A THEORETICAL FRAMEWORK FOR MODELLING AND SIMULATING SECURITY PROTOCOLS

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A THEORETICAL FRAMEWORK FOR MODELLING AND
SIMULATING SECURITY PROTOCOLS

• Frantz. Iwu
• Richard Zobel

Department of Computer Science University of
Manchester
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Studied Problem

• Objective of this work to model and simulate
  cryptographic protocols using Agent-Based
  Simulation
• Interests
• agents-based simulation, cryptographic
  protocols,cryptographic protocol validation
• Main Requirements
• modelling cryptographic protocol behaviour and
  interaction
• a generic framework for cryptographic protocol
  simulation
• determining the correctness and efficiency of the
  design using simulation

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Summary

• Setting the scene
• DEV agent framework
• The simulation model
• Evaluating the Protocol Design
• Conclusion and Perspectives

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Summary

• Setting the scene
• DEV agent framework
• The simulation model
• Evaluating the Protocol Design
• Conclusion and Perspectives

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Setting the scene

• Cryptographic protocols are designed to provide
  security services
• Research has shown that a good number of these
  protocols are flawed
• lack of proper universally accepted technique and
  methodology for analysing protocols
• weaknesses are not due to the underlying
  cryptographic algorithms but are as a result of
  logical errors.

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Setting the scene

• Several methods have been proposed
• specification languages and verification tools
  Varadharajan, 1990
• modal logic, expert systems, algebraic reasoning,
  and model-based approaches Nieh, 1992 Gong,
  1990 Burrows, 1990.
• An approach to reasoning about protocol is
  proposed and it involves
• the use of agent models to characterises how
  principals interact

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Setting the scene

• to describe how messages are sent and received
• what messages a particular agent can assemble and
  transmit
• the actions an agent can perform at a particular
  time
• the use of simulation framework in modelling the
  activities of these agents.
• These characterisations form the bases for asking
  security related questions such as
• what are the possibilities of security
  compromises

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Setting the scene

• The proposed approach requires
• first, a conceptual model of the system needs to
  be designed in (DEVS) formalism
• second, there is a need to design a simulation
  model, which enables agents to react and respond
  to events such as an intruder activity
• finally, the Needham-Schroeder and DSE Transfer
  (DSET) protocols are considered using this
  approach

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Summary

• Setting the scene
• DEV Agent Framework
• The Simulation Model
• Evaluating the Protocol Design
• Conclusion and Perspectives

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DEV Agent Framework

• Discrete Event System Specification (DEVS)
• this is a system based simulation tool that
  provides expandability with modular and
  hierarchical features and flexibility
• DEVS framework consists of
• the real system (the protocol to be simulated)
• the model
• the simulator
• There are two relations
• modelling relation
• simulation relation

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DEV Agent Framework

• In the DEVS formalism, there are two models to be
  specified
• atomic model must contain
• set of input ports,set of output ports
• set of state variables and parameters
• internal transition,external transition
• output function
• coupled model must contain
• set of components
• set of input ports, set of output ports
• coupling specification

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DEV Agent Framework

• Modelling with DEVS involves
• outline the function
• identify the input events
• identify internal states
• identify output events

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Summary

• Setting the scene
• DEV Agent Framework
• The Simulation Model
• Evaluating the Protocol Design
• Conclusion and Perspectives

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The Simulation Model

• A simple protocol model
• the aim is to convey the session key Kab
• and data from agent A to agent B
• agent A makes initial request to agent S
• agent S provides agent A with key and
• data(key) encrypted with agent B's key.
• agent A sends the data to agent B who decrypts
  the data and stores the session key

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The Simulation Model
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The Simulation Model

• Needham-Schroeder protocol
• message 1 A ? SA, B, Na
• message 2 S ? ANa, B, Kab, Kab, AKbs Kas
• message 3 A? B Kab, AKbs
• message 4 B ? A NbKab
• message 5 A ? B Nb -1Kab

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The Simulation Model

• Needham-Schroeder protocol

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The Simulation Model

• DSE transfer (DSET) protocol
• message 1 B ? S B,Rb, Tb, dkb, SL, Hbkbs
• message 2 A ? S A, Ra, Ta, SL, Hbkas
• message 3 S ? A Tb, dkbkas, Kb-1

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The Simulation Model

• DSE transfer (DSET) protocol

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The Simulation Model
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Summary

• Setting the scene
• DEV Agent Framework
• The Simulation Model
• Evaluating the Protocol Design
• Conclusion and Perspectives

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Evaluating the Protocol Design

• Prototyping the Agent Model
• the dynamics of the DEVS models were implemented
  using Simplex3
• Attack Model Description includes
• attempt to subvert the protocols objective by
  defeating the manner in which such mechanisms are
  combined
• impersonation where the attack agent attempts to
  play the role of the sender or receiver
• message interception where message content is
  modified.
• agents could be simulated with this capability
  and other known security breaches

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Summary

• Setting the scene
• DEV Agent Framework
• The Simulation Model
• Evaluating the Protocol Design
• Conclusion and Perspectives

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Conclusion and Perspectives

• Main Points and Originalities
• when complete will provide a benchmark for
  testing the security of a protocol with the hope
  of uncovering any potential failures in the
  design
• the attack model should be capable of performing
  a number of attack scenarios
• ability to send messages but not read messages
  that are not addressed to it
• ability to send and read messages but not block
  messages
• ability to send, read and block messages but
  could not replace the blocked messages with other
  messages
• other capabilities

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Conclusion and Perspectives

• Summary
• a framework, which utilises the merits of
• agent-based and
• simulation technologies for analysing
  cryptographic protocols has been proposed.
• this approach is based on simulating an
  environment appropriate for describing
• the DSE transfer protocol
• the Needham Schroeder protocol
• other known protocols
• the environment allows agents to
• interact amongst themselves and
• react to external activities such as an intruder
  attack.
• potentially useful for examining security flaws
  in protocol simulation.