Combining cryptography with channel coding to reduce complicity

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Combining cryptography with channel coding to reduce complicity

  1. 1. International Journal of Electronics and Communication Engineering & TechnologyAND INTERNATIONAL JOURNAL OF ELECTRONICS (IJECET), ISSN COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEMEISSN 0976 – 6464(Print)ISSN 0976 – 6472(Online)Volume 3, Issue 2, July- September (2012), pp. 346-351 IJECET© IAEME: www.iaeme.com/ijecet.htmlJournal Impact Factor (2012): 3.5930 (Calculated by GISI) ©IAEMEwww.jifactor.com COMBINING CRYPTOGRAPHY WITH CHANNEL CODING TO REDUCE COMPLICITY Sunaina Sharma Electronics and Communication Sunaina.sh39@gmail.com ABSTRACT Cryptography is a form of hiding the text so to increase the security of the information. On the other hand the main purpose of using coding is to reduce the error probability and to increase the efficiency of the channel. As the word complicity means criminal offence. This paper presents an overview how complicity can be reduce by combining Channel coding with cryptography with the use of LFSR shift register Keywords: Include at least 5 keywords or phrases I. INTRODUCTION The general communication system consist separate block for channel coding and for encryption [1]. The general diagram for has been shown below: Source Quantization Digital Data Input Source Encrypti Channel Modul Coding on Coding ation Channel Source Channel Equaliza Demodul Decoding Decoding tion ation D/A Digital Data Convertor Output Fig 1.1: Communication System 346
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME This paper provides the information how to merge channel coding with the cryptographyto provide more security to the signal. In the network security and cryptography, the study ofconfidentiality, authenticity and error correction are very important [4][6]. Many of themodern communication systems are limited in resources such as battery power andcomputational power. Mobile sensor networks, smart cards etc., are some examples. Hence amajor research in communication concentrates on designing systems with low computationalor hardware complexity. To reduce the computational and communication cost of two majorcryptographic operations say channel coding and cryptography has been combined. And theproposed work as [1] [2]: Source Quantization Combining Blocks Source Encrypti Channel Modul Coding on Coding ation Channel Source Channel Equaliza Demodul Decoding Decoding tion ation D/A Convertor Fig 1.2: Purposed Communication SystemII.COMBINING CRYPTOGRAPHY WITH CHANNEL CODING The objective of the paper is to combine Cryptography with channel coding to reduce thecomputational and communication cost and to increase the security per bit [7] [8]. The blockdiagram shows how encryption and coding has been done on the signal [2]: LFSR G Matrix Sound Signal Digital Signal Channel Noise is converted divided into (White Gaussian into digital bits of 4 (i) Noise) Comparison Received between Word Coded and Uncoded word Finding out Calculating Coset Leader Standard Error Vector and Array Syndrome Fig 1.3: Block dig of channel coding with LFSR 347
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME An approach to improve the performance of a communication system without increase incomplexity is to embed encryption within channel coding. For this, programming has beendone in Matlab. Since Matlab is commonly used for programming purposes, it providesseveral of inbuilt functions and tools used for programming purposes. A voice signal is firstconverted into digital and then encoded and encrypted. And at the receiver side it is decodedand decrypted. The flow diagram for this is as under [2]: LFSR Start XORing the Sound Signal tapes and generating the sequence Digital Signal Signal Divided Selecting G into Bit of 4(i) Matrix according to the sequence Codeword generated CW = i×G LFSR Channel Received word Standard valid Array Syndrome & G Coset leader matrix (errV) CW = i- errV Decoded Word Comparison between Coded and Un-coded Signal Stop Fig 14: Flow dig of cryptography with channel coding 348
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEMEIII. LINEAR FEEDBACK SHIFT REGISTER A linear feedback shift register (LFSR) is a shift register whose input bit is a linearfunction of its previous state. The most commonly used linear function of single bits is XOR.Thus, an LFSR is most often a shift register whose input bit is driven by the exclusive-or(XOR) of some bits of the overall shift register value. The initial value of the LFSR is calledthe seed, and because the operation of the register is deterministic, the stream of valuesproduced by the register is completely determined by its current (or previous) state. Likewise,because the register has a finite number of possible states, it must eventually enter a repeatingcycle [9]. A 12 bit key is given as input to the filter then this filter will generate 4095 (212-1)number of sequence. According to which the G matrix is selected. There are approximately6000 equivalent G matrixes generated by applying different linear process on the basic matrix[2]. Key Define XORing Generating (As input) Tapping Tapings Numbers Fig 1.5: LFSRIV. ENCODING AND ENCRYPTING The Number of G matrix has been created using permutation and linear expirations. Suchas addition of scalar multiple of one row to another, permutation of columns. Then using thisnumbers generated by the LFSR the respective matrix from the set of matrix has beenselected. Then that particular matrix is multiplied with that codeword only [2]. Information Signal i (4 bits) Creating Choosing number G matrix Codeword of G according CW matrix LFSR Fig 1.6: Generating codeword using G matrix and LFSR Note: It must be noted here that for every 4 bit of information signal different G matrix ismultiplied every time according to LFSR. As the intruder is not known to the key and the actual sequence of the number generatedby the LFSR and the matrix to which the codeword is being multiplied he/she won’t be ableto reconstruct the signal even if the codeword is known to them. And the reverse process hasbeen employed to reconstruct the signal again at the receiver [8]. Coding rate R= k/n 349
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME Block k n k n-k Information Bits Parity Bits n digital codewords Fig 1.7: Generating CodewordV. DECODING AND DECRYPTING The signal is received at the receiver end. And the standard array has been created. Oncethe standard array has been created, now next step is to check if the received word is corrector not. Now divide the received signal in bits of 7. This is the codeword. Now first step is tomultiply the codeword with the parity check matrix if the resulted is zero that means no errorhas occurred otherwise the signal is in error. Compare this codeword with the standard arraythat the codeword falls in which column. The coset leader of that column is in error. Subtractthe coset leader of the error vector with every received word the resultant is the actualcodeword which has been send [2] [8]. Standard array has been created, now next step is to check if the received word is correct ornot. Now divide the received signal in bits of 7. This is the codeword. Now first step is tomultiply the codeword with the parity check matrix if the resulted is zero that means no errorhas occurred otherwise the signal is in error. Compare this codeword with the standard arraythat the codeword falls in which column. The coset leader of that column is in error. Subtractthe coset leader with every received word the resultant is the actual codeword which has beensend [5]. Note: It must be noted here that the weight which is being added should not be a codewordand the resultant should not be a repeating number i.e. all the numbers in the standard arrayshould be unique and non repeating number. Received word Comparing Multiplied code with with Standard array Parity H matrix Column multiplied multiplied with according HT (syndrome) to LFSR Codeword = Error vector – received Define error word vector according to syndrome Fig 1.8: Decoding diagram 350
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEMEVI. CONCLUSIONS Till now the work on channel coding consist of the single G matrix which is beenmultiplied with the complete data to produce the codewords but in this paper the number of Gmatrix has been produced by permutation and adding of one row with another. These Gmatrixes are randomly selected by LFSR register and multiplied with the block of data. Forevery new block different G matrix is selected and codeword is generated. As different Gmatrix is used every time it would be very hard for intruder to guess the right G matrix everytime and to interpret the right information.ACKNOWLEDGMENT I would like to thank my Parents to provide financial and emotional spot to me andstanding with me in every even and odds. I would like to thank almighty for showing me theright direction out of the blue, to help me stay calm in the oddest of the times and keepmoving even at times when there was no hope.REFERENCES[1] Sunaina Sharma, Combining Cryptography with Channel Coding, ISOR, vol. 2. July 2012.[2] Sunaina Sharma, Combining Cryptographic Operation for complexity reduction, Lovely Professional University Jalandhar, M.Tech, 2012.[3] Natasa Zivic And Christoph Ruland, Channel coding as cryptographic Enhancer, Wseas Transactions On Communications, Issue 2, Volume 7, February 2008.[4] G. Julius Caesar, John F. Kennedy, Security Engineering: A Guide to Building Dependable Distributed Systems.[5] Anonym, Coding In Communication System.[6] Gary C. Kessler, An Overview of Cryptography, Auerbach, September 1998. Books[7] Richard E. Blahut, Algebraic code for data transmission (Cambridge University Press, 2003).[8] Ranjan Bose, Information theory, Coding and Cryptography (Tata McGraw Hill, 2008). Websites[9] www.wekipedia.com 351

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