The log-based index update mechanism in flash-based database system has following shortage: low query efficiency, expensive update cost, unreasonable space allocation and merge for the log. In order to solve these problems, a new adaptive index structure named LM-B+TREE was proposed. LM-B+TREE can map the page for index update buffer into corresponding node of traditional B+ TREE. Furthermore, according to the read/write workload and read/write overhead, LM-B+TREE can dynamically maintain the update buffer and adjust the index frame adaptively. The experimental results show that LM-B+ TREE can dynamically adjust the index structure to adapt to the read-write workload, significantly reduce the overhead of index update and improve the query performance.

In most attribute-based encryption schemes, access policy, which is used to encrypt message by encryptor, is often sent to the decryptor along with the ciphertext, but sometimes the policy itself is sensitive. This paper proposed a new construction to hide the access policy. During the encryption process, encryptor achieve the indistinguishability between the well-formed ciphertext components and the malformed. Compared with other constructions, ours was more efficient by reducing the times of exponent and pairing, and the sizes of ciphertext and keys were smaller. In addition, new attributes could be added in the ciphertext policy after setup was executed and the existing public parameters can remain unchanged. These analyses show the flexibility of construction. Security gets proved based on decisional bilinear Diffie-Hellman assumption.