Design of Efficient and Secure
Multiple Wireless Mesh Network
Speaker: Hsien-Pang Tsai
Teacher: Kai-Wei Ke
Date: 2005/06/28
Outline
Introduction
Background
Secure Wireless Mesh Network
Security Analysis
Conclusion
2
Introduction
Wireless Mesh Network
Secure Architecture
Tree Topology
Security Analysis
3
Outline
Introduction
Background
Wireless Mesh Network
Wireless Security
Secure Wireless Mesh Network
Security Analysis
Conclusion
4
Wireless Mesh Network (WMN)
Last-mile broadband Internet access.
Similar to ad hoc network.
Provides:
Reliability,
Market Coverage,
Scalability.
5
Infrastructure Network
Wired Network
AP AP
Mobile
Mobile Mobile
Mobile Mobile
6
Ad hoc Network
Mobile
Mobile
Mobile
Mobile
Mobile
Mobile 7
WMN’s Architecture
Wired Network
Wireless Birdge
Wireless Birdge
AP
AP Access Point
Mobile
Mobile
Mobile
Mobile
8
Mobile
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.
9
Wireless Security
A wireless network is broadcast by
nature, and the media is reachably-
broadcast.
Authentication and data encryption.
10
Attacks
Man-in-Middle (MIM)
Forge AP
Session Hijack
Route Swindle
Denial of Service (DoS)
11
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)
12
Forge AP
a b c a b c
k
d e f d e f
h i j h i j
(a) (b)
13
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
14
Route Swindle
Modify the hop count filed in the
routing packet.
d d
b b
g g
a a
e e
c c
h h
f f
(a) (b)
15
Denial of Service (DoS)
DoS attacks are a big problem for all
types of networks.
Limited CPU and memory.
Continually send streams of association
and disassociation packets.
16
Security Solution
Wired Equivalent Privacy (WEP)
IEEE 802.1x
Public Key Infrastructure
17
WEP
RC4(iv, k)
Ciphertext
P = {M, c(M)}
18
Problems with WEP
Key size is too small (40 bits)
be crackable in less than 50 hrs by brute
force.
Key Sequence Reuse (Initial Vector)
Message can’t be Authenticated
19
IEEE 802.1x
IEEE 802.1x is a security framework must
provide network access authentication.
Authenticator
Supplicant
Authentication Server 20
IEEE 802.1x (1)
Supplicant Authenticator Authentication Server
Authentication
Association
EAPOL start
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
21
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
decryption key.
22
Outline
Introduction
Background
Secure Wireless Mesh Network
Tree Topology
Two functions of Wireless Mesh Network
Security Analysis
Conclusion
23
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.
24
Tree Topology
a b c
b c
a
d e f
d e f
g h
g h
25
WMN’s Relationship
(b)
J
Management system(MS)
G
D H
A E I
Authentication Agent F
26
Supplicant
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.
27
The Actors of Secure WMN (1)
Management System (MS)
Authentication Server
Maintain the topology of WMN
Create signature for APs
28
Two functions of WMN
Self-Organization
Self-Configuration
Self-Reconfiguration
Self-Healing
29
Self-Organization
7.Authorization
8.Send Resp_Join_f
b c
a
6.Forward Req_Join_fd e f 2.Return Resp_Start
9.Send Req_Auth. 1.Broadcast Req_Start
g h 4.Send Req_Join
5.Send Req_Join_f 3.Choise authentication agent
30
Self-Organization (1)
Supplicant Authentication Agent Management System
1.Req_Start(broadcast)
2.Resp_Start(unicast,infos)
3.Req_Join(unicast,join_message)
4. Session Key Exchange
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
31
Trust Model
First, a new AP should do…
Register its “MAC Address”, “Confirm Key”
to MS.
Get “Group Key” and “WMN public key”
from MS.
When it gets Resp_Join…
Use “WMN public key” to determine the
legal nodes.
32
Trust Model (1)
Use “Group Key” to start session key
exchange process with its AA.
When it gets Req_Auth…
AA has get “Confirm Key” from MS.
Return its “Confirm Key” to response
Req_Auth, then AA will compare these
“Confirm Key”.
33
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.
34
Session Key Exchange
The session key should be modified
periodically.
Default Key: K group
Supplicant use “KeyUpdate” message to
notify AA exchange key.
35
Supplicant Authentication Agent
Receive
Send Key_Update
Key_Update &
to Authentication
Generate a new
Agent
key
Send new key
Receive new key encrypted by old
key to Supplicant
Send
Key_Updated Receive
encrypted by new Key_Updated
key
Restore old key
Is decrypted
right?
yes
Is receive Send
no
Key_Update_o Key_Update_ok
k? to Supplicant
yes
Finish 36
Self-Configuration
Self-Healing
Self-Reconfiguration
37
Self-Healing
a b c a b c a b c a c
d e f d e f d e f d e f
h i j h i j h i j h i j
(a) (b) (c) (d)
1. Determine the authentication agent fail.
2. Start Self-Organization process.
38
Self-Reconfiguration
a b c d a b c d
e f g h e f g h
i j k l i j k l
m n o p m n o p
(a) (b)
a b c d a b c d
e f g h e f g h
i j k l i j k l
n o p n o p
(c) (d) 39
Outline
Introduction
Background
Secure Wireless Mesh Network
Security Analysis
Conclusion
40
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.
41
Forge AP
Supplicant will update new key with its
AA periodically.
Attacker doesn’t know what the key is used
now.
42
Session Hijack
Session key exchange first
Supplicant should start session key
exchange before authentication.
Attacker can’t hijack any session.
43
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.
44
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.
45
Outline
Introduction
Background
Secure Wireless Mesh Network
Security Analysis
Conclusion
46
Conclusion
Propose tree topology for secure WMN.
Define WMN’s basic functions of WMN.
Analysis security problems.
47
Future Work
Consider more available attacks.
Consider performance in “choose AA” .
Other application:
Sensor network
Ad hoc network
48
The End
49