Enhanced pixel value differencing with cryptography algorithm

. The combination of Steganography and cryptography algorithms can improve the security of data you want to keep secret. Pixel Value Differencing (PVD) algorithm combined with Word Auto Key Encryption (WAKE) algorithm and Modular Multiplication Block Cipher algorithm can produce good ciphertext and inserted on image media by using PVD algorithm that convert each ciphertext into pixel.


Introduction
Today's communication and information technology is growing rapidly and almost all communications are connected with internet technology. For example the development of Internet network that allows anyone to exchange data or information through the internet network. Communication becomes very important and there are times when communication is confidential and do not want to know the other party [1][2][3].
Steganography and cryptography [4][5][6][7][8] is an existing technique to accommodate the security of communication made by users, steganography is a technique used to hide information on the media. The most important aspect of steganography is the security level of information concealment, which refers to how much the inability of third parties to detect the existence of hidden information [9][10][11]. Cryptography has a different way of working, especially in terms of data security, cryptography change the data you want to secure in a form that is difficult to understand by others but this raises suspicion for others [12,13].
Pixel Value Differencing [6,14,15] is a steganography algorithm that can be used to hide messages into image pixels by converting messages into RGB hexadecimal shapes and replacing pixel values in images with hexadecimal RGB message values [14], the pixel value differencing method is quite good compared to other steganography algorithms [15] but to increase the security of hidden messages is combined with Word Auto Key Encryption (WAKE) [16] cryptographic algorithms and Modular Multiplication Block Cipher (MMB) [13,17].
The combination of WAKE and MMB algorithm in encryption process on steganography Pixel Value Differencing will be increase security of message and it is not easy to be known by irresponsible party.

Pixel Value Differencing
Pixel Value Differencing Scheme using a pixel value between two blocked pixel and determine how many secret bits to be embedded [6]. Pixel Value differencing was using Wu and Tsai scheme for wide range and large capacity. The insertion process in this method perform by comparing the two neighboring pixels Pi and Pi + 1 using equation.  [6]. The scheme determines the range of values to be between 2 pixels, then the value of the range is calculated by the equation [14,15].
Wi: The smallest value of the scheme Wu and Tsai. Furthermore, the difference value is calculated a new value for insertion into the image using equation Where m obtained from the difference d'i within using the equation All processes are performed continuously until all message bits inserted into the image.

Word Auto Key Encryption
WAKE stands for Word Auto Key Encryption, this method was invented by David Wheeler in 1993. The WAKE method uses a 128 bit key and a 256 x 32 bit table.
In the algorithm, this method uses XOR, AND, OR and Shift Right operations [16,18]. The main process of WAKE consists of: 1) The process of forming table S-Box (Substitution Box).
2) The process of forming the key.
The core of the WAKE method lies in the process of forming the S-Box table and the key building process. The S-Box table of the WAKE method is flexible and varies for each round. The core of the WAKE method does not lie in the encryption and decryption process, since the encryption and decryption process are just XOR operations of the plaintext and keys to generate ciphertext or XOR ciphertext operations and keys to produce plaintext. P = C  K C = P  K

Modular Multiplication Block Cipher
The weakness of IDEA method using 64 bit plaintext and multiplication of modulo 216 + 1 is solved by the presence of MMB algorithm (Modular Multiplication Block cipher). MMB algorithm uses 64 bit plaintext (4 pieces 16 bit subblock text) [13]. The cryptography MMB algorithm uses 128-bit plaintext and iterative algorithms such as XOR as well as parallel applications of four reversible non-linear substitutions. This substitution is determined by a multiplication operation modulo 2 32 -1 with a constant factor, which has a higher securities rate. A non-linear function, f, is applied six times along with the XOR function. The process of encryption and decryption MMB method can be seen in the following diagram:

Results and Discussion
The first experiment is determine the message and key that will be used for the encryption process using the WAKE algorithm. The pixel values above assumption are only given to testing steganography with Pixel Value Differencing Algorithm after the pixel values obtained subsequent process can continue by inserting a message with the following steps: a. Messages to hidden is Ã = 11000011 b. Take a neighboring pixel of the image is pixel (0,0) and pixel (0.1), the pixel value is made to do the insertion, the following is a table of neighboring pixel values are 50 and 167. c. Message extraction process can be perform in the same way as the embedded process and using Wu and Tsai scheme, and then use MMB and WAKE algorithm for decryption process by using key for each algorithm too.

Conclusion
WAKE and MMB algorithm on the process of inserting messages in the image with Pixel Value Differencing algorithm can provide a better level of security because the message will be encrypted before it is inserted, and for cryptanalyst takes a very long time to decrypt the ciphertext.