Yuanlong Cai

On the security of a chaotic encryption scheme: problems with computerized chaos in finite computing precision

Zhou et al. have proposed a chaotic encryption scheme, which is based on a kind of computerized piecewise linear chaotic map (PWLCM) realized in finite computing precision. In this paper, we point out that Zhous encryption scheme is not secure enough from strict cryptographic viewpoint. The reason lies in the dynamical degradation of the computerized piecewise linear chaotic map employed by Zhou et al. The dynamical degradation of the computerized chaos induces many weak keys to cause large information leaking of the plaintext. In addition, we also discuss three simple countermeasures to enhance the security of Zhous cryptosystem, but none of them can essentially enhance the security.

Chaotic encryption scheme for real-time digital video

In this paper, we propose a novel video encryption scheme based on multiple digital chaotic systems, which is called CVES (Chaotic Video Encryption Scheme). CVES is independent of any video compression algorithms, and can provide high security for real-time digital video with fast encryption speed, and can be simply realized both by hardware and software. Whatí»s more, CVES can be extended to support random retrieval of cipher-video with considerable maximal time-out; the extended CVES is called RRS-CVES (Random-Retrieval-Supported CVES). Essentially speaking, CVES is a universal fast encryption system and can be easily extended to other real-time applications. In CVES, 2n chaotic maps are used to generate pseudo-random signal to mask the video, and to make pseudo-random permutation of the masked video. Another single chaotic map is employed to initialize and control the above 2n chaotic maps. Detailed discussions are given to estimate the performance of CVES/RRS-CVES, respectively from the viewpoints of speed, security, realization and experiments.

Improving security of a chaotic encryption approach

E. Alvarez et al. presented a new chaotic encryption approach recently. But soon G. Alvarez et al. broke it with four cryptanalytic methods and found some other weaknesses. In this Letter we point out why the original scheme is so vulnerable to the proposed four attacks. The chief reasons are two essential defects existing in the original scheme. Based on such a fact, we present an improved encryption scheme to obtain higher security. The cryptographic properties of the improved scheme are studied theoretically and experimentally in detail.

Baptista-type chaotic cryptosystems: problems and countermeasures

In 1998, M.S. Baptista proposed a chaotic cryptosystem, which has attracted much attention from the chaotic cryptography community: some of its modifications and also attacks have been reported in recent years. In [Phys. Lett. A 307 (2003) 22], we suggested a method to enhance the security of Baptista-type cryptosystem, which can successfully resist all proposed attacks. However, the enhanced Baptista-type cryptosystem has a non-trivial defect, which produces errors in the decrypted data with a generally small but non-zero probability, and the consequent error propagation exists. In this Letter, we analyze this defect and discuss how to rectify it. In addition, we point out some newly-found problems existing in all Baptista-type cryptosystems and consequently propose corresponding countermeasures.

Performance analysis of Jakimoski-Kocarev attack on a class of chaotic cryptosystems

Recently Jakimoski and Kocarev cryptanalyzed two chaotic cryptosystems without using chaotic synchronization—Baptista cryptosystem and Alvarez cryptosystem. As a result, they pointed out that neither of the two cryptosystems are secure to known-plaintext attacks. In this Letter, we re-study the performance of Jakimoski–Kocarev attack on Baptista cryptosystem and find that it is not efficient enough as a practical attack tool. Furthermore, a simple but effective remedy is presented to resist Jakimoski–Kocarev attack, and the detailed discussion on its performance are given.

Novel method of vessel axis reconstruction from the rotary projections based on furcation model

The three-dimensional reconstruction of human brain vessels has been the research focus in recent year. Reconstructing the axis and the cross section of vessels respectively is one effective method in 3D vessel reconstruction. However the conventional reconstruction methods usually take the complicated space relations of different projections into counts to match a vessel segment in different angles. Obviously, this kind of method is very convoluted and can not be easily used in general situations. Considering that the underlying cause of the difficulty in reconstruction is the complexity of brain vesselsí» intricate directions and bifurcation styles, this paper proposes a novel method of vessel axis reconstruction based on vessel bifurcation model. The experiments are satisfying.

Reconstruction of rotary DSA vessel axis based on the matching of multiple projections

A novel method of the matching and reconstruction of DSA vessel axis is proposed based on the redundant information from multiple two-dimensional (2-D) projections of the object. First, a correlation scheme on pixels gray level is used to extract the vessel structure on every projection. Through this way, we acquire a binary image. Secondly, Hit-Miss Transform (HMT) is applied on the binary image to produce a vessel axis image. Thirdly, an arbitrary projection is chosen as base image, and others are chosen as reference images. For each key point in the base image, the matching points are found from the key points of the reference images according to epipolar geometry and the topological linking relations of vessel branches. The matching segments are determined from matched key points. If one segment of vessel axis in the base image is confirmed to be matching with one in the reference image, an interpolation process may be used to find out the corresponding relationship of points on these two segments. Then we can get a continuous 3-D segment of DSA vessel axis according to reconstruction the matched points between two views. The whole process is executed repeatedly when another image is selected as base image. The experiment result shows that this method may provide satisfactory reconstruction even the vessel extraction result is not very accurate.

Segment self-guide reconstruction algorithm based on object-oriented quantization

Aiming at the problem of inaccurate imaging model of threedimensional (3D) reconstruction of rotational DSA (digital subtraction angiography) images, firstly a nonlinear model based on object-oriented quantization is introduced. The model quantizes the projective pixel of 3D vessel slice as the vessel number that the X-ray goes through. Then, under the constraint of limited views and sparse projections, a slice reconstruction algorithm named segment self-guide reconstruction (SSGR) is developed. It converts the slice reconstruction of N+1 level nonlinear quantized DSA image to the reconstruction of N vessel cross-sections. The SSGR is especially suitable for solving the problem of sparse projections and limited-views. Finally, the simulated results have proved the feasibility of the model and the validity of the algorithm.

3D reconstruction model of vessels based on object-oriented quantization

This paper discusses such a binary three-dimensional (3D) vessel model whose voxel will be 1 if it belongs to vessel volume otherwise it will be 0. The model can be considered as a stack piled up by a series of slices, and each slice is a 2D binary image. A digital subtraction angiogram (DSA) image is a projection of the 3D vessel model in certain angle, while the projection of a slice is a line in the DSA image. The paper is thus to discuss the representation of the slice projection and the reconstruction model. Based on an assumption of parallel ray geometry, a binary projection model of the slice is introcded, which can be describe by Boolean Radon Transform (BRT). Then a nonlinear quantitative model of DSA image is presented. Simultaneous a slice reconstruction algorithm is developed, which is called optimal square wave decomposition (OSWD). In the end, some simulation results are given, which prove validity of the models.

Parametrical model of vessel cross-section reconstruction based on elasticity quality

As an extremely important part of vessels three-dimensional reconstruction, the vessel cross-sections reconstruction has been incisively researched around the world. Up to now, most of the reconstruction methods use circle or ellipse vessel cross-section as prior information model and search optimal cross-section contour with complex arithmetic. Most researchers have paid little attention to exploiting the vessels elasticity qualities, which virtually can bring many advantages to the whole reconstruction process. Based on this viewpoint, a novel parametrical model of vessel cross-section is presented using vessels elasticity qualities in this paper. Sufficient experiments have been made to test the effects of the elasticity model. These results indicate that the parametrical model can excellently describe the various real vessels cross-section contour by controlling these limited parameters. For instance, when ten parameters are adopted, the models reconstruction error can be reduced to 2.5%. The study of the elasticity model is quite promising in many aspects of 3D reconstruction of vessel, and the models further application potential is apparent.