Image encryption and decryption using aes algorithm
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This document summarizes an article that describes using the AES algorithm to encrypt and decrypt images. It begins with background on AES and its advantages over DES such as larger key sizes. It then describes modifications made to the AES key expansion to improve encryption quality and avalanche effect. The implementation takes an input key, generates expanded keys using a modified key expansion, then encrypts images by applying AES operations to blocks of 16 pixels using the expanded keys. Decryption reverses this process to recover the original image. Results show the encrypted image is secure and decrypts correctly when using the proper key.
![International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME
25
2.1 The Rijndael Algorithm
For Rijndael, the length of both the block to be encrypted and the encryption key are not
fixed. They can be independently specified to 128, 192 or 256 bits. The number of rounds, however,
varies according to the key length. It can be equal to 10, 12 and 14 when the key length is 128bits,
192 bits and 256 bits, respectively. The basic components of Rijndael are simple mathematical,
logical, and table lookup operations. The latter is actually a composite function of an inversion over
Galois Field (GF) with an affine mapping. Such structure makes Rijndael suitable for hardware
implementation.
3. IMPLEMENTATION
The algorithm is based on AES Key Expansion technique.
AES Key Expansion technique in detail.
3.1 AES Key Expansion
Pseudo code for AES Key Expansion: The key-expansion routine creates round keys word by
word, where a word is an array of four bytes. The routine creates 4x(Nr+1) words. Where Nr is the
number of rounds.
The process is as follows
The first four words are made from the cipher key (initial key). The key is considered as an
array of 16 bytes (k0 to k15). The first four bytes (k0 to k3) become w0, the four bytes (k4 to k7)
become w1, and so on.
The rest of the words (wi for i=4 to 43) are made as follows
If (i mod 4) != 0, wi=wi-1 xor wi-4.
If (i mod 4) = 0, wi=t xor wi-4. Here t is a temporary word result of applying SubByte
transformation and rotate word on wi-1 and XORing the result with a round constant.
3.2 Modifications in AES Key Expansion
Certain changes made in the above key expansion process improves the encryption quality,
and also increases the avalanche effect. The changes are
a) The Rcon value is not constant instead it is being formed from the initial key itself, this
improves the avalanche effect.
b) Both the s-box and Inverse s-box are used for the Key Expansion process which improves non-
linearity in the expanded key and also improves the encryption quality.
c) We do not use the S-box and Inverse S-box as such for this algorithm; instead we perform
some circular shift on the boxes based on the initial key this improves the key sensitivity.
The above changes in the algorithm can be represented as
1) Formation of Rcon values
Rcon [0]=key[12:15]; Rcon [1]=key[4:7];
Rcon [2]=key[0:3]; Rcon [3]=key[8:11];
2) Using Inverse S-Box for key expansion
The ‘temp’ value used in the algorithm is formed as
temp = SubWord(RotWord(temp)) XOR InvSubWord(Rcon[i/4]);
Where InvSubWord: InverseSubByte transformation table value](https://image.slidesharecdn.com/imageencryptionanddecryptionusingaesalgorithm-150307034046-conversion-gate01/85/Image-encryption-and-decryption-using-aes-algorithm-3-320.jpg)
![International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME
26
3) Shifting of S-box and Inverse S-box
Sbox_offset = sum(key[0:15])mod256;
Inv_Sbox_offset = (sum(key[0:15])*mean(key[0:15]))mod256;
The initial key is represented as blocks key[0],key[1],..,key[15]. Where each block is 8bits long
(8*16=128 bits).
3.3 Steps Involved
3.3.1 Key Selection
The sender and receiver agree upon a 128 bit key. This key is used for encryption and
decryption of images. It is a symmetric key encryption technique, so they must share this key in a
secure manner. The key is represented as blocks k[0],k[1]...k[15]. Where each block is 8bits long
(8*16=128 bits).
3.3.2 Generation of Multiple keys
The sender and receiver can now independently generate the keys required for the process
using the above explained Modified AES Key Expansion technique. This is a one time process; these
expanded keys can be used for future communications any number of times till they change their
initial key value.
3.3.3 Encryption
Encryption is done in spans, where we process 16 pixels in each span. For both its Cipher and
Inverse Cipher, the AES algorithm uses a round function that is composed of four different byte-
oriented transformations: SubBytes, ShiftRows, MixColumns and AddRoundKey.
3.3.4 Decryption
The decryption process is similar as encryption, but we use Inverse SubByte Transformation.
The whole AES structure is sketched in Fig 1.
Fig 1: Structure of AES Algorithm](https://image.slidesharecdn.com/imageencryptionanddecryptionusingaesalgorithm-150307034046-conversion-gate01/85/Image-encryption-and-decryption-using-aes-algorithm-4-320.jpg)
Image encryption and decryption using aes algorithm
- 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME 23 IMAGE ENCRYPTION AND DECRYPTION USING AES ALGORITHM Roshni Padate1 , Aamna Patel2 1 Computer Engineering Department, Fr. Conceicao Rodrigues College of Engineering, Fr. Agnel Ashram, Bandstand, Bandra(West), Mumbai-400050, India 2 Electronics Department, Fr. Conceicao Rodrigues College of Engineering, Fr. Agnel Ashram, Bandstand, Bandra(West), Mumbai-400050, India, ABSTRACT Data Security is primary concern for every communication system. The relentless growth of Internet and communication technologies has made the extensive use of images unavoidable. There are many ways to provide security to data that is being communicated. This Paper describes a design of effective security for communication by AES algorithm for encryption and decryption. It is based on AES Key Expansion in which the encryption process is a bit wise exclusive or operation of a set of image pixels along with the a 128 bit key which changes for every set of pixels. The National Institute of Standards and Technology (NIST) has initiated a process to develop a Federal information Processing Standard (FIPS) for the Advanced Encryption Standard (AES), specifying an Advanced Encryption Algorithm to replace the Data Encryption standard (DES) the Expired in 1998. The Advanced Encryption Standard can be programmed in software or built with pure hardware. Keywords: AES, Block Cipher, Cryptography, DES, NIST 1. INTRODUCTION In the past few years the security and integrity of data is the main concern. In the present scenario almost all the data is transferred over computer networks due to which it is vulnerable to various kinds of attacks. To make the data secure from various attacks and for the integrity of data we must encrypt the data before it is transmitted or stored. Cryptography is a method of storing and transmitting data in a form that only those it is intended for can read and process. It is a science of protecting information by encoding it into an INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME: http://www.iaeme.com/IJECET.asp Journal Impact Factor (2014): 7.2836 (Calculated by GISI) www.jifactor.com IJECET © I A E M E
- 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME 24 unreadable format. It is an effective way of protecting sensitive information as it is stored on media or transmitted through network communication paths. Purpose of cryptography: 1.1 Authentication The process of proving one's identity. It is another part of data security that we encounter with everyday computer usage. Just think when you log into your email, or blog account. The simple sign-in process is a form of authentication that allows you to log into applications, files, folders and even an entire computer system. Once logged in, you have various given privileges until logging out. Some system will cancel a session if your machine has been idle for a certain amount of time, requiring that you prove authentication once again to re-enter. The simple sign-on scheme is also implemented into strong user authentication systems. However, it requires individuals to login using multiple factors of authentication. Non-repudiation: In this, the receiver should know whether the sender is not faking. For example, if suppose when one purchases something online, one should be sure that the person whom one pays is not faking. 1.2 Integrity Many a times data needs to be updated but this can only be done by authenticated people. 1.3 Privacy/confidentiality Ensuring that no one can read the message except the intended receiver. Encryption is the process of obscuring information to make it unreadable without special knowledge. Encryption has been used to protect communications for centuries, but only organizations and individuals with an extraordinary need for secrecy had made use of it. In the mid-1970s, strong encryption emerged from the sole preserve of secretive government agencies into the public domain, and is now used in protecting widely-used systems, such as Internet e-commerce, mobile telephone networks and bank automatic teller machines. 2. AES ALGORITHM In January, 1997 NIST began its effort to develop the AES, a symmetric key encryption algorithm, and made a worldwide public call for the algorithm to succeed DES. Initially 15 algorithms were selected, which was then reduced down to 4 algorithms, RC6, Rijndael, Serpent and Two-fish, all of which were iterated block ciphers. The four finalists were all determined to be qualified as the AES. The algorithm had to be suitable across a wide range of hardware and software systems. The algorithm had to be relatively simple as well. After extensive review the Rijndael algorithm was chosen to be the AES algorithm. Difference between AES and DES Factors DES AES Key Length 56 bits 128, 192, 256 bits Block Size 64 bits 128, 192, 256 bits Cipher Text Symmetric block cipher Symmetric block cipher Developed 1977 2000 Security Proven inadequate Considered secure Possible Keys 256 2128 , 2192 , 2256
- 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME 25 2.1 The Rijndael Algorithm For Rijndael, the length of both the block to be encrypted and the encryption key are not fixed. They can be independently specified to 128, 192 or 256 bits. The number of rounds, however, varies according to the key length. It can be equal to 10, 12 and 14 when the key length is 128bits, 192 bits and 256 bits, respectively. The basic components of Rijndael are simple mathematical, logical, and table lookup operations. The latter is actually a composite function of an inversion over Galois Field (GF) with an affine mapping. Such structure makes Rijndael suitable for hardware implementation. 3. IMPLEMENTATION The algorithm is based on AES Key Expansion technique. AES Key Expansion technique in detail. 3.1 AES Key Expansion Pseudo code for AES Key Expansion: The key-expansion routine creates round keys word by word, where a word is an array of four bytes. The routine creates 4x(Nr+1) words. Where Nr is the number of rounds. The process is as follows The first four words are made from the cipher key (initial key). The key is considered as an array of 16 bytes (k0 to k15). The first four bytes (k0 to k3) become w0, the four bytes (k4 to k7) become w1, and so on. The rest of the words (wi for i=4 to 43) are made as follows If (i mod 4) != 0, wi=wi-1 xor wi-4. If (i mod 4) = 0, wi=t xor wi-4. Here t is a temporary word result of applying SubByte transformation and rotate word on wi-1 and XORing the result with a round constant. 3.2 Modifications in AES Key Expansion Certain changes made in the above key expansion process improves the encryption quality, and also increases the avalanche effect. The changes are a) The Rcon value is not constant instead it is being formed from the initial key itself, this improves the avalanche effect. b) Both the s-box and Inverse s-box are used for the Key Expansion process which improves non- linearity in the expanded key and also improves the encryption quality. c) We do not use the S-box and Inverse S-box as such for this algorithm; instead we perform some circular shift on the boxes based on the initial key this improves the key sensitivity. The above changes in the algorithm can be represented as 1) Formation of Rcon values Rcon [0]=key[12:15]; Rcon [1]=key[4:7]; Rcon [2]=key[0:3]; Rcon [3]=key[8:11]; 2) Using Inverse S-Box for key expansion The ‘temp’ value used in the algorithm is formed as temp = SubWord(RotWord(temp)) XOR InvSubWord(Rcon[i/4]); Where InvSubWord: InverseSubByte transformation table value
- 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME 26 3) Shifting of S-box and Inverse S-box Sbox_offset = sum(key[0:15])mod256; Inv_Sbox_offset = (sum(key[0:15])*mean(key[0:15]))mod256; The initial key is represented as blocks key[0],key[1],..,key[15]. Where each block is 8bits long (8*16=128 bits). 3.3 Steps Involved 3.3.1 Key Selection The sender and receiver agree upon a 128 bit key. This key is used for encryption and decryption of images. It is a symmetric key encryption technique, so they must share this key in a secure manner. The key is represented as blocks k[0],k[1]...k[15]. Where each block is 8bits long (8*16=128 bits). 3.3.2 Generation of Multiple keys The sender and receiver can now independently generate the keys required for the process using the above explained Modified AES Key Expansion technique. This is a one time process; these expanded keys can be used for future communications any number of times till they change their initial key value. 3.3.3 Encryption Encryption is done in spans, where we process 16 pixels in each span. For both its Cipher and Inverse Cipher, the AES algorithm uses a round function that is composed of four different byte- oriented transformations: SubBytes, ShiftRows, MixColumns and AddRoundKey. 3.3.4 Decryption The decryption process is similar as encryption, but we use Inverse SubByte Transformation. The whole AES structure is sketched in Fig 1. Fig 1: Structure of AES Algorithm
- 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 4. RESULTS 4.1 Encryption and Decryption Fig 2: 4.2 If key for encryption and decryption is different Fig 3: Encryption and Decryption with different keys International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 27 Fig 2: Encryption and Decryption Output If key for encryption and decryption is different than the original image is not Encryption and Decryption with different keys International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 9 © IAEME the original image is not retrieved.
- 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 4.3 Time required for encryption 5. CONCLUSION Image is encrypted and decrypted using AES Algorithm. encryption quality. Even AES-128 offers a sufficiently large number of possible keys, making an exhaustive search impractical for many decades Encryption and decryptio encryption by AES Algorithm is less than the time required by DES Algorithm. the algorithm is suitable for image encryption in real time applications. 6. REFERENCES 1. P.Karthigaikumar, Soumiya Rasheed, IJCA Special Issue on Computational Science 2011, 166-172. 2. Shraddha Soni, Himani Agrawa between AES and DES Cryptographic Algorithm Innovative Technology (IJEIT) Volum 3. The First 10 Years of Advanced Encryption Reliability Societies, 2010 IEEE, 4. Irfan AbdulGani Landge, International J. of Engg. Research & Indu. Appls. (IJERIA). ISSN 0974 (August 2011), 395-406. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 28 Time required for encryption Fig 4: Encryption time Image is encrypted and decrypted using AES Algorithm. The proposed algorithm offers high 128 offers a sufficiently large number of possible keys, making an exhaustive search impractical for many decades Encryption and decryption of image is possible using AES Algorithm. Time required for encryption by AES Algorithm is less than the time required by DES Algorithm. the algorithm is suitable for image encryption in real time applications. higaikumar, Soumiya Rasheed, Simulation of Image Encryption using AES Algorithm IJCA Special Issue on Computational Science - New Dimensions & Perspectives Shraddha Soni, Himani Agrawal, Dr. (Mrs.) Monisha Sharma, Analysis and between AES and DES Cryptographic Algorithm, International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 6, December 2012, 362 10 Years of Advanced Encryption, Copublished by the IEEE Computer and ility Societies, 2010 IEEE, 72-74. Irfan AbdulGani Landge, Implementation of AES Encryption and Decryption using VHDL International J. of Engg. Research & Indu. Appls. (IJERIA). ISSN 0974 International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 9 © IAEME The proposed algorithm offers high 128 offers a sufficiently large number of possible keys, making an n of image is possible using AES Algorithm. Time required for encryption by AES Algorithm is less than the time required by DES Algorithm. Due to these features Simulation of Image Encryption using AES Algorithm, New Dimensions & Perspectives NCCSE, Analysis and Comparison International Journal of Engineering and 362-365 Copublished by the IEEE Computer and ption and Decryption using VHDL, International J. of Engg. Research & Indu. Appls. (IJERIA). ISSN 0974-1518, Vol. 4, No. III
- 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 6, Issue 1, January (2015), pp. 23-29 © IAEME 29 5. B.Subramanyan, Vivek.M.Chhabria, T.G.Sankar babu, Image Encryption Based on AES Key Expansion, 2011 Second International Conference on Emerging Applications of Information Technology 978-0-7695-4329-1/11 $26.00 © 2011 IEEE DOI 10.1109/EAIT.2011.60, 217- 220 6. About AES – Advanced Encryption Standard, Copyright 2007 Svante Seleborg Axantum Software AB. 7. Dhanya Pushkaran and Neethu Bhaskar, “AES Encryption Engine For Many Core Processor Arrays For Enhanced Security” International journal of Electronics and Communication Engineering &Technology (IJECET), Volume 5, Issue 12, 2014, pp. 106 - 111, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. 8. Priyanka Chauhan and Girish Chandra Thakur, “Efficient Way of Image Encryption Using Generalized Weighted Fractional Fourier Transform with Double Random Phase Encoding” International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 5, Issue 6, 2014, pp. 45 - 52, ISSN Print: 0976-6480, ISSN Online: 0976-6499. 9. Prof. Maher K. Mahmood and Jinan N. Shehab, “Image Encryption and Compression Based on Compressive Sensing and Chaos” International journal of Computer Engineering & Technology (IJCET), Volume 5, Issue 1, 2014, pp. 68 - 84, ISSN Print: 0976 – 6367, ISSN Online: 0976 – 6375. 10. J. V. Gorabal and Manjaiah D. H, “Image Encryption Approach for Security Issues” International Journal of Information Technology and Management Information Systems (IJITMIS), Volume 5, Issue 2, 2010, pp. 59 - 64, ISSN Print: 0976 – 6405, ISSN Online: 0976 – 6413. 11. Ahmad Salameh Abusukhon, “Block Cipher Encryption For Text-To-Image Algorithm” International journal of Computer Engineering & Technology (IJCET), Volume 4, Issue 3, 2013, pp. 50 - 59, ISSN Print: 0976 – 6367, ISSN Online: 0976 – 6375.