Nanrun Zhou

Flexible multiple-image encryption algorithm based on log-polar transform and double random phase encoding technique

We present a novel multiple-image encryption algorithm by combining log-polar transform with double random phase encoding in the fractional Fourier domain. In this algorithm, the original images are transformed to annular domains by inverse log-polar transform and then the annular domains are merged into one image. The composite image is encrypted by the classical double random phase encoding method. The proposed multiple-image encryption algorithm takes advantage of the data compression characteristic of log-polar transform to obtain high encryption efficiency and avoids cross-talk in the meantime. Optical implementation of the proposed algorithm is demonstrated and numerical simulation results verify the feasibility and the validity of the proposed algorithm.

Image encryption combining multiple generating sequences controlled fractional DCT with dependent scrambling and diffusion

Based on the fractional discrete cosine transform with multiple generating sequences (MGSFrDCT) and the dependent scrambling and diffusion (DSD), an image encryption algorithm is proposed, in which the multiple-generating sequences greatly enlarge the key space of the encryption system. The real-valued output of MGSFrDCT is beneficial to storage, display and transmission of the cipher-text. During the stage of confusion and diffusion, the locations and values of all MGSFrDCT transformed coefficients change due to DSD, and the initial values and fractional orders of encryption system depend not only on the cipher keys but also on the plain-image due to introduction of a disturbance factor, which allows the encryption system to resist the known-plaintext and chosen-plaintext attacks. Experimental results demonstrate that the proposed encryption algorithm is feasible, effective and secure and able to resist common classical attacks.

Color Image Encryption Algorithm Combining Compressive Sensing with Arnold Transform

A new color image encryption algorithm combining compressive sensing with Arnold transform is proposed, which can encrypt the color image into a gray image. Considering the dimensional reduction and random projection of compressive sensing, we utilize compressive sensing to encrypt and compress the three color components of color image simultaneously. The three encrypted and compressed color components’ dimensions are smaller than the original image, thus they can be grouped into a gray image, and then the gray image is scrambled by Arnold transform to enhance the security. The proposed algorithm can also be applied in the multiple-image encryption. The experimental results show the validity and the reliability of the proposed algorithm.

Color image encryption combining a reality-preserving fractional DCT with chaotic mapping in HSI space

A color image encryption algorithm by combining the reality-preserving fractional DCT (RPFrDCT) with chaotic mapping in HSI space is presented, in which the generating sequence (GS) is introduced and produced by 2D chaotic mapping to ensure the uniqueness of the transform matrix and enlarge the cipher key space of the encryption system. In addition, the color image is converted from standard RGB space into HSI space and the nonlinearity of the spatial transform makes the proposed encryption algorithm more secure than linear ones. Three components, namely H, S and I, are encrypted by the RPFrDCT with fractional orders and GS as cipher keys. Three-dimensional (3D) scrambling is adopted to further enhance the security of the encryption algorithm. The nonlinearity of the spatial transform from RGB to HSI, the real-valued output and the high cipher key-sensitivity guarantee the security and the feasibility of the proposed encryption algorithm. Experimental results demonstrate that the proposed encryption algorithm is sensitive to cipher keys and, to some extent, robust to noise and occlusion attacks.

Image encryption based on a reality-preserving fractional discrete cosine transform and a chaos-based generating sequence

A novel image encryption technique based on a reality-preserving fractional discrete cosine transform (FrDCT) and a chaos-based generating sequence is proposed. The FrDCT is a generalization of the discrete cosine transform (DCT). This reality-preserving FrDCT inherits the virtues of both the DCT and fractional transform, providing improved security and flexibility by employing the generating sequence as an extra key in addition to the fractional orders. The most fascinating advantage of the FrDCT is its reality-preserving property, which ensures real ciphertext for real plaintext, which is conducive to display, storage, and transmission. Performance and security analysis demonstrates that this algorithm is valid, secure, sensitive to keys, and robust to noise and occlusion attacks.

Image encryption scheme based on random fractional discrete cosine transform and dependent scrambling and diffusion

Abstract An image encryption scheme is proposed by combining the random fractional discrete cosine transform (RFrDCT) with the dependent scrambling and diffusion (DSD). The application of the randomization, irrational choice and vectorization of fractional orders and the randomization of generating sequences improves the key-sensitivity and thus enlarges the key space greatly. Both the locations and the values of RFrDCT transformed coefficients are changed during the stage of DSD to further enhance the security of image encryption scheme. Numerical simulations demonstrate that the proposed image encryption scheme is feasible, secure and capable of resisting common classical attacks.