💾 Archived View for gmi.noulin.net › rfc › rfc5836.gmi captured on 2024-08-19 at 02:31:39. Gemini links have been rewritten to link to archived content
⬅️ Previous capture (2022-01-08)
-=-=-=-=-=-=-
Keywords: eap early authentication
Internet Engineering Task Force (IETF) Y. Ohba
Request for Comments: 5836 Toshiba
Category: Informational Q. Wu, Ed.
ISSN: 2070-1721 Huawei
G. Zorn, Ed.
Network Zen
April 2010
Extensible Authentication Protocol (EAP)
Early Authentication Problem Statement
Abstract
Extensible Authentication Protocol (EAP) early authentication may be
defined as the use of EAP by a mobile device to establish
authenticated keying material on a target attachment point prior to
its arrival. This document discusses the EAP early authentication
problem in detail.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5836.
Ohba, et al. Informational [Page 1]
RFC 5836 Early Authentication PS April 2010
Copyright Notice
Copyright (c) 2010 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Ohba, et al. Informational [Page 2]
RFC 5836 Early Authentication PS April 2010
Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................4
3. Problem Statement ...............................................6
3.1. Handover Preparation .......................................6
3.2. Handover Execution .........................................6
3.2.1. Examples ............................................7
3.3. Solution Space .............................................7
3.3.1. Context Transfer ....................................7
3.3.2. Early Authentication ................................8
4. System Overview .................................................8
5. Topological Classification of Handover Scenarios ................9
6. Models of Early Authentication .................................10
6.1. EAP Pre-Authentication Usage Models .......................10
6.1.1. The Direct Pre-Authentication Model ................11
6.1.2. The Indirect Pre-Authentication Usage Model ........11
6.2. The Authenticated Anticipatory Keying Usage Model .........13
7. Architectural Considerations ...................................13
7.1. Authenticator Discovery ...................................13
7.2. Context Binding ...........................................14
8. AAA Issues .....................................................14
9. Security Considerations ........................................16
10. Acknowledgments ...............................................17
11. Contributors ..................................................17
12. References ....................................................17
12.1. Normative References .....................................17
12.2. Informative References ...................................18
1. Introduction
When a mobile device, during an active communication session, moves
from one access network to another and changes its attachment point,
the session may be subjected to disruption of service due to the
delay associated with the handover operation. The performance
requirements of a real-time application will vary based on the type
of application and its characteristics such as delay and packet-loss
tolerance. For Voice over IP applications, ITU-T G.114 [ITU]
recommends a steady-state end-to-end delay of 150 ms as the upper
limit and rates 400 ms as generally unacceptable delay. Similarly, a
streaming application has tolerable packet-error rates ranging from
0.1 to 0.00001 with a transfer delay of less than 300 ms. Any help
that an optimized handoff mechanism can provide toward meeting these
objectives is useful. The ultimate objective is to achieve seamless
handover with low latency, even when handover is between different
link technologies or between different Authentication, Authorization,
and Accounting (AAA) realms.
Ohba, et al. Informational [Page 3]
RFC 5836 Early Authentication PS April 2010
As a mobile device goes through a handover process, it is subjected
to delay because of the rebinding of its association at or across
several layers of the protocol stack and because of the additional
round trips needed for a new EAP exchange. Delays incurred within
each protocol layer affect the ongoing multimedia application and
data traffic within the client [WCM].
The handover process often requires authentication and authorization
for acquisition or modification of resources assigned to the mobile
device. In most cases, these authentications and authorizations
require interaction with a central authority in a realm. In some
cases, the central authority may be distant from the mobile device.
The delay introduced due to such an authentication and authorization
procedure adds to the handover latency and consequently affects
ongoing application sessions [MQ7]. The discussion in this document
is focused on mitigating delay due to EAP authentication.
2. Terminology
AAA
Authentication, Authorization, and Accounting (see below). RADIUS
[RFC2865] and Diameter [RFC3588] are examples of AAA protocols
defined in the IETF.
AAA realm
The set of access networks within the scope of a specific AAA
server. Thus, if a mobile device moves from one attachment point
to another within the same AAA realm, it continues to be served by
the same AAA server.
Accounting
The act of collecting information on resource usage for the
purpose of trend analysis, auditing, billing, or cost allocation
[RFC2989].
Attachment Point
A device, such as a wireless access point, that serves as a
gateway between access clients and a network. In the context of
this document, an attachment point must also support EAP
authenticator functionality and may act as a AAA client.
Authentication
The act of verifying a claimed identity, in the form of a
preexisting label from a mutually known name space, as the
originator of a message (message authentication) or as the end-
point of a channel (entity authentication) [RFC2989].
Ohba, et al. Informational [Page 4]
RFC 5836 Early Authentication PS April 2010
Authenticator
The end of the link initiating EAP authentication [RFC3748].
Authorization
The act of determining if a particular right, such as access to
some resource, can be granted to the presenter of a particular
credential [RFC2989].
Candidate Access Network
An access network that can potentially become the target access
network for a mobile device. Multiple access networks may be
candidates simultaneously.
Candidate Attachment Point (CAP)
An attachment point that can potentially become the target
attachment point for a mobile device. Multiple attachment points
may be candidates simultaneously.
Candidate Authenticator (CA)
The EAP authenticator on the CAP.
EAP Server
The entity that terminates the EAP authentication method with the
peer [RFC3748]. EAP servers are often, but not necessarily,
co-located with AAA servers, using a AAA protocol to communicate
with remote pass-through authenticators.
Inter-AAA-realm Handover (Inter-realm Handover)
A handover across multiple AAA realms.
Inter-Technology Handover
A handover across different link-layer technologies.
Intra-AAA-realm Handover (Intra-realm Handover)
A handover within the same AAA realm. Intra-AAA-realm handover
includes a handover across different authenticators within the
same AAA realm.
Intra-Technology Handover
A handover within the same link-layer technology.
Master Session Key (MSK)
Keying material that is derived between the EAP peer and server
and exported by the EAP method [RFC3748].
Peer
The entity that responds to the authenticator and requires
authentication [RFC3748].
Ohba, et al. Informational [Page 5]
RFC 5836 Early Authentication PS April 2010
Serving Access Network
An access network that is currently serving the mobile device.
Serving Attachment Point (SAP)
An attachment point that is currently serving the mobile device.
Target Access Network
An access network that has been selected to be the new serving
access network for a mobile device.
Target Attachment Point (TAP)
An attachment point that has been selected to be the new SAP for a
mobile device.
3. Problem Statement
The basic mechanism of handover is a two-step procedure involving
o handover preparation and
o handover execution
3.1. Handover Preparation
Handover preparation includes the discovery of candidate attachment
points and selection of an appropriate target attachment point from
the candidate set. Handover preparation is outside the scope of this
document.
3.2. Handover Execution
Handover execution consists of setting up Layer 2 (L2) and Layer 3
(L3) connectivity with the TAP. Currently, handover execution
includes network access authentication and authorization performed
directly with the target network; this may include full EAP
authentication in the absence of any particular optimization for
handover key management. Following a successful EAP authentication,
a secure association procedure is typically performed between the
mobile device and the TAP to derive a new set of link-layer
encryption keys from EAP keying material such as the MSK. The
handover latency introduced by full EAP authentication has proven to
be higher than that which is acceptable for real-time application
scenarios [MQ7]; hence, reduction in handover latency due to EAP is a
necessary objective for such scenarios.
Ohba, et al. Informational [Page 6]
RFC 5836 Early Authentication PS April 2010
3.2.1. Examples
3.2.1.1. IEEE 802.11
In IEEE 802.11 Wireless Local Area Networks (WLANs)
[IEEE.802-11.2007] network access authentication and authorization
involves performing a new IEEE 802.1X [IEEE.802-1X.2004] message
exchange with the authenticator in the TAP to execute an EAP exchange
with the authentication server [WPA]. There has been some
optimization work undertaken by the IEEE, but these efforts have been
scoped to IEEE link-layer technologies; for example, the work done in
the IEEE 802.11f [IEEE.802-11F.2003] and 802.11r [IEEE.802-11R.2008]
Task Groups applies only to intra-technology handovers.
3.2.1.2. 3GPP TS33.402
The Third Generation Partnership Project (3GPP) Technical
Specification 33.402 [TS33.402] defines the authentication and key
management procedures performed during interworking between non-3GPP
access networks and the Evolved Packet System (EPS). Network access
authentication and authorization happens after the L2 connection is
established between the mobile device and a non-3GPP target access
network, and involves an EAP exchange between the mobile device and
the 3GPP AAA server via the non-3GPP target access network. These
procedures are not really independent of link technology, since they
assume either that the authenticator lies in the EPS network or that
separate authentications are performed in the access network and then
in the EPS network.
3.3. Solution Space
As the examples in the preceding sections illustrate, a solution is
needed to enable EAP early authentication for inter-AAA-realm
handovers and inter-technology handovers. A search for solutions at
the IP level may offer the necessary technology independence.
Optimized solutions for secure inter-authenticator handovers can be
seen either as security context transfer (e.g., using the EAP
Extensions for EAP Re-authentication Protocol (ERP)) [RFC5296], or as
EAP early authentication.
3.3.1. Context Transfer
Security context transfer involves transfer of reusable key context
to the TAP and can take two forms: horizontal and vertical.
Ohba, et al. Informational [Page 7]
RFC 5836 Early Authentication PS April 2010
Horizontal security context transfer (e.g., from SAP to TAP) is not
recommended because of the possibility that the compromise of one
attachment point might lead to the compromise of another (the
so-called domino effect, [RFC4962]). Vertical context transfer is
similar to the initial establishment of keying material on an
attachment point in that the keys are sent from a trusted server to
the TAP as a direct result of a successful authentication. ERP
specifies vertical context transfer using existing EAP keying
material obtained from the home AAA server during the initial
authentication. A cryptographically independent re-authentication
key is derived and transmitted to the TAP as a result of successful
ERP authentication. This reduces handover delay for intra-realm
handovers by eliminating the need to run full EAP authentication with
the home EAP server.
However, in the case of inter-realm handover, either ERP is not
applicable or an additional optimization mechanism is needed to
establish a key on the TAP.
3.3.2. Early Authentication
In EAP early authentication, AAA-based authentication and
authorization for a CAP is performed while ongoing data communication
is in progress via the serving access network, the goal being to
complete AAA signaling for EAP before the mobile device moves. The
applicability of EAP early authentication is limited to the scenarios
where candidate authenticators can be discovered and an accurate
prediction of movement can be easily made. In addition, the
effectiveness of EAP early authentication may be less significant for
particular inter-technology-handover scenarios where simultaneous use
of multiple technologies is not a major concern.
There are also several AAA issues related to EAP early
authentication, discussed in Section 8.
4. System Overview
Figure 1 shows the functional elements that are related to EAP early
authentication. These functional elements include a mobile device, a
SAP, a CAP, and one or more AAA and EAP servers; for the sake of
convenience, the AAA and EAP servers are represented as being
co-located. When the SAP and CAP belong to different AAA realms, the
CAP may require a different set of user credentials than those used
by the peer when authenticating to the SAP. Alternatively, the CAP
and the SAP may rely on the same AAA server, located in the home
realm of the mobile device (MD).
Ohba, et al. Informational [Page 8]
RFC 5836 Early Authentication PS April 2010
+------+ +-------+ +---------+ +---------+
| MD |------| SAP |------| | | |
+------+ +-------+ | IP | | EAP/AAA
. | |------| |
. Move | Network | | Server |
v +-------+ | | | |
| CAP |------| | | |
+-------+ +---------+ +---------+
Figure 1: EAP Early Authentication Functional Elements
A mobile device is attached to the serving access network. Before
the MD performs handover from the serving access network to a
candidate access network, it performs EAP early authentication with a
candidate authenticator via the serving access network. The peer may
perform EAP early authentication with one or more candidate
authenticators. It is assumed that each attachment point has an IP
address. It is assumed that there is at least one CAP in each
candidate access network. The serving and candidate access networks
may use different link-layer technologies.
Each authenticator is either a standalone authenticator or a pass-
through authenticator [RFC3748]. When an authenticator acts as a
standalone authenticator, it also has the functionality of an EAP
server. When an authenticator acts as a pass-through authenticator,
it communicates with the EAP server, typically using a AAA transport
protocol such as RADIUS [RFC2865] or Diameter [RFC3588].
If the CAP uses an MSK [RFC5247] for generating lower-layer ciphering
keys, EAP early authentication is used to proactively generate an MSK
for the CAP.
5. Topological Classification of Handover Scenarios
The complexity of the authentication and authorization part of
handover depends on whether it involves a change in EAP server.
Consider first the case where the authenticators operate in pass-
through mode, so that the EAP server is co-located with a AAA server.
Then, there is a strict hierarchy of complexity, as follows:
1. inter-attachment-point handover with common AAA server: the CAP
and SAP are different entities, but the AAA server is the same.
There are two sub-cases here:
(a) the AAA server is common because both attachment points lie
within the same network, or
Ohba, et al. Informational [Page 9]
RFC 5836 Early Authentication PS April 2010
(b) the AAA server is common because AAA entities in the serving
and candidate networks proxy to a AAA server in the home
realm.
2. inter-AAA-realm handover: the CAP and SAP are different entities,
and the respective AAA servers also differ. As a result,
authentication in the candidate network requires a second set of
user credentials.
A third case is where one or both authenticators are co-located with
an EAP server. This has some of the characteristics of an inter-AAA-
realm handover, but offers less flexibility for resolution of the
early authentication problem.
Orthogonally to this classification, one can distinguish intra-
technology handover from inter-technology handover thinking of the
link technologies involved. In the inter-technology case, it is
highly probable that the authenticators will differ. The most likely
cases are 1(b) or 2 in the above list.
6. Models of Early Authentication
As noted in Section 3, there are cases where early authentication is
applicable while ERP does not work. This section concentrates on
providing some models around which we can build our analysis of the
EAP early authentication problem. Different usage models can be
defined depending on whether
o the SAP is not involved in early authentication (direct pre-
authentication usage model),
o the SAP interacts only with the CAP (indirect pre-authentication
usage model), or
o the SAP interacts with the AAA server (the authenticated
anticipatory keying usage model).
It is assumed that the CAP and SAP are different entities. It is
further assumed in describing these models that there is no direct L2
connectivity between the peer and the candidate attachment point.
6.1. EAP Pre-Authentication Usage Models
In the EAP pre-authentication model, the SAP does not interact with
the AAA server directly. Depending on how the SAP is involved in the
pre-authentication signaling, the EAP pre-authentication usage model
can be further categorized into the following two sub-models, direct
and indirect.
Ohba, et al. Informational [Page 10]
RFC 5836 Early Authentication PS April 2010
6.1.1. The Direct Pre-Authentication Model
In this model, the SAP is not involved in the EAP exchange and only
forwards the EAP pre-authentication traffic as it would any other
data traffic. The direct pre-authentication model is based on the
assumption that the MD can discover candidate authenticators and
establish direct IP communication with them. It is applicable to any
of the cases described in Section 5.
Mobile Candidate Attachment AAA Server
Device Point(CAP)
+-----------+ +-------------------------+ +------------+
| | | Candidate | | |
| Peer | | Authenticator | | EAP Server |
| | | | | |
+-----------+ +-------------------------+ +------------+
| MD-CAP |<-->| MD-CAP | | CAP-AAA |<-->| CAP-AAA |
| Signaling | | Signaling | | Signaling | | Signaling |
+-----------+ +-----------+ +-----------+ +------------+
Figure 2: Direct Pre-Authentication Usage Model
The direct pre-authentication signaling for the usage model is shown
in Figure 3.
Mobile Serving Candidate AAA/EAP
Device Attachment Point Authenticator Server
(SAP)
| | | |
| | | |
| EAP over MD-CAP Signaling (L3) | EAP over AAA |
|<------------------+------------------->|<----------------->|
| | | |
| | | |
Figure 3: Direct Pre-Authentication Signaling for the Usage Model
6.1.2. The Indirect Pre-Authentication Usage Model
The indirect pre-authentication usage model is illustrated in
Figure 4.
Ohba, et al. Informational [Page 11]
RFC 5836 Early Authentication PS April 2010
Mobile Device Serving Candidate AAA
(MD) Attachment Point Attachment Point Server
(SAP) (CAP)
+----------+ +----------------+ +--------+
| | | | | |
| EAP Peer | | Candidate | | EAP |
| | | Authenticator | | Server |
| | | | | |
+----------+ +---------+-------+ +-------+--------+ +--------+
| MD-SAP |<->| MD-SAP |SAP-CAP|<->|SAP-CAP|CAP-AAA |<->|CAP-AAA |
+----------+ +---------+-------+ +-------+--------+ +--------+
{-----------------------------Signaling----------------------------}
Figure 4: Indirect Pre-Authentication Usage Model
In the indirect pre-authentication model, it is assumed that a trust
relationship exists between the serving network (or serving AAA
realm) and candidate network (or candidate AAA realm). The SAP is
involved in EAP pre-authentication signaling. This pre-
authentication model is needed if the peer cannot discover the
candidate authenticators identity or if direct IP communication
between the MD and CAP is not possible due to security or network
topology issues.
The role of the SAP in this pre-authentication model is to forward
EAP pre-authentication signaling between the mobile device and CAP;
the role of the CAP is to forward EAP pre-authentication signaling
between the peer (via the SAP) and EAP server and receive the
transported keying material.
The pre-authentication signaling for this model is shown in Figure 5.
Mobile Serving Candidate AAA/EAP
Device Attachment Point Attachment Point Server
(SAP) (CAP)
| | | |
| EAP over | EAP over | EAP over AAA |
| MD-SAP Signaling | SAP-CAP Signaling | |
| (L2 or L3) | (L3) | |
|<----------------->|<------------------<|<----------------->|
| | | |
| | | |
Figure 5: Indirect Pre-Authentication Signaling for the Usage Model
Ohba, et al. Informational [Page 12]
RFC 5836 Early Authentication PS April 2010
In this model, the pre-authentication signaling path between a peer
and a candidate authenticator consists of two segments: peer-to-SAP
signaling (over L2 or L3) and SAP-to-CAP signaling over L3.
6.2. The Authenticated Anticipatory Keying Usage Model
In this model, it is assumed that there is no trust relationship
between the SAP and the CAP, and the SAP is required to interact with
the AAA server directly. The authenticated anticipatory keying usage
model is illustrated in Figure 6.
Mobile Serving AAA Server Candidate
Device Attachment Point Attachment
(SAP) Point (CAP)
+---------+ +------------------+ +-----------------+ +--------+
| | | | | | | |
| Peer | | Authenticator | | EAP Server | | AAA |
| | | | | | | Client |
+---------+ +------------------+ +-----------------+ +--------+
| MD-SA |<->| MD-SAP |SAP-AAA |<->|SAP-AAA |CAP-AAA |<>|CAP-AAA |
+---------+ +------------------+ +--------+--------+ +--------+
{------------------------------Signaling---------------------------}
Figure 6: Authenticated Anticipatory Keying Usage Model
The SAP is involved in EAP authenticated anticipatory keying
signaling.
The role of the serving attachment point in this usage model is to
communicate with the peer on one side and exchange authenticated
anticipatory keying signaling with the EAP server on the other side.
The role of the candidate authenticator is to receive the transported
keying materials from the EAP server and to act as the serving
attachment point after handover occurs. The MD-SAP signaling is
performed over L2 or L3; the SAP-AAA and AAA-CAP segments operate
over L3.
7. Architectural Considerations
There are two architectural issues relating to early authentication:
authenticator discovery and context binding.
7.1. Authenticator Discovery
In general, early authentication requires the identity of a candidate
attachment point to be discovered by a peer, by a serving attachment
point, or by some other entity prior to handover. An attachment
point discovery protocol is typically defined as a separate protocol
Ohba, et al. Informational [Page 13]
RFC 5836 Early Authentication PS April 2010
from an early authentication protocol. For example, the IEEE 802.21
Information Service (IS) [IEEE.802-21] provides a link-layer-
independent mechanism for obtaining neighboring network information
by defining a set of Information Elements (IEs), where one of the IEs
is defined to contain an IP address of an attachment point. IEEE
802.21 IS queries for such an IE may be used as a method for
authenticator discovery.
If IEEE 802.21 IS or a similar mechanism is used, authenticator
discovery requires a database of information regarding the target
network; the provisioning of a server with such a database is another
issue.
7.2. Context Binding
When a candidate authenticator uses different EAP transport protocols
for normal authentication and early authentication, a mechanism is
needed to bind link-layer-independent context carried over early
authentication signaling to the link-layer-specific context of the
link to be established between the peer and the candidate
authenticator. The link-layer-independent context includes the
identities of the peer and authenticator as well as the MSK. The
link-layer-specific context includes link-layer addresses of the peer
and the candidate authenticator. Such context binding can happen
before or after the peer changes its point of attachment.
There are at least two possible approaches to address the context
binding issue. The first approach is based on communicating the
link-layer context as opaque data via early authentication signaling.
The second approach is based on running EAP over the link layer of
the candidate authenticator after the peer arrives at the
authenticator, using short-term credentials generated via early
authentication. In this case, the short-term credentials are shared
between the peer and the candidate authenticator. In both
approaches, context binding needs to be securely made between the
peer and the candidate authenticator. Also, the peer is not fully
authorized by the candidate authenticator until the peer completes
the link-layer-specific secure association procedure with the
authenticator using link-layer signaling.
8. AAA Issues
Most of the AAA documents today do not distinguish between a normal
authentication and an early authentication, and this creates a set of
open issues:
Ohba, et al. Informational [Page 14]
RFC 5836 Early Authentication PS April 2010
Early authentication authorization
Users may not be allowed to have more than one logon session at
the time. This means that while such users actively engage in a
session (as a result of a previously valid authentication), they
will not be able to perform early authentication. The AAA server
currently has no way of distinguishing between a normal
authentication request and an early authentication request.
Early authentication lifetime
Currently, AAA protocols define attributes carrying lifetime
information for a normal authentication session. Even when a user
profile and the AAA server support early authentication, the
lifetime for an early authentication session is typically valid
only for a short amount of time because the peer has not completed
its authentication at the target link layer. It is currently not
possible for a AAA server to indicate to the AAA client or a peer
the lifetime of the early authenticated session unless AAA
protocols are extended to carry early authentication session
lifetime information. In other words, it is not clear to the peer
or the authenticator when the early authentication session will
expire.
Early authentication retries
It is typically expected that, shortly following the early
authentication process, the peer moves to the new point of
attachment and converts the early authentication state to a normal
authentication state (the procedure for which is not the topic of
this particular subsection). However, if the peer has not yet
moved to the new location and realizes that the early
authentication session is expiring, it may perform another early
authentication. Some limiting mechanism is needed to avoid an
unlimited number of early authentication attempts.
Completion of network attachment
Once the peer has successfully attached to the new point of
attachment, it needs to convert its authentication state from
early authenticated to fully attached and authorized. If the AAA
server needs to differentiate between early authentication and
normal authentication, there may need to be a mechanism within the
AAA protocol to provide this indication to the AAA server. This
may be important from a billing perspective if the billing policy
does not charge for an early authenticated peer until the peer is
fully attached to the target authenticator.
Session resumption
In the case where the peer cycles between a network N1 with which
it has fully authenticated and another network N2 and then back to
N1, it should be possible to simply convert the fully
Ohba, et al. Informational [Page 15]
RFC 5836 Early Authentication PS April 2010
authenticated state on N1 to an early authenticated state. The
problems around handling session lifetime and keying material
caching need to be dealt with.
Multiple candidate attachment points
There may be situations where the peer needs to choose from a
number of CAPs. In such cases, it is desirable for the peer to
perform early authentication with multiple candidate
authenticators. This amplifies the difficulties noted under the
point "Early authentication authorization".
Inter-AAA-realm handover support
There may be situations where the peer moves out of the home AAA
realm or across different visited AAA realms. In such cases, the
early authentication should be performed through the visited AAA
realm with the AAA server in the home AAA realm. It also requires
AAA in the visited realm to acquire the identity information of
the home AAA realms for routing the EAP early authentication
traffic. Knowledge of realm identities is required by both the
peer and AAA to generate the early authentication key for mutual
authentication between the peer and the visited AAA server.
Inter-technology support
Current specifications on early authentication mostly deal with
homogeneous 802.11 networks. AAA attributes such as Calling-
Station-ID [RADEXT-WLAN] may need to be expanded to cover other
access technologies. Furthermore, inter-technology handovers may
require a change of the peer identifier as part of the handover.
Investigation on the best type of identifiers for peers that
support multiple access technologies is required.
9. Security Considerations
This section specifically covers threats introduced to the EAP model
by early authentication. Security issues on general EAP and handover
are described in other documents such as [RFC3748], [RFC4962],
[RFC5169], and [RFC5247].
Since early authentication, as described in this document, needs to
work across multiple attachment points, any solution needs to
consider the following security threats.
First, a resource consumption denial-of-service attack is possible,
where an attacker that is not on the same IP link as the legitimate
peer or the candidate authenticator may send unprotected early
authentication messages to the legitimate peer or the candidate
authenticator. As a result, the latter may spend computational and
bandwidth resources on processing early authentication messages sent
Ohba, et al. Informational [Page 16]
RFC 5836 Early Authentication PS April 2010
by the attacker. This attack is possible in both the direct and
indirect pre-authentication scenarios. To mitigate this attack, the
candidate network or authenticator may apply non-cryptographic packet
filtering so that only early authentication messages received from a
specific set of serving networks or authenticators are processed. In
addition, a simple solution for the peer side would be to let the
peer always initiate EAP early authentication and not allow EAP early
authentication initiation from an authenticator.
Second, consideration for the channel binding problem described in
[RFC5247] is needed as lack of channel binding may enable an
authenticator to impersonate another authenticator or communicate
incorrect information via out-of-band mechanisms (such as via a AAA
or lower-layer protocol) [RFC3748]. It should be noted that it is
relatively easier to launch such an impersonation attack for early
authentication than normal authentication because an attacker does
not need to be physically on the same link as the legitimate peer to
send an early authentication trigger to the peer.
10. Acknowledgments
The editors would like to thank Preetida Vinayakray, Shubhranshu
Singh, Ajay Rajkumar, Rafa Marin Lopez, Jong-Hyouk Lee, Maryna
Komarova, Katrin Hoeper, Subir Das, Charles Clancy, Jari Arkko, and
Bernard Aboba for their valuable input.
11. Contributors
The following people all contributed to this document: Alper E.
Yegin, Tom Taylor, Srinivas Sreemanthula, Madjid Nakhjiri, Mahalingam
Mani, and Ashutosh Dutta.
12. References
12.1. Normative References
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC4962] Housley, R. and B. Aboba, "Guidance for Authentication,
Authorization, and Accounting (AAA) Key Management",
BCP 132, RFC 4962, July 2007.
[RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible
Authentication Protocol (EAP) Key Management Framework",
RFC 5247, August 2008.
Ohba, et al. Informational [Page 17]
RFC 5836 Early Authentication PS April 2010
12.2. Informative References
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC5169] Clancy, T., Nakhjiri, M., Narayanan, V., and L. Dondeti,
"Handover Key Management and Re- Authentication Problem
Statement", RFC 5169, March 2008.
[RFC5296] Narayanan, V. and L. Dondeti, "EAP Extensions for EAP
Re-authentication Protocol (ERP)", RFC 5296, August 2008.
[RADEXT-WLAN]
Aboba, B., Malinen, J., Congdon, P., and J. Salowey,
"RADIUS Attributes for IEEE 802 Networks", Work
in Progress, February 2010.
[RFC2989] Aboba, B., Calhoun, P., Glass, S., Hiller, T., McCann, P.,
Shiino, H., Zorn, G., Dommety, G., C.Perkins, B.Patil,
D.Mitton, S.Manning, M.Beadles, P.Walsh, X.Chen,
S.Sivalingham, A.Hameed, M.Munson, S.Jacobs, B.Lim,
B.Hirschman, R.Hsu, Y.Xu, E.Campell, S.Baba, and E.Jaques,
"Criteria for Evaluating AAA Protocols for Network
Access", RFC 2989, November 2000.
[IEEE.802-1X.2004]
Institute of Electrical and Electronics Engineers,
"Port-Based Network Access Control", IEEE Standard 802.1X,
2004.
[IEEE.802-21]
Institute of Electrical and Electronics Engineers,
"Standard for Local and Metropolitan Area Networks: Media
Independent Handover Services", IEEE Standard 802.21,
2008.
[IEEE.802-11.2007]
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, 2007.
Ohba, et al. Informational [Page 18]
RFC 5836 Early Authentication PS April 2010
[IEEE.802-11R.2008]
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 - Amendment 2: Fast BSS
Transition", IEEE Standard 802.11R, 2008.
[IEEE.802-11F.2003]
Institute of Electrical and Electronics Engineers, "IEEE
Trial-Use Recommended Practice for Multi-Vendor Access
Point Interoperability via an Inter-Access Point Protocol
Across Distribution Systems Supporting IEEE 802.11
Operation", IEEE Recommendation 802.11F, 2003.
[TS33.402] 3GPP, "System Architecture Evolution (SAE): Security
aspects of non-3GPP accesses (Release 8)", 3GPP
TS33.402 V8.3.1, 2009.
[ITU] ITU-T, "General Characteristics of International Telephone
Connections and International Telephone Circuits: One-Way
Transmission Time", ITU-T Recommendation G.114, 1998.
[WPA] The Wi-Fi Alliance, "WPA (Wi-Fi Protected Access)",
Wi-Fi WPA v3.1, 2004.
[MQ7] Lopez, R., Dutta, A., Ohba, Y., Schulzrinne, H., and A.
Skarmeta, "Network-layer Assisted Mechanism to Optimize
Authentication Delay During Handoff in 802.11 Networks",
The 4th Annual International Conference on Mobile and
Ubiquitous Systems: Computing, Networking and
Services (MOBIQUITOUS 2007), 2007.
[WCM] Dutta, A., Famorali, D., Das, S., Ohba, Y., and R. Lopez,
"Media-independent pre-authentication supporting secure
interdomain handover optimization", IEEE Wireless
Communications Volume 15, Issue 2, April 2008.
Ohba, et al. Informational [Page 19]
RFC 5836 Early Authentication PS April 2010
Authors' Addresses
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
Qin Wu (editor)
Huawei Technologies Co., Ltd
Huawei Nanjing R&D Center, Floor 1F, Software Avenue, No.101.,
Yuhua District
Nanjing, JiangSu 210012
China
Phone: +86 25 56622908
EMail: sunseawq@huawei.com
Glen Zorn (editor)
Network Zen
1463 East Republican Street
Seattle, Washington 98112
USA
EMail: gwz@net-zen.net
Ohba, et al. Informational [Page 20]