Focused on the high computational complexity and long encoding time problems in the traditional fractal image compression, an orthogonalized fractal encoding algorithm based on texture features of gray-level co-occurrence matrix was proposed. Firstly, from the perspective of feature extraction and image retrieval, the similarity measurement matrix between range blocks and domain blocks was established to transform the global search into the local search, so as to reduce the codebook. Then, by defining a new normalized block as the new gray-level description feature, the transformation process between blocks was simplified. Finally, the concept of Simultaneous Orthogonal Matching Pursuit (SOMP) sparse decomposition orthogonalized fractal encoding was introduced, so that the gray-level matching between blocks was transformed into solving the corresponding sparse coefficient matrix, which realized the matching relationship between one range block and multiple domain blocks. Experimental results show that compared with Sparse Fractal Image Compression (SFIC) algorithm, the proposed algorithm can save about 88% of the encoding time on average without reducing the quality of image reconstruction; compared with the sum of double cross eigenvalues algorithm, the proposed algorithm can significantly shorten coding time while maintaining better reconstruction quality.

Since previous Multi-Authority Attribute-Based Encryption (MA-ABE) schemes limit each attribute to appear only once in the access structure, and suffer from superfluous computation overhead on repetitive encoding technique, an adaptively secure and unrestricted Multi-Authority Ciphertext-Policy ABE (MA-CP-ABE) scheme was proposed on prime order groups. Firstly, based on dual pairing vector space and linear secret-sharing schemes technology, an MA-CP-ABE scheme was constructed on prime order groups. Then, q-Parallel BDHE (Bilinear Diffie-Hellman Exponent) assumption was introduced to solve the problem that classical dual system encryption depends on a statistical hypothesis which requires each attribute to appear only once in the access structure, and a series of attacking games indistinguishable from each other was designed to prove that this scheme was adaptively secure in the standard model. Finally, performance analysis indicated that in comparison with another two adaptively secure MA-CP-ABE schemes on prime order groups, the speed of decryption was obviously improved by nearly 20%-40% and 0%-50% respectively as the number of participating attributes increasing, without considering the attribute repetition. This scheme is more efficient in real applications.