Abstract:Encryption is mainly used to transmit the data over networks. There are so many techniques introduced which are used to protect the confidential image data from any unauthorized access. Multimedia data contains different types of data that includes text, audio, video, graphic,images with the increasing use of multimedia data over internet, here comes a demand of secure multimedia data. Most of the encryption algorithm available is generally used for text data and not suitable for multimedia data. In this paper we discuss a block based transformation algorithm in which image is divided in to number of blocks. These blocks are transformed before going through an encryption process. At the receiver side these blocks are retransformed in to their original position and performed a decryption process which gives the original image. Advantage of this approach, is that it reproduce the original image with no loss of information for the encryption and decryption process we used a blowfish algorithm.
KEYWORDS:Image Encryption, Image Correlation, Decryption, Image Entropy, Permutation.
Encryption is a common technique to uphold image security in storage and transmission of digital images are exchanged over network types. The information security has become more important with the progress in the exchange of data and various encryption systems to encrypt and decrypt image and no single encryption algorithm which is satisfied different types of image. In order to dissipate the high correlation among pixels and increase the entropy value, we haveintroduced a transformation algorithm that divides the image into blocks and then shuffles their positions before it passes
them to the encryption algorithm. In this case that
correlation, histograms and entropy has used to measure the security level of the images, advantages of this results in a lower correlation , higher entropy value and a more uniform histogram is compared to using the blowfish encryption algorithm, measures to the security level of the encrypted images. This is similar or different encryption of the variable length secret key is needed in the transformation and encryption process, which is used to build the secret transformation table with a variable number of blocks. If the secret key is changed, another seed will be generated and then the different secret transformation table is obtained. The variable secret key of the Blowfish encryption algorithm is used to encrypt the transformed image. Themutual information among the encrypted image varies and thus increasing the entropy value.
3. PROPOSED ALGORITHM
The proposed algorithm is divided the image in to it random number of blocks with predefined maximum and minimum number of pixels, resulting in a stronger encryption and a decreased correlation.
An Overview of the Transformation Algorithm
The transformation technique works as follows  : here the original image is divided into number of blocks which are shuffled within the image to build a newly transformed image. The generated (or transformed image) is then fed to the blowfish encryption algorithm and thus generated one can be viewed as an arrangement of blocks. This perceivable information can be reduced todecreasing the correlation among the image elements using certain transformation technique. The secret key of this approach is used to determine the seed. The seed plays as role in building the transformation table which is then used to generate the transformed image with different random number of block sizes. In this case, the transformation process refers to the operation of dividing and replacing an arrangement of the original image. Block based encryption and decryption algorithm is based on the combination of image transformation followed by encrypted images and image measurements of correlation,...