# A Cross-Chain-Based Access Control Framework for Cloud Environment
## 2 Related Works
The access control is deployed by a smart contract in the consortium BC, which also contains the public keys of the requesters, their access privileges, and data hashes. The public key has a central role in the proposed access control model, in which only requesters with public keys stored in the consortium BC can communicate with the notary nodes for granting access. Based on the survey, it is important to highlight that there are several solutions designed for AC (summarized in Table 1) based on smart contracts and cryptographic techniques, which reflect the capability of blockchain to tackle pressing concerns such as privacy preservation, data security, and scalability. While smart contracts (chain code) automate the process of enforcing access control policies, cryptographic techniques safeguard the confidentiality, integrity, and authenticity of shared data. In [7; 8; 9; 10; 12; 13], authors deployed ACs alongside certificate authorities (CAs) as a third-party solution for key management, which represents a single point of failure despite its existence for 53 years. This infrastructure, as it stands, embraces risks and problems in its usage [15]. To tackle the highlighted issue, researchers in [11] adopted Hyperledger Fabric's permissioned network with a membership service provider (MSP) to establish a P2P connection and the IPFS's proof-of-replication (PoRep) mechanism to maintain data storage. However, MSPs have limited interoperabilty with non-Fabric networks, and as the network grows, the MSP becomes complex to manage, reflecting scalability issues. Cross-chain is used in [14] as a reliable technology to eliminate trust problems attached to third-party certification authorities. However, using one attribute (the public key) to check access to the consortium blockchain may fall short in communicating and sharing resources between entities defining their access policies in a granular vocabulary. On the other hand, our framework adopts the built-in Cosmos ecosystem accounts, in which token ownership and cryptographic proofs act as memberships for the cloud stakeholders. The proof-of-stake (PoS) consensus mechanism we use allows for faster broadcasting and validation of access transactions. We thus address the scalability and single point of failure issues of MSPs and CAs, respectively. We also integrated ABAC as a standardized AC mechanism over cross-chain, supporting it with semantic reasoning based on ontologies. Our work deals with transactions that originate from different types of chains (cloud clients), defined in a variety of CSC business vocabularies, and transported using the inter-blockchain communication (IBC) protocol, thereby addressing the inter-chain interoperability issue. Table 2 compares the cross-chain-based access control framework in this paper with the other access control mechanisms. We base this comparison between our work and the current state of the art on criteria such as freshness (replay attack resistance), the addition of blocks to the chain, the heterogeneity reflecting the ability to support different technical implementations, the fine-grainedness of the access control mechanism used, whether the systems can scale to rising demands, and whether the solution can adapt to any CSC's