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Secure CommunicationA View From The Transport LayerMANET and WSN

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Overview

•Transport Layer and Security Issues•Anonymity

▫E-mail▫WSN and MANET

•Traffic Analysis•DOS Attacks

▫flooding▫de-synchronization

•Summary•References

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Transport Layer and Security Issues

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Transport Layer Basics

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Transport Layer - Security

•Securing end-to-end communication•Keys distribution and use for secure

communication•Anonymous communication•Preventing traffic analysis•Preventing DOS attacks

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Mobile Sensor Networks - Basics•Security Constraints

▫Low Power▫Limited processing power▫Limited memory▫Limited bandwidth

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Keys

•Base Station assigns keys▫Symmetric Key Algorithms

Saves computation resources▫Establishes trust with sensor nodes

Saves computation and power Computing and exchanging keys

▫Base station transmits the keys directly to the node Saves power

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Anonymity E-mail

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E-mail Anonymity

•Untraceable E-mail

•Untraceable Return Addresses

•Digital Pseudonyms

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E-Mail Anonymity - Untraceable

•Using Public Key encryption

•Uses▫Elections▫Part of an organization, but want identity

kept secret (CIA)

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E-Mail Anonymity - Untraceable

•Additional computer called the “Mix”•Bob wants to send Alice an untraceable

message.•Bob sends the message encrypted with

Alice’s public key, encrypted again with the Mix’s public key:▫Km(R1, Ka(R0, M), A) Ka(R0,M),A

•Mix decrypts, eliminates R1, and forwards the message to Alice.

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E-Mail Anonymity - Untraceable

•Mix hides the correspondences between items in its input and output.▫Outputs in uniformly sized items in

lexicographically ordered batches.▫Ensures no duplicate output (would show a

pattern to an eavesdropper) make R a timestamp change Mix’s keys

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E-Mail Anonymity - Untraceable

•Multiple Mix’s▫Cascade encryptions▫First Mix’s (M2) input:

Km2(R2,Km1(R1,Ka(R0, M),A),Am1) ▫First Mix’s output:

Km1(R1,Ka(R0, M),A)) ▫Final Result:

Ka(R0, M),A)

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E-Mail Anonymity – Return Address

•What if Alice wants to respond to Bob? He is anonymous!

•Bob can sends his address, encrypted so that only the Mix can read, and deliver it.▫Km(R1,Ab), Kb(R0,M) Ab, R1(Kb(R0, M))

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E-Mail Anonymity – Return Address

•Mix can verify recipient received the message▫Certified Mail Service▫Last Mix sends back to Bob:

Alice’s address Message itself Each Mix may sign the receipt

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E-Mail Anonymity

•Preventing Traffic Analysis▫Send same number of messages per each

batch Pro - Hides number of messages sent from

Bob Con - Uses resources (power, bandwidth)

▫Send same number of messages to subsets of participants Pro - Hides number of messages Bob sends to

Alice, and minimizes dummy messages Con - Still uses resources for dummy

messages

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E-Mail Anonymity - Pseudonyms•Digital Pseudonym:

▫A public key used to verify signatures made by the anonymous holder of the corresponding private key.

•Roster:▫List of pseudonyms kept by a trusted

authority•Uses:

▫Elections – Roster of eligible voters

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E-mail Anonymity – Pros & Cons•Pros:

▫Ability to be anonymous▫Verified message delivery

•Cons:▫Additional hardware (mix)▫What if you want to know the addressee (threat)▫Trusted Authority

who and what determines this▫Lots of additional encryption (time and

resources)

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Anonymity –MANET and WNS

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Anonymity – Why

•If an attacker can ID a node, and eavesdrop on traffic, they may be able to identify actual network traffic patterns.

•Track a moving node•Identify what network a node belongs in

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Anonymity – Cont.

Wired connections with dedicated links Wireless connections with shared media

• Wireless communication broadcast property makes it hard to see where where a node is, but makes it easier to eavesdrop. [picture - 11]

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Anonymity – How

•We will analyze how to achieve anonymity in both:▫MANET

Mix-net▫WNS

Anonymity done through preventing traffic analysis attacks

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Anonymity - MANET•Similar to e-mail, uses Mix’s

A Mix-Net example in MANET [2]

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Anonymity - MANET•Encryption and decryption of messages is

the same as used with Mix’s in e-mail:•Multiple Mix’s

▫Cascade encryptions▫First Mix’s (M2) input:

Km2(R2,Km1(R1,Ka(R0, M),A),Am1) ▫First Mix’s output:

Km1(R1,Ka(R0, M),A)) ▫Final Result:

Ka(R0, M),A)

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Anonymity - MANET•Mix Advertisement

▫Sends message “I’m here”▫Non-Mix node hears this and determine a

dominant Mix-node If it doesn’t hear an advertisement message

from it’s Mix in some interval of time, it finds another Mix.

•Mix Route Discovery and Update▫Sender node (S) sends RREQ message to

destination node (D)

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Anonymity - MANET•Mix Route Discovery and Update

▫RREQ Phase: Sender node (S) sends RREQ message to destination node (D)

▫DREG Phase: D knows it is part of end-to-end communication, registers with it’s closest Dominator Mix

▫RUPD Phase: Mix broadcasts RUPD messages to nodes with a list of nodes registered to the Mix

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Anonymity - MANET

Broadcasted RUPD Messages [2]

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Anonymity - MANET•Potential security problem:

▫An attacker could hear S send a RREQ message, then hear D send a DREG message shortly after.

•Solution: S can send dummy RREQ messages to itself,

to hide the real RREQ message to D

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Anonymity - MANET•Pros:

▫Compromised node in the middle of the route does not reveal source or destination nodes

▫Dominant Mix could hide identity of S▫Mix can also aide in preventing traffic

analysis•Cons:

▫Additional hardware: Mix’s▫Additional encryption

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Anonymity – MANET - PPCS•PPCS – Privacy Preserving

Communication•Three mechanisms:

▫Dynamic Flow Identification▫Random Node Identification▫Resilient Packet Forwarding

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Anonymity – MANET - PPCS•Dynamic Flow Identification

▫Two flow pseudonyms, Pdi, Psi are defined for the forward and backward flows Replaces the source and destination

addresses Source broadcasts RREQ packet containing

these pseudonyms <RREQ, Psi, Pdi, Ksd(m)>▫Intermediate nodes receive and try to

decrypt Psd “Trap door check”

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Anonymity – MANET - PPCS•Random Node Identification

▫Dissociates a real node identifier from location information

▫RNI – random node identifiers

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Anonymity – MANET - PPCS•Resilient Packet Forwarding

▫Multi-path random forwarding (MPRF) Provides protection against traffic analysis Helps avoid traffic congestion Intermediate nodes randomly selects the next

hop by it’s local list of possible next hop nodes.

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Anonymity – MANET - PPCS•Potential problems:

▫Message could be followed from end-to-end Solution: Encrypt again between

intermediate nodes•Pros:

▫Node anonymity established•Cons:

▫More difficult to implement▫Each intermediate node must look at the

Psd of a RREQ message

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Anonymity - WSN▫Base Station ID hidden

Could take out entire network▫How:

Hide which node is the base station by limiting traffic analysis

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Anonymity - Summary

•Some situations may require node anonymity▫Ex: Election, CIA

•E-mail anonymity▫Mix

•MANET and WSN anonymity▫Mix and routing▫Traffic Analysis

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Preventing Traffic Analysis

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Preventing Traffic Analysis – Why

•High traffic and/or traffic patterns could indicate a base node/station▫Base Node/Station

Entire network depends on it▫Ex: Military

Determine critical nodes , chain of command Forthcoming action State change or network alertness

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Traffic Analysis – Example

Data traffic patterns using shortest path routing [7]

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Traffic Analysis – Two Classes

•Two classes of traffic analysis

1.) Rate Monitoring Attack– monitor packet sending rate

2.) Time Correlation Attack – deduce path by listening to nodes forward packets

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Preventing Traffic Analysis – How

•Multiple parent routing▫Rate monitoring attacks

•Controlled random walk▫Rate monitoring attacks

•Random fake paths▫Time correlation attacks

•Multiple, random areas of high communication activity ▫Rate Monitoring Attacks

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Multi-Parent Routing

•Reduces effectiveness of rate-monitoring attacks

•Each node has multiple parents•Randomly select one parent each time it

forwards a packet▫Any level higher is a parent or▫Record beacons as parents

•Problems:▫Does not eliminate rate-monitoring attacks▫Still subject to time-correlation attacks

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Multi-Parent Routing

Multi-parent routing for node “u”

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Random Walk

•Reduces rate monitoring attack effectiveness

•Forwarding packets:▫To parent with probability of p▫To neighbor with probability of (1-p)

•Problems:▫Still vulnerable to time correlation attack▫Longer route consumes more energy (more

hops to base station)

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Random Fake Paths

•AKA Fractal Propagation•Makes time-correlation attacks less

effective•Fake packets are created and propagated

through the network▫Fake packets have a TTL parameter, K

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Random Fake Paths Cont.

•When a node receives a fake packet, it▫decrements TTL (if zero, it drops the

packet)▫forwards the packet to a neighbor node

•If a node hears it’s neighbor transmitting a fake packet with a TTL of k :▫generates and forwards another fake

packet TTL = k-1 probability

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Random Fake Paths Cont.

•Problems:▫Already limited power is used on fake

transmissions▫Does not completely eliminate time

correlation attacks▫Generates a large amount of traffic by base

station If transmitting real packets more frequently,

reduce the probability of sending a fake packet

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Multiple, random areas of high communication activity

•AKA Hot Spots•Makes rate monitoring more difficult•Node keeps track of which neighbors it

sends fake messages to. •All neighbors start with the same

probability of receiving a fake message from me

•If I send a fake message to neighbor A, I increase the probability I send another fake message to it

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Multiple, random areas of high communication activity – Cont.

•Ability to create and destroy hotspots

•Problems:▫Does not eliminate rate monitoring, but

does make an attacker waist time with a hotspot

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Traffic Analysis - Summary

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Traffic Analysis – Summary Cont.•Pros:

▫Only a limited time delay of real packets▫Applicable to large scale WSN’s

•Cons:▫Does not eliminate traffic analysis▫Uses already limited power

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DOS Attacks

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DOS Attack - Flooding

•Attacker repeatedly makes new connection requests

•Uses nodes resources•Proposed Solution:

▫puzzle▫limit connections to a node (or connection

requests)

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DOS Attack – De-Synchronization•Attacker repeatedly forges messages to

one (or both) end points, asking for packet retransmission.

•Uses nodes resources•Proposed solution:

▫Authenticate packet headers

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Conclusion

•E-mail anonymity is desired for some people/organization▫Can be achieved using

Mix Trusted Authority

•MANET and WSN▫Limited resources make security difficult

Let the Base Station do the work

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Conclusion Cont.

•Preventing Traffic Analysis▫Hide which node is base station

•DOS▫Flooding▫De-synchronization Attack

•Future work

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Questions

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References• [1] D. Chaum, “Untraceable Electronic Mail, Return Addresses, and Digital

Pseudonyms”,• Communications of the ACM, 1981.• [2] S. Jiang, N. H. Vaidya and W. Zhao, A Mix Route Algorithm for Mix-Net in

Wireless Ad• Hoc Networks, IEEE International Conference on Mobile Ad-hoc and Sensor

Systems (MASS),• October 2004.• [3] B. R. Venkatraman and N. E. Newman-Wolfe, Transmission schedules to prevent

traffic• analysis, Ninth Annual Computer Security and Applications Conferences, 1993.• [4] B. Radosavljevic, B. Hajek, Hiding traffic flow in communication networks,

MILCOM 1992.• [5] S. Jiang, N. H. Vaidya, W. Zhao, Preventing traffic analysis in packet radio

networks,• DISCEX 2001.• [6] SPINS: Security Protocols for Sensor Networks (Perrig)• [7] J. Deng, R Han, S. Mishra; Countermeasures Against Traffic Analysis Attacks in

Wireless Sensor Networks; University of CO; 2005

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References• [8] Sk. Md. Mizanur Rahman, Nidal Nasser, Atsue Inomata, Takeski Okamoto, M

Mambo, E Okamoto; Anonymous authentication and secure communication protocol for wireless mobile ad hoc networks; Wiley InterScience; 2008; p. 179-189

• [9] S. Tilak, N. Abu-Ghazaleh, W. Heinzelman; A Taxonomy of Wireless Micro-Sensor Network Models; Mobile COmuting and Communications Review, Vol. 6, No. 2; 2004

• [10] Y. Zhang, W. Liu, W. Lou, Y. Fang; MASK: Anonymous On-Demand Routing in Mobile Ad Hoc Networks; IEEE Transactions on Wireless Communications, Vol. 5, No. 9, 2006

• [11] Dijiang Huang; On An Information Theoretic Approach to Model Anonymous MANET Communications; ISIT 2009, Seoul, Korea; June 28-July 3, 2009

• [12] H. Choi, P. McDaniel, T. F. La Porta; Privacy Preserving Communications in MANETs; The Pennsylvania State University; 2007

• [13] S. Kaplantzis and N. Mani, ”Classification Techniques for Network Intrusion Detection”, in NCS’06 - Proceedings of the IASTED International Conference on Networks and Communications Systems, March 2006

• [14] T. Kevitha, D. Sridharan; Security Vulnerabilities In Wireless Sensor Networks: A survey; Journal of Information Assurance and Security 5, 031-044; 2010