A Benchmarking assessment of known visual cryptography algorithms

With the growth of digital media, it is becoming more prevalent to find a method to protect the security of that media. An effective method for securely transmitting images is found in the field of Visual Cryptography. While this method is effective for securely transmitting images, many methods have been developed since the first algorithm was proposed in 1994 by Naor and Shamir. A benchmarking scheme is proposed to give the algorithm capabilities, understand the implementation method, evaluate the algorithm development, and provide image reconstruction information. Additionally, the algorithms are ranked according to a Visual Cryptography standard. This would allow an easy way to differentiate between algorithms and determine the ideal algorithm for a given task or project

Coexistence and Secure Communication in Wireless Networks

In a wireless system, transmitted electromagnetic waves can propagate in all directions and can be received by other users in the system. The signals received by unintended receivers pose two problems; increased interference causing lower system throughput or successful decoding of the information which removes secrecy of the communication. Radio frequency spectrum is a scarce resource and it is allocated by technologies already in use. As a result, many communication systems use the spectrum opportunistically whenever it is available in cognitive radio setting or use unlicensed bands. Hence, efficient use of spectrum by sharing users is crucial to increase maximize system throughput. In addition, secrecy of a wireless communication system is traditionally provided by computational complexity of cryptography techniques employed. However, cryptography systems depend on either a random secret key generation mechanism or a trusted key distribution system. Recent developments in the wireless communication area provided a solution to both key generation and distribution problem via exploiting randomness of the wireless channel unconditional to the computational complexity. In this dissertation, we propose solutions to the problems discussed. For spectrum sharing, we present a detailed analysis of challenges of efficient spectrum sharing without a central enforcing mechanism, provide insight to already existing power control algorithms and propose a novel non-greedy power allocation algorithm. Numerical simulations show that the proposed algorithm increases system throughput more than greedy algorithms and can use available spectrum to the fullest, yet it is robust to the presence of greedy users. For secrecy, we propose a practical and fast system for random secret key generation and reconciliation. We extend the proposed system to multiple-input-multiple-output systems and increase security via role reversal of the nodes while making it quicker by pre-encoding procedure. Information theory calculation and numerical simulations demonstrates that the proposed system provides a secure channel for legitimate users in the presence of a passive eavesdropper

植基於區塊漸進還原之非擴展式視覺機密分享

[[abstract]]In the related works of progressive visual secret sharing (PVSS), Wang et al. (2007) and Wang (2009) all have the following drawbacks: (1) The design of the dispatching matrices is not regular. (2) Shares are m-times larger than the original secret image. (3) Restored image's quality is poor. (4) Their schemes are not suitable to apply in grayscale and color secret images. In order to solve the above limitations, we propose a non-expanded PVSS approach, in which the recovery method is based on secret blocks, namely Block-based Progressive Visual Secret Sharing (BPVSS). We divide a secret image into n non-overlapped image blocks, and an additional portion of secret will be restored after superimposing one more transparency. When superimposing any t shares, there have t (2≤t≤n) secret blocks being restored. Compared with other related works, BPVSS has several advantages: (1) The concept of this model is concise, easy to implement, and the number of participants will not be restricted. (2) In the situation of noise-like shares, the contrast of the restored image is 50%, which means that the hidden message can be clearly recognized by the naked eyes. (3) When transparencies are shifted from noise-like into meaningful, the contrast of the stego-image and the restored image will be 25% which is still superior to other related studies. (4) Our scheme is more suitable for grayscale and color secret images than previous related studies. (5) The size of transparencies is the same as the size of secret image.[[notice]]補正完畢[[incitationindex]]TSSCI[[booktype]]電子

Primary and secondary processes in normal and dyslexic word identification

Skilled visual word identification is an effortless component of fluent reading, subserved by a relatively fast, automatic, primary lexical access process. Experimental tasks and neuropsychological conditions that restrict information flow to primary process invoke task specific or secondary process mediated identification. These secondary processes may be alternative routes to identification, used infrequently by skilled readers, but more frequently while acquiring literacy, or when primary process fails. They are sometimes referred to as guessing and meta-linguistic functions. The focus of mainstream research on primary lexical access has meant that they remain relatively unexplored components of normal word recognition. The thesis proposes a limited set of secondary 'completion' processes, to avoid using the term 'guess'. Completion processes 'complete' degraded input to deliver candidate identifications. Lexical completions are mediated by the orthographic input lexicon, and involve the amplification of sub-threshold representations, either by serial deployment of attention to enhance letter level representations, or by parallel attentional modulation of word level activation. Sublexical completion processes explicitly identify letters, and 'retrieve' or 'assemble' words from letter identities or names. These completions are under constant 'revision' in the normal, motivated, system. In conjunction with primary process, these secondary processes form a broader view of normal word recognition formalised in a flow model call the primary secondary process model Experimental results indicate that lexical completion is associated with inhibitory effects of neighbourhood size, and that sublexical completion may result in inhibitory or facilitatory effects of neighbourhood size depending on the nature of fragments and procedures used. Neuropsychological results indicate that secondary process deficits may restrict the compensatory strategies open to peripheral dyslexics, and hence, that their performance is best described in terms of both residual primary and residual secondary processes. The explanatory role of secondary processing may extend beyond peripheral dyslexia and fragment completion, to encompass strategic and individual differences in adult performance, and developmental differences in the acquisition of literacy

Programming and Problem Solving: A Transcript of the Spring 1999 Class

This report contains edited transcripts of the discussion held in Columbia's Programming and Problem-Solving course, taught as W4995-01during Spring 1999. The class notes were taken by the teaching assistant so that students could focus on the class material. As a service to both the students and to others who would like to get some insight into the class experience, we have drawn all of the class handouts, discussion, and some of the results into this technical report

Interaction and interest management in a scripting language.

Interaction management is concerned with the protocols that govern interactive activities among multiple users or agents in networked collaborative environments. Interest management is concerned with the relevance-based data filtering in networked collaborative environments. The main objective of the former is to structure interactive activities according to the requirements of the application concerned, while the main objective of the latter is to provide secured data transmission of a subset of information relevant to each recipient. The research in these two important aspects of networked software has largely been carried out in specific application domains such as online meetings, online groupware and online games. This thesis is concerned with the design and implementation of high-level language constructs for interaction and interest management. The work that has been undertaken includes: an abstract study of interactive activities and data transmission in networked collaborative environments through a large number of variations of the noughts and crosses game; the design of a set of language constructs for specifying a variety of interaction protocols; the design of a set of language constructs for specifying secured data sharing with relevance-based filtering; the implementation of these language constructs in the form of a major extension of a scripting language JACIE (Java-based Authoring Language for Collaborative Interactive Environments); the development of two demonstration applications, namely e-leaming on Simulation of Network Trouble Shooting and online Bridge, using the extended JACIE for demonstrating the technical feasibility and usefulness of the design. These high-level language constructs support a class of complicated software features in networked collaborative applications, such as turn management, interaction timing, group formation, dynamic protocol changes, distributed data sharing, access control, authentication and information filtering. They enable programmers to implement such features in an intuitive manner without involving low-level system programming directly, which would otherwise require the knowledge and skills of experienced network programmers

Robust digital image watermarking algorithms for copyright protection

Digital watermarking has been proposed as a solution to the problem of resolving copyright ownership of multimedia data (image, audio, video). The work presented in this thesis is concerned with the design of robust digital image watermarking algorithms for copyright protection. Firstly, an overview of the watermarking system, applications of watermarks as well as the survey of current watermarking algorithms and attacks, are given. Further, the implementation of feature point detectors in the field of watermarking is introduced. A new class of scale invariant feature point detectors is investigated and it is showed that they have excellent performances required for watermarking. The robustness of the watermark on geometrical distortions is very important issue in watermarking. In order to detect the parameters of undergone affine transformation, we propose an image registration technique which is based on use of the scale invariant feature point detector. Another proposed technique for watermark synchronization is also based on use of scale invariant feature point detector. This technique does not use the original image to determine the parameters of affine transformation which include rotation and scaling. It is experimentally confirmed that this technique gives excellent results under tested geometrical distortions. In the thesis, two different watermarking algorithms are proposed in the wavelet domain. The first algorithm belongs to the class of additive watermarking algorithms which requires the presence of original image for watermark detection. Using this algorithm the influence of different error correction codes on the watermark robustness is investigated. The second algorithm does not require the original image for watermark detection. The robustness of this algorithm is tested on various filtering and compression attacks. This algorithm is successfully combined with the aforementioned synchronization technique in order to achieve the robustness on geometrical attacks. The last watermarking algorithm presented in the thesis is developed in complex wavelet domain. The complex wavelet transform is described and its advantages over the conventional discrete wavelet transform are highlighted. The robustness of the proposed algorithm was tested on different class of attacks. Finally, in the thesis the conclusion is given and the main future research directions are suggested