx:PAR[C]("EAP-Payload");
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - (Receiving EAP-Timeout or invalid message) - - - - -
EAP_TIMEOUT || SessionTimerStop(); CLOSED
EAP_DISCARD Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
--------------------
State: WAIT_SUCC_PAN
--------------------
Event/Condition Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - (PAN Processing)- - - - - - - - - - -
Rx:PAN[C] RtxTimerStop(); OPEN
SessionTimerReStart
(LIFETIME_SESS_TIMEOUT);
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
--------------------
State: WAIT_FAIL_PAN
--------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - - (PAN Processing)- - - - - - - - - -
Fajardo, et al. Informational [Page 26]
RFC 5609 PANA State Machines August 2009
Rx:PAN[C] RtxTimerStop(); CLOSED
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-----------
State: OPEN
-----------
Event/Condition Action Exit State
------------------------+--------------------------+------------
- - - - - - - - (re-authentication initiated by PaC) - - - - - -
Rx:PNR[A] NONCE_SENT=Unset; WAIT_EAP_MSG
EAP_Restart();
Tx:PNA[A]();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - (re-authentication initiated by PAA)- - - - - -
REAUTH || NONCE_SENT=Unset; WAIT_EAP_MSG
REAUTH_TIMEOUT EAP_Restart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - (liveness test based on PNR-PNA exchange initiated by PAA)-
PANA_PING Tx:PNR[P](); WAIT_PNA_PING
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - (Session termination initiated from PAA)- - - -
TERMINATE Tx:PTR[](); SESS_TERM
SessionTimerStop();
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - (Session termination initiated from PaC)- - - -
Rx:PTR[] Tx:PTA[](); CLOSED
SessionTimerStop();
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
--------------------
State: WAIT_PNA_PING
--------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - -(PNA processing) - - - - - - - - - -
Rx:PNA[P] RtxTimerStop(); OPEN
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - (re-authentication initiated by PaC) - - - - - -
Rx:PNR[A] RtxTimerStop(); WAIT_EAP_MSG
NONCE_SENT=Unset;
Fajardo, et al. Informational [Page 27]
RFC 5609 PANA State Machines August 2009
EAP_Restart();
Tx:PNA[A]();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - (Session termination initiated from PaC)- - - -
Rx:PTR[] RtxTimerStop(); CLOSED
Tx:PTA[]();
SessionTimerStop();
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
----------------------
State: WAIT_PAN_OR_PAR
----------------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
- - - - - - - - - - - - - (PAR Processing)- - - - - - - - - - -
Rx:PAR[] TxEAP(); WAIT_EAP_MSG
RtxTimerStop();
Tx:PAN[]();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - (Pass EAP Response to the EAP authenticator)- - - -
Rx:PAN[] && TxEAP(); WAIT_EAP_MSG
PAN.exist_avp RtxTimerStop();
("EAP-Payload")
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - (PAN without an EAP response) - - - - - - -
Rx:PAN[] && RtxTimerStop(); WAIT_PAN_OR_PAR
!PAN.exist_avp
("EAP-Payload")
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - -(EAP retransmission) - - - - - - - - - -
EAP_REQUEST RtxTimerStop(); WAIT_PAN_OR_PAR
Tx:PAR[]("EAP-Payload");
RtxTimerStart();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - - (EAP authentication timeout or failure)- - - - -
EAP_FAILURE || RtxTimerStop(); CLOSED
EAP_TIMEOUT || SessionTimerStop();
EAP_DISCARD Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
----------------
State: SESS_TERM
----------------
Exit Condition Exit Action Exit State
------------------------+--------------------------+------------
Fajardo, et al. Informational [Page 28]
RFC 5609 PANA State Machines August 2009
- - - - - - - - - - - - - -(PTA processing) - - - - - - - - - -
Rx:PTA[] RtxTimerStop(); CLOSED
Disconnect();
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
9. Implementation Considerations
9.1. PAA and PaC Interface to Service Management Entity
In general, it is assumed that each device or network equipment has a
PANA protocol stack available for use by other modules within the
device or network equipment. One such module is the Service
Management Entity (SME). The SME is a generic term for modules that
manage different services (including network protocols) that are
installed on a device or equipment. To integrate the PANA protocol
with the SME, it is recommended that a generic interface (i.e., the
SME-PANA interface) between the SME and the PANA protocol stack be
provided by the implementation. This interface should include common
procedures such as startup, shutdown, and re-authenticate signals.
It should also provide for extracting keying material. For the PAA,
the SME-PANA interface should also provide a method for communicating
filtering parameters to the Enforcement Point(s) when cryptographic
filtering is used. The filtering parameters include keying material
used for bootstrapping secured transport such as IPsec. When a PAA
device interacts with the backend authentication server using a AAA
protocol, its SME may also provide an interface to the AAA protocol
to obtain authorization parameters such as the authorization lifetime
and additional filtering parameters.
10. Security Considerations
This document's intent is to describe the PANA state machines fully.
To this end, any security concerns with this document are likely a
reflection of security concerns with PANA itself.
11. Acknowledgments
This work was started from state machines originally made by Dan
Forsberg.
12. References
12.1. Normative References
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
Fajardo, et al. Informational [Page 29]
RFC 5609 PANA State Machines August 2009
12.2. Informative References
[RFC4137] Vollbrecht, J., Eronen, P., Petroni, N., and Y. Ohba,
"State Machines for Extensible Authentication Protocol
(EAP) Peer and Authenticator", RFC 4137, August 2005.
Authors' Addresses
Victor Fajardo (editor)
Telcordia Technologies
1 Telcordia Drive
Piscataway, NJ 08854
USA
Phone: +1 732 699 5368
EMail: vfajardo@research.telcordia.com
Yoshihiro Ohba
Toshiba Corporate Research and Development Center
1 Komukai-Toshiba-cho, Saiwai-ku
Kawasaki, Kanagawa 212-8582
Japan
Phone: +81 44 549 2230
EMail: yoshihiro.ohba@toshiba.co.jp
Rafa Marin-Lopez
University of Murcia
Campus de Espinardo S/N, Facultad de Informatica
Murcia 30100
Spain
Phone: +34 868 888 501
EMail: rafa@um.es
Fajardo, et al. Informational [Page 30]