Australian Journal of Basic and Applied Sciences. Chaos Based Secure Communication Scheme Using Voltage Controlled Oscillator and

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1 Australian Journal o Basi and Applied Sienes, 8(4) Speial 2014, Pages: AENSI Journals Australian Journal o Basi and Applied Sienes ISSN: Journal home page: Chaos Based Seure Communiation Sheme Using Voltage Controlled Osillator and ogisti Map S. Narendra and S. Aloka Department o Physis, Indian Institute o Tehnology Delhi, Hauz Khas, New Delhi , INDIA A R T I C E I N F O Artile history: Reeived 20 November 2013 Reeived in revised orm 24 January 2014 Aepted 29 January 2014 Available online 5 April 2014 Keywords: Chaos Based Seure Communiation Sheme Voltage Controlled Osillator ogisti Map A B S T R A C T We propose and experimentally demonstrate a new haos based opto-eletroni seure ommuniation system using voltage ontrol osillator. The haoti signal has been generated using a modiied eletroni iruit o the logisti map. The output o the haos generator is translated to a haotially varying instantaneous requeny o the voltage ontrolled osillator (VCO). The proposed tehnique enodes the signal using this haotially varying instantaneous requeny. The proposed tehnique has been demonstrated by using an optial iber as a ommuniation hannel. Experimental results have been presented as a proo o onept AENSI Publisher All rights reserved. To Cite This Artile: S. Narendra and S. Aloka., Chaos Based Seure Communiation Sheme Using Voltage Controlled Osillator and ogisti Map. Aust. J. Basi & Appl. Si., 8(4): , 2014 INTRODUCTION The transmission o huge amount o data has led to remarkable researh eorts in the area o data seurity. In the past deade, several algorithms and arhitetures or optial image-enryption and seurity systems have been proposed (B. Javidi, 2005; P. Reregier, and B. Javidi 1995; M. Singh, A. Kumar, and K. Singh 2008; Z. iu, J. Dai, X. Sun, and S. iu 2009; C. C. aborde, R. Duhowiz, R. Torroba, and E.E. Sire 2008; H. i 2009; X. i, and D. Zhao; M. Ouhsain, and A.B. Hamza 2009) in whih, we desire to enode inormation in suh a way that, even i it is viewed or reorded, only the use o the orret key would eth the orret inormation or the guaranteed privay. Chaos has the potential to guarantee privay or transmitted signal due to its attrative properties (G. James, 1988 ; K.T. Alligood, T.D.Sauer, and J.A. Yorke. 2001; R.C. Hilborn. Chaos and nonlinear dynami, 2000). Chaoti waveorms have been generated using dierent hardware systems (] M. Suneel, 2006; I.C.Canton, E. C. Canton, J.S. Murguia, and H.C. Rosu, 2008; K. Murali, Sudeshna Sinha, William. and Ditto, 2003). Their attrative eatures are their broadband spetrum and the possibility o synhronizing them. The hardware-oriented (R.A. Gayakward, 2004; B.P. athi, 2005) seure system ould guarantee greater privay than that obtained with onventional sotware-oriented ryptography (A. Argyris, D. Syvridis,. arger, V. A. odi, P. Colet, I. Fisher, J.G. Ojalvo, C.R. Mirasso,. Pesquera, and K.A, 2005). Reently haoti based signal have been utilized to enode inormation and provide added seurity (A. Argyris, D. Syvridis,. arger, V. A. odi, P. Colet, I. Fisher, J.G. Ojalvo, C.R. Mirasso,. Pesquera, and K.A, 2005; C.R. Mirasso, I. Fisher, and. arger). In this paper, we propose and experimentally demonstrate a new haos based opto-eletroni seure ommuniation system using VCO. The haoti signal has been generated using a modiied eletroni iruit o the logisti map. The output o the haos generator is translated to a haotially varying instantaneous requeny o the voltage ontrolled osillator. The proposed tehnique enodes the signal using this haotially varying instantaneous requeny. The proposed tehnique has been demonstrated by using an optial iber as a ommuniation hannel. Experimental results have been presented as a proo o onept. The proposed tehnique is dierent rom the earlier tehniques. In the previous tehniques, enryption has been perormed when signal is transormed rom one domain to another domain (the signal has been transormed using a transorm to the requeny domain by using Fourier transorm (FT) (B. Javidi, 2005 ; X. i, and D. Zhao-8). Chaoti signal has haoti variation in both the amplitude and the instantaneous requeny. In all the earlier proposed tehniques, masking (enryption) o the message has been perormed by using the haoti variation in amplitude o the haoti signal (A. Argyris, D. Syvridis,. arger, V.A. odi, P. Colet, I. Fisher, J.G. Ojalvo, Corresponding Author: S. Narendra, Department o Physis, Indian Institute o Tehnology Delhi, Hauz Khas, New Delhi , INDIA

2 764 S. Narendra and S. Aloka, 2014 Australian Journal o Basi and Applied Sienes, 8(4) Speial 2014, Pages: C.R. Mirasso,. Pesquera, and K.A, 2005;.-B. Cuenot,. arger, J.-P. Goedgebuer, and William T. Rhodes, 2001;. arger, and J-P Goedgebuer, 2004;. arger, J-P Goedgebuer, and V. Udaltsov, 2004; K. Suzuki, and Y. Imai, 2006; C.R. Mirasso, I. Fisher, and. arger). In the proposed tehnique, the VCO output is not the FT o haoti waveorm generated by the haos generator but the VCO output remains in the temporal domain i.e. the domain does not hange or the enryption proess. The masking (enryption) o the message has been done by using the haoti variation in instantaneous requeny o the haoti signal. 2. Voltage Controlled Osillator: An osillator whose requeny an be ontrolled by an external voltage is a VCO (R.A. Gayakward, 2004 ; B.P.athi, 2005). In a VCO, the osillation requeny varies linearly with the input voltage is ( (t) ). Its output is a sinusoid o requeny given by ( t) e ( t) (1) o where is a onstant o the VCO and is the ree- running requeny o the VCO ( the VCO requeny when ( t) 0 ). The multiplier output is urther low pass iltered by the loop ilter and then applied to the input o e o the VCO. This voltage hanges the requeny o the osillator and keeps the loop loked. This untion is ahieved in the VCO.VCO is also alled a voltage to requeny onverter. Phase loked loop (P) serves as a VCO demodulator. The P an be used to trak the phase and the requeny o the arrier omponent o an inoming signal. It is, thereore, a useul devie or synhronous demodulation o amplitude modulation (AM) signals with suppressed arrier or with a little arrier (the pilot). A P has three basi omponents. First is a VCO, seond is, a multiplier, serving as a phase detetor or a phase omparator and third is a loop ilter. The operation o the P is similar to that o a eedbak system. The entral requeny o the P is determined by the ree-running requeny o the VCO, whih is given by the equation e o Fig. 1: The shemati blok diagram or enryption and deryption proess. 1.2 out (2) 4RC where R and C are the resistor and apaitor. The lok range 8 V and apture range o the P are given by out (3) 1/ 2 8 (4) (2 )(3.6)(10 )( C) where is the ree running requeny o VCO and V is the supply voltage. The lok range usually out inreases with an inrease in the input voltage but dereases with an inrease in the supply voltage. 3. Chaos Funtion: ogisti map [10-12] is a haoti map. Chaoti maps generate haoti signals whih have properties suh as the wideband wave orm does not repeat itsel. It has noise like appearane and is very sensitive to the initial onditions. These random iterative values are limited between bounds. The logisti map is used or our study and is deined as ( x). x.(1 x) (5)

3 765 S. Narendra and S. Aloka, 2014 Australian Journal o Basi and Applied Sienes, 8(4) Speial 2014, Pages: This untion is bounded or 0 4.The iterative orm o this untion is written as x x.(1 x ) (6) n 1. n 1 n 1 with x 0 as the initial value. This haoti map is used to generate the haoti signal. The enryption proess and the deryption proess o the proposed tehnique are shown in Fig. 1. et S(t) be the input signal and the C (t) be the haoti signal, where C (t) is the random waveorm generated by the eletroni iruit o the logisti map. Both the input signal and the haoti signal are proessed by the VCO. The VCO onverts the input signal into another signal S VCO (t) o varying instantaneous requeny. Similarly, the haoti signal is onverted into a signal C VCO (t) with haotially varying instantaneous requeny. Both are then multiplied together to give the enrypted signal E(t). It is given by E(t) = C VCO (t) S VCO (t) (7) The deryption proess is the inverse o the enryption proess. C VCO (t)is multiplied with E(t) and then the VCO demodulation operation is perormed. The obtained signal is the derypted signal whih is expressed as D(t) and is given by D(t)=VCOdemodulation[E(t) C VCO (t)] (8) Fig. 2: Modiied iruit diagram or logisti map. The modiied iruit diagram o the logisti map is shown in Fig. 2. Some modiiations have been introdued between the present iruit diagram o the logisti map and the earlier proposed iruit diagram o the logisti map (M. Suneel, 2006). These modiiations are as ollows. There is an option to hange the seed value o the eletroni iruit o the logisti map. Every time the seed value an be hanged by using the variable resistane at pin no. 6 o the seond multiplier. IC 741 (single output general- purpose operational ampliier) is used to design the eletroni iruit o subtrator and ampliier respetively. F633 IC is used to design the eletroni iruit o irst and seond multipliers respetively. A simple iruit using single F398 IC (sample and hold IC) is used to iterate the loop o the eletroni iruit o logisti map. Here R 1 = R 2 = R 3 = 2.2KΩ and R 4 = R 5 = R 6 = R 7 = 22KΩ. IC 633 is used to implement M 1 and M 2. Here C 1 = C 2 = C 3 = C 4 = 0.1 F. Here C 5 = 0.1 F. R 8, R 13 and R 14 are the variable resistane o 5KΩ. The trigger o the sample-and hold iruit is a TT-ompatible square-wave generated by using the untion generator. Here V = +15V and V EE = -15V. Frequeny o the trigger signal is equal to 300Hz and amplitude is equal to 5Volt. For VCO and P, IC M566CN serves as the VCO and IC M565CN serves as the P respetively. In the opto-eletroni implementation o the enryption and the deryption tehnique, the optial iber has been used to demonstrate the proposed tehnique. Experimental Results: Experimental results have been presented to validate the proposed tehnique. Eletroni iruit o the logisti map has been designed to generate the haoti signal. The input signal is a sinusoidal wave having a amplitude o 0-5V and requeny o 300Hz. Trigger pulse or the logisti map iruit is TT pulse o amplitude 0-5V and requeny 300Hz. Amplitude o the haoti signal is 1volt. The amplitude o the VCO output when input signal is input o the VCO is kept in between -1V to 1V. The amplitude o the VCO output when haoti

4 766 S. Narendra and S. Aloka, 2014 Australian Journal o Basi and Applied Sienes, 8(4) Speial 2014, Pages: signal is input o the VCO is kept in between -1V to 1V. The requeny o the input signal and the trigger signal is kept equal. TT pulse and the input signal is given by untion generator. The experimental results or the enryption and the deryption proess are give in Fig. 3. The input signal,a sinusoid, is given in Fig. 3(a). The haoti signal generated by our iruit is shown in Fig. 3(b). The ombined signal o the input and the haoti signal is given in Fig. 3(). (d) the enrypted signal (signal ater perorming PPM and at the transmitter end o the HFBR) is shown in Fig. 3(d). Finally the derypted signal.is shown in Fig. 3(e). Conlusion: In onlusion, we propose and experimentally demonstrate a new haos based opto-eletroni seure ommuniation system using VCO. The proposed tehnique is dierent rom the previous tehniques. In the previous tehniques, the enryption is arried out by irst transorming the signal rom one domain to another domain. Masking is done by using the haoti variation in the amplitude o the haoti signal. In the proposed tehnique, the enryption has been perormed in the same domain (time domain) and it is irst time that the masking has been done by using the haoti variation o the instantaneous requeny o the haoti signal. A modiied eletroni iruit has been used to generate the haoti signal. The proposed tehnique has been validated by using an optial iber as a ommuniation hannel. Fig. 3: The experimental results (a) The input signal, (b) the haoti signal, () the ombined signal o the input and the haoti signal, (d) the enrypted signal (signal ater perorming PPM and at the transmitter end o the HFBR), and (e) the derypted signal.

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