network access control for mobile ad hoc network pan wang north carolina state university

Network Access Control for Mobile Ad Hoc Network

Pan Wang

North Carolina State University

2

Outline

• Background

• Problem statement

• Related work

• Proposed scheme– Key Synchronization– Packet Retransmission

• Analysis, simulation and field test

• Summary

3

Background

• Mobile Ad Hoc Network (MANET)– A MANET consists of mobile platforms (e.g., a

router with multiple hosts and wireless communications devices), which are free to move about arbitrarily. -- IETF RFC2501

– Characteristics of MANET• No pre-determined infrastructure

• Ease of deployment

• Dynamic topologies (e.g., mobility, network partition )

• Constrained resources (e.g., bandwidth, energy )

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Background (Cont)

• Network access control– Not media access control – Who has the right to access the network

• Physical*

• Technical *

• Administrative *

– Firewalls • Conventional network

• Using network topology and service information

* H. F. Tipton, Handbook of information security management

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Problem Statement

• An attacker may inject “bogus” packets to consume the network resources, or insert itself into critical routes

• No mature access control scheme for MANET– more complicated due to open media and dynamic

topology

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Related Work

• DHCP Access Control Gateway

• Kerberos

• Distributed firewall

• Pebblenets

• Distributed access control scheme for consumer operated MANET

• LHAP

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Related Work --Cont

• LHAP: a lightweight hop-by-hop authentication protocol for ad-hoc networks– Based on one-way key chain and TESLA– Hop-by-hop authentication– Each transmitted packet associated with a traffic key, – Receiver (or intermediate node) verifies to decide whether

forward (accept) the packet

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A

B

D

(i)KFA

(i)KFA

S

Cert &Commit

S

M, KF(i)

S

M, KF(I+1)

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Proposed Scheme – cryptographic tools

• Group key agreement• Group key distribution

– Controller chooses key

– Stateful vs. Stateless

• Stateless key distribution – Each user is assigned an

unique set of personal keys

– New key is encrypted with the personal keys only known to the legitimate users

– Nice stateless property

k1 k2

K1-

2

K3-

4

k3

k4

K1-

4

M1 M2 M3 M4

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Proposed Scheme – underlying models

• Network model– All nodes come from one domain – A node’s access to the network is controlled by a

domain manager (i.e., key manager) – Each node has a unique ID and a set of personal

secret keys

• Attack model– Attackers inject packets to deplete the resources of

node relaying the packets

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Proposed Scheme - outline

• Basic idea– Cryptography-oriented (using group key)

– Authenticate all the packets with a network-wide access control (group session) key.

– Any “bogus” packet that has incorrect authentication information will be filtered out immediately.

– As a result, illegitimate nodes will be excluded from communication (routes).

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Research challenges

• Two critical challenges – Synchronization of network access control key

– Interaction between data transmission and key distribution

If these two challenges can be solved, the proposed group key based network access control scheme will be done.

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Key Synchronization

• Problem statement– A key update message may fail to propagate

across MANET. Thus, two legitimate user may simultaneously hold different session key (lack of key synchronization)

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Key Synchronization (Cont-1)

• An example of lack of key synchronization

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B

C

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KeyManager

P1

P2

P3

F*

F

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• Solution– Exploit the stateless feature of the proposed

stateless group key distribution scheme

– Each user buffers the key update message most recently received

– Transmit the buffered message to the other users that are using old session keys

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• Scheme details– Proactive part

• Broadcast the buffered key update message every t time unites

– Reactive part• Send a key synchronization request, if a received

packet has higher session ID

• Send the buffered key update message, if a received packet has a lower session ID

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• Illustration of the proposed key synchronization scheme

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Broadcast

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Represents a node that has the most recent key

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• Security analysis (possible attacks)– Resource consumption via forged key update

message• Solution: lightweight authentication methods (One-

way key chain & Merkle hash tree)

– Resource consumption via forged data packet• Constrained to one-hop •

– Logically partition MANET via refusing forwarding key update message

• Multiple paths, watchdog

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One-way key chain

k0 k1 ki ki+1 kn-1 kn

k0=h(k1) ki=h(ki+1) kn-1=h(kn)

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Merkle hash tree

m07

m01

m0 m1

k0 k1

m23

m2 m3

k2 k3

m45

m4 m5

k4 k5

m67

m6 m7

k6 k7

m03 m47

m0=f(k0)

m01=h(m0,m1)

m03=h(m01,m23)

m07=h(m03,m47)

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• Performance analysis– Rely on the adopted stateless group key

distribution scheme

– Storage• One message

– Computation

– Communication• Depends on t and number of users using an old key

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Packet Retransmission

• Problem statement – The interaction between data transmission and key

distribution. That is, in the case of a lack of key synchronization, a user may receives some (unverified) packets authenticated with a different session key.

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Packet Retransmission (Cont-1)

• Possible options– Simply drop

– Buffer and then verify

– Synchronize the keys before sending every data packet

• All of them have serious drawbacks

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• Proposed solution– Drop, synchronize keys, and then retransmit.

– ACK mechanism

– Unicast & broadcast

D

S B2. ReTx Request

4. ReTx Packet

1. Tx failed due tolack of key Syn

3. Key SynA

5. ACK

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Algorithm of the proposed scheme

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• Security analysis (possible attacks)

– Resource consumption attack

– Forged ACK message

– Packet modification

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• Performance analysis– Computation

• Authentication & verification

• Pentium 4 2.1 GHz processor *

MD5 216.674 MB/s SHA-1 67.977 MB/s

– Communication• Retransmission rate

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Simulation Evaluation

• The simulation modal– 40/80 nodes randomly

placed in a fixed area (a square of size 1km x 1km)

– Random walk with a maximum speed 20m/s

– Communication range 200m

– 2000 simulations, using different random number seeds

0%

20%

40%

60%

80%

100%

20 40 60 80 100

Number of Nodes

Perc

enta

ge o

f Rea

chab

le N

odes

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Simulation Evaluation (Cont-2)

Average percentage of nodes which got the latest session key

0%

20%

40%

60%

80%

100%

1 2 3 4 5 6 7 8

Rounds of Key Update (P_lost=0, 40 nodes)

Stateful Scheme

Stateless Scheme

After 1 Cycle of K. Syn

After 2 Cycles of K. Syn


0%

20%

40%

60%

80%

100%

1 2 3 4 5 6 7 8Rounds of Key Update (P_lost=0.25, 40 nodes)

Stateful Scheme

Stateless SchemeAfter 1Cycle of K. Syn

After 2 Cycles of K. SynAfter 3 Cycles of K. Syn

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Average percentage of nodes which got the latest session key

65%

70%

75%

80%

85%

90%

95%

100%

1 2 3 4 5 6 7 8

Rounds of Key Updaye (P_lost=0, 80 nodes)

Stateful Scheme

Stateless Scheme




65%

70%

75%

80%

85%

90%

95%

100%

1 3 5 7Rounds of Key Updates (P_lost=0.25, 80 nodes)

Stateful Scheme

Stateless Scheme




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0%

2%

4%

6%

8%

10%

12%

14%

0 0.5 1 1.5 2 2.5 3

Packet Sending Rate (# packets per second )

Re

tra

ns

mis

sio

n R

ate

40 nodes

80 nodes

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Implementation

• Based on Netfilter

• Two daemons– Adopt the stateless scheme proposed by Liu & Ning

Pre-Routing ROUTE Forward Post-

Routing

ROUTE

LocalOut

Verification Authentication

LocalIn

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Field Test

• Test bed– One Dell P4 laptop with Linux 9.0 (kernel 2.4.20)

– Two Compaq iPAQ 3970 PDAs with Familiar v0.7.2 (kernel 2.4.19-rmk-pxal-hh30)

– Lucent Orinoco wireless cards

• Tests– Key distribution

– User revocation

– Packet authentication and verification

– Key synchronization

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Summary

• Network access control is an important issue for MANET

• Cryptography-oriented solution exploiting the stateless feature of stateless group key distribution scheme

• Simulation as well as functioning prototype indicates it practical and effective

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Question

network access control for mobile ad hoc network pan wang north carolina state university

Documents

key manager

network manet

key stateful

traffic key

key chain

network resources

network topology

network physical