Research Of The Data Confidentiality Schemes In Cloud Storage Environment

The researches of cloud storage security are mainly about data confidentiality, availability, and integrity. In this thesis, we focus on the data confidentiality schemes, and we use the cryptographic methods, such as secret sharing and attribute-based encryption, to design security schemes.1. A Fair (t,n) Threshold Secret Sharing Scheme. In this thesis, combining the scheme of Tian et al, with the Lin and Ham’s scheme, we design a new fair (t,n) threshold secret sharing scheme. In every round of the secret reconstructing process, the Lagrange interpolation polynomial and polynomial solution verification methods are used to detect whether the participants are cheating. In the meantime, by hiding the secret value in the sequence of random values, we reduce the probability of the dishonest participant achieving a successful guess, and thus improve the fairness of our scheme. Moreover, we use the multi-secret sharing scheme to reduce the storage cost of the user.2. Attribute-Based Access Control with Revocation in Cloud Storage. We suppose the cloud storage server is "honest but curious". Based on this assumption, we use attribute-based encryption and minimal cover subset technique to design an efficient access control scheme. In addition, we offer proxy decryption function to increase the convenience for users holding devices with low computing capability. The system has high computational effectiveness and decreases the computational load of both data owner and users. Our scheme reduces the storage cost of keys for the users, realizes data confidentiality of the system and ensures backward security and forward security. It is resistant to collusion attack. It also realizes the fine-grained access control and offers various expressive policies.