Modified Advanced Encryption Standard For Text And Images

Transcription

1 Computer Science Journal Volume 1, Issue 3, December 211 Modified Advanced Encryption Standard For Text And Images Sumira Hameed 1, Faisal Riaz 2,Riaz Moghal 3, Gulraiz Akhtar 4, Anil Ahmed 5, Abdul Ghafoor Dar 6 1,4,5 Computer Science & IT Dept. Mirpur University of Sciences & Technology 2,6 IQRA University Islamabad Campus, 3 Computer System Engineering Dept, Mirpur University of Science & Technology sa_scud@yahoo.com,fazi_ajku@yahoo.com, riazdat@yahoo.com gulraiz@yahoo.com,anilahmed8@gmail,agdar@yahoo.com Abstract: Security of multimedia data is an imperative issue because of fast evolution of digital data exchanges over unsecured network. Multimedia data security is achieved by methods of cryptography, which deals with encryption of data. Standard symmetric encryption algorithms provide better security for the multimedia data. But applying symmetric key encryption algorithm on more complex multimedia data (mostly images); we might face the problem of computational overhead. To overcome that problem, we analyze the Advanced Encryption Standard (AES) and modify it, to reduce the calculation of algorithm and for improving the encryption performance. In modified AES algorithm instead of using Mixcolumn we use the permutation step, taking from Data Encryption Standard (DES) algorithm. Theoretical analysis and experimental results prove that this technique provides high speed as well as fewer overheads on data. Modified-AES algorithm is a fast lightweight encryption algorithm for security of multimedia data. All above advantages make algorithm highly suitable for the images and plaintext transfer as well, than the AES algorithm. Keywords: Advanced Encryption standard (AES), cryptography, DES, encryption, multimedia data, and symmetric key algorithms. Received: August 211, Published: December 211 *Corresponding Author: Faisal Riaz, fazi_ajku@yahoo.com 12

2 Sumira et al: Modified Advanced Encryption Standard For Text And Images 1. Introduction It is important aspect to protect the confidential multimedia data from unauthorized access. Multimedia content can be text, audio, still images, animation and video. Such contents are protected by multimedia security method. Commonly, this is attained by techniques that are profoundly based on cryptography. These schemes facilitate communication security, piracy and shelter. [2] Large size of images causes certain challenges for encryption. Normally a typical image has a very large size. Using traditional encryption algorithm will make encryption difficult for large volume of multimedia data. For the encryption of any multimedia data we need such algorithms that require less computation because of large size of data. [1, 2, 3] Symmetric-key algorithms are fewer computationally serious than any Asymmetric key algorithms. Typically, symmetric key algorithms are thousands times sooner than those of the asymmetric algorithms. [6] So the better suitable method to encrypt the multimedia data is, to encrypt it with symmetric key encryption algorithms. One of the methods to protect any multimedia data is to encrypt that data with DES (Data Encryption Standard). DES, the encryption algorithm is very complicated and it involves very large computations. DES implementation software is not so fast to process the vast amounts of multimedia generated data. [1] As a consequence of hardware implementation AES is very fast symmetric block algorithm. This method is known as naïve approach. Applying the naïve approach on enormous amount of data takes large computation and makes the encryption speed very slow due to variety of restrictions. [2, 3] In particular, we achieve fortification using symmetric key encryption techniques (such as AES, DES) by applying on multimedia contents as sequence of binary. But unluckily when we apply these techniques on more complex multimedia (mostly images) or when the size of text data is very large, it produces significant computational overhead. [1, 2, 3] Our research is concerned with optimizing the existing standards of cryptography (AES) for the images and text data encryption. It is also slanting towards exploiting the huge amount of data, in order to attain preferred speed. This edited AES is referred to as Modified-AES algorithm. The modification is done by totaling the Initial Permutation step, takes from DES (Data Encryption Standard), in order to enlarge the encryption performance. This modification indubitably increases the efficiency of encryption and makes the algorithm speedier than the existing one. The paper is prearranged as follows. Brief introduction to Advanced Encryption Standard is detailed in Section 2. In section 3, Proposed Technique is elucidated. Experimental results are conversed in section 4. The paper is concluded in section ADVANCED ENCRYPTION STANDARD (AES) Joan Daemen and Vincent Rijmen urbanized a block cipher called Rijndael. In AES the span of each block and the key can be autonomously specified to be 128, 192, or 256 bits. In this paper we will only stress on block length and key length of 128 bits of AES. 121

3 Computer Science Journal Volume 1, Issue 3, December 211 The AES arrangement exploits data of 128 bits and same three key size alternatives. [7] This 128 bit data can be divided into four operation blocks, which are represented as a square matrix of bytes. These operation blocks are copied into a state array. The state array is organized as a 4 4 matrix. The data is conceded through Nr rounds (Nr = 1, 12, 14) for encryption. [1, 7] These rounds are performed by the following transformations: Bytesub transformation: In this process 8-bit byte block is replaced with another 8- bit byte block, for subsituion purpose we use S-box..[7] Shiftrows transformation:in this process we leave the first row of data, perform once shift left on 2 nd row, two times shift left on 3 rd row and three times shift left on 4 th row.it is a simple Permutation. [7] Mixcolumns transformation: Is a substitution; the bytes in the columns are linearly combined. The matrix multiplication is performed over the same GF (28) as used in the design of the S-box. Addroundkey transformation:when working state and expanded key are XOR with each other, process is called Addround Key. [5,7] All four layers expressed above (including key scheduling) have analogous converse methods. [8] Procedure of encryption follows more than a few ladders. An initial addroundkey is applied. After this a round function is applied to the block. Each block consists of bytesub, shiftrows, mixcolumns and addroundkey transformation. These blocks are repeated Nr times, depending upon the length of the key applied. [7] Same sequence of transformations is applied on decryption structure as which is applied in encryption structure. The transformations i.e. Inv-Bytesub, InvShiftrows, Inv- Mixcolumns, and Addroundkey permit the type of key schedules to be matched for encryption and decryption. [1, 7] Here it must be noted that the MixColumn reverse operation requires matrix elements. These matrix elements are quite complicated as compared to {1}, {2} or {3} of the forward one. [8] 3. PROPOSED TECHNIQUE To overcome the problem of high calculation and computational overhead, we analyze the Advanced Encryption Standard (AES) and modify it, to reduce the calculation of algorithm and for improving the encryption performance. So we develop and implement a modified AES based Algorithm for all kind of data. The basic aim to modify AES is to provide less computation and better security for data. The modify AES algorithm adjusts to provide better encryption speed. In Modified-AES the block length and the key length are specified according to AES specification: three key length alternatives 128, 192, or 256 bits and block length of 128 bits. We assume a key length of 128 bits, which is most commonly implemented. In Modified-AES encryption and decryption process resembles to that of AES, in account of number of rounds, data and key size. The round function consists of four stages. To overcome the problem of high calculation we skip the Mixcolumn step and add the permutation. Mixcolumn gives better security but it takes large calculation that makes the encryption algorithm slow [8]. The other three junctures remain unbothered as it is in 122

4 Sumira et al: Modified Advanced Encryption Standard For Text And Images the AES. A single 128-bit block is the input to the encryption and decryption algorithms. This block is a 4 4 square matrix consisting of bytes. This block is copied into the state array. The state array is modified at each stage of encryption or decryption. Similarly the 128-bit key is also depicted into a square matrix. The 128-bit key is expressed into an array of key schedule words: each word is of four bytes. The totals key schedule words for ten rounds are 44 words; each round key is similar to one state. The block diagram of the Modified-AES algorithm with 128 bits data is shown below. Fig.1 Modified-AES algorithm: Encryption & Decryption Structure 123

5 Computer Science Journal Volume 1, Issue 3, December 211 The algorithm is divided into four operational blocks where we observe the data at either bytes or bit levels and the algorithm is designed to treat any combination of data and is flexible for key size of 128 bits. These four operational blocks represent one round of Modified-AES. [7, 8] 3.1 Rounds of Modified-AES Algorithm There are 1 rounds for full encryption. The four different stages that we use for Modified-AES Algorithm are: Substitution bytes ShiftRows Permutation AddRoundKey Substitution Bytes, ShiftRows and AddRoundKey remain unaffected as it is in the AES. Here the important function is Permutation which is used instead of Mixcolumn. These rounds are managed by the following the conversions shown in Fig.1 Permutation is widely used in cryptographic algorithms. Permutation operations are interesting and important from both cryptographic and architectural points of view. Tables characterize the permutation and its contrary; the DES algorithm will provide us permutation tables. The inputs to the IP table consist of 64 bits. Modified-AES algorithm takes 128 bits as input. The functions Substitution Bytes and ShiftRows are also interpreted as 128 bits whereas the Permutation function takes 64 bits. We divide the consequential bits of ShiftRows function into two parts of 64 bits and then take each part of 64 bits as input of permutation tables and shift bits one by one according to that table. We fetch one bit from the source, and put it into the correct position in the destination. Each bit of a block is subject to initial permutation, which can be represented by the following initial permutation (IP) table: In the permutation table each entry indicates a specific position of a numbered input bit consisting of 64 bits in the output. While reading the table from left to right and then from top to bottom, we observe that the 58th bit of the 64-bit block is in first position, the 5th is in second position and so forth. After applying permutation on both sections of 128 bits we again combine both sets of 64 parts into a complete set of 128 bits and 124

6 Sumira et al: Modified Advanced Encryption Standard For Text And Images then perform next remaining functions of algorithm. If we take the inverse permutation it gives again the original bits, the output result is a 64-bit cipher text. The inverse permutation is performed according to following tables. For the full decryption of Modified-AES algorithm the transformation processes are, Inv-Bytesub, Inv-Shiftrows, Inv-Permutation, and the Addroundkey, which are performed in 1 rounds as it is in the encryption process. 4. RESULTS For testing the algorithm we use a very simple code that checks the efficiency of algorithm. This test shows that the modified-aes algorithm is much better than AES algorithm. In this tutorial we have tested several files and images in order to check that how fast the Modified-AES algorithm than the real AES. Following is the simple coding that we include in algorithm to calculate the time that algorithm takes for encryption and decryption. DateTime start = DateTime.Now; this.startselectedprocess (); DateTime end = DateTime.Now; TimeSpan result = end - start; lblprogress.text = "Elapsed Time: " + result.tostring(); This simple code will calculate the time that the Algorithm takes and will display it on the screen. 125

7 Computer Science Journal Volume 1, Issue 3, December Tests on Text files To test the algorithm we take the different size of text and image files and compare the calculated time of both the Modified-AES with Advanced Encryption Standard (AES). Table 1 shows the comparison results performed on different sizes of text files using Modified-AES and the AES algorithm. File size AES Modified-AES 1kb ::1:9624 :::7332 2kb ::5:9436 ::1:3884 3kb ::9:24 ::2:418 4kb ::12:276 ::3:864 5kb ::16:7232 ::6:998 6kb ::2:2488 ::8:8296 7kb ::25:3812 ::1:68 8kb ::3:786 ::14:118 9kb ::36:98 :: TABLE.1 ENCRYPTION RESULTS FOR TEXT FILES The above table shows the size of different files that we take to check the performance of algorithm. We tested AES algorithm as well as modified AES algorithm and show these results comparatively in following graph. We used AES algorithm first and encrypt text files. We noticed that the difference between the AES and Modified-AES encrypted file is huge. Moreover, the AES overhead using Modified- AES is very low. The difference between the encrypted packets, using Modified-AES and AES is sufficient, which makes using Modified-AES a better solution. The results of Table.1 comparatively, shown in figure

8 Sumira et al: Modified Advanced Encryption Standard For Text And Images Figure.2 Graphical representation of Encryption results for different text files 4.2. Tests on Images In the second part of test we applied the proposed encryption algorithm on different size of images and compare its results with the real AES results. Table 2 shows the different image size and the time calculated by the Modified-AES and the Advanced Encryption Standard (AES). This shows the comparison between the new proposed scheme and the existing one. Image size AES Modified-AES 4kb ::3:9624 5kb ::55:9436 6kb :1:9:24 7kb :1:22:276 75kb :1:46:7232 8kb :1:59:2488 9kb :2:1:3812 1kb :2:18:786 11kb :2:26:98 ::14:7732 ::21:5312 ::28:8756 ::31:2372 ::42:9624 ::48:9528 ::59:2676 :1:13:4916 :1: TABLE 2. ENCRYPTION RESULTS ABOUT IMAGE 127

9 Computer Science Journal Volume 1, Issue 3, December 211 The results of Table.2 comparatively, shown in figure 4. Figure 3 Graphical representation of Encryption results for different image file 5. CONCLUSION Usually lightweight encryption algorithms are very attractive for multimedia applications. Luckily we have achieved through our research a fast lightweight encryption algorithm to secure our multimedia data from unauthorized access. For the security of multimedia data, we have proposed an encryption algorithm that is based on AES using symmetric key encryption algorithm. In version of security analysis and experimental results our proposed encryption scheme is fast and on the other hand it provides good security and adds very less overhead on the data, this today is the requirement of most of the multimedia applications. Theoretical analysis and experimental results of the achievement makes it very suitable for high rate and less overhead on the data. For all these compensation it is suitable for any large scale text and image transfer. 6. FUTURE WORK We will perform the security analysis of MAES, to see that how; much more or less secure it is, as compare to the AES. We will compare it with other Modified versions of AES, work done by other researchers. References 1. Dominik Engel Thomas stutz,andreas Uhl, A survey on JPEF2 encryption, Multimedia systems[online] SpringerLink Verlag pp.1-29,, Shtewi,A.M. An Efficient Modified Advanced Encryption Standard (MAES) adapted for image cryptosystems IJCSNS International Journal of Computer Science and Network Security, VOL.1 No.2, pp February

10 Sumira et al: Modified Advanced Encryption Standard For Text And Images 3. Shiguo Lian, Quasi-commutative watermarking and encryption for secure media content distribution,[online], Multimedia Tools and Applications Volume 43, Number 1 / May, Tanya E. Seidel, Daniel Socek, Designs, Codes and Cryptography [EBOOK], Volume 32, Issue 1-3 (May-July 24) Kluwer Academic Publishers Norwell, MA, USA 5. Announcing the ADVANCED ENCRYPTION STANDARD (AES), Federal Information Processing Standards Publication 197 November 26, Fahad Bin Muhaya. Modified AES Using Chaotic Key Generator for Satellite Imagery Encryption, Emerging Intelligent Computing Technology and Applications Volume 5754/29 PP , Krishnamurthy G N, V Ramaswamy. Making AES Stronger: AES with Key Dependent S- Box, IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.9, pp , September P. Noo-intara, S. Chantarawong, and S. Choomchuay Architectures for MixColumn Transform for the AES Department of Electronics, Faculty of Engineering, and Research Center for Communications and Information Technology (ReCCIT) King Mongkut's Institute of Technology Ladkrabang (KMITL), Bangkok 152, Thailand. 129