EFFECTIVE AES IMPLEMENTATION

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1 International Journal of Electronics and Communication Engineering & Technology (IJECET) Volume 7, Issue 1, Jan-Feb 2016, pp , Article ID: IJECET_07_01_001 Available online at Journal Impact Factor (2016): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication EFFECTIVE AES IMPLEMENTATION Ayushi Arya Dept ECE, Student Royal Institute of Management & Technology V.P.O Chidana, Gohana, Haryana, India Mohinder Malhotra Dept. ECE, H.O.D Royal Institute of Management & Technology V.P.O Chidana, Gohana, Haryana, India ABSTRACT The importance of cryptography knuckle down to the security in electronic data transmissions has gained an essential relevance during past years. Cryptography security mechanisms uses some algorithms to muddle the data into unreadable text with a key which can only be decoded/decrypted by one who has that associated key for the locked data. Cryptography techniques are of two types: Symmetric & Asymmetric. In this paper we ve used symmetric cryptography method-advance Encryption Standard algorithm with 200 bit block size as well as 200 bit key size. We ve used 5*5 matrix to implement same 128 bit conventional AES algorithm for 200 bit block size. After implementing the algorithm, the proposed work is compared with 128,192 & 256 bits AES techniques in context with Encryption and Decryption Time & Throughput at both Encryption and Decryption ends. Key words: Block Cipher, Plain Text, Cipher Text, AES, S-Box, Inverse S- Box Cite this Article: Ayushi Arya and Mohinder Malhotra. Effective AES Implementation. International Journal of Electronics and Communication Engineering & Technology, 7(1), 2016, pp INTRODUCTION From a global perspective there exists a growing awareness and need to prepare for and react to domestic and international security threats for wireless communication, which is directly attributed to continuously increasing demand for high quality security services and devices to protect user data transmitted over wireless channels. Cryptography has emerged as a solution which plays mandatory role in information 1 editor@iaeme.com

2 Ayushi Arya and Mohinder Malhotra security against various attacks. For this purpose two types of cryptography systems has been developed: Symmetric (secret key) & asymmetric (public key). Symmetric key uses homogenous key for sender and receiver to encrypt the plain text and to decrypt the cipher text, as in DES, 3DES, AES. Asymmetric key uses different key for encryption and decryption of data such as in RSA algorithm. Symmetric cryptography is more worthy for the encryption of a huge amount of data. AES is the most recent of the four current algorithms approved for federal in the United States by the National Institute of Standards and Technology (NIST) and widely accepted to replace old standard DES as the new symmetric encryption algorithm [2]. The AES algorithm is a symmetric block cipher that processes data blocks of 128 bits using a cipher key of length 128, 192, or 256 bits. Each data block consists of a 4 4 array of bytes called the state, on which the basic operations of the AES algorithm are performed [2].The proposed AES algorithm in this paper differs from conventional AES as it is using 200 bits block size and 200 bits key size both. Number of rounds is constant and equal to ten in this algorithm. The key expansion and substitution box generation are done in the same manner as in conventional AES block cipher. AES has 10 rounds for 128-bit keys, 12 rounds for 192-bit keys, and 14 rounds for 256-bit keys [3]. 2. PROPOSED ALGORITHM Initiating Phase: Encryption Algorithm At the beginning of encryption step, input of 200 bit is copied to the state array of 5*5 matrix. The data bytes are filled initially in columns then in rows. After that next step initial round key addition is performed, following to that ten rounds of encryption is performed. The first nine rounds are similar with minor difference in it s final round. As described below in fig1 each of the first nine rounds follows four transformations: Sub byte; Shift rows; Mix columns; Add round Key. In last and final step mix column transformation is not performed. Figure 1 Encryption Phase for AES algorithm 2 editor@iaeme.com

3 Effective AES Implementation 2.1 Sub bytes Transformation In this transformation step, each of the byte in the state matrix is replaced with another byte as per the S-box (Substitution Box) as its name implied. The S-box is generated initially by calculating the respective reciprocal of that byte in GF (2^8) and then affine transform is applied. The S-box used for this transformation is given in table 1 below: Table 1 S Box [3] 2.2. Shift Rows Transformation In this step, bytes in the first row of the State remains unchanged. The second, third, fourth and fifth rows of the state shift cyclically to the left by one byte, two bytes, three bytes and four bytes respectively, as illustrated below In Fig. 2 [1]. Figure 2 Shift Row Transformation 2.3 Mix Column Transformations As the name implies this operation mixes the bytes in each column by multiplication of the state with a fixed polynomial matrix [2]. It completely alters the scenario of the cipher even if all the bytes looks very similar to each other. The Inverse Polynomial Matrix is the reciprocal of the polynomial matrix does exist in order to reverse the mix column transformation. Here, both of the matrixes are drawn below in fig.3 and fig.4 respectively. 3 editor@iaeme.com

4 Ayushi Arya and Mohinder Malhotra Figure 3 Polynomial Matrix for mix column transformation [3] Figure 4 Inverse polynomial matrix for Mix Column Transformation 2.4. AddRoundKey Transformation In AddRound Key transformation, a round key is added to the State by using bit wise Exclusive-OR (XOR) operation. 3. DECRYPTION ALGORITHM Decryption is the process of decoding the data into plain text that has been encrypted into the secret form. The Decryption structure for proposed algorithm as shown below in figure.5 is obtained by simply inverting the encryption structure which is explained above. In accordance with the transformations steps in the encryption, Inv Sub Bytes, Inv Shift Rows, Inv Mix Columns, and Add RoundKey are the transformations used in the decryption as shown in Fig. below. The round keys are the same as those in encryption generated by Key Expansion, but are inverted before use (used in reverse order )[1]. Figure 5 Decryption Structure of Proposed Algorithm 4 editor@iaeme.com

5 Effective AES Implementation 3.1. Inv SubBytes Transformation Inv Sub Bytes is the inverse transformation of Sub Bytes, in which the inverse S-box is applied to individual bytes in the State. The inverse S-box is constructed by first applying the inverse of the affine transformation in (1), then computing the multiplicative inverse in GF(2^8). The inverse S-box used for this transformation is given in table 2 below: Table 2 Inverse S-Box 3.2. Inv Shift Rows Transformation Inv Shift Rows as its name implied is the inverse transformation of Shift Rows. In this step, the bytes in the first row of the State remains same; while second row is shifted cyclically by one byte, same as third row by two bytes fourth row by three bytes and fifth rows are shifted cyclically by four bytes to the right Direction [1] Inv Mix Columns Transformation Inv Mix Column is the inverse transformation step of Mix Columns. Function. Mix Column transformation is little bit complicated as compared to other steps as it involves severely the byte multiplication under GF (2^8). The whole state is to be multiplied with pre-defined matrix called Inverse Polynomial Matrix as illustrated in Figure 4. Key Expansion: Key expansion in AES is difficult task to perform, as it uses several transformations. The key is expanded in the same manner as in conventional AES algo. Following is the Pseudo code for the key expansion: Key Expansion (byte Key [5*Nk] word W [Nb*(Nr+1)]) { for (i = 0; i<nk; i++) W[i] = (Key [5*i], Key [5*i+1], Key [5*i+2], Key [5*i+3]), Key [5*i+4]); for (i = Nk; i<nb * (Nr + 1); i++) { temp = W [i - 1]; if (i % Nk == 0) temp = SubByte(RotByte(temp)) ^ Rcon[i / Nk]; 5 editor@iaeme.com

6 Ayushi Arya and Mohinder Malhotra W[i] = W [i - Nk] ^ temp; } 4. EXPERIMENT AND RESULT 4.1. Encryption and decryption time The encryption and decryption time is one of the very important parameter while observing performance of any kind cipher. Although encryption takes long time as compared to decryption. Several symmetric block ciphers (specifically ones like AES, DES, Blowfish, RC5) will take the same amount of time (within measurement error) for encryption and decryption, when operating on a single block (e.g., 128-bits for AES). It appears different when encrypting/decrypting multiple blocks. Fig 6.1 and Fig 6.2 below shows how much time the various AES standards will take in encryption process and in decryption process for large data size respectively Figure 6.1. Comparison of encryption time of algorithms for large data Figure 6.2 Comparison of decryption time of algorithms for large for large data From the above graphs, it can be observed that for large block of data AES-200 encryption time per bit is reduced up to 20% and decryption time per bit is increased up to 25% Throughput The throughput is defined as number of bits that can be encrypted or decrypted during one unit of time. As it was explained previously hat all AES variant has equal block 6 editor@iaeme.com

7 Effective AES Implementation size of 128 bits and the proposed algorithm has block size of 200 bits. Thus, in form of equation the throughput may be defined as: =128/ =200/ Where, is representation of throughput for conventional algorithms, is representation of throughput for proposed algorithm, denotes the time taken to encrypt the 128 bit block message, represents time taken to encrypt the 200 bit block message of conventional algorithm. In Fig 7.1 below, throughput for encryption side is drawn while the throughput at the decryption side is plotted in Fig 7.2. Fig 7.1: Comparison of throughput at Encryption side Figure 7.2 Comparison of Throughput at Decryption side From the above plots, it is observed that the throughput at encryption end of AES- 200 is 15% more than AES-128, 20% more than AES-192 and 30% more than AES The decryption process of AES-200 is slower than conventional AES. It can be seen from the graph that the proposed algorithm is 50% slower from AES-128, 40% from AES-192, and 25% from AES editor@iaeme.com

8 Ayushi Arya and Mohinder Malhotra 5. CONCLUSION The work explained in this paper represents a new AES model using large block size with 200 bits instead of conventional AES using 128 bit block size. The block used in this model comprises of 5 no. of rows as well as columns i.e. 5*5 matrix. Increased matrix size doesn t cause any change to the basic functional operations. Thus all the steps are same as used in conventional AES algorithm excluding the Mix Column Step transformation only. In mix column transformation function in finite filed diffusion occurs n form of multiplication of matrix. As we ve used large block size, thus it requires a new 5* 5 matrix to enable the matrix multiplication [3]. In this paper initially we have compared encryption and decryption time for various AES standards and then compared the same with our proposed algorithm s time. Generally encryption time is longer than decryption time because encryption takes place sequentially while decryption takes place in parallel manner. We ve concluded that for large block of data AES-200 encryption time per bit is reduced up to 20% and decryption time per bit is increased up to 25% than conventional AES. Later on, we compared the throughput of various AES standards and concluded that that the throughput at encryption end of AES-200 is 15% more than AES-128, & 20% more than AES-192 and 30% more than AES-256. The decryption process of AES-200 is slower than conventional AES. On the basis of Security the proposed model is tested by performing: Strict Avalanche Criterion and Bit Independence Criterion. SAC reveals the probability of the bit change while the BIC reveals the correlation that output bit possess. Both criteria analyzed that the proposed algorithm falls within the desired level of security. Hence, it can be said that the proposed model is secure and can be highly preferred for huge data communication. REFERENCES [1] Journals: [1] Xinmiao Zhang and Keshab K. Parhi, Implementation approaches for the advanced encryption standard algorithm, IEEE Transactions X/ IEEE. [2] Chih-Pin Su, Tsung-Fu Lin, Chih-Tsun Huang, and Cheng-Wen Wu, National Tsing Hua University, A high throughput low cost AES processor IEEE Communications Magazine / IEEE. [3] Fahmy A., Shaarawy M., El-Hadad K., Salama G. and Hassanain K., A Proposal for A Key-Dependent AES, SETIT, Tunisia, [4] Fakariah Hani Mohd Ali, Ramlan Mahmod, Mohammad Rushdan and Ismail Abdullah, A Faster Version of Rijndael Cryptographic Algorithm Using Cyclic Shift and Bit Wise Operations International Journal of Cryptology Research 1(2): (2009) [5] Advanced Encryption Standard (AES), Federal Information Processing Standards Publication 197, November 26, [6] Seyed Hossein Kamali, Reza Shakerian, Maysam Hedayati, Mohsen Rahmani, A New Modified Version of Advance Encryption Standard (AES) Based Algorithm for Image Encryption (2010). [7] Chong Hee Kim, Improved Differential Fault Analysis on AES Key Schedule IEEE Transaction on Information Forensics and Security, Vol. 7, No. 1, Feb [8] Mohan H.S and A Raji Reddy, Performance analysis of AES and MARS encryption algorithm IJCSI International Journal of Computer Science Issues, Vol. 8, Issue 4, No 1, July editor@iaeme.com

9 Effective AES Implementation [9] [9] Amish Kumar, Mrs. Namita Tiwari, Efficient implementation and avalanche effect of AES International Journal of Security, Privacy and Trust Management (IJSPTM), Vol. 1, No 3/4, August [10] A Review of Cryptography Techniques and Implementation of AES for Images, International Journal of Computer Science and Electronics Engineering (IJCSEE) Volume 1, Issue 4 (2013) ISSN X; EISSN [11] Diaa Salama Abdul. Elminaam, Hatem M. Abdul Kader and Mohie M. Hadhoud, Performance Evaluation of Symmetric Encryption Algorithms on Power Consumption for Wireless Devices International Journal of Computer Theory and Engineering, Vol. 1, No. 4, October, [12] B.Sujitha, Dr.B.Karthikeyan, Study, Simulation and Analysis of Advanced Encryption Standard (AES) Algorithm IJIRSET Volume 3, Special Issue 1, February 2014 [13] Atul Kahate, Cryptography [14] Stallings W., Cryptography and Network Security, Third Edition, Pearson Education, [15] Roshni Padate and Aamna Patel. Image Encryption and Decryption Using AES Algorithm. International Journal of Electronics and Communication Engineering & Technology, 6(1), 2015, pp [16] Dhanya Pushkaran and Neethu Bhaskar. AES Encryption Engine for Many Core Processor Arrays for Enhanced Security. International Journal of Electronics and Communication Engineering & Technology, 5(12), 2014, pp AUTHOR PROFILE AYUSHI ARYA Received her B. Tech Degree in Bio Medical Engineering from CITM, Faridabad, (Maharishi Dayanand University) in 2012 and she is M. Tech student now in Royal Institute of Management and Technology affiliated to DCRUST, Haryana, respectively. She had worked as an Application and service engineer for Medical Devices Industries. Her research interests include medical with electronics, Telecommunication, cryptography, Scope of electronics and communication in field of medical devices. MOHINDER MALHOTRA Head of Department, (Dept. of Electronics and Communication Engineering), Royal Institute of Management and Technology, Affiliated to DCRUST, Haryana. 9 editor@iaeme.com