Biblio

Recently, with the development of the cloud environment, users can store their data or share it with other users. However, various security threats can occur in data sharing systems in the cloud environment. To solve this, data sharing systems and access control methods using the CP-ABE method are being studied, but the following problems may occur. First, in an outsourcing server that supports computation, it is not possible to prove that the computed result is a properly computed result when performing the partial decryption process of the ciphertext. Therefore, the user needs to verify the message obtained by performing the decryption process, and verify that the data is uploaded by the data owner through verification. As another problem, because the data owner encrypts data with attribute-based encryption, the number of attributes included in the access structure increases. This increases the size of the ciphertext, which can waste space in cloud storage. Therefore, a ciphertext of a constant size must be output regardless of the number of attributes when generating the ciphertext. In this paper, we proposes a CP-ABE based data sharing system that provides signature-based verifiable outsourcing. It aims at a system that allows multiple users to share data safely and efficiently in a cloud environment by satisfying verifiable outsourcing and constant-sized ciphertext output among various security requirements required by CP-ABE.

Blockchain is a database technology that provides the integrity and trust of the system can't make arbitrary modifications and deletions by being an append-only distributed ledger. That is, the blockchain is not a modification or deletion but a CRAB (Create-Retrieve-Append-Burn) method in which data can be read and written according to a legitimate user's access right(For example, owner private key). However, this can not delete the created data once, which causes problems such as privacy breach. In this paper, we propose an on-off block-chained Hybrid Blockchain system to separate the data and save the connection history to the blockchain. In addition, the state is changed to the distributed database separately from the ledger record, and the state is changed by generating the arbitrary injection in the XOR form, so that the history of modification / deletion of the Off Blockchain can be efficiently retrieved.