A novel image encryption scheme based on different block sizes for grayscale and color images

Abstract

In this paper, two image encryption schemes are proposed for grayscale and color images. The two encryption schemes are based on dividing each image into blocks of different sizes. In the first scheme, the two dimension (2D) input image is divided into various blocks of size N × N . Each block is transformed into a one dimensional (1D) array by using the Zigzag pattern. Then, the exclusive or (XOR) logical operation is used to encrypt each block with the analogous secret key. In the second scheme, after the transformation process, the first block of each image is encrypted by the corresponding secret key. Then, before the next block is encrypted, it is XORed with the first encrypted block to become the next input to the encrypting routine and so on. This feedback mechanism depends on the cipher block chaining (CBC) mode of operation which considers the heart of some ciphers because it is highly nonlinear. In the case of color images, the color component is separated into blocks with the same size and different secret keys. The used secret key sequences are generated from elliptic curves (EC) over a binary finite field F2m . Finally, the experimental results are carried out and security analysis of the ciphered images are demonstrated that the two proposed schemes had a better performance in terms of security, sensitivity and robustness.

A Hyperchaotic Color Image Encryption Algorithm and Security Analysis

“…Figure 7 indicates that this algorithm has good robustness. [17] -0.0102 0.0076 -0.0153 Ciphertext [18] 0.0129 0.0065 0.0013 Ciphertext [19] 0.0034 0.0050 0.0056 Ciphertext [20] 0…”

“…Information Entropy plaintext 7.4481 ciphertext 7.9991 ciphertext [4] 7.8556 ciphertext [17] 7.8534 ciphertext [20] 7.9994 ciphertext [24] 7.9551…”

“…According to Table 2, by comparing the information entropy of plaintext, ciphertext of this algorithm, and ciphertext image of [4,17,20,24], it can be concluded that the information entropy value of the encrypted image of this algorithm is closer to the ideal value 8 which means that the encrypted image is closer to the random signal source and this algorithm has the ability to resist entropy attack.…”

“…, , ) = ( , , ) [4] 99.63 33.54 Ciphertext [17] 86.55 33.47 Ciphertext [18] 99.63 33.51 Ciphertext [20] 99.60 30.34…”

“…When the NPCR and UACI of the ciphertext are greater than 99.6% and 33.46%, respectively, it indicates that the algorithm has good security. As shown in Table 3, by comparing the NPCR and UACI values of [4,17,18,20], this algorithm is more sensitive to plaintext than the references listed in Table 3. Therefore, this algorithm can meet the security requirements and has good resistance to differential attack.…”