Research On Collaborative Visual Secret Sharing Scheme

Collaborative visual secret sharing scheme is a novel type of image secret sharing technology combined image secret sharing(ISS)scheme with visual cryptography scheme(VCS),which can achieve fast preview and precise decryption simultaneously.Binary secret image and grayscale image are the shared secrets.Shadow images of the former are generated via VCS,while noise shares of the latter are produced by ISS encryption.Then we gain the shadow images of the whole scheme utilizing embedding operation,that is,conceal grayscale noise shares into binary shadow images.Assign these generated grayscale shadows to participants.There are two phases in the overall decryption process: superposition and extraction.It means the first phase stacks shadow images printed in transparencies.Thus visually restore a vague black-andwhite secret image.The second phase extracts the embedded grayscale information from the shadows in authorization set.Reconstruct the grayscale secret image through ISS decryption algorithm,which is the same as grayscale image.It achieves lossless recover with computer device.The purpose of this thesis is to increase the visual quality of fuzzy image,narrow size expansion and enhance the amount of embedded information.The main research contents are as follows:One is to combine the q-bit grayscale visual cryptography scheme(q GVCS)on the basis of the existing scheme and construct a collaborative visual secret sharing scheme.It achieves the goal of higher quality of previewed image.The difference between q GVCS and grayscale visual cryptography scheme is that the embedded grayscale value is q-bit instead of general 8-bit pixel.Similarly,the grayscale information extracted from shadows during decryption needs to be converted from q bits to 8 bits,and then continue to recovery.A smaller value q can obtain better visual quality and larger size expansion,which increases resource consumption in the process of information storage and transmission.Hence establish a mathematical model between visual quality of previewed image and size expansion according to actual needs.Choose the appropriate value q to encrypt the information.The other is to define the embeddable canonical visual cryptography scheme(ECVCS)and propose the construction method of the ECVCS basic matrices.Only the black secret pixels can perform the embedding operation,when the white secret pixels cannot meet the security conditions or conceal gray information in the existing fusion schemes.In order to solve this problem,the proposed ECVCS has the function of embedding information in both black and white pixels.This greatly improves the embedding capacity.On the other hand,the Boolean-based multiple secret image sharing scheme(BMSIS)gain no size expansion,so using BMSIS to encode grayscale secret image and obtain noise images with equal size.Thus share more secret information in the embedding process if hiding the same grayscale images.The amount of embedded information is increased as well.Above all,this paper mainly focuses on the two aspects of embedded information capacity and visual quality of previewed image.Theoretical analysis and experimental results guarantee security,feasibility and effectiveness of the proposed schemes.