CSCE 715

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CSCE 715

• Anonymous Communication in Mobile Ad Hoc Networks

Vishal Patel
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Introduction

• What is Mobile Ad-hoc Network?
• Also called as MANET
• They became popular for research in mid late
  1990s
• Vehicular ad hoc networks (VANETs)

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Introduction

• This paper proposes.
• Security
• Traffic Analysis

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Introduction

• Military uses of MANETs
• Civilian uses of MANETS
• Personal Uses of MANETS

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Security Issues/Countermeasures

• MANETS ARE EASILY HACKABLE!!!!
• Countermeasures
• -LPI/LPD
• -Traffic Padding
• -End to End Encryption

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MASK-Routing Protocol

• An on-demand anonymous routing protocol for
  MANETS
• Fulfills the routing task without disclosing real
  identity
• --Anonymous neighborhood
• --Anonymous route discovery

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MASK is designed to meet

• Sender, receiver anonymity
• Untraceability and Unlocatability
• Anonymous secure authentication
• Low cryptographic overhead
• Resistance to a wide range attacks

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Preliminaries and Models

• Let G1 and G2 be two groups of the same prime
  order q
• G1 additive group and G2 multiplicative group
• Paring is a computable bilinear map where f
  G1XG1 ? G2

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Adversarial Model

• Active attacks
• -Visible attack (radio jamming, DoS)
• Countermeasures to active attacks
• -IDS, frequency hopping

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Adversarial Model

• Passive Attacks
• - Invisible attack (Eavesdropping, inject
  packets)
• Countermeasures
• - LPI/LPD, spread spectrum

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Network Model

• Limited transmission
• Non-neighboring nodes must communicate via
  multi-hop
• Wireless links are unreliable
• MAC interface in promiscuous mode

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MASK System Design

• Nodes changes vigorously.
• H1 z0,1 ? G1
• H2 0,1 ? 0,1ß
• PSi collision resistant pseudonyms
• Si secret point set
• Given one pseudonym and secret pair cannot deduce
  the master key

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Anonymous Neighborhood Authentication

• Ensure two neighboring nodes have trust
  relationship
• The nodes create there own key

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Example (Alice Bob)

• Alice wants to send a message to Bob
• A random pseudonym is picked from their set
• A session key from bob and secret point set is
  calculated to send the message

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Example continued

• The message is send to Alice
• After Alices receives a reply, she then
  calculates her session key and authenticates Bob
  based on his authenticator
• She then send the message same way bob replied
• And now we have anonymous authentication

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Example continued

• After authentication, they can compute how many
  pairs of session key can be used
• With the same process, Alice knows all her
  neighbors and will create a table which will have
  session key and link identifier
• The link ID will be used to identify the packets
  transmitted between Alice and Bob
• When all pairs have been used, they need to
  generate another set of pairs

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Example Continued

• Only Trusted Authority and give pseudonym to a
  node, the hacker does not learn anything
• The hacker (Trudy) cannot compute the link
  identifier or the shared key

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Anonymous Route Discovery

• Neighbors authenticate and establish session key
  and link ID pairs
• Each node has
• Forwarding routing table ltdest_id, destSeq,
  pre-link, next-linkgt
• Reverse route table ltdest_id, destSeq,
  pre-hop-pseudonymgt
• Target link table

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Anonymous Route Request

• ARREQ
• Packet format of ltARREQ, ARREQ_id, dest_id,
  destSeq, PSxgt
• Intermediate node C received ARREQ
• Rebroadcasts ARREQ
• Previously seen ARREQ_ids are discarded
• Continues until all nodes have broadcast

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Anonymous Data Forwarding

• Random routes
• MASK doesnt use best path, which could delay the
  packet
• Anonymous route are used so the nodes inform the
  network to remove the path that was taken

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Attacks against MASK

• Message Coding Attack
• -- attack happens when contents are not changed
  during transmissions
• Countermeasures
• Random padding
• Per-hop link encryption

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Flow Recognition and Message Replay Attacks

• Recognize packets that belong to same ongoing
  communication
• Countermeasures
• Multipath packet forwarding
• LinkIDs should be change periodically

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Timing Analysis Attack

• Attacker learns what time packets come in/out
• Countermeasures
• Forge a packet with fake LINKID
• Wait random amount of time

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Performance Evaluation

• Cryptographic Operations
• -Anonymous Neighborhood Authentication
• -Hop-by-Hop link encryption/decryption

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Performance

• Routing performance
• -MASK v/s AODV
• Three metrics used
• -Packet Delivery Ratio
• -Average end-to-end delay of data packets
• -Normalized routing load

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PDR v/s MASK

• Normal load 20 sources
• -No difference
• Large load 40 sources
• -MASK is advantageous

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PDR v/s MASK Cont.

• Same as Packet delivery ratio
• Finds long path less frequently

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PDR v/s MASK Cont.

• Normal traffic
• -AODV is better
• Heavy traffic
• -MASK is better
• MAC layer collisions

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Conclusion

• Anonymity
• Unlocatability
• Untraceability
• Can immune to wide range of attacks
• Comparable routing performance