# Ad hoc Networking Security: Solving Node Selfishness Problem - PowerPoint PPT Presentation

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Ad hoc Networking Security: Solving Node Selfishness Problem. Presented by : Ali N M Noman PhD Student CSI 5148 anoma033@uottawa.ca Course Instructor: Professor Ivan Stojmenovic. Outline. Problem Definition & Security Challenges

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Ad hoc Networking Security: Solving Node Selfishness Problem

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## Ad hoc Networking Security: Solving Node Selfishness Problem

Presented by : Ali N M Noman

PhD Student

CSI 5148

anoma033@uottawa.ca

Course Instructor: Professor Ivan Stojmenovic

## Outline

Problem Definition & Security Challenges

Background Information

Basic Cryptography- Encryption, Digital Signature

DSR

Analyzing Solutions

Conclusion

## Node Selfishness Problem:

Scenario 1: Node S wants to send a packet(p) to Node D using the route <S,1,2,3,D> , where Node 2 is a selfish node

Selfishness problem:

A form of misbehavior where a node does not participate in network operation in order to save its power.

P

P

S

1

2

3

D

Did not forward P

Can a selfish node do its own network operation?

## Node Selfishness Problem

Scenario 2: However Node 2 can send a packet (p1) using the route<2,3,D>

Selfishness problem:

A form of misbehavior where a node does not participate in network operation in order to save its power.

P1

P1

S

1

2

3

D

## Node Selfishness Problem: Security Challenges

Is it an active attack? No

However it degrades the network performance.

“10 to 40% of misbehaving nodes cause 16 to 32% of degradation of the average throughput of the network”.

Can traditional cryptographic solution (i.e. integrity, authentication) solve this problem?No

Bob wants to send a msg, M to Tom

## Background: Basic Security Goals

Bob

Tom

Confidentiality/secrecy:Encode(encrypt) M(plain text) into a unreadable text , C(cipher text) prior to transmission so that no one except bob and tom can decode(decrypt) it.

Integrity: Tom can verify whether M was not modified in transmission or not.

Authentication:Tom can verify that M was really sent by Bob.

Non Repudiation: After sending the msg M, Bob cannot deny.

Recall the purpose of our handwritten signature. (Digital Signature)

(Digital Signature) is one of the main motivation behind developing public key cryptography

Bob wants to send a msg, M to Tom

## Public Key Cryptography:RSA

Bob

Public key:(e_bob, N)

Private Key: (d_bob, N)

Tom

Public key:(e_tom, N)

Private Key: (d_tom, N)

Public key is known to all; private key is a secret.

Encryption: Encrypt M with receiver’s public key.

Here, C= (M)e_tom mod N

Decryption: Receiver (i.e. Tom) will decrypt it using its private key which is a secret to all.

Here, M= (C)d_tom mod N

[assuming C is not modified in transmission]

Bob wants to send a msg, M to Tom

## Public Key Cryptography:RSA

Tom

Public key:(e_tom, N)

Private Key: (d_tom, N)

Bob

Public key:(e_bob, N)

Private Key: (d_bob, N)

Digital Signature : Sender(Bob) will encrypts(i.e. sign) the message, M with its private key and send (M | DS) to Tom. Here DS= (M)d_bob mod N

Signature Verification: Tom verifies Bob’s signatureas follows:

If M== (DS)e_bob mod N

correct signature

Else

It is not signed by Bob

Remark: This solution ensures integrity and authentication and non repudiation but does not provide secrecy.

How can you also include secrecy here??

## RSA: Computational Challenges

Example: assume C(encrypted text)= 542;Receiver’d private key(d,n)=(157,2773)

In this case, P= 542157 mod 2773 =805

But you can do that using this trick:

## Question 1:

Question : Alice has the public key {e = 13, n = 899} and the private key {d = 517, n =899}. Bob has the public key {e = 17, n = 851} and the private key {d = 233, n = 851}. Suppose Bob has received the plain/unencrypted message 67 and the signature 129. Describe how Bob verifies the signature . [ Note: In this case, message is directly used to calculate signature using RSA]

Solution:

Here, M=67 and DS=129.

Step 1. Bob should decrypt the DS using Alice’s public key

M’= (DS)13 mod 899=67

[use the trick given in the presentation]

Step 2. Now Bob will compare M’ with M . If they match then the signature is verified.

## DSR: Dynamic Source Routing

DSR Example(simplified): S wants to send a packet ,P to Destination

4

5

An on demand routing protocol

Each data packet carries a complete path(i.e. ordered list of nodes towards destination)

S

1

2

3

D

S chooses a(best) route to D from its cache : <S,1,2,3,D> . This route is added in packet header of P.

2. (If everything goes well) the packet will traverse to D using the red path

• 2 main mechanisms:

• Route discovery: Discover (multiple) routes to D.

• Route maintenance : Updating route cache in nodes in order to ensure data transfer from S to D.

## DSR: Dynamic Source Routing

DSR Example(simplified): Route Discovery (S to D)

<S,4>

4

<S,1>

<S,1, 2>

<S,1, 2,3>

RR=<S,1, 2,3, D>

S

1

2

3

D

<S,5>

5

Route Request : (S, D, request ID,RR=<S>).

Each intermediate node adds itself in the RR if it is not D or does not know a path to D

D will send back the RR to S using a Route Reply. D can choose an already discovered path to S or can initiate another R. request to S if necessary .

• Route Maintenance:

• Sending Route Error Massage to S: Intermediate Node informs S if link is broken

• Packet Salvaging: Intermediate Node should forward packet to D using other path(if known) if the given path is broken.

## Solving Node Selfishness Problem

Solutions can be categorized as:

Monitoring Based

Watchdog

End-End Ack

2H-ack

Reputation Based

CORE

CONFIDANT

Signed Token

Preventive

Nuglets (not feasible)

## Watchdog

First proposal for mitigating routing misbehavior in MANET

Most of the later solutions rely on it.

2 components:

Watchdog(monitoring) : Misbehavior(selfish) node detection

Pathrater: choose a best path by avoiding a path with misbehaving(selfish) node.

Build on top of source routing protocol, DSR.

Watchdog Summary: Selfish Node detection. All nodes operates in promiscuous mode to monitor its neighbor nodes. If it finds that its neighbor node is misbehaving(selfish) for t (threshold) times, the node reports it to the source node.

## Watchdog : in selfish node detection

P

P

S

1

2

3

D

Did not forward P

Node 1 does not over hear forwarding of P from Node 2

Selfish Node detection using Watchdog: Example(simplified)

Confirms it by checking t times

Reports to S: Node 2 is selfish

• Initially a node gives a rate of 0.5 to all of its known nodes and a (fixed) rate of 1 to itself.

• Adds 0.01 to all nodes in the DSR packet forwarding path if it is successful

• Deduct -0.05 from all unreachable nodes of a DSR packet forwarding path (if it is unsuccessful due to broken link).

• Maximum rating of each node (except the initiator) is 0.8.

• A misbehavior node will get the rating of -100.

• Source Node, S will calculate the average rating of all nodes in each path and choose the path with maximum average rating.

## How Pathrater works?

Steps involved in finding the best path using pathrater (simpified)

• Consider the following Scenario:

• 1. Node S has the following rate for its known nodes:

• 2.Assumefollowing events occur in order:

• E-1: packet forwarding to 3 using route <S,4,1,2,3> is successful

• E-2: packet forwarding to 3 using route <S,5,1,6,2,3> fails as link between 6 & 2 is broken (i.e. node 2 & node 3 is unreachable)

• E-3: Packet forwarding attempt using <S,5,7,2,3> identifies Node 7 as a selfish node

6

4

S

1

2

3

7

5

## Executing the entire Watchdog Algorithm

Question 2:What is the updated node rating table of node S? Which one of the following 3 routes S will choose to send a packet to Node 3: Is it <S,5,7,2,3> or <S,4,1,2,3> or <S,5,1,2,3>?

Rating of <S,5,7,2,3> = (1.0+0.5-100+0.46+0.46)/5

Rating of <S,4,1,2,3> =(1.0+0.61+0.56+0.46+0.46)/5

• Rating of <S,5,1,2,3>=(1.0+0.5+0.56+0.46+0.46)/5

<S,4,1,2,3> has the highest rating. So it will be chosen

## Watchdog Algorithm: Pros & Cons

Simple. Enhance the network performance.

Weaknesses in Monitoring: collision, limited power transmission.

• It does not give any penalty to a selfish node, instead it helps the selfish node to save its energy. How??

• What if A lies??  Reputation of A??

## End-End Ack-How it works?

Basis: Monitoring the reliability of routes by acknowledging in an end-end manners

If S gets an ack (within the time out interval) from D after sending a packet, the route is fine. Otherwise not

Successful delivery of a packet will increase the route rating and unsuccessful delivery decrease route rating

If a route’s goes under a threshold(not reliable any more) the route will not be used (may be for a specific time)

Cross layer mechanism makes it possible to use TCP ack instead of implementing end –end ack in network layer

end-end ack

D

S

TCP

TCP

Network

Network

## End-End Ack-Pros & Cons

Unreliable routes can be avoided. So routes having selfish node can also be avoided.

Cross layer mechanism makes it possible to use TCP ack instead of adding explicit ack in network layer .

Ack needs to be signed (specially in network layer ack implementation). In this case, end-end security association is required

Can it detect the selfish/misbehaving node? No

---This is the main drawback of this solution.

## Signed token based Solution

Collaborative localized monitoring.

Only Nodes with a valid token(signed collaboratively by its neighbors) can participate in network operation.

A misbehaving/selfish node’s token will be revoked by its neighbors.

RSA is used

Based on threshold secret sharing(polynomial secret sharing).

Here private/secret key(sk) is shared among n nodes. Signing a token with private key , sk is same as if k(out of n) nodes sign the token with the part of sk it posses ”

## Signed token: How it works?

3 components:Collaborative monitoring, token renewal, token revocation.

Token Renewal: K out of N neighbor nodes issue/renew a token for a node.

## Signed token: How it works? contd

Steps Involved(simplified):

Upon detecting misbehavior of a neighbor ,a node broadcast a SID( single intrusion detection) to its neighbor.

Once a node received m (e.g. m=k) independent SID it broadcasts a GID(Global Intrusion Detection) to its neighbors.

When a node received K independent GID, it constructs a signed TREV(token revocation) packet and broadcasts it.

Upon receiving the signed TREV, a node checks its TREV table, if there is no entry for this node include it into the TREV table.

Any active link with a revoked node will be considered as broken

## Signed token: Pros & Cons

Localized solutions. Signature management is also done locally.

Self organized.

Very much suitable for a dense network; protect misbehavior in routing and packet forwarding.

A node with less than K neighbors cannot communicate. –> Main Drawback

## CONFIDANT

A reputation based solution. Can be considered as an extension of DSR. Treats Misbehavior as an exception.

4 components: Monitor, Reputation System, Trust Manager, Path Manager

1. Misbehavior detected

Exceed the threshold

Rate the selfish node considering other’s feedback also .

Informs it to others as an alarm

Other Nodes will do the same thing. However they will also consider informer’s trustworthiness

If the node rate is less than the threshold , avoid the path with misbehaving node

## Executing CONFIDANT : (simplified example)

Route Cache of A

empty

1. Route Request: A wants to send a packet to E

2. Route Reply: D and E both know a path to E

Route Cache of A

[A,B,E]

[A,C,D,E]

## Executing CONFIDANT : (simplified example)

3 . Data Flow & Alarm: A sends data and receives alarm from C that D is misbehaving

Route Cache of A

[A,B,E]

[A,C,D,E]

4. Act on Alarm: A chooses an alternative path to E

Route Cache of A

[A,B,E]

Updated

## CONFIDANT: Pros & Cons

Overhead(O): In this case additional alarm messages are transmitted along with all DSR’s regular messages(i.e. Route Request, Route Reply and Route Error Message)

In the last execution of CONFIDANT,

[ This is Question3]

Trust issue. Alarm msg needs to be signed

## Conclusion

Monitoring is the basis for most of the proposed solutions.

Where as Watchdog solution only avoids a route having misbehaving node , the reputation based solutions (e.g. CONFIDANT and Signed) also penalize the selfish/misbehaving node/

However most of the solutions have some limitations.

End-End ack selfish node undetected

Signed Token Node needs at least K neighbors to perform

## References:

Yang, H.; Meng, X.; Lu, S. Self-organized network layer security in mobile ad hoc networks. ACM MOBICOM Wireless Security Workshop (WiSe 2002), Atlanta, GA,Sept 28, 2002.

S. Buchegger and J.-Y. Le Boudec, Nodes Bearing Grudges: Towards Routing Security, Fairness,

and Robustness in Mobile Ad Hoc Networks, in Proceedings of the 10th Euromicro Workshop

on Parallel, Distributed and Network-based Processing.

S. Buchegger and J.-Y. Le Boudec, Performance Analysis of the CONFIDANT Protocol, in

Proceedings of MobiHoc 2002.

S. Marti, T. Giuli, K. Lai, and M. Baker, Mitigating Routing Misbehavior in Mobile Ad Hoc

Networks, in Proceedings of MOBICOM 2000.

P. Michiardi and R. Molva, Core: A COllaborativeREputation mechanism to Enforce Node Cooperation in Mobile Ad Hoc Networks, in Proceedings of IFIP Communication and Multimedia

Security Conference 2002.

Conti, M.; Gregori, E.; Maselli, G. Improving the performability of data transfer in mobile ad hoc networks. The 2nd IEEE International Conference on Sensor and Ad Hoc Communications and Networks (SECON 2005), Santa Clara, CA, Sept 26–29, 2005.

“Ad Hoc Network Security” by PietroMichiardi & RefikMolva

Steps Involved:

34

## Appendix2: Question 1 Digital Signature

Digital Signature (DS): DS is created by encrypting the message with sender’s private key. Receiver can verify it by decrypting DS with sender’s public key.

Question 1 : Alice has the public key {e = 13, n = 899} and the private key {d = 517, n =899}. Bob has the public key {e = 17, n = 851} and the private key {d = 233, n = 851}. Suppose Bob has received the plain/unencrypted message 67 and the signature 129. Describe how Bob verifies the signature. [ Note: In this case, message is directly used to calculate signature using RSA]

Solution:Here, M=67 and DS=129.

Step 1. Bob should decrypt the DS using Alice’s public key

M’= (DS)13 mod 899=67

[use the trick discussed during presentation]

Step 2. Now Bob will compare M’ with M. If they match then the signature is verified.

## Appendix3: Question 2 on Pathrater

Question 2:What is the updated node rating table of node S? Which one of the following 3 routes S will choose to send a packet to Node 3: Is it <S,5,7,2,3> or <S,4,1,2,3> or <S,5,1,2,3>?

Rating of <S,5,7,2,3> = (1.0+0.5-100+0.46+0.46)/5

Rating of <S,4,1,2,3> =(1.0+0.61+0.56+0.46+0.46)/5

• Rating of <S,5,1,2,3>=(1.0+0.5+0.56+0.46+0.46)/5

• [ Follow Slide No 17-19 . The algorithm is given there]

<S,4,1,2,3> has the highest rating. So it will be chosen

## Appendix 4: Question 3 on CONFIDANT

Communication Overhead in CONFIDANT: In this case additional alarm messages are transmitted along with all DSR’s messages (i.e. Route Request, Route Reply and Error Message). It is calculated as follows:

Question 3: Consider the following execution of the CONFIDANT Algorithm to calculate overhead(0).

## Appendix 4: Question 3 on CONFIDANT

Solution:

In this case Overhead(O) = 2/(6+4)=1/5= 20%