[[alternative]]An Optimization Model for Sharing Multiple Secret Images without Pixel Expansion

計畫編號：NSC93-2213-E032-033研究期間：200408~200507研究經費：475,000[[abstract]]視覺密碼方法的特色在於其解密過程是透過人類視覺系統，而不需要利用任何計算 機資源與複雜的解密演算法。因此，在一些無法使用電腦解密的情況下，視覺式秘密分 享機制是一個很好的解決方案。大部分的視覺密碼方法都是使用像素擴展的技巧；因 此，分享影像會被擴展成機密影像的若干倍。像素擴展的結果不但使得分享影像不易攜 帶，也會造成儲存空間的浪費。此外，大部分的視覺密碼方法只允許分享單一機密影像， 而無法分享多張機密影像。在本研究中，我們將提出一個方法來解決視覺式秘密分享機 制中的影像擴張問題。我們將以機率的觀念來達成分享影像不擴展的目標。此外，我們 將探討視覺密碼的安全性與對比，並定義安全性與對比指標。我們將以這兩個指標來建 構出一個不需要像素擴展的視覺式秘密分享機制之最佳化模型。在不作像素擴展的前提 之下，我們期望我們的模型不僅可以處理單機密影像與多機密影像的任意使用結構；同 時，我們也將進一步將我們的模型推廣到有意義之分享影像的任意使用結構的問題上。 最後，我們將應用遺傳演算法的尋優能力，來驗證我們的做法的可行性。[[sponsorship]]行政院國家科學委員

On Real-valued Visual Cryptographic Basis Matrices

Visual cryptography (VC) encodes an image into noise-like shares, which can be stacked to reveal a reduced quality version of the original. The problem with encrypting colour images is that they must undergo heavy pre-processing to reduce them to binary, entailing significant quality loss. This paper proposes VC that works directly on intermediate grayscale values per colour channel and demonstrates real-valued basis matrices for this purpose. The resulting stacked shares produce a clearer reconstruction than in binary VC, and to the best of the authors’ knowledge, is the first method posing no restrictions on colour values while maintaining the ability to decrypt with human vision. Grayscale and colour images of differing entropies are encrypted using fuzzy OR and XOR, and their PSNR and structural similarities are compared with binary VC to demonstrate improved quality. It is compared with previous research and its advantages highlighted, notably in high quality reconstructions with minimal processing

Optimal Colored Threshold Visual Cryptography Schemes

Visual cryptography schemes allow the encoding of a secret image into n shares which are distributed to the participants. The shares are such that only qualified subsets of participants can visually recover the secret image. Usually the secret image consist of black and white pixels. In colored threshold visual cryptography schemes the secret image is composed of pixels taken from a given set of c colors. The pixels expansion and the contrast of a scheme are two measures of the goodness of the scheme. In this paper, we study c-color (k,n)-threshold visual cryptography schemes and provide a characterization of contrast-optimal schemes. More specifically we prove that there exists a contrast-optimal scheme that is a member of a special set of schemes, which we call canonical schemes, and that satisfy strong symmetry properties. Then we use canonical schemes to provide a constructive proof of optimality, with respect to the pixel expansion, of c-color (n,n)-threshold visual cryptography schemes. Finally, we provide constructions of c-color (2,n)-threshold schemes whose pixels expansion improves on previously proposed schemes

ESSVCS: an enriched secret sharing visual cryptography

Visual Cryptography (VC) is a powerful technique that combines the notions of perfect ciphers and secret sharing in cryptography with that of raster graphics. A binary image can be divided into shares that are able to be stacked together so as to approximately recover the original image. VC is a unique technique in the sense that the encrypted message can be decrypted directly by the Human Visual System (HVS). The distinguishing characteristic of VC is the ability of secret restoration without the use of computation. However because of restrictions of the HVS, pixel expansion and alignment problems, a VC scheme perhaps can only be applied to share a small size of secret image. In this paper, we present an Enriched Secret Sharing Visual Cryptography Scheme (ESSVCS) to let the VC shares carry more secrets, the technique is to use cypher output of private-key systems as the input random numbers of VC scheme, meanwhile the encryption key could be shared, the shared keys could be associated with the VC shares. After this operation, VC scheme and secret sharing scheme are merged with the private-key system. Under this design, we implement a (k; t; n)-VC scheme. Compared to those existing schemes, our scheme could greatly enhance the ability of current VC schemes and could cope with pretty rich secrets

Acknowledgement based Intrusion-Detection System for MANETS

In the next generation of wireless communication systems, there will be a need for the quick deployment of independent mobile users. notable examples include establishing survivable, efficient, flush communication for emergency/ recover operations, defeat relief efforts, and Army networks. Such network scenarios cannot count on centralized and organized connectivity, and can be make up as applications of  Mobile Ad Hoc Networks.  The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic. An intrusion detection system (IDS) is a device or software application that monitors network or system activities for malicious activities or policy violations and produces reports to a management station. IDS come in a variety of “flavors” and approach the goal of detecting suspicious traffic in different ways. The self configuring ability of nodes in MANET made it popular among critical mission applications like army use or emergency recovery. However, the open medium and wide distribution of nodes make MANET vulnerable to malicious attackers. In this case, it is decisive to develop efficient intrusion-detection mechanisms to protect MANET from attacks. By using technology support  we are cut in hardware costs, we are witnessing a current trend of expanding MANETs into industrial applications. To adjust to such trend, we strongly believe that it is vital to address its potential security problem. In this paper, we propose and implement a new intrusion-detection system named Enhanced Adaptive Acknowledgment (EAACK) specially made for MANETs. Compared to contemporary approaches, Enhanced Adaptive ACK demonstrates higher malicious-behavior-detection rates in certain circumstances while does not greatly affect the network performance

Secret color images sharing schemes based on XOR operation

This paper presents two new constructions for the secret color images sharing schemes .One is a (n, n) threshold scheme, which can be constructed based on XOR operation. The other is a (2, n) threshold scheme, which can be constructed by using AND and XOR operations. The two schemes have no pixel expansion, and the time complexity for constructing shared images is O(k1n), excluding the time needed for generating n distinct random matrices (here k1 is the size of the shared image). The reconstructed images can be obtained in the two schemes by using the XOR operation alone. The relative differences of the two schemes are 1 and 1/2, respectively. The time complexity of the recovered images is O(k1n) and O(2k1), respectively. The two schemes also provide perfect secrecy

Embedded Extended Visual Cryptography Schemes

Visual cryptography scheme (VCS) is a kind of secret sharing scheme which allows the encoding of a secret image into n shares that distributed to n participants. The beauty of such scheme is that a set of qualified participants is able to recover the secret image without any cryptographic knowledge and computation devices. Extended visual cryptography scheme (EVCS) is a kind of VCS which consists of meaningful shares (compared to the random shares of traditional VCS). In this paper, we propose a construction of EVCS which is realized by embedding random shares into meaningful covering shares, and we call it the embedded extended visual cryptography scheme (embedded EVCS). Experimental results compare some of the well-known EVCS\u27s proposed in recent years systematically, and show that the proposed embedded EVCS has competitive visual quality compared with many of the well-known EVCS\u27s in the literature. Besides, it has many specific advantages against these well-known EVCS\u27s respectively