Design of Efficient and Secure Multiple Wireless Mesh Network

Speaker: Hsien-Pang TsaiTeacher: Kai-Wei Ke

Date: 2005/06/28

2

Outline

Introduction Background Secure Wireless Mesh Network Security Analysis Conclusion

3

Introduction

Wireless Mesh Network Secure Architecture Tree Topology

Security Analysis

4

Outline

Introduction Background

Wireless Mesh Network Wireless Security

Secure Wireless Mesh Network Security Analysis Conclusion

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Wireless Mesh Network (WMN)

Last-mile broadband Internet access.

Similar to ad hoc network. Provides:

Reliability, Market Coverage, Scalability.

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Infrastructure Network

Wired Network

APAP

Mobile

Mobile

MobileMobile

Mobile

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Ad hoc Network

Mobile

Mobile

Mobile

Mobile

Mobile

Mobile

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WMN’s ArchitectureWired Network

Wireless Birdge

AP

AP

Mobile

Mobile

Mobile

Mobile

Wireless Birdge

Access Point

Mobile

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WMN’s Actor Wireless Gateway:

Bridge wired and wireless traffic. Access Point (AP):

Provide service to mobile user. Connect with other AP.

Mobile: End Users.

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Wireless Security

A wireless network is broadcast by nature, and the media is reachably-broadcast.

Authentication and data encryption.

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Attacks

Man-in-Middle (MIM) Forge AP Session Hijack Route Swindle Denial of Service (DoS)

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Man-in-Middle

An intruder introduces himself as a new node between a valid host and its AP or between AP and AP.

a b a b

(a) (b)

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Forge AP

a

d

h i j

e f

cb a

d

h i j

e f

cb

k

(a) (b)

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Session Hijack

Supplicant Authenticator Attacker

1.Authentication

2.Association

3.EAP req

4.EAP res

5.Req_auth(auth_info)

6.Resp_auth

7.Resp_success

8.Disassociation

9.Transmission

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Route Swindle

Modify the hop count filed in the routing packet.

a

c

b

f

e

d

h

g

a

c

b

f

e

d

h

g

(a) (b)

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Denial of Service (DoS) DoS attacks are a big problem for all t

ypes of networks. Limited CPU and memory. Continually send streams of associati

on and disassociation packets.

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Security Solution

Wired Equivalent Privacy (WEP) IEEE 802.1x Public Key Infrastructure

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WEPRC4(iv, k)

P = {M, c(M)}

Ciphertext

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Problems with WEP

Key size is too small (40 bits) be crackable in less than 50 hrs by brute f

orce. Key Sequence Reuse (Initial Vector) Message can’t be Authenticated

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IEEE 802.1x IEEE 802.1x is a security framework must pr

ovide network access authentication.

AuthenticatorSupplicant

Authentication Server

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IEEE 802.1x (1)Supplicant Authenticator Authentication Server

Authentication

Association

EAP req

EAP res

forward(unicast,Auth_message)

req_auth(unicast,auth_info)

req_auth(auth_info)

res_auth(auth_info)

res_success

session key exchange

EAPOL start

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Public Key Infrastructure

Two problems with shared-key ： Key distribution Digital signatures

Key feature of public key cryptosystem Two keys: Public Key & Private Key Computational infeasible to determine d

ecryption key.

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Outline

Introduction Background Secure Wireless Mesh Network

Tree Topology Two functions of Wireless Mesh

Network Security Analysis Conclusion

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The Properties of WMN Similar to ad hoc network

AP will select a routing path to transfer data.

The routing path is always fix. Most data flow is transfer to

wireless gateway. Combine all routing path, we can

create a hierarchy architecture - Tree Topology.

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Tree Topology

d

a

g

b

e

h

c

f

ba c

d e f

g h

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WMN’s Relationship(b)

A

Authentication Agent

Supplicant

D

E

F

G

H

I

JManagement system(MS)

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The Actors of Secure WMN Supplicant:

A new AP wants to join WMN Authentication Agent (AA):

Helps supplicant to authenticate with management system.

Create secure tunnels with supplicants.

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The Actors of Secure WMN (1)

Management System (MS) Authentication Server Maintain the topology of WMN Create signature for APs

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Two functions of WMN

Self-Organization Self-Configuration

Self-Reconfiguration Self-Healing

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Self-Organization

d

a

g

b

e

h

c

f

1.Broadcast Req_Start

2.Return Resp_Start

3.Choise authentication agent4.Send Req_Join

5.Send Req_Join_f

6.Forward Req_Join_f

7.Authorization

8.Send Resp_Join_f

9.Send Req_Auth.

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Self-Organization (1)Supplicant Authentication Agent Management System

1.Req_Start(broadcast)

2.Resp_Start(unicast,infos)

3.Req_Join(unicast,join_message)

5.Req_Join_f(unicast,join_message)

6.Resp_join_f(unicast,auth_infos)

7.Req_Auth(unicast)

8.Resp_Auth(unicast,auth_info)

9.Resp_Success(nodie_id,Sign)

10.Session Key Exchange

4. Session Key Exchange

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Trust Model

First, a new AP should do… Register its “MAC Address”, “Confirm

Key” to MS. Get “Group Key” and “WMN public ke

y” from MS. When it gets Resp_Join…

Use “WMN public key” to determine the legal nodes.

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Trust Model (1) Use “Group Key” to start session key ex

change process with its AA. When it gets Req_Auth…

AA has get “Confirm Key” from MS. Return its “Confirm Key” to response R

eq_Auth, then AA will compare these “Confirm Key”.

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Choose Authentication Agent Two factors

Hop count Node loading

1. Choose the node has smallest hop count value.2. If there are two nodes has equal hop count value.

1. Compare their node loading value.2. Select the smaller one.

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Session Key Exchange

The session key should be modified periodically.

Default Key: Supplicant use “KeyUpdate” messa

ge to notify AA exchange key.

groupK

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Send Key_Update to Authentication

Agent

Receive Key_Update &

Generate a new key

Finish

Supplicant Authentication Agent

Send new key encrypted by old key to Supplicant

Receive new key

Send Key_Updated

encrypted by new key

Receive Key_Updated

Is decrypted right?

Send Key_Update_ok

to Supplicant

yes

Is receive Key_Update_o

k?

yes

Restore old key

no

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Self-Configuration

Self-Healing Self-Reconfiguration

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Self-Healing

a

d

h i j

e f

b c a

d

h i j

e f

b ca

d

h i j

e f

b c a

d

h i j

e f

c

(a) (b) (c) (d)

1. Determine the authentication agent fail.

2. Start Self-Organization process.

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Self-Reconfigurationa

e

i j k

f g

b c

m n o

l

h

d

p

a

e

i j k

f g

b c

n o

l

h

d

p

a

e

i j k

f g

b c

n o

l

h

d

p

a

e

i j k

f g

b c

m n o

l

h

d

p

(a) (b)

(c) (d)

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Outline

Introduction Background Secure Wireless Mesh Network Security Analysis Conclusion

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MIM

Supplicant use secret key to establish a secret tunnel with AA. Attacker can’t read the transmission

data directly. Supplicant will update new key

with its AA periodically. Attacker can’t collect enough packets

to determine the secret key.

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Forge AP

Supplicant will update new key with its AA periodically. Attacker doesn’t know what the key is

used now.

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Session Hijack

Session key exchange first Supplicant should start session key

exchange before authentication. Attacker can’t hijack any session.

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Route Swindle

When AP receive Req_Start, it returns Resp_Start (signature). Signature can prove its legality. Supplicant will only trust the legal Resp_

Start.

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Denial of Service

There are not any solution to solve this problem.

When a node be crashed, the self-healing process will be started by other nodes.

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Outline

Introduction Background Secure Wireless Mesh Network Security Analysis Conclusion

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Conclusion

Propose tree topology for secure WMN.

Define WMN’s basic functions of WMN.

Analysis security problems.

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Future Work

Consider more available attacks. Consider performance in “choose

AA” . Other application:

Sensor network Ad hoc network

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The End