Secure message transmission over wireless communication

Transcription

1 Research Journal of Physical and Applied Sciences Vol. 2(3), pp , June Wudpecker Journals Secure message transmission over wireless communication Md. Mizanur Rahman and Farhana Enam Dept. of ICE, Rajshahi University, Rajshahi, Bangladesh. *Corresponding author Accepted 23 May 2013 The primary aim of this project paper is to provide an overview of wireless communication fundamentals. A long way in a remarkably short time has been achieved in the history of wireless. Evolution of wireless access technologies is about to reach its fifth generation (5G). Looking past, wireless access technologies have followed different evolutionary paths aimed at unified target: performance and efficiency in high mobile environment. The first generation (1G) has fulfilled the basic mobile voice, while the second generation (2G) has introduced capacity and coverage. This is followed by the third generation (3G), which has quest for data at higher speeds to open the gates for truly mobile broadband experience, which will be further realized by the fourth generation (4G). The Fourth generation (4G) will provide access to wide range of telecommunication services, including advanced mobile services, supported by mobile and fixed networks, which are increasingly packet based, along with a support for low to high mobility applications and wide range of data rates, in accordance with service demands in multiuser environment. This paper provides a high level overview of the evolution of Mobile Wireless Communication Networks from 1G to 4G.In this paper a security algorithm is implemented. This shows the way of securely text message transmission over wireless communication. For security purpose a message is first encrypted using Playfair encryption algorithm and then sent through wireless communication. At the receiver end the received message is decrypted and the original message retrieved. Matlab 2009b was used as a simulation tool. Key Word: Cyclic Redundancy Check (CRC), AWGN, playfair encryption algorithm, wireless communication, 1G, 2G, 3G and 4G. INTRODUCTION Wireless communication systems are not new, but they have been continually evolving for many years, especially in the area of mobile communications. First generation analogue mobile systems began to emerge in the late 1970s and in the early 1980s (Bondyopadhyay, 1998). In the early 1990s migration to the second generation system started momentum and within two years all of the major European operators had started to operate commercial GSM networks. During the mid-1990s, ground work preparations that would eventually lead to the development of third generation systems started and the first commercial network was launched in the early More recently, mobile WiMAX has begun to emerge and there was a growing interest in its potential as an alternative to the other mobile networks and their planned migration paths. When third generation systems began to emerge this coincided with the appearance of the first Wi- Fi systems, which had the key difference to be designed primarily for indoor operation in license-exempt spectrum rather than outdoor operation in licensed spectrum (Gallager, 2001). However, it was not until the IEEE802.11a and b standards were ratified in the late 1990s that Wi-Fi began to be widely adopted. Since then these systems have continued to evolve and grow in popularity (Toh, 2002). Comparing the evolution paths of the various mobile systems it can be found that the trend was migration from analogue to digital, and from kbit/s operating speeds for first generation systems through to the low Mbit/s rates for third generation systems, with migration to 100s of Mbit/s being on their fourth generation evolution paths. For Wi-Fi, the trend was migration from low Mbit/s rates to low 100s of Mbit/s. However, the advances that have been made in both mobile and Wi-Fi systems largely reflected technological advances that enabled increasingly advanced fundamental wireless communication concepts to become practically viable

2 031 Res. J. Phy. and Appl. Sci. (Yue, 2003). Therefore, these advances are, in principle, generally applicable for use in any type of wireless system. For this reason, the aim of this paper is to provide an overview of the wireless fundamentals. A high-level consideration of a representative set of current mobile and Wi-Fi systems will be then used to argue that their performance differences are largely a reflection of different regulatory constraints and the fundamental limits set by thermal noise, advanced modulation schemes and the channel transport technique used (Enam et al., 2013). This paper is organized in the following ways: The first section is an introduction. In this section, the evolution of Wireless communication and its generations were discussed. Also the detail of 1G, 2G, 3G and 4G were described. The second section describes a simulation model to be implemented. Model parameters and assumptions made in simulation study were clearly explained. In this paper Payfair encryption algorithm was used. The Third section highlights the various simulation runs associated with the different parameters setting used to study the performance of the communication system under consideration. The fourth section describes the conclusions as well as some recommendations for future research work in the field of digital communication. SIMULATION MODEL This section discusses the steps made to develop the simulation model of the Wireless communication. The implemented simulation model was capable to evaluate the performance of encrypted message transmission under different modulation techniques and communication channels. This task involved modeling of the propagation environment. Simulation was chosen to be the primary tool for the study and the employed Matlab r2009a environment was used to develop the simulator. At first, the parameters that were used to develop the wireless communication simulator were defined. The parameters used were listed in Table 1. The main part of the implemented transmitter and receiver sections of the wireless communication was shown in the block diagram of Figure 1. In its setup, there were implemented the mandatory features of the specification, while leaving the implementation of optional features for future work. The channel coding part was composed of Cyclic Redundancy Check (CRC) coding with code rate 2/3. The complementary operations are applied in the reverse order at channel decoding in the receiver end. Through the rest of the paper, all the individual blocks of the setup were discussed with corresponding implementation techniques. INPUT SOURCE MESSAGE This indicates the place from where the original message or, data is to be conveyed. A data source is a notepad object. DATA ENCRYPTION Input message were encrypted using Playfair encryption algorithm. The best known multiple letter encryption cipher us the playfair, which treats diagram in the plaintext as single units and translates these units into ciphertext diagrams. The playfair algorithm is based on the use of a 5*5 matrix of letters constructed using a keyword. Here is an example; solved by Lord Peter Wimsey in Dorothy Sayers Have His Carcase was presented in table 2. In this case, the keyword is monarchy. The matrix is constructed by filling in the letters of the keyword (minus duplicates) from left to right and from top to bottom, and then filling in the remainder of the matrix with the remaining letters in alphabetic order. The letters I and J count as one letter. Plaintext is encrypted two letters at a time, according to the following rules: 1. Repeating plaintext letters that are in the same pair are separated with a filter letter, such as x, so that ballon would be treated as ba lx lo on. 2. Two plaintext letters that fall in the same row of the matrix are each replaced by the letter on the right, with the first element of the row circularly following the last. For example, ar is encrypted as RM. 3. Two plaintext letters that fall in the same column are each replaced by the letter beneath, with the top element of the column circularly following the fast. For example, mu is encrypted as CM. 4. Otherwise, each plaintext letter in a pair is replaced by the letter that lies in its own row and the column occupied by the other plaintext letter. Thus, hs becomes BP and ea becomes IM (or JM, as the encipherer wishes). The playfair cipher is a great advance over simple monoalphabetic ciphers. For the one thing, whereas there are only 26 letters, there are 26*26=676 diagrams, so that identification of individual diagrams is more difficult. Furthermore, the relative frequencies of individual letters exhibit a much greater range than that of diagrams, making frequency analysis much more difficult. For these reasons, the playfair cipher was for a long time considered unbreakable. It was used as the standard field system by the British Army in World War I and still enjoyed considerable use by the U.S. Army and other Allied forces during World War II. Despite this level of

3 Rahman and Enam 032 Table 1. Simulation parameter. Parameters Values Transmitted source Message Coding CRC Encryption Algorithm Play Fair Key Student CRC rate 2/3 SNR 0-25 Modulation Noise Channels AWGN Input Text Message Encryption Using Playfair Bit CRC Coding Modulation AWGN channel Retrieve Message Decryption Using Playfair Bit CRC Decoding Demodulati on Figure 1: Block diagram of wireless communication. Table 2. Matrix of playfair algorithm. S T U D E N A B C F G H I/J K L M O P Q R V W X Y Z confidence in its security, the playfair cipher is relatively easy to break because it still leaves much of the structure of the plaintext language intact. A few hundred letters of cipher text are generally sufficient. CYCLIC REDUNDANCY CHECK (CRC) The output of encryption algorithm is converted into bit which is encoded using CRC coding with code rate of 2/3 (Halim et al., 2012). QUADRATURE PHASE SHIFT KEYING () Quadrature phase shift keying () has twice the bandwidth efficiency of BPSK, since 2 bits are transmitted in a single modulation symbol. The phase of the carrier takes on 1 of 4 equally spaced values, such as 0, π/2, π, and π3/2, where each value of phase

4 033 Res. J. Phy. and Appl. Sci. Q E s I Figure 2. constellation. Figure 3. AWGN channel model. corresponds to a unique pair of message bits (Islam and Islam, 2012). The signal for this set of symbol states may be defined as: S ( t) 2E T s s cos 2f ct i=1,2,3,4, (1) 2 i 1 0 t T s Where T s is the symbol duration and is equal to two bit period. From the constellation diagram of a signal, it can be seen that the distance between adjacent points in the constellation is 2E s Since each symbol corresponds to two bits, then E s = 2E b, thus the distance between two neighboring points in the constellation is equal to 2 E b. The average probability of bit error in the additive white Gaussian noise (AWGN) channel is obtained as: P 2E b e, Q N..(2) Islam et al., 2012). 0 ADDITIVE WHITE GAUSSIAN NOISE (AWGN) A reasonable assumption for a fixed, LOS wireless channel is the additive white Gaussian noise (AWGN) channel (Awon et al., 2012), which is flat and not frequency-selective as in the case of the fading channel. Particularly fast, deep frequency-selective fading as often observed in mobile communications is not considered in this paper, since the transmitter and receiver are both fixed. This type of channel delays the signal and corrupts it with AWGN. The AWGN is assumed to have a constant PSD over the channel bandwidth, and a Gaussian amplitude probability density function. This Gaussian noise is added to the transmitted signal prior to the reception at the receiver as shown in Figure 3 (Chen, 2004), therefore the transmitted signal, white Gaussian noise and received signal are expressed by the following equation with s(t), n(t) and r(t) representing those signals respectively: r(t)=s(t)+n(t) (3) Where n(t) is a sample function of the AWGN process with probability density function (pdf) and power spectral density (Islam et al., 2012). The in-phase and quadrature components of the AWGN are assumed to be statistically independent, stationary Gaussian noise process with zero mean and two-sided PSD of NO/2 Watts/Hz. As zero-mean Gaussian noise is completely characterized by its variance, this model is particularly simple to use in the detection of signals and in the design of optimum receivers (Chen, 2004). So, it was developed using AWGN function which is also available in Matlab. SIMULATION RESULTS In this Section the simulation results were shown and discussed. In the following sections, firstly the structure of the implemented simulator is presented before simulation results both in terms of validation of implementation and values for various parameters that characterize the performance of the security. Matlab 9b has been used to

5 Rahman and Enam 034 Figure 4. Plaintext message. Figure 7. Replain text decrypted by shared secret key for SNR=4. Figure 5. Encrypted plaintext with student key. Figure 8. Replain text decrypted by shared secret key for SNR=7. Figure 6. Replain text decrypted by shared secret key for SNR=0. Figure 9. Replaintext decrypted by shared secret key for SNR=10. write a computer program designed for simulation study. The developed program provides different replain text by decrypting different cipher text for different values of signal to noise ratio. The plain text message was shown in figure 4 which was encrypted using a shared secret key Student. The secret key must be shared before transmitting the messages. The cipher text produced by the shared secret key was shown in figure 5. Then encrypted message were transmitted in a wireless communication system. To modulate the encrypted message modulation 4 was used. The channel used in this simulation was AWGN channel. In receiver end for various values of signal to noise ratio various ciphertext were found. These cipher texts were then decrypted using the same key of student. For modulation and 0, 4, 7, 10 values of signal to noise ratio the replaintext messages were shown in figure 6, 7, 8, 9 respectively. CONCLUSION An encryption process named playfair, was used to produce a cipher text which was sent to the intended destination. First, the original plain text message was encrypted with the key student and then was sent to the destination through the communication channels. In the receiving end, the receiver first decrypted the cipher text by the shared secret key student. Finally, the receiver decrypted the intended message. In this way a message was securely transmitted to the destination. REFERENCES Bondyopadhyay PK (1998). Sir J. C. Bose diode detector received Marconi s first transatlantic wireless signal of December 1901 (the Italian navy coherer scandal revisited), Proceedings of the IEEE, 86(1): Gallager RG (2001). Claude E. Shannon: A retrospective on his life, work, and impact, IEEE Transactions on Information Theory, 47(7): Toh CK (2002). Ad Hoc Mobile Wireless Networks: Protocols and Systems, Prentice Hall, New, USA. Yue C (2003). Soft Handover Issues in Radio Resource Management for 3G WCDMA Networks, Queen Mary, University of London, [Online] Available: Chen J (2004). CARRIER RECOVERY IN BURST- MODE 16-QAM, June. Islam MA, Islam AZMT (2012). Performance of WiMAX Physica Layer with Variations in Channel Coding and Digital Modulation Under Realistic Channel Conditions, Int. J. Info. Sciences and Techniques, 2(4): Halim MA, Islam MA, Islam T, Homyara H and Zaman M (2012). Performance of Cyclic Redundancy Check(CRC) encoded Fixed WiMAX Wireless Communication System under Implementation of M-ary Quadrature Amplitude Modulation(QAM) Technique, Int. J. Eng. Res. and

6 035 Res. J. Phy. and Appl. Sci. Applications, 2(5): Islam MA, Homyara H, Zaman M, Rahman MM (2012). Analyzing the effect of FEC coding on BER performance of M-Ary modulation scheme based fixed WiMax wireless communication system with application of digital audio transmission under the influence of realistic communication channel, Int. Res. J. Eng. Sci. Technol. and Innovation, 1(7): , October. Available online WiMAX communication system with transmission of digital colour image, International Research Journal of Engineering Sci., Technol. and Innovation, 1(9): Available online Enam F, Islam MA, Rahman MM, Rahman MM (2013). Analyze the effect of least mean square (LMS) equalization technique over reed-solomon encoded orthogonal frequency division multiplexing (OFDM) based wireless communication system, Int. Re s. J. Comp. Sci. and Info. Syst., 2(1): 1-7. Islam MA, Homyara H, Zaman M, Rahman MM (2012). Analysis the effect of Reed-Solomon (RS) coding over