Novel Cascaded Chaotic Masking for Secure Communications

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Novel Cascaded Chaotic Masking for
SecureCommunications

• Rupak Kharel, Krishna Busawon Zabi Ghassemloy
• Northumbria Communication Research Lab
• Northumbria University

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Outline

• Chaos Introduction
• Application to communication
• Different techniques for chaotic communication
• Problem statement
• Cascaded chaotic masking technique
• Results
• Final Comments

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CHAOS INTRODUCTION

• Deterministic system
• means that the system has no random or noisy
  inputs or parameters. The irregular behaviour
  arises from the systems nonlinearity rather than
  from the noisy driving forces.
• Aperiodic long term behaviour
• means that there should be trajectories which do
  not settle down to fixed points, periodic orbits
  or quasiperiodic orbits as t ?8.
• Sensitive dependence on initial conditions
• means that nearby trajectories separate
  exponentially fast, which means the system has
  positive Liapunov exponent.

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CHAOS EXAMPLE LORENZ EQUATIONS

• Are dynamical system exhibiting chaotic property
• Three dimensional system given as
• States are evolving in a complex non repetitive
  pattern over time.

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CHAOS APPLICATIONS IN COMMUNICATION

• Chaotic signal has a broadband spectrum, hence
  the presence of information does not necessarily
  change the properties of transmitted signal.
• Power output remains constant regardless of the
  information content.
• It is resistant against multi-path fading and
  offers cheaper solution to traditional spread
  spectrum systems.
• Chaotic signal are aperiodic therefore limited
  predictability.
• Hence, chaotic signal can be used for providing
  security at physical level.

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CHAOTIC SYNCHRONIZATION (HOW???)

• Chaotic systems are very sensitive
• Slightly different initial conditions and initial
  parameters lead to totally different
  trajectories.
• slight errors between transmitter and receiver
  can be expected to grow exponentially.
• Q1 How can one achieve synchronization?
• Q2 Can this sensitive chaotic system be used in
  
• communication?
• Pecora Carroll1 showed that it is possible to
  synchronize two chaotic system if they are
  coupled with common signals.
• Cuomo Oppenheim2 practically utilized chaotic
  synchronization for transmitting message signal.
• 1) L. M. Pecora and T. L. Carroll,
  Synchronization in chaotic systems, Phys. Rev.
  Lett., 64, pp. 821-824, 1990
• 2) K. M. Cuomo and A. V. Oppenheim, Circuit
  implementation of synchronized chaos with
  applications to communications, Phy. Rev. Lett.,
  71, pp. 65-68, 1993.

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CHAOTIC COMMUNICATION TECHNIQUES

• Chaotic Masking Technique
• Chaotic Parameter Modulation Technique
• Message Inclusion Technique
• Chaotic Shift Keying (CSK)
• Almost all other methods falls into one or
  more of these categories.

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Chaotic masking technique

• Message signal (m) is buried in the broad chaos
  spectrum by adding m to a chaotic mask y.
• At receiver, the chaotic mask that is estimated
  from chaotic synchronization, is removed from
  received signal to obtain m.

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Parameter modulation technique

• Some parameters of chaotic system are varied by
  adding the message signal.
• At receiver an adaptive controller is used to
  tune the chaotic system parameters to ensure zero
  synchronization error .

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Message inclusion technique

• Rather than changing the chaotic parameter, the
  message is included in one of the states of the
  chaotic oscillator. By doing this, we are
  directly changing the chaotic attractor at phase
  space.
• A transmitted signal will be different than the
  state where the message will be included.
• Encryption rule can also be applied.

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Chaotic shift keying (csk)

• Used for transmitting digital message signal.
• Two statistically similar chaotic attractor are
  respectively used to encode bit 1 or 0.
• These two attractors are generated by two chaotic
  systems having the same structure but slightly
  different parameters.
• At receiver, the received signal is used to drive
  a chaotic system similar to one of the
  transmitters.
• The message is recovered by thresholding the
  synchronization error signal.

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CHAOS TECHNIQUES PROBLEMS

• Masking, parametric modulation technique and CSK
  has been proved to be insecure1,2,3.
• Breaking methods were based on forecasting and
  predicting the carrier values, which when
  subtracted revealed the spectrum of message.
• Inclusion method is secure, however presents a
  problem of inversion.
• Hence, the need to improve the security of the
  above techniques.
• K. M. Short, "Steps toward unmasking secure
  communications," International Journal of
  Bifurcation and Chaos, vol. 4, pp. 959-977, 1994.
• G. Alvarez, F. Montoya, M. Romera, and G. Pastor,
  "Breaking parameter modulated chaotic secure
  communication systems," Chaos Solitons
  Fractals, vol. 21, pp. 783-787, 2004.
• T. Yang, L. B. Yang, and C. M. Yang, "Application
  of neural networks to unmasking chaotic secure
  communication," Physica D, vol. 124, pp. 248-257,
  1998.

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CHAOS PROBABLE SOLUTION

• Cascaded Masking Technique (CMT).
• Two chaotic signals (generated by two
  oscillators) are added together at roughly equal
  power to generate a carrier of sufficient
  complexity.
• Forecasting and predicting carrier behaviour is
  hence not possible.
• Simpler masking technique thus can be extended as
  cascaded structure for more secure links.

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Cascaded masking technique (cmt)

• Chaotic receiver B synchronizes with oscillator
  B to estimate and recover ym to drive chaotic
  receiver A to synchronize with oscillator A.

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CMT APPLICATION USING LORENZ SYSTEM

• Transmitter A
• Transmitter B

• Receiver B
• Receiver A

Note A scaled Lorenz equation is used as done by
Cuomo Oppenheim for favourable electronic
implementation, otherwise wide dynamic range of
the solution will exceed typical power supply
limit.
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CMT RESULTS

• Parameters adopted and assumption made
• s, r, b 16,45.6 and 4
• m(t) 0.1 sin(2pt)
• All the gains are set to zero
• Arbitrary Initial conditions
• Ideal channel and no noise

Fig. 2 Output ym after first level of masking
(transmitted signal)
Fig. 1 Output ym after first level of masking
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CMT RESULTS (CONTD)

• Input and output waveforms

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Limitations future work

• Taking into consideration non-ideal channel with
  noise.
• The synchronization robustness of receiver B is
  critical for the proper synchronization of
  receiver A and proper message extraction.
• Expanding the system to work with other chaotic
  oscillator such Chuas circuit, Duffing
  oscillator, Colpitts oscillator, etc.
• Hardware implementation.

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Conclusion

• A novel cascaded masking technique to increase
  the security of the chaotic communication system
  was presented.
• Theoretical analysis was given. Simulation
  results presented demonstrated successful
  recovery of the message signal.
• Limitation and future works were also outlined.

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acknowledgements

• I would like to thank
• Northumbria University for providing me with PhD
  studentship to carry out the research.
• My supervisors Dr. Krishna Busawon and Prof. Zabi
  Ghassemlooy.
• My collegues in NCRLab.

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Thank you. (Any questions !!!)