Combination of RGB Substitution for Text to Image Encryption Technique using AES

Transcription

1 Combination of RGB Substitution for Text to Image Encryption Technique using AES Sourabh Singh 1 Department of Computer Science and Engineering Radharaman Institute of Technology and Science Bhopal (M.P), India sourabhsingh_tct@yahoo.com Anurag Jain 2 Department of Computer Science and Engineering Radharaman Institute of Technology and Science Bhopal (M.P), India anurag.akjain@gmail.com Abstract Network security works on the principle of Encryption and Decryption. Every algorithm make use of a secret key which is responsible to Encrypt data in some unreadable type of message or changes original data into a different data. In this paper we have given a novel approach which transforms a text file into an image using RGB substitution hence an intruder will be confused weather actual data to be transmitted is a text or an image. Further it also undergoes an AES encryption stage which encrypts the generated image, at last the encryption key is also attached into the encrypted image file. Hence this approach also solves the key exchange problem. The encryption and decryption phenomenon makes use of a combination database for transformation of text into image. Index Terms - Encryption, Decryption, AES. I. INTRODUCTION This paper is divided into following five sections; in section- I, we presented basic introduction of Network Security, in section-ii, a survey on related algorithms has been presented, section-iii discusses the proposed model, section IV presents the Result Analysis and finally section V concludes the paper and provides Future work. With the rapid growth of network applications, security has become an important factor while communicating and transferring data on a public network. Some of the popular network security techniques are described as under: Substitution: In cryptography the substitution techniques are oldest but still a powerful method to hide the original text, this method replaces letters with some other letters or set of letters. In this methodology the letters can also be easily replaced by numbers. The most praised method developed by Julius Caeser[12] in Caesar Cipher each letter in a message is replaced by an letter three places down the line. Monoalphabetic Cipher is another technique which makes use of the random substitution. Another technique Homophonic Substitution involves substitution of a single plain text character by a cipher text character which can be any one of the chosen set. The Polygram substitution cipher technique is also a substitution technique which substitutes one block of plain text with a block of cipher text hence it does not work on a character by character basis. Transposition: Transposition techniques are different from substitution techniques as it does not simply replace one letter with another [12]; these techniques also perform some permutation over the plain text letters. The most popular technique used here is a rail fence technique which constitutes of two steps, in first step plain text is written as sequence of diagonals while in second step the plain text is read row by row which generates cipher text. Another technique is Simpler Columnar Transposition Technique in which plain text is arranged in a sequence of rows & columns randomly. Vernam cipher is another method which uses a one-time pad hence it is only suitable for short messages. Encryption: In the science of cryptography [10], encryption is a method of converting readable information into unreadable data. Message Authentication Code (MAC), Hash Functions or digital signatures are the dominating techniques used for encryption. Message Authentication Code is useful in providing message integrity while digital signatures proves authenticity of a message, digital signatures confirms the identity of the sender Clear Text or Plain Text: A message that we can read and understand without the aid of any means especially complex Cipher text or Cryptogram: The cryptogram is the result of the transformation of a clear message through the use of a mathematical function. Encryption: The transformation of a message that modifies it in substance and makes it illegible Decryption: The inverse process of encryption that allows obtaining the message in clear form a cryptogram Fig-1: Cryptography Process Page 1 of 7

2 Private Key Encryption: In symmetric encryption or private Key encryption a single key is used for encryption and decryption of a message which is to be sent in an unsecured channel. Here both the sender and the receiver shares the same secret code, called the key. Sender encrypts the message using the key. On receiving the message Receiver decrypts it using the same key. Systematic key management or the transfer of key is a major concern while using private key encryption [11]. Public Key Encryption: In Public key cryptography or asymmetric key cryptography pair of keys is used for encryption and decryption. To privately communicate with the other users the public key is distributed to everyone. Hence this approach overcomes the key exchange problem between users which was the primary concern in private key encryption. In this method each user has a private key, public key pair. Here private key is never shared between the users while public key is widely available. Asymmetric key encryption is slower as compared to private key encryption due to multiple key distribution management between users [11]. AES Algorithm: AES Algorithm is based over a cryptographic technique Rijndael which is a block cipher technique developed by Joan Daemen and Vincent Rijmen[13]. This algorithm is very flexible as it supports 128, 192, and 256 bits combination of data and key size. On the other hand AES mandates that the plain text must be 128 bit long which can be divided into four operation blocks. These blocks functions on an array which is made up of bytes organized in a 4 4 matrix. This arrangement is termed as state. For achieving complete encryption, the data is passed through Nr number of rounds (Nr = 10, 12, 14).These rounds performs the following transformations: Subbyte Transformation: This transformation includes a non linear byte Substitution with the help of substitution table (sbox), Affine Transformation and multiplicative inverse are the basic building blocks used for the construction of substitution table. Shift rows transformation: It is a simple byte transposition method. In this transformation bytes in the last three rows of the state are cyclically shifted and offset of the left shift varies from one to three bytes. Mix columns transformation: It is based on the method of multiplication of columns of the matrix in which each column vector is multiplied by a fixed matrix. Treating the bytes as polynomials rather than numbers. Add round key transformation: It is a simple XOR operation between the working state and the round key. This transformation is its own inverse. Inverse Substitute Bytes: It is the reverse procedure of the Substitute Bytes transformation; here the inverse S-box is applied on each byte of the State. This is obtained by taking the inverse of the affine transformation followed by taking the multiplicative inverse Inverse Shift rows: It is the inverse process of the shift rows here the first row of the state array remains unchanged. The bytes present in the second, third and forth rows are cyclically shifted by one, two and three bytes to the right respectively. Inverse Mix columns: In the Inverse Mix Columns transformation, every column of the state array is considered as a polynomial. Modulo x4+1 is multiplied with a fixed polynomial and the result generated is the corresponding column of the output state. Fig-2: Diagram of AES Encryption Algorithm The key value cannot be determined by any known means, even if any eavesdropper knows many pairs of plaintext and the cipher text security of AES algorithm remains unchanged. AES algorithm is so well designed that it supports the use one of any of the three key sizes (Nr). AES-128, AES-196 and AES-256 use 128 bit (16 bytes, 4 words), 196 bit (24 bytes, 6 words) and 256 bit (32 bytes, 8 words) key sizes respectively. AES have no known weaknesses and hence is a better approach as compared to DES. AES is extremely fast as compared to other block ciphers (Though there are some mismatches between size and speed). In dedicated hardware where round transformation is parallel by design AES allows even faster execution. II. Literature Survey Page 2 of 7

3 This Research is based on the work done by Ahmad Abusukhon and Mohammad Talib [1]. In their work, there are mainly two stages.. First stage deals with the transformation here Plain Text to be transmitted over the network is transformed to image. This transformation has been designed by the respective authors. The second level contains Image-Shuffle Encryption which is based on Efficient digital encryption algorithm based on matrix scrambling technique [2] where the Image generated by the transformation is stored in the matrix form at the bit level and this matrix has been shuffled by the technique described in [2]. The two operations involved here are performed on the client side and to obtain the original text same operations are performed in reverse direction on the receiver side. In the first level i.e. Text-To-Image Encryption each letter of text file is transformed into three random integers say RGB R for Red, G for Green and B for Blue. Range of Random numbers are from 0 to 255. Each of the three random numbers represents single pixel in the image. In their algorithm, they have generated an individual pixel (R, G, and B values calling them RGB value) for each letter in the plain text. During this process key1 is generated which contains the random numbers RGB for all the letters. This key1 is stored in one string and used to transform the plaintext into an image. At the bit level the result of this process is stored in a two dimensional array or Matrix of Pixels MP. In this Matrix each 3 contiguous columns in a row represent one letter. In order to make it more secure they used the second level of encryption, here they determine the number of times the image matrix is shuffled [2]; say N. Here N is equal to the number of column of MP. On shuffling the matrix MP every time two random numbers are generated say R1, and R2, where R1 represents row/column number and R2 represents another row/column number. R1 is replaced by R2 and R2 is replaced by R1. The Shuffled matrix generated say SP, is finally sent to the Receiver. When Receiver receives SP it uses key 2 to retrieve the original matrix MP and then each pixel in original matrix MP is decomposed into R, G, and B values. Then using key 1 these 3 contiguous values (R, G, and B) are transformed to a specific letter. In our proposed algorithm there is an AES encryption stage where image generated after the transformation of text is encrypted using a key, the AES has been very popular to encrypt data and now a days frequently used for encrypting images as well. Praveen.H.L, H.S. Jayaramu, M.Z.Kurian [9] states that AES provides an error-free encryption system and error is much more reduced even in radiation in satellites. They have developed a model which can easily encrypt the images obtained from satellites. In their research the satellite not have to wait for long time to receive next block of data even If a faulty or noisy data occurs. Ahmed Bashir Abugharsa, Abd Samad Bin Hasan Basari and Hamida Almangush[8] has also used AES encryption algorithm for image encryption, with the help of magic cube method they have rotated the plain image to generate another image. The original image taken is divided into six sub-images which are subdivided between a number of blocks and finally attached to the faces of a Magic Cube further to confuse the relation between the plain image and the encrypted image, an AES algorithm which is applied to the rotated image which again encrypts the image. Jawad Ahmad and Fawad Ahmed [6] have given an analysis on comparing two encryption algorithms namely Advanced Encryption Standard (AES) and Compression Friendly Encryption Scheme (CFES). They have also explored the security estimations of both AES and CFES for digital images against brute-force, statistical, and differential attacks, the results obtained by testing algorithms for digital images shows some weaknesses in CFES. These weaknesses were due to low entropy and horizontal correlation in encrypted images, the authors also states that the images which were encrypted by CFES has correlation in horizontal direction while same images when encrypted by AES results in very less correlation in all directions. Correlation is inversely propotional to security. Manoj. B, Manjula N Harihar[5] also proved that Image Encrypted and Decrypted using AES can be designed and implemented to protect the confidential image data from an unauthorized access. The authors found that Successful implementation of AES algorithm is one of the best encryption and decryption standard available in market. Page 3 of 7

4 P. Radhadevi, P. Kalpana[7] has also presented the encryption and decryption of an image using AES algorithm, they have concluded that the AES can be used very efficiently for secure image transmission. P.Karthigaikumar,Soumiya Rasheed[4] has also implemented AES algorithm for simulation of image encryption. They have successfully implemented the AES algorithm in MATLAB on Xilinx platform, They have converted an image into a binary form and then encrypted with the help of an AES algorithm.timing simulation is also performed which verifies the functionality of the designed circuit. III. PROPOSED MODEL This section, describes the proposed algorithm. This algorithm is designed to improve the algorithm proposed by the Ahmad Abusukhon and Mohammad Talib [1]. The main drawback of their algorithm is that it does not solve the key exchange problem. Another disadvantage is that they are transferring the whole key value. This is very big in size (key1) as each character in plain text is replaced by three random numbers. Therefore it requires transferring at least three times more data as compared to actual data for decrypting the packet. Fig.3 shows the Data flow diagram of proposed algorithm [3]. As we know encryption is more secure method as compared to shuffle operations so the proposed technique executes an encryption stage rather shuffling the positions of bits by matrix scrambling technique. The sender & receiver side has a combination database which contains number of combinations of text to digits mapping. It has various combinations of transforming characters into equivalent RGB values also each combination have assigned a unique number which ranges from 1 to N. N denotes the total number of combinations in the database. The steps involved in the Algorithm are as follows: 1. Generate a Random number between 1 to N. 2. Generate Combination corresponding to N. 3. Transform Text into RGB values. 4. Attach N in RGB values and Generate Image1. 5. Generate a Random number between 1 to K. 6. Generate key corresponding to K. 7. Encrypt Image1 by AES and key to Generate Image2. 8. Attach K in Image2 9. Generate Image Send Image3 to Receiver. Page 4 of 7

5 11. Read K to Generate Key. 12. Remove K to Generate Image Decrypt Image2 by AES using Generated Key to get Image Read N to Generate Combination Number. 15. Remove N and Transform Image1 to Plain Text. The process starts from the sender side. In this paper we have taken N as 10. The sender generates a random number between 1 to 10. This represents the combination number to be applied for transformation Text to Image. Using the corresponding combination (key1) transformation method proposed in [1] is applied which results in the generation of an image. The number N is attached in the image by adding one more pixel in the image at last. Now sender generates a random number between 1 to K. Here we have taken K as 10. Sender Matches the corresponding key (Key2) in combination database. This key2 is used for AES Encryption. Now the image generated by Text to image transformation is encrypted by key using an AES algorithm [13]. The number K is finally attached in the image by adding one more pixel in the image at last. Finally this single file is transferred to the Receiver. When Receiver receives the final image the first task is to read the last pixel to get the combination number. When this number is obtained the number is matched in the combination database which retrieves the corresponding key (key2). Now the last pixel is discarded from the image and the resultant image is decrypted using key2 and AES algorithm. Now Receiver reads the last pixel to get the combination number. When this number is obtained the number is matched in the combination database which retrieves the corresponding key (key1). Now the last pixel is discarded from the image. Finally key1 is applied on the generated image which transforms image into original plain text. Fig-4 shows the transformation step. Here a plain text Hello Guys has been transformed into image using an RGB substitution. First N is calculated for applying a combination number here it is 4. Every character has a different RGB value for the conversion of character to pixel. For e.g.: value for H is 10 for R, 63 for G and 109 for B similarly for e is 52 for R, 54 for G and 124 and so on. By this combination following image has been formed which is made up matrix of pixels of order 6X2 (((N/2)+1)X2). This image looks like image Fig: 5. Fig-5: Transformed image from text The combination number N is smartly attached as a last pixel and finally after encrypting the image with an AES algorithm and adding Combination number of the key2 K the image or cipher obtained looks like a corrupted file rather than any useful information. It looks like fig-6: We have taken Abstract of this research paper for experimental analysis. The Abstract is of the size 1137 bytes, we have taken first 200,400,600,800 IV. RESULT ANALYSIS We have used java as software to carry out our experiments. We have built the sender s and Receiver s programs on different machines and use the following text message for our experiments: "encryption is the process of converting data to a form called a cipher text which cannot be easily understood by unauthorized people decryption is the reverse process for converting encrypted data back to its original form so that it can be understood. Fig-6: Final Image to be transferred and 1000 bytes of Abstract for analysis. Text Size (Bytes) Encryption Time (Sec) Decryption Time (Sec) Fig-4: Image formation from text Page 5 of 7

6 Experimental Results obtained In this Research work we have proposed an Encryption Decryption technique which developed a highly secure transmission of text. If any intruder somehow decrypts the image the technique transfers him to another image which is also in an unreadable format, this further confuses the intruder that the actual information is in text or in image format, the blending of transformation of a text into an image and further encrypting the result with an AES encryption makes information (plain text) highly secure for transmitting it on an extremely vulnerable and insecure network environment. The proposed algorithm also solves key exchange problem since it attaches key with the cipher itself in a very secure manner. We have implemented this method by converting text into a PNG image as it is a lossless compression format. In future the Researchers can further work on other image formats and can analyze the results. Further AES can also be implemented in 256 bit key block while other encryption algorithms can also be implemented in place of AES and changes in the results can be investigated. Fig-7: Graphical Analysis for Experimental Results The best outcome is that only a single file is being transferred which in itself contains key, The Encryption time includes time taken in attachment of key and similarly Decryption time also includes the fetching of key from the cipher. Fig-8 shows that the Encryption and Decryption time is nearly same and is very efficient and fast. The approach used in [1] only undergoes transformation of 26 characters. We have used 84 character set including special characters of the keyboard. With the simple calculation, the number of possible Permutations to encrypt 84 letters is ((256) 3 ) 84. Since each pixel is made by the combination of three values (RGB) and each one of these values ranges from 0 to 255, choosing three values has (256) 3 permutations. We have 84 letters and thus the permutations for 84 letters is ((256) 3 ) 84 which is equal to exp+606. Our approach also uses AES encryption stage hence one need different numbers of combination to break the cipher. Hence we can say that our approach is highly secure. V. CONCLUSION AND FUTURE WORK REFERENCES [1] Ahmad Abusukhon Mohammad Talib A Novel Network Security Algorithm Based on Private Key Encryption IEEE International Conference on Cyber Security, Cyber Warfare and Digital Forensic (CyberSec), [2] Kiran Kumar, M., Mukthyar Azam, S., and Rasool, S.(2010) Efficient digital encryption algorithm based onmatrix scrambling technique. International Journal ofnetwork Security and its Applications (IJNSA), 2(4). [3] Sourabh Singh, Anurag Jain An Enhanced Text to Image EncryptionTechnique using RGB Substitution and AES.International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May [4] P.Karthigaikumar Soumiya Rasheed Simulation of Image Encryption using AES Algorithm IJCA Special Issue on Computational Science - New Dimensions & Perspectives NCCSE, [5] Manoj.B, Manula N Harihar Image Encryption and Decryption using AES International Journal of Engineering and Advanced Technology (IJEAT) ISSN: , Volume-1, Issue-5, June [6] Jawad Ahmad and Fawad Ahmed Efficiency Analysis and Security Evaluation of Image Encryption Schemes International Journal of Video & Image Processing and Network Security IJVIPNS-IJENS Vol:12 No:04. Page 6 of 7

7 [7] P. Radhadevi, P. Kalpana Secure Image Encryption Using AES International Journal of Research in Engineering and Technology Volume: 1 Issue: 2. [8] Ahmed Bashir Abugharsa, Abd Samad Bin Hasan Basari and Hamida Almangush A Novel Image Encryption using an Integration Technique of Blocks Rotation based on the Magic cube and the AES Algorithm International Journal of Computer Science Issues (IJCSI); Vol. 9 Issue 4, p41 Jul2012. [9] Praveen.H.L, H.S Jayaramu, M.Z.Kurian Satellite Image Encryption Using AES International Journal of Computer Science and Electrical Engineering (IJCSEE), Vol-1, Iss-2, [10] Stalling, W. (2005) Cryptography and network security principles and practices, 4th edition Prentice Hall. Available at: security-4thedition.html. [11] Dr. Mahesh Motwani Cryptography & Network Security Balaji Learning Book. [12] Atul Kahate, Cryptography and Network Security, Second Edition, Tata McGraw-Hill Edition [13] AES.pdf Page 7 of 7