A Combination of Block-Based Chaos with Dynamic Iteration Pattern and Stream Cipher for Color Image Encryption

This research proposes an encryption method on images using a combination of chaotic methods, streams, and hash functions. SHA-1 is used as a hash function to encrypt key inputs to be more secure and can produce more dynamic keys at chaotic and stream encryption stages. Chaos encryption is done by dividing the image into small blocks where each encrypted block differs based on a dynamic key pattern based on chaotic keys. At the last stage, all blocks are made as whole images again to be encrypted by the stream method. Tests carried out on standard RGB images and Indonesian batik images. Encryption quality measurements using entropy, histogram analysis, UACI, NPCR, SSIM, PSNR, and the avalanche effect. Based on the results of trials the proposed method is proven to be resistant to various attacks such as statistics as evidenced by the average entropy value of 7.9996, avalanche effect value of 50.0366 and a relatively uniform histogram, while differential attack as evidenced by the value of UACI 33.5716 and NPCR 99.6082 where this value is very close to ideal. Also visually the results of the encryption look very chaotic and very different from the original image, which is evidenced by the value of PSNR 8.0191 and SSIM 0.0081. The decryption process can also be done perfectly wherein the resulting infinity value on PSNR and value 1 on SSIM.

High-Capacity Reversible Data Hiding in Encrypted Images by Information Preprocessing

With the development of cloud computing, high-capacity reversible data hiding in an encrypted image (RDHEI) has attracted increasing attention. The main idea of RDHEI is that an image owner encrypts a cover image, and then a data hider embeds secret information in the encrypted image. With the information hiding key, a receiver can extract the embedded data from the hidden image; with the encryption key, the receiver reconstructs the original image. In this paper, we can embed data in the form of random bits or scanned documents. The proposed method takes full advantage of the spatial correlation in the original images to vacate the room for embedding information before image encryption. By jointly using Sudoku and Arnold chaos encryption, the encrypted images retain the vacated room. Before the data hiding phase, the secret information is preprocessed by a halftone, quadtree, and S-BOX transformation. The experimental results prove that the proposed method not only realizes high-capacity reversible data hiding in encrypted images but also reconstructs the original image completely.