Enhanced Block Based color Image Encryption technique with confusion

Encryption is used to disguise data making it unintelligible to unauthorized observers. Providing such security is especially important when data is being transmitted across open networks such as the Internet. Since, image data have special features such as bulk capacity, high redundancy and high correlation among pixels that imposes special requirements on any encryption technique. In this paper, an extension is proposed to the block-based image encryption algorithm (BBIE) scheme that works in combination with Blowfish encryption algorithm [16]. Whereas BBIE is meant for 256-color bitmap images, the proposed technique also handles RGB color images and, for the cases studied, improves the security of digital images. In this enhanced technique, which we call the enhanced block based image encryption technique (EBBIE) the digital image is decomposed into blocks, then two consecutive operations - rotating each 3D true color image block by 90deg followed by flipping row-wise down - are performed to complicated the relationship between original and processed image. These rendered blocks are then scrambled to form a transformed confused image followed by Blowfish cryptosystem that finally encrypts the image with secret key. Experimental results show that correlation between adjacent pixels is decreased in all color components and entropy is increased for the cases studied.