Blowfish Encryption Using Key Secured Block Based Transformation

Encryption is a process of converting a one form of information in another form which is hard to understand .Now a days, a large amount of information get transfer with wired or wireless network. Information contents may be textual data or image data. Therefore encryption of text or image is most important during secure transmission of information. Images are widely used in several processes like military field, medical imaging, video conferencing where confidentiality about image information is very important. As we know, pixels in plain image are strongly correlated. Image information get perceive due to this high correlation. Most of available image encryption algorithms are used for encryption of pixel information only but key secured block based transformation technique change the position of pixels and provide low correlation among image pixels so that less amount of information get perceived . The block transformation algorithm divides the image in to no. of blocks and shuffles their position of blocks to decrease the Correlation and increase its entropy value. Divide an image in more no. of blocks gives the more security of image. Transformation table will decide new positions of blocks. The aim of Key secured block transformation is to enhance the security of an image. Here, key provide a security for transformation table .Different keys generated for different types of image so ,if input image data changed automatically key will also get change. Here key is used for two purposes, one for to build transformation table and second to encrypt image data. So as key changed, transformation table will also get change and image get transformed with this new transformation table. Block Transformed image is then passed for encryption process. Here we used Blowfish image encryption algorithm because of variable and longest key size. At the receiver side these blocks are retransformed in to their original position and performed a decryption process which gives the original image.