DATA SECURITY USING ADVANCED ENCRYPTION STANDARD (AES) IN RECONFIGURABLE HARDWARE FOR SDR BASED WIRELESS SYSTEMS

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1 INTERNATIONAL JOURNAL OF COMPUTER ENGINEERING & TECHNOLOGY (IJCET) International Journal of Computer Engineering and Technology (IJCET), ISSN (Print), ISSN (Print) ISSN (Online) Volume 6, Issue 1, January (2015), pp IAEME: Journal Impact Factor (2015): (Calculated by GISI) IJCET I A E M E DATA SECURITY USING ADVANCED ENCRYPTION STANDARD (AES) IN RECONFIGURABLE HARDWARE FOR SDR BASED WIRELESS SYSTEMS Sharanagouda N Patil 1, R.M.Vani 2, P.V.Hunagund 3 1 Dept. of Applied Electronics, Gulbarga University, India 2 Dept. of USIC, Gulbarga University, India 3 Dept. of Applied Electronics, Gulbarga University, India ABSTRACT A software defined radio (SDR) is a radio transmitter/receiver that uses reconfigurable hardware and software for encoding/decoding, modulation/demodulation, and encrypting/decrypting. This allows much more power and flexibility when designing any radio system. The AES algorithm is a block cipher that can encrypt and decrypt digital information. The AES algorithm is capable of using cryptographic keys of 128, 192, and 256 bits. The Rijndael cipher has been selected as the official Advanced Encryption Standard (AES) as it is well suited for reconfigurable hardware. The Advanced Encryption Standard can be programmed in software or built with hardware. However Field Programmable Gate Arrays (FPGAs) offer a more customized solution. This paper talks of AES 128 bit block and 128 bit cipher key and is implemented using VHDL as the hardware description language. Here a new FPGA-based implementation scheme of the AES-128 (Advanced Encryption Standard, with 128-bit key) encryption algorithm is proposed for software defined radio applications. This system aims at reduced hardware structure and high throughput. Xilinx - Project Navigator, ISE 9.1i suite is used for simulation and synthesis. Keywords: AES, Cipher text, FPGA, SDR, VHDL I. INTRODUCTION With ever increasing demand for mobile communication and emergence of many new systems and standards like 3G and 4G and even many researches are going to develop new wireless standards. It has become imperative to implement and design a flexible architecture of radio system 95

2 which accommodates the feature of interoperability and multi functionality and operation of the devices in heterogeneous, variable operating conditions. Different standards of Mobile communication use different type of hardware circuitry. The existing mobile communication standards are primarily designed along national standards and not using a common global standard. So efforts are going on to develop systems which can support multiple mobile communication standards using same hardware but changing the software / firmware or a combination of both. This gave rise to Software Defined Radio which is a new technology being developed. A SDR refers to any reconfigurable or reprogrammable radio system that can show different functionality with the same hardware. A Software Defined Radio can simply be defined as Radio in which some or all of the physical layer functions are software defined. The encryption/decryption functions of the system are defined using higher abstraction levels of HDLs. Today software defined technology offers advantages such as improvements or enhancements without altering the radio hardware, terminals that can cope with the unpredictable dynamic characteristics of highly variable wireless links, efficient use of radio spectrum and power, and many others. The users can use relatively generic reprogrammable hardware and customize it to their needs by choosing only the software implementation that fits their specific application [1,2]. The difference between a digital radio and an SDR is that a digital radio is not reconfigurable. Although a Digital radio has software running on it; the functionality of the components cannot be changed on air. New technology insertion is not available. II. BACKGROUND OF SOFTWARE DEFINED RADIO One of the first software radios was the US Air Force s Integrated Communications Navigation and Identification Avionics (ICNIA) system, which was developed in the late 1970 s. The system used a DSP based modem that is reprogrammable for different platforms. ICNIA s technology has been the foundation for many other military radios. SDR is a radio communication technology which is capable of being re-programmed or reconfigured. SPEAKeasy is a joint Department of Defense and industry program initiated to develop a software programmable radio operating in the range from 2 MHz to 2 GHz, employing waveforms selected from memory or downloaded from disk or reprogrammed over the air [3]. The improvements in DSP and ADC technologies facilitated the shift to software defined radios. Modern functions can be implemented in software with today s high DSPs and General Purpose Processors (GPPs). The low power requirements of the processors enable them to be used in hand terminals. The increased dynamic operating ranges and higher conversion rates of modern ADCs enables digital processing at higher bands. The improvements in middleware technologies permit software functionality to be independent of the underlying hardware [4].The General structure of SDR are given below Figure 1. Figure 1: General Block Diagram of a SDR 96

3 III. BACKGROUND OF AES The AES algorithm is a symmetric block cipher that can encrypt and decrypt information. Encryption converts data to an unintelligible form called cipher-text [5]. Decryption of the ciphertext converts the data back into its original form, which is called plain-text. 3.1 AES encryption The AES algorithm operates on a 128-bit block of data and executed Nr - 1 loop times. A loop is called a round and the number of iterations of a loop, Nr, can be 10, 12 or 14 depending on the key length. The key length is 128, 192 or 256 bits in length respectively. The first and last rounds differ from other rounds in that there is an additional AddRoundKey transformation at the beginning of the first round and no MixCoulmns transformation is performed in the last round. In this paper, we use the key length of 128 bits (AES-128) as a model for general explanation SubBytes Transformation The SubBytes transformation is a non-linear byte substitution, operating on each of the state bytes independently. The SubBytes transformation is done using a once-pre-calculated substitution table called S-box. That S-box table contains 256 numbers (from 0 to 255) and their corresponding resulting values. More details of the method of calculating the S-box table refers to [4]. In this design, we use a look-up table as shown in Table 1. This approach avoids complexity of hardware implementation and has the significant advantage of performing the S-box computation in a single clock cycle, thus reducing the latency ShiftRows Transformation In ShiftRows transformation, the rows of the state are cyclically left shifted over different offsets. Row 0 is not shifted, row 1 is shifted one byte to the left, row 2 is shifted two bytes to the left and row 3 is shifted three bytes to the left. 97

4 3.1.3 MixColumns Transformation In MixColumns transformation, the columns of the state are considered as polynomials over GF (2 8 ) and multiplied by modulo x with a fixed polynomialc(x), given by: c(x)={03}x 3 + {01}x 2 + {01}x + {02} AddRoundKey Transformation In the AddRoundKey transformation, a Round Key is added to the State - resulted from the operation of the MixColumns transformation - by a simple bitwise XOR operation. The RoundKey of each round is derived from the main key using the Key Expansion algorithm [1]. The encryption/decryption algorithm needs eleven 128-bit RoundKey, which are denoted RoundKey[0] RoundKey[10] (the first RoundKey [0] is the main key). 3.2 AES decryption Decryption is a reverse of encryption which inverse round transformations to computes out the original plaintext of an encrypted cipher-text in reverse order. The round transformation of decryption uses the functions AddRoundKey, InvMixColumns, InvShiftRows, and InvSubBytes successively AddRoundKey AddRoundKey is its own inverse function because the XOR function is its own inverse. The round keys have to be selected in reverse order. The description of the other transformations will be given as follows InvShiftRows Transformation InvShiftRows exactly functions the same as ShiftRows, only in the opposite direction. The first row is not shifted, while the second, third and fourth rows are shifted right by one, two and three bytes respectively InvSubBytes transformation The InvSubBytes transformation is done using a once-pre- calculated substitution table called InvSbox. That InvS-box table contains 256 numbers (from 0 to 255) and their corresponding values. InvS-box is presented in Table II. 98

5 3.2.4 InvMixColumns Transformation In the InvMixColumns transformation, the polynomials of degree less than 4 over GF(2 8 ), which coefficients are the elements in the columns of the state, are multiplied modulo (x 4 + 1) by a fixed polynomial d(x) = {0B}x 3 + {0D}x 2 + {09}x + {0E}, where {0B}, {0D}; {09}, {0E} denote hexadecimal values.the implementation of the AES is carried out using VHDL. IV.AES IMPLEMENTATION USING VHDL The Figure 2 shows the AES core architecture implemented for Software Defined radio framework. Figure 2: Architecture of AES core V. RESULTS The following results were obtained for individual steps on AES encryption method. The design has been coded by VHDL. All the results are simulated using Xilinx ISE simulator. The results of simulating the encryption algorithm from the ISE simulator are shown in Figure.3 a) b) 99

6 c) d) Figure 3: Simulation waveforms on Xilinx ISE simulator for different steps of encryption. a) S Box transformation b) Shift row c) Top byte substitution d) Shift row transformation: VI. CONCLUSIONS The Advanced Encryption Standard algorithm is a symmetric block cipher that can process data blocks of 128 bits through the use of cipher keys with lengths of 128, 192, and 256 bits. An efficient FPGA implementation of 128 bit block and 128 bit key AES algorithm has been presented in this paper. This can be used for secure data transmission in various wireless communication standards without changing the hardware. The proposed design is implemented based on the iterative approach for cryptographic algorithms. There is a lot of potential applications of SDRs and in future we will see that a wide array of radio applications like Blue- tooth, WLAN, GPRS, Radar, WCDMA etc. being implemented by using SDR technology [6]. VII. REFERENCES 1. J. Mitola III. Software Radio Architecture. Wiley-Interscience, B. Bing and N. Jayant. A Cell phone for all Standards.IEEE Spectrum, May SPEAKeasy web page, 4. M. W. Oliphant. Radio Interfaces Make the Difference in 3G Cellular Systems. IEEE Spectrum Magazine, Vol. 37,No. 10, October FIPS 197, Advanced Encryption Standard (AES), November 26, Online reference, Available: 7. Anubhav Gupta and Harish Bansal, Design of Area Optimized AES Encryption Core Using Pipelining Technology International journal of Electronics and Communication Engineering &Technology (IJECET), Volume 4, Issue 2, 2012, pp , ISSN Print: , ISSN Online: