Compressive Sharing System For Images Using Transform Coding and Blackely Method
Ali Hatem Ahmed · Iraqi Journal for Computers and Informatics · 2017
Abstract: On the subject of data protection, to prevent the confidential information from being tampered one needs to apply some cryptographic techniques. Most of cryptographic strategies have one similar weak point that is the information is centralized. To overcome this drawback secret sharing was introduced. The (k, n) threshold secret sharing scheme, where n is the number of generated shares and k is the minimum needed shares for revealing. The common drawback facing most of the sharing systems is the high shadow size, for this reason compression is required to bypass the shadow size problem. In this thesis project a fast compression sharing system is introduced. Different transform coding strategies are utilized in order to get as much as possible smallest share size; so the developed system is entitled Visual Compressive Crypto System Using Transform Coding (VCCS). Blakley's secret sharing is one of commonly used methods to do data sharing. It uses the principles of hyperplane geometry to resolve the secret sharing problem. For making certain high security level each produced share is passed through stream ciphering that depends on an individual encryption key belonging to the shareholder. The major challenges facing image compression it is how to compress color images and get a high compression ratio while keeping acceptable image accuracy, In order to make the resulting file from the compression process as small as possible and then take advantage of it to make files resulting from the share process smaller, VCCS is a low cost lossy color image crypto-compression system. In the first stage, the RGB image data is transformed to YUV color space, then the chromatic bands U & V are down-sampled using dissemination method. The bi-orthogonal wavelet transform is used to decompose each color sub band, separately. Then, the Discrete Cosine Transform (DCT) is used to encode the Low-Low (LL) sub band. The other wavelet sub bands are coded using scalar Quantization. Also, the quad tree coding process was applied on the outcomes of DCT and quantization processes. Finally, the adaptive shift coding is applied as high order entropy encoder to remove the remaining statistical redundancy to achieve efficiency in the performance of the compression process. In the second stage the crypto-sharing process is accomplished; it start by feeding the output (i.e., compressed image data) to stream ciphering; which is applied to remove any statistical redundancy or bits important attribute that may exist within the compression stream; this encryption step is done using single key (named Shares- Group Key) which should be known by all shareholders. Then the encryption output is passed to Blakley sharing generation engine. As last stage, each generated share is passed again to encryption process using single-encryption key called “Private share key” which should be known only by the shareholder. For handling the involved complexity associated reveal stage, the benefit of using the fast memory access was utilized to achieve fast reveal process. The introduced system was applied on a set of standard color image; the attained compression results indicated good efficiency in reducing the size while keeping the fidelity level above the acceptable level, where it was obtained compression ratio which is around 1:40 for Color Lena, 1:30 for color Barbara. While, the introduced system produces a share file have a size (3.5 KB) compression size for color Lena image (256x256). The produced share file size was (5 KB) for color Barbara image (256x256). Compressive Sharing System For Images Using Transform Coding and Blackely Method