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Inspired by the fact that attribute-based encryption technology can effectively realize cloud data security sharing and access control, this paper proposed a block chain data sharing model based on attribute-based encryption to ensure the privacy protection and full security in the current block chain system. The model was based on the ciphertext policy attribute-based encryption ( CP-ABE) scheme proposed by Waters. First of all, in the secret key generation phase, the data user entrusted multiple nodes to jointly calculate and store part of the private key, while other data users were not allowed to obtain the complete key, thus improving the efficiency of private key generation. Secondly, in order to prevent the abuse of key and the management of parameters in the algorithm, this paper defined a key transfer transaction data structure, and realized the accountability of CP-ABE algorithm. Finally, by building a shared chain with the function of collaborative computing and storage on and off the chain, it realized the effective integration of attribute-based encryption and block chain system. Security analysis and experimental simulation results show that the proposed model has certain optimization in the computational efficiency of key generation and actual business scenarios to meet the needs of engineering applications. [ABSTRACT FROM AUTHOR]

Shared data access maximizes resource utilization on the Internet but raises the issue of data security. We consider a method of shared data access control whereby the data is sub-divided into categories and each encrypted with a unique cryptographic key that is distributed to the user group requiring access. Key management can be simplified by classifying every user into exactly one of a number of disjoint groups that are partially ordered such that lower level keys are mathematically derivable from higher level keys, but not the reverse. The drawback in this approach is that changes in group membership imply updating both the affected group key and those that are derivable from it. Moreover, the data encrypted with the affected keys must be re-encrypted with the new keys to preserve data security. In the worst case, when the affected group is at the highest level of the hierarchy, the entire hierarchy is affected. This paper presents an algorithm that minimizes the cost of key replacement (rekeying) by associating a timestamp to each key. The timestamp and key are used to compute a verification signature that is used to authenticate users before data access is granted. Thus, whenever group membership changes, instead of rekeying and re-encrypting the affected data, only the timestamp is updated and a new verification signature computed. The new scheme is analyzed using both a time complexity and experimental analysis. [ABSTRACT FROM AUTHOR]