Design of image cipher using block-based scrambling and image filtering

Highlights

• An image cipher using block-based scrambling and image filtering (IC-BSIF) is introduced;

• It is the first time that image filtering is used to do encryption;

• IC-BSIF uses the well-known substitution-permutation network and strictly follows the principles of confusion and diffusion;

• The block-based scrambling is to fast separate neighboring pixels to different rows and columns, and thus can sufficiently weaken the strong correlation between adjacent pixels;

• IC-BSIF can encrypt different kinds of images into noise-like ones, and security evaluations demonstrate that it can achieve better performance than some state-of-the-art encryption schemes.

Abstract

The operation of image filtering is widely used to deblur digital images. However, using inappropriate masks, it can also blur images. Motivated by this concept, this paper introduces an image cipher using block-based scrambling and image filtering (IC-BSIF). To the best of our knowledge, this is the first time that image filtering has been used for image encryption. IC-BSIF uses the well-known substitution-permutation network and strictly follows the concepts of confusion and diffusion. The block-based scrambling is able to separate neighboring pixels to different rows and columns, and thus can efficiently weaken the strong correlations between adjacent pixels. Using randomly generated masks by the secret key, the image filtering can spread little change of plain-images to the entire pixels of cipher-images. Simulation results show that IC-BSIF can encrypt different kinds of images into noise-like ones, and security evaluations demonstrate that it can achieve better performance than several state-of-the-art encryption schemes.

Introduction

The two-dimensional (2D) digital images play more and more important roles in the modern digital technology. A 2D digital image is a type of 2D data, which carries data with a visualized and meaningful way. Then, if secret images are stolen, used or viewed by unauthorized users, disastrous security issues may happen. For example, if the spy steals the images of one new martial weapon, the hostile country may obtain the detail settings and parameters of the weapon by analyzing these images. Therefore, it is quite important to protect digital images and image cipher is an efficient solution of image security issue by encrypting a digital image into a random-like cipher-image [3], [31], [35]. Only with the correct secret key, one can recover the original image from the cipher-image.

Up to now, researchers have developed many image ciphers using different kinds of techniques [8], [15], [16], [17], [18], [23], [29]. Among these techniques, chaos theory is the most widely used one [1], [21], [34], [36], [37]. This is due to that chaotic maps have the properties of initial state sensitivity, unpredictability and ergodicity, and these properties can be found similar counterparts in image cipher [7], [9]. Some examples of chaos-based image ciphers are as follows. In [33], a new image encryption scheme was designed using a new one-dimensional (1D) chaotic map, which is developed by combining two existing chaotic maps. In [11], an image cipher was developed using a new 2D chaotic map, named 2D-SLMM. In [10], another image cipher was proposed using a new 2D chaotic map, called 2D-LASM. For these chaos-based image ciphers, their security levels are highly dependent on the performance of their used chaotic maps. However, the chaotic behaviors of chaotic maps may degrade to periodic behaviors when they are implemented in the finite precision platforms. This greatly reduces the security levels of the corresponding encryption schemes [22]. Many researchers have proved that some chaos-based ciphers owning low security levels can be successfully attacked [13], [14], [20], [28].

Besides chaos theory, many other techniques were also applied to designing image ciphers [2], [6], [30]. Some examples are as follows. In [27], the authors developed an image encryption scheme, which uses the Latin sequences to do pixel permutation and substitution. In [5], the authors proposed a novel image encryption scheme using Gray code. The Gray code is used to do pixel permutation and a plain pixel-related image diffusion structure is used to achieve the diffusion property.

It is well-known that image filtering is widely used in many digital image processing technologies, such as image deblurring, image smoothing and edge detection. This paper first presents the concept of using image filtering to encrypt a digital image, and then designs a new image cipher using block-based scrambling and image filtering (IC-BSIF). IC-BSIF adopts the well-known substitution-permutation network and strictly follows the confusion and diffusion concepts. The block-based scrambling first divides image into blocks, and then randomly shuffles pixels of each block into different rows and columns. It can simultaneously shuffle the row and column positions of a pixel and thus can achieve a high efficiency to reduce the strong correlations between adjacent pixels. Using randomly generated masks, the image filtering operation can spread little change in plain-image to the entire cipher-image. Simulation results and security analysis show that IC-BSIF can encrypt different kinds of digital images into random-like ones with high security levels.

The rest of this paper is organized as follows. Section 2 presents the concepts of image filtering. Section 3 introduces IC-BSIF and Section 4 displays its simulation results. Section 5 evaluates the security performance of IC-BSIF and the last section concludes this paper.