Progressive sharing for a secret image

Based on the wavelet transform, a new progressive sharing scheme is proposed to share a secret image into several shadow images using SPIHT encoding processes and Shamir’s threshold scheme. Quality refinement of the recovered image is achieved by the data consumed from the threshold number (r) of shadow images and each single shadow image reveals no information about the secret image. The size of each shadow image is smaller than 1/r of the secret image and any number of shadow images that is less than r reveals no information about the secret image. The proposed approach is secure for image sharing and provides excellent peak signal-to-noise ratio (PSNR) versus rate performance. Experimental results have demonstrated the promising performance of this method in progressive sharing.     

On identification secret sharing schemes

Let be a set of participants sharing a secret from a set of secrets. A secret sharing scheme is a protocol such that any qualified subset of can determine the secret by pooling their shares, the messages which they receive, without error, whereas non-qualified subsets of cannot obtain any knowledge about the secret when they pool what they receive. In (optimal) schemes, the sizes of shared secrets depend on the sizes of shares given to the participants. Namely the former grow up exponentially as the latter increase exponentially. In this paper, instead of determining the secret, we require the qualified subsets of participants to identify the secret. This change would certainly make no difference from determining secret if no error for identification were allowed. So here we relax the requirement to identification such that an error may occur with a vanishing probability as the sizes of the secrets grow up. Under relaxed condition this changing allows us to share a set of secrets with double exponential size as the sizes of shares received by the participants exponentially grow. Thus much longer secret can be shared. On the other hand, by the continuity of Shannon entropy we have that the relaxation makes no difference for (ordinary) secret sharing schemes. We obtain the characterizations of relations of sizes of secrets and sizes of the shares for identification secret sharing schemes without and with public message. Our idea originates from Ahlswede–Dueck’s awarded work in 1989, where the identification codes via channels were introduced.     

Medical image security and EPR hiding using Shamir's secret sharing scheme

Medical applications such as telediagnosis require information exchange over insecure networks. Therefore, protection of the integrity and confidentiality of the medical images is an important issue. Another issue is to store electronic patient record (EPR) in the medical image by steganographic or watermarking techniques. Studies reported in the literature deal with some of these issues but not all of them are satisfied in a single method. A medical image is distributed among a number of clinicians in telediagnosis and each one of them has all the information about the patient's medical condition. However, disclosing all the information about an important patient's medical condition to each of the clinicians is a security issue. This paper proposes a (k, n) secret sharing scheme which shares medical images among a health team of n clinicians such that at least k of them must gather to reveal the medical image to diagnose. Shamir's secret sharing scheme is used to address all of these security issues in one method. The proposed method can store longer EPR strings along with better authenticity and confidentiality properties while satisfying all the requirements as shown in the results.     

Distortion-free secret image sharing mechanism using modulus operator

The (t, n)-threshold has been extended to secret image sharing due to its practicability. In this article, we provide a novel version that employs the modulus operator to embed the secret share into a host image. The simulator shows that the modulus operator is useful for decreasing shadow image distortion. Using Rabin's signature cryptosystem, participants can detect if a cheater exists in the cooperation. In particular, the new mechanism permits involved members to restore a lossless secret image and to reconstruct a distortion-free host image.     

Visual secret sharing with cheating prevention revisited

Visual secret sharing (VSS) is a variant form of secret sharing, and is efficient since secret decoding only depends on the human vision system. However, cheating in VSS, first showed by Horng et al., is a significant issue like a limelight. Since then, plenty of studies for cheating activities and cheating prevention visual secret sharing (CPVSS) schemes have been introduced. In this paper, we revisit some well-known cheating activities and CPVSS schemes, and then categorize cheating activities into meaningful cheating, non-meaningful cheating, and meaningful deterministic cheating. Moreover, we analyze the research challenges in CPVSS, and propose a new cheating prevention scheme which is better than the previous schemes in the aspects of some security requirements.     

Reduce shadow size in aspect ratio invariant visual secret sharing schemes using a square block-wise operation

An aspect ratio invariant visual secret sharing (ARIVSS) scheme is a perfectly secure method for sharing secret images. Due to the nature of the VSS encryption, each secret pixel is expanded to m sub-pixels in each of the generated shares. The advantage of ARIVSS is that the aspect ratio of the recovered secret image is fixed and thus there is no loss of information when the shape of the secret image is our information. For example, a secret image of a circle is compromised to an ellipse if m does not have a square value. Two ARIVSS schemes based on processing one and four pixel blocks, respectively, were previously proposed. In this paper, we have generalized the square block-wise approach to further reduce pixel expansion.     

Visual multiple secret sharing based upon turning and flipping

The secret sharing schemes in conventional visual cryptography are capable of sharing one secret image into a set of random transparencies (called shares) in the form of rectangles, which reveal the secret image to the human visual system when they are superimposed. Recently, visual secret sharing schemes involving multiple secrets have attracted much attention. By adopting rotations on one of the two encoded circle shares, more than two secrets could be shared. Yet, the encoding and decoding processes of circle shares need more sophisticated mechanisms than those of rectangular or square ones. In this paper, we explore the possibilities of visual multiple secret sharing using simply two rectangular or square shares. Specifically, we define some operations onto a transparency based upon turning over or flipping around. Then we propose visual cryptographic schemes that are able to encode two or four secrets into two rectangular shares and up to eight secrets into two square shares such that the secrets cannot be obtained from any single share, whereas they are revealed by stacking the two shares under various combinations of turning or flipping operations. The proposed schemes, which solidly elaborate the relationship between the encoded shares and the shared secrets, broaden the research scope and enrich the flexibility and applicability of visual cryptography or image encryption theoretically and practically.     

一个SMS增值应用系统

介绍了一个SMS增值应用系统的设计框架及相应的技术特点。通过对现有移动通信网络的分析，引出SMS自身的特点，以及针对这些特点提出一些与之相应的适合服务。详细分析了短消息的PDU组帧格式。同时结合其他相关技术构架和设计出了一个具体服务系统，具体阐述了其实现过程和应用价值。最后提出本系统的服务易扩充性，只要通过一定的方法步骤即可方便地达到系统服务的升级。     

A novel secret image sharing scheme in color images using small shadow images

Over the past several years, secret image sharing techniques have become another branch of the effort to prevent secret images from being eavesdropped on, in addition to traditional cryptography. Because smaller shadows can speed up the transmission of a secret color image, in this paper we combine Chang and Wu’s gradual search algorithm for a single bitmap BTC (GSBTC) and Shamir’s (k, n) threshold concept to propose a novel secret color image sharing scheme that generates smaller shadows. Experimental results confirm that the proposed scheme successfully reduces shadow size and that each shadow behaves as a random-like image that prevents leakage of information about the secret color image. Furthermore, the correlation between two vertically or horizontally adjacent pixels in each shadow is significantly less than those in a color secret image, and the presented scheme also achieves, on average, an NPCR = 0.414% and AUCI = 32.78%. Thus, with our scheme one-pixel difference could cause a significant difference in the corresponding shadows. Therefore, the security of the presented scheme is also confirmed.     

Lower bounds on the information rate of secret sharing schemes with homogeneous access structure

We present some new lower bounds on the optimal information rate and on the optimal average information rate of secret sharing schemes with homogeneous access structure. These bounds are found by using some covering constructions and a new parameter, the k-degree of a participant, that is introduced in this paper. Our bounds improve the previous ones in almost all cases.     

A general (k, n) scalable secret image sharing scheme with the smooth scalability

A novel (k, n) scalable secret image sharing (SSIS) scheme was proposed to encrypt a secret image into n shadow images. One can gradually reconstruct a secret image by stacking k or more shadows, but he/she cannot conjecture any information from fewer than k shadows. The advantage of a (k, n)-SSIS scheme is that it provides the threshold property (i.e., k is a threshold value necessary to start in to reveal the secret) as well as the scalability (i.e., the information amount of a reconstructed secret is proportional to the number of shadows used in decryption). All previous (k, n)-SSIS schemes did not have the smooth scalability so that the information amount can be “smoothly” proportional to the number of shadows. In this paper, we consider the smooth scalability in (k, n)-SSIS scheme.     

Contrast-optimal k out of n secret sharing schemes in visual cryptography

Visual cryptography and (k,n)-visual secret sharing schemes were introduced by Naor and Shamir (Advances in Cryptology — Eurocrypt 94, Springer, Berlin, 1995, pp. 1–12). A sender wishing to transmit a secret message distributes n transparencies amongst n recipients, where the transparencies contain seemingly random pictures. A (k,n)-scheme achieves the following situation: If any k recipients stack their transparencies together, then a secret message is revealed visually. On the other hand, if only k−1 recipients stack their transparencies, or analyze them by any other means, they are not able to obtain any information about the secret message. The important parameters of a scheme are its contrast, i.e., the clarity with which the message becomes visible, and the number of subpixels needed to encode one pixel of the original picture. Naor and Shamir constructed (k,k)-schemes with contrast 2^−(k−1). By an intricate result from Linial (Combinatorica 10 (1990) 349–365), they were also able to prove the optimality of these schemes. They also proved that for all fixed kn, there are (k,n)-schemes with contrast . For k=2,3,4 the contrast is approximately and . In this paper, we show that by solving a simple linear program, one is able to compute exactly the best contrast achievable in any (k,n)-scheme. The solution of the linear program also provides a representation of a corresponding scheme. For small k as well as for k=n, we are able to analytically solve the linear program. For k=2,3,4, we obtain that the optimal contrast is at least and . For k=n, we obtain a very simple proof of the optimality of Naor's and Shamir's (k,k)-schemes. In the case k=2, we are able to use a different approach via coding theory which allows us to prove an optimal tradeoff between the contrast and the number of subpixels.     

A necessary and sufficient condition for the asymptotic idealness of the GRS threshold secret sharing scheme

The study of the asymptotic idealness of the Goldreich–Ron–Sudan (GRS, for short) threshold secret sharing scheme was the subject of several research papers, where sufficient conditions were provided. In this paper a necessary and sufficient condition is established; namely, it is shown that the GRS threshold secret sharing scheme is asymptotically ideal under the uniform distribution on the secret space if and only if it is based on 1-compact sequences of co-primes.     

Robot programming using augmented reality: An interactive method for planning collision-free paths

Current robot programming approaches lack the intuitiveness required for quick and simple applications. As new robotic applications are being identified, there is a greater need to be able to programme robots safely and quickly. This paper discusses the use of an augmented reality (AR) environment for facilitating intuitive robot programming, and presents a novel methodology for planning collision-free paths for an n-d.o.f. (degree-of-freedom) manipulator in a 3D AR environment. The methodology is interactive because the human is involved in defining the free space or collision-free volume (CFV), and selecting the start and goal configurations. The methodology uses a heuristic beam search algorithm to generate the paths. A number of possible scenarios are discussed.     

An energy-efficient mobile transaction processing method using random back-off in wireless broadcast environments

Broadcast is widely accepted as an efficient technique for disseminating data to a large number of mobile clients over a single or multiple channels. Due to the limited uplink bandwidth from mobile clients to server, conventional concurrency control methods cannot be directly applied. There has been many researches on concurrency control methods for wireless broadcast environments. However, they are mostly for read-only transactions or do not consider exploiting cache. They also suffer from the repetitive aborts and restarts of mobile transactions when the access patterns of mobile transactions are skewed. In this paper, we propose a new optimistic concurrency control method suitable for mobile broadcast environments. To prevent the repetitive aborts and restarts of mobile transactions, we propose a random back-off technique. To exploit the cache on mobile clients, our method keeps the read data set of mobile transactions and prefetches those data items when the mobile transactions are restarted. As other existing optimistic concurrency control methods for mobile broadcast environments does, it works for both read-only and update transactions. Read-only transactions are validated and locally committed without using any uplink bandwidth. Update transactions are validated with forward and backward validation, and committed after final validation consuming a small amount of uplink bandwidth. Our performance analysis shows that it significantly decreases uplink and downlink bandwidth usage compared to other existing methods.     

A high quality and small shadow size visual secret sharing scheme based on hybrid strategy for grayscale images

Many secret sharing schemes for digital images have been developed in recent decades. Traditional schemes typically must deal with the problem of computational complexity, and other visual secret sharing schemes come with a higher transmission cost and storage cost; that is, each shadow size is m times as big as the original secret image. The new (2,n) secret sharing scheme for grayscale images proposed in this paper is based a combination of acceptable image quality using block truncation coding (BTC), high compression ratio discrete wavelet transform (DWT) and good subjective performance of the vector quantization (VQ) technique. Experimental results confirm that our proposed scheme not only generates a high quality reconstructed original image but also generates small, random-like grayscale shadows.