Authentication Optimization for Vertical Handover in Heterogeneous

Wireless Networks

Ikram Smaoui

, Faouzi Zarai

, Mohammad S. Obaidat

and Lotfi Kamoun

LETI Laboratory, University of Sfax, Sfax, Tunisia

Computer Science and Software Engineering Department, Monmouth University, NJ 07764, West Long Branch, U.S.A.

Keywords: Authentication, Seamless Handover, Security, EAP-AKA Protocol, Heterogeneous Networks.

Abstract: In this paper, we present a scheme for reducing vertical handover delay in heterogeneous wireless networks

by optimizing the network access authentication procedure as it is a heavy burden due to its latencies and

overhead. Indeed, optimizing the authentication procedure while at the same time providing the same or best

level of security represents a key factor in the design of the next generation of heterogeneous wireless

networks. In this context, the aim of our work in this paper is to provide a security framework accounting

for heterogeneity in wireless access networks without degrading the security level currently provided by

each wireless system. We also demonstrate using simulation analysis the handover performance

improvement provided by our proposed security frame work.

1 INTRODUCTION

The Next Generation of Heterogeneous Wireless

Networks (NGHWNs) is migrating towards the

interworking of diverse access systems such as

(3GPP Long Term Evolution/Service Architecture

Evolution (LTE/SAE), Universal Mobile

Telecommunications System (UMTS), Wireless

Local Area Network (WLAN) and Worldwide

Interoperability for Microwave Access (WiMax))

(Smaoui, 2007). In fact, interworking these access

networks requires seamless mobility management

with optimized network authentication and keying

material establishment and distribution to guarantee

uninterrupted services continuity especially in case

of mobile terminals’ handover across the integrated

heterogeneous networks owned by a single operator

or by different operators having roaming agreement

between them. In fact, each access system has its

specific network access authentication procedure

and its key management mechanism. Therefore,

when a Mobile Terminal (MT) handovers to a new

network, the MT has to do network specific

authentication procedure and establishes the keys to

secure its communication. Thus, the number of

messages exchanged for network access

authentication during vertical handover imposes a

heavy burden on both the MT as well as the network

side, which increases the vertical handover latency

(Rajavelsamy, 2007).

The NGHWNs are expected to support seamless

mobility between all integrated heterogeneous

wireless networks. On the other hand, security is

also an important concern in handover operation.

Indeed, while moving from one network to another

network, MT should be authenticated. Thus, as

authentication procedure incurs high latency;

executing pre-authentication is becoming essential,

especially for non-delay tolerant connections.

Consequently, security becomes a crucial issue when

this authentication is between heterogeneous

networks. In this context, the NGHWNs tend to

provide an authentication framework independent of

the wireless network technology and a mobility

management that does not degrade security.

In this paper, we propose a security framework

accounting for heterogeneity in wireless access

networks without degrading the security level

currently provided by each individual wireless

system. The main idea of our proposed optimized

authentication scheme is to securely transfer the

temporary identity and its correspondent handover

key already generated by the Hybrid Interworking

Unit (HIU) (Smaoui, 2010) to the mobile terminal

that will be used in the target network, during

handover preparation phase. By means of obtaining

temporary identity and handover key in the handover

249

Smaoui I., Zarai F., S. Obaidat M. and Kamoun L..

Authentication Optimization for Vertical Handover in Heterogeneous Wireless Networks.

DOI: 10.5220/0004011602490254

In Proceedings of the International Conference on Signal Processing and Multimedia Applications and Wireless Information Networks and Systems

(WINSYS-2012), pages 249-254

ISBN: 978-989-8565-25-9

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

preparation phase, the authentication process in the

target network can be reduced considerably.

The rest of this paper is organized as follows.

Section 2 represents overview of the EAP-AKA

(Extensible Authentication Protocol Method for

Authentication and Key Agreement), protocol that

allows the authentication of a MT in heterogeneous

wireless environment. In section 3, we describe the

proposed security authentication procedure. Section

4 represents the performances evaluation of the

proposed scheme and we conclude the paper in

section 5.

2 EAP-AKA PROTOCOL

The EAP-AKA protocol is an authentication

mechanism used in a 3G-WLAN interworking to

authenticate user equipment that attempts to access

Non-3GPP network such as the WLAN. Indeed, the

EAP-AKA is a Universal Subscriber Identity

Module (USIM) based mechanism for authentication

and session key distribution that allows usage of

AKA over the EAP protocol (Arkko, 2006). This

authentication mechanism is used in case of 3GPP

and non-3GPP networks interworking such as the

3GPP-LTE and WLAN interworking.

As in the UMTS-AKA (3GPP, 2006), the USIM

and the network have agreed on a pre-shared secret

key. The authentication vector (AV) components for

EAP-AKA are transmitted on AKA-Challenge

Message of EAP Request and EAP Response

Packets. In EAP-AKA, the User Equipment (UE)

executes a mutual authentication with an EAP server

located at the network side. On successful mutual

authentication, both derive Ciphering Key (CK) and

Integrity Key (IK) which will be used to derive the

EAP Master Key (MK), from which both derive the

EAP Master Session Key (MSK). The MSK is

transferred to the Authenticator (e.g., Access Point

(AP)) in order to protect further communications.

In fact, we distinguish two EAP-AKA

procedures, a full and a fast re-authentication

mechanisms. The full authentication is considered as

an initial authentication procedure to generate new

keys in an USIM card and the network. On the other

hand, the fast re-authentication reuses the keys

already generated from the previous authentication

process to save processing time in the UE and the

AAA server and to save power consumption in the

UE. Indeed, The AAA server aggregates the use of a

fast re-authentication with the UE by sending a re-

authentication identity in any authentication process.

When a re-authentication procedure is initiated by

the network, the UE replies with the re-

authentication identity received in the previous

successful authentication. Moreover, the use of the

fast re-authentication procedure depends on the

operator's policies.

Figure 1: EAP-AKA authentication procedure.

However, the EAP-AKA protocol represents

several vulnerabilities which can cause man-in-the-

middle attacks or bandwidth consumption (Mun,

2009). In fact, on the first connection between the

UE and the EAP server, the IMSI is sent in plaintext.

Therefore, an attacker may intercept the

International Mobile Subscriber Identity (IMSI) and

can modify or misuse it.

Furthermore, although the UE and the EAP

server can be successfully authenticated each other,

the EAP server sends EAP Success message with

MSK to the AP and the UE without authentication.

Consequently, an attacker who impersonates the AP

can receive EAP Success message with MSK,

modify the received message and then send it to the

UE or to another UE. Moreover, the EAP server

requests again the user identity before the

challenge/response procedure because immediate

nodes can modify user identity. For this reason,

EAP-AKA has additional bandwidth consumption.

3 PROPOSED

AUTHENTICATION

OPTIMIZATION MECHANISM

In our proposed solution, the hybrid interworking

unit generates temporary identities (temp IDs) with

their respective authentication keys (temp K) for

WINSYS2012-InternationalConferenceonWirelessInformationNetworksandSystems

250

mobile

WLAN

authenti

stations that

system. T

ation with

prepare to

e MT can

the visited

Figure 2: Pro

handover to

do a fast

network d

osed authenti

the

re-

ring

ation protocol.

dover in ord

consequentl

r to reduce t

reducing th

e authentica

handover de

ion delay

ay.

AuthenticationOptimizationforVerticalHandoverinHeterogeneousWirelessNetworks

251

Thus, in our proposed authentication procedure,

we assume the following:

• Secure tunnels are established between the

Mobility Management Entity (MME) and the Home

Subscriber Server (HSS) server on one hand and

between the HSS and the HIU on the other hand to

secure the transfer of the users’ authentication

parameters.

• The hybrid interworking unit shares a key

MME/HIU

) with the MME that will be dynamically

refreshed by the HSS. The same, the HIU shares also

a key (K

AAA/HIU

) with the Authentication,

Authorization and Accouting AAA server of the

WLAN network (AAA

WLAN

• The HIU may choose any authentication vector

(pair of tempID and temp K) to authenticate the MT

(i.e. there is not a specific authentication vector for a

specific MT).

• An efficient authentication process in our case

(i.e. handover from LTE system to WLAN system)

should enclose three types of mutual authentication:

First, a mutual authentication between the MT and

the home network (LTE network). Second, a mutual

authentication between the LTE network and the

WLAN network. Finally, a mutual authentication

between the MT and the visited network (WLAN

network).

Figure 2 explains our proposed authentication

procedure for handover from LTE system to WLAN

system.

The messages sequences are presented below:

1. MT initiates the measurement process

periodically or after a new discovered pre-handover

trigger such as MT velocity variation, LTE

performance degradation, or a new discovered

network, etc.

2. Based on these measurements (MT velocity,

network load…), if the WLAN system is pre-

selected as the best available network in the MT

coverage area, the MT decides to execute a pre-

handover process to the WLAN network.

3. The MT initiates a pre-authentication procedure

with the MME of its home network by sending a

pre-authentication request containing the MT

temporary identity in the LTE system (ID

MTTemp LTE

As the MT has already execute successfully the

initial authentication process with the MME since its

first attachment to the LTE network, the MME at

this step uses one unused authentication vector

already retrieved from the HSS since the initial

authentication to do the mutual authentication with

the MT.

4. At this step, the MME initiates a mutual

authentication with the HIU to secure the

communication between them. So, the MME sends

to the HIU a message that contains the permanent

identity of the MT (IMSI

), a random number

(Rand1), its signature (SRES1), a Timestamp (T

MME

)

and the MME identity (id

MME

). All encrypted with

their shared key K

MME/HIU

5. As a response, the HIU sends a second random

number Rand2, its signature (SRES2), a Timestamp

HIU

) and the MT’s identity and key in the WLAN.

The message is encrypted by the shared key

MME/HIU

. In fact, the ID

MT/WLAN

is a function of the

MT permanent identity (IMSI

) and the temporary

identity (temp ID) generated by the HIU in one

authentication vector. The same, the K

MT/WLAN

is a

function of the MT permanent identity (IMSI

) and

the temporary key (temp K) in this same selected

authentication vector.

6. In case of successful authentication, the MME

sends to the MT an authentication request that

contains the values of RAND and AUTN.

7. The MT at its turn authenticates the MME by

checking the AUTN, generates the CK and IK keys

and calculates the RES.

8. The MME compares the obtained RES with the

XRES retrieved from the authentication vector and if

the MT is successfully authenticated, the MME

sends its authentication parameters (ID

MT/WLAN

) encrypted with MT’s CK,

9. At this step, the MT and the HIU compute the

Master Key (MK) and the Local Re-authentication

key (LRK). The (MK) key is obtained by the

application of a pseudo random function (prf) on the

MT/WLAN

and the K

MT/WLAN

according to equation (1)

while the (LRK) is derived by using a key derivation

function on the MK and the AAA

WLAN

identity.

 = 

/



/



(1)

 = 











(2)

10. The HIU sends the LRK to the AAA

WLAN

encrypted with their shared key K

AAA/HIU

11. The K

AAA/HIU

at this step derives the Master

Session Key MSK from the LRK.

12. The last part of this authentication procedure

concerns the one established between the MT, the

AP and the AAA

WLAN

to secure the communication

between these equipment. Therefore, firstly, the AP

requires the identity of the MT through an EAP

request. The MT at its turn responds by an EAP

response that contains its ID

MT/WLAN

. The AP relays

this response to the AAA

WLAN

through an access

request. At this step, an EAP method is executed and

WINSYS2012-InternationalConferenceonWirelessInformationNetworksandSystems

252

in case of successful authentication, the AAA

WLAN

authorizes the access to the WLAN system and

sends the MSK key to the AP. This key is also

generated by the MT by applying the same function.

13. In case of MT’s horizontal handover to a new AP

that belongs to a new AAA

WLAN

, this later can

demand a new LRK from the HIU to re-authenticate

the MT which reduces considerably the

authentication latency.

4 PERFORMANCES

EVALUATION

In this section, we analyze our protocol and then

compare its performance with the EAP-AKA

protocol through simulation analysis.

4.1 Security Analysis

Our protocol has several security properties

improvement as summarized below:

• Our proposed authentication mechanism protects

the user identity (IMSI) by using the MT’s

temporary identity (ID

MTTemp LTE

) in the mutual

authentication between the MT and the MME on one

hand and then by generating a temporary identity for

the MT to use it on handover on the other hand.

• All messages between the authentication entities

are encrypted by correspondent keys in order to

ensure messages confidentiality.

• Our protocol can prevent replay attack by using

Timestamps in exchanged messages and verifying

random numbers (steps 4 and 5).

• Our proposed protocol provides several mutual

authentication procedures such as between the MT

and the MME, the MME and the HIU and between

the AAA

WLAN

and the AP. These procedures prevent

man-in-the-middle attacks, which make

communications more secure.

4.2 Performances Analysis

To evaluate our proposed authentication protocol,

we used the simulator developed by us (Daly, 2011)

that implements the WLAN and the LTE systems,

the mobility, the propagation and the traffic models.

We consider a WLAN network covering 300*300m

containing 9 access points and a variable number of

WLAN terminals (the total number is fixed to 200)

and also some LTE terminals switching to the

WLAN network. The simulated network is shown in

Figure 3.

Figure 3: Simulated network.

We evaluate the simulation results based on the

following performance evaluation metrics:

• Handover latency which represents the time

elapsed between the point of attachment change

request and the association with the new one.

• Blocking rate represents the number of blocked

handover connections for the total number of

handover requests.

Thus, Figure 4 shows the influence of our proposed

protocol and of the EAP-AKA protocol on handover

latency. Indeed, we notice that handover latency

increases when the number of terminals increases in

the WLAN system. This can be explained by the fact

that the increase of handover requests introduces

additional delays during handover procedure

generally due to layer treatments and the query

waiting time in different network nodes. However,

by comparing the two curves, we notice that our

proposed protocol offers the reduced latency since it

uses the pre-authentication mechanism which

reduces the authentication latency and consequently

the handover latency.

Figure 4: Handover latency.

Figure 5 shows the influence of our proposed

protocol and of the EAP-AKA protocol on the

handover blocking rate. Thus, we see that our

AuthenticationOptimizationforVerticalHandoverinHeterogeneousWirelessNetworks

253

protocol offers a reduced blocking rate. This result

can be explained by the elimination of blocked

connections caused by authentication latency.

In fact, the obtained simulation results associated

to the security policy reinforcement in the

authentication procedure constitute satisfactory

results for the user experience as well as the network

performance.

Figure 5: Handover blocking probability.

5 CONCLUSIONS

In this paper, we have study the EAP-AKA protocol

that allows user authentication in 3G-WLAN

interworking and we have identified its

vulnerabilities. Then, we have proposed our

authentication mechanism in case of 3GPP-LTE and

WLAN interworking. The performance results have

shown that our proposed protocol outperforms the

EAP-AKA protocol in terms of offered security

level and handover performance which satisfy the

user requirements and the network capacity. Our

future works in this topic will include the evaluation

of the implementation overheads of our proposed

protocol compared with the EAP-AKA protocol.

REFERENCES

Smaoui, I., Zarai, F., Kamoun, L., 2007. “Vertical handoff

management for next generation heterogeneous

networks”, 5th International Conference on

Information and Communications Technology (ICICT

2007), pp. 19-25.

Rajavelsamy, R., Jeedigunta, V., Osok Song, 2007. “A

Novel Method for Authentication Optimization during

Handover in Heterogeneous Wireless Networks”, 2nd

International Conference on Communication Systems

Software and Middleware, COMSWARE 2007, pp.1-5.

Smaoui, I. Zarai, F., Banat, M., Kamoun, L., 2010.

“Heterogeneous Wireless Networks: Configuration

and Vertical Handoff Management”, Wireless

Personal Communications, Vol. 54, No. 3, pp. 417-

445.

Arkko, J., Haverinen, H., 2006. “Extensible

Authentication Protocol method for 3rd Generation

Authentication and Key Agreement (EAPAKA)”, RFC

4187.

3GPP TS 33.102, 2006. “Technical Specification group

services and system aspects, 3G security; Security

Architecture”, release 7.

Mun, H., Han, K., Kim, K., 2009. "3G-WLAN

Interworking: Security Analysis and New

Authentication and Key Agreement based on EAP-

AKA", IEEE Wireless Telecommunications

Symposium, WTS 2009, pp. 1-8.

Daly, I., Zarai, I., Kamoun, L., 2011.“Design and

implementation of a simulation environment for the

evaluation of authentication protocols in IEEE 802.11s

networks”, 3rd International ICST Conference on

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