An Authentication Service Against Dishonest Users in Mobile Ad Hoc Networks

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An Authentication Service Against Dishonest Users
in Mobile Ad Hoc Networks

• Edith Ngai
• Group Meeting Presentation
• 23 Feb 2004
• Dept. of Computer Science Engineering, CUHK

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Outline

• Introduction
• Related Work
• Models
• Security Operations
• Simulation Results
• Conclusion

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Mobile Ad Hoc Networks

• Infrastructure-less
• Multi-hops
• Wireless communications
• Highly mobile
• Dynamic topology
• Vulnerable to security attacks

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Introduction

• Certificate-based approach
• Fully distributed manner
• Detect false public key certificates
• Isolate dishonest users
• Propose a secure, scalable and distributed
  authentication service
• Assure correctness of public key certification

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Related Work

• Traditional network authentication solutions rely
  on physically present, trust third-party servers,
  or called certificate authorities (CAs).
• Partially-distributed certificate authority makes
  use of a (k,n) threshold scheme to distribute the
  services of the certificate authority to a set of
  specialized server nodes.
• Fully-distributed certificate authority extends
  the idea of the partially-distributed approach by
  distributing the certificate services to every
  node.

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Related Work

• Pretty Good Privacy (PGP) is proposed by
  following a web-of-trust authentication model.
  PGP uses digital signatures as its form of
  introduction. When any user signs for another
  user's key, he or she becomes an introducer of
  that key. As this process goes on, a web of trust
  is established.
• Self-issued certificates issue certificates by
  users themselves without the involvement of any
  certificate authority.

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Our Work

• Propose a secure public key authentication
  service in mobile ad hoc networks with malicious
  nodes
• Prevent nodes from obtaining false public keys of
  the others
• Based on a network model and a trust model
• Security operations include public key
  certification and trust value update

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Architecture

• Clustering-based network model
• Trust model with an authentication metric
• Security operations to detect and isolate
  malicious nodes

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The Network Model

• Obtain a hierarchical organization
• Minimize the amount of storage for communication
  information
• Optimize the use of network bandwidth
• Direct monitoring capability is limited to
  neighboring nodes
• Allow the monitoring work to proceed more
  naturally
• Improve network security

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The Network Model

• Divide the network into different regions
• Each region with similar number of nodes
• Unique group ID
• E.g. Zonal distributed algorithm, MST algorithm

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The Trust Model

• Define a fully-distributed trust management
  algorithm that is based on the web-of-trust
  model, in which any user can act as a certifying
  authority
• This model uses digital signatures as its form of
  introduction. Any node signs another's public key
  with its own private key to establish a web of
  trust
• Our trust model does not have any trust root
  certificate it just relies on direct trust and
  groups of introducers in certification

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The Trust Model

• Define the authentication metric as a continuous
  value between 0.0 and 1.0
• A direct trust is the trust relationship between
  two nodes in the same group
• A recommendation trust is the trust relationship
  between nodes of different groups

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Security Operations

• Public key certification
• Trust value update

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Public Key Certification

• Authentication in our network relies on the
  public key certificates signed by some trustable
  nodes.
• Nodes in the same group are assumed to know each
  other by means of their monitoring components and
  the short distances among them

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Operation of Node

• Node s requests for public certificate of node t
• Select introducers
• Compare certificates
• Update trust table

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Trust Value Update

• s denotes the requesting node
• t denotes the target node
• Nodes i1, i2, , in are the introducers
• Each Vs, i and Vi, t form a pair to make up a
  single trust path from s to t

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Trust Value Update

• Compute the new trust relationship from s to t of
  a single path
• Combine trust values of different paths to give
  the ultimate trust value of t
• Insert trust value Vt to the trust table of s

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Simulation Set-Up

• Network simulator Glomosim
• Evaluate the effectiveness in providing secure
  public key authentication in the presence of
  malicious nodes

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Metrics

• Successful rate
• of public key requests that lead to a correct
  conclusion
• Failure rate
• of public key requests that lead to an
  incorrect conclusion
• Unreachable rate
• of public key requests that cannot be made due
  to not enough number of introducers

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Ratings to Periods of Time
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Ratings to Malicious Nodes
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Ratings to Trustable Nodes at Initialization
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Comparison with PGP- Successful Rate
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Comparison with PGP - Failure Rate
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Comparison with PGP - Unreachable Rate
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Conclusions

• We developed a trust- and clustering-based public
  key authentication mechanism
• We defined a trust model that allows nodes to
  monitor and rate each other with quantitative
  trust values
• We defined the network model as clustering-based
• The authentication protocol proposed involves new
  security operations on public key certification,
  update of trust table, discovery and isolation on
  malicious nodes
• We conducted security evaluation
• We compared with the PGP approach to demonstrate
  the effectiveness of our scheme