Blockchain is a technology that enables the implementation of a decentralized system by replacing the role of the centralized entity with the consensus of participants in the system to solve the problem of subordination to the centralized entity. Blockchain technology is being considered for application in numerous fields; however, the scalability limitation of a public blockchain has led many researchers to consider private blockchains, which reduce the security of the system while improving scalability. A state channel represents a leading approach among several scalability solutions, intended to address public blockchain scalability challenges while ensuring the security of the blockchain network. Participants in the channel perform the process of updating the state of the channel outside the blockchain. This process can proceed very quickly because it does not require the consensus of the blockchain network, but still, like on-chain, it can guarantee features such as irreversibility. In this paper, we propose the PyRos protocol, an access control system that supports the trading and sharing of data between individuals on a public blockchain based on the state channel. As far as we know, the research using the off-chain state channel for access control has not been proposed yet, so PyRos is a new approach in this field. In PyRos, user-defined access control policies are stored off-chain, and policy updates are always rapid regardless of the performance of the blockchain network. Moreover, PyRos provides means to prevent malicious participants from arbitrarily using the channel’s previous state while resolving constraints due to scalability problems, along with privacy guarantees for the transaction content. To evaluate the efficiency and security of PyRos, we provide qualitative analysis of security requirements and analysis in terms of the performance of public blockchain platforms.

Since deduplication inevitably implies data sharing, control over access permissions in an encrypted deduplication storage is more important than a traditional encrypted storage. Therefore, in terms of flexibility, data deduplication should be combined with data access control techniques. In this paper, we propose an authorized deduplication scheme using CP-ABE to solve this problem. The proposed scheme provides client-side deduplication while providing confidentiality through client-side encryption to prevent exposure of users’ sensitive data on untrusted cloud servers. Also, unlike existing convergent encryption schemes, it provides authorized convergent encryption by using CP-ABE to allow only authorized users to access critical data. The proposed authorized deduplication scheme provides an adequate trade-off between storage space efficiency and security in cloud environment and is very suitable for the hybrid cloud model considering both the data security and the storage efficiency in a business environment.