Research On Key Technologies Of Distribution And Search For Encrypted Data

With the growing popularity of cloud computing technology, data outsourcing services, represented by the cloud storage, are more and more welcomed by users because of its low price and buy on-demand characteristics. However, while bringing many advantages, it also generates a lot of security problems, such as data confidentiality, integrity and availability. To those individuals or organizations who want to use cloud storage to manage private or sensitive data, data’s confidentiality is usually the most important factor that needs to be considered. How to ensure data’s confidentiality has become the current hot topic in cloud data security.The effective way to ensure data’s confidentiality is to encrypt the data. However, conventional data encryption technologies will lose many data’s original characteristics. Though service providers cannot pry user’s data, they cannot provide users those common features, such as data sharing, distribution, and keyword search. Currently, various methods can be used to solve these problems, such as secure multicast, broadcast encryption, and searchable encryption. However, in practice, these methods have defects at various levels. This paper considered the service provider as an untrusted entity, improved the inadequacy of these methods respectively, and proposed specific methods and measures. The main work and results are as follows.(1) For the current group key agreement protocols’ security issues, this paper proposed a novel distributed multicast key management protocol that based on certificate and trigeminal key tree. The protocol is based on bilinear mapping and tripartite key agreement protocol, and uses public key certificates to authenticate member’s identity. The protocol’s security is based on the decisional hash bilinear Diffie-Hellman assumption, and possesses the basic multicast security properties such as group key confidentiality and independence. In addition, the protocol can authenticate member’s identity, which can resist the man-in-the-middle attack. Performance analysis shows that the group key agreement protocol is superior to existing agreements on the overall performance.(2) For the problem that the existing public-key broadcast encryption method cannot simultaneously send message to both large and the small receiver set efficiently, this paper proposed an efficient public-key broadcast encryption scheme. It is based on the existential unforgeable signature and bilinear Diffie-Hellman exponent assumptions, and uses system parameter sharing method to achieve efficient encryption towards large and small set. Security analysis shows that the scheme can resist chosen ciphertext attack and external users’ collusion attack. Experimental results show that, compare with the existing schemes, this scheme’s encryption and decryption efficiency has been greatly improved.(3) For the current anonymous broadcast encryption schemes’ lower efficiency problem, this paper proposed an efficient dynamic anonymous broadcast encryption scheme. The scheme is constructed based on the composite decisional bilinear Diffie-Hellman assumption and the subgroup decision assumption in the composite order bilinear groups, and uses Lagrange interpolation polynomial to hide receiver’s identity, which achieves the shortest broadcast ciphertext and higher decryption efficiency. Security analysis shows that the scheme has ciphertext confidentiality and receiver anonymity against the adaptive adversary’s attack in the standard model. Compare with similar schemes, this scheme also has the arbitrary sender, dynamic joining, and identity-based functionalities.(4) For the problem that the single keyword searchable encryption cannot be efficiently applied to large amount of data, this paper proposed a dynamic multi-keyword searchable encryption scheme. The scheme uses file’s inverted index and the pseudo-random function to construct the secure index, and uses the chosen plaintext secure symmetric encryption and the homomorphic encryption to achieve the multi-keyword searchable encryption. This scheme supports dynamic file set update, and can resist adversary’s dynamic adaptive chosen keyword attack.(5) For the problem that current existing multi-keyword searchable encryption method cannot verify the search result’s integrity, this paper proposed an authenticate method for multi-keyword search result that based on the authenticated data structure and the bilinear q-strong Diffie-Hellman assumption. Using the Merkle tree as the basic structure, the scheme adopts bilinear map accumulator and extended Euclidean algorithm to prove the correctness of the set operation. Security analysis and experimental results show that the scheme is efficient and unforgeable.