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					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




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