# A Cross-Chain-Based Access Control Framework for Cloud Environment
## 2 Related Works  
Blockchain technology has influenced the workflow in cloud environments by implementing access control mechanisms in the cloud through blockchain. Several authors have addressed this in different ways according to the cloud application domain and the desired security impact. [PERSON] et al. [7] developed a mechanism of data sharing and access control for the cloud utilizing blockchain technology. The data are encrypted and uploaded to an interplanetary file system (IPFS) by the data owner. The smart contracts store a secure file location and a secure key to simplify the sharing of data across multi-cloud storage platforms. Only a selected group of users registered by the data owner has access to retrieve it from the IFPS. [PERSON] et al. [8] suggested a different access control method using blockchain technology by implementing ABAC technology into a smart contract, creating fine-grained access control on the edge cloud servers. Each of the core ABAC components is designed into a corresponding smart contract. To minimize the execution time of the access control mechanism, policy reduction using rule clustering was deployed on the policy decision point (PDP). The execution result of these smart contracts is also stored on the blockchain. Using ciphertext policy attribute-based encryption (CP-ABE) and Ethereum blockchain, [PERSON] et al. [9] proposed a lightweight access control for fog-assisted IoT cloud medical data. It deploys an encryption/decryption algorithm for data sharing, capitalizing on fog nodes and BC capabilities. The aggregated data are partially encrypted, then sent through a trusted proxy to the nearest fog node, which encrypts and stores the indexed data on the cloud storage. It also serves to authenticate, verify, and manage user sessions. [PERSON] [10] developed a framework called ACE-BC for information sharing based on attribute-based encryption (ABE). The access control is deployed on the edge gateways, which connect to the blockchain as peers. The main aim of this work is to eliminate non-trusted third parties and use blockchain as an authority for key management so the data owner can check the data user's identity before authorizing access to a cloud service. [PERSON] and [PERSON] [11] proposed an access control framework based on Hyperledger Fabric using chain code for health organizations. The framework benefits plainly from blockchain technology. It allows secure storage of patient data while access is granted by a deployed chain code on the P2P hyper-ledger network. Access to data stored in cloud servers is granted to peers satisfying the smart contract endorsement policy. In this framework, transactions are made through a specific channel of the ledger network. [PERSON] et al. [12] suggested a framework called BSAF, established on blockchain-based technology, to manage access to the services offered by a cloud service provider (CSP). This entity uses homomorphic encryption (TFHE) to encrypt its offering. Service solicitants send access requests directly to the cloud server. Access-seeking requests are redirected to the blockchain network for verification, at which point penalties might be applied. As a result, a confirmation is sent to the users via the deployed smart contract on the blockchain network. For privacy protection, [PERSON] et al. [13] proposed an access control framework based on the EOS blockchain: the data owner (DO) uploads his resources to the cloud and publishes his permission and authorization to the blockchain. In this framework, the data user (DU) requests the cloud servers directly; this later authenticates DU and queries permissions from the BC. While the cloud grants or denies DU requests to access its resources, the BC is used as a policy database that stores permissions and authorizations as trustworthy tiers. [PERSON] et al. [14] elaborated a cross-chain solution for access control between Tangle as a side chain and Fabric as the consortium BC, using the notary node network as a gateway between the two for routing and verifying transactions.