In traditional cloud storage systems, attribute-based encryption (ABE) is regarded as an important technology for solving the problem of data privacy and fine-grained access control. However, in all ABE schemes, the private key generator has the ability to decrypt all data stored in the cloud server, which may bring serious problems such as key abuse and privacy data leakage. Meanwhile, the traditional cloud storage model runs in a centralized storage manner, so single point of failure may leads to the collapse of system. With the development of blockchain technology, decentralized storage mode has entered the public view. The decentralized storage approach can solve the problem of single point of failure in traditional cloud storage systems and enjoy a number of advantages over centralized storage, such as low price and high throughput. In this paper, we study the data storage and sharing scheme for decentralized storage systems and propose a framework that combines the decentralized storage system interplanetary file system, the Ethereum blockchain, and ABE technology. In this framework, the data owner has the ability to distribute secret key for data users and encrypt shared data by specifying access policy, and the scheme achieves fine-grained access control over data. At the same time, based on smart contract on the Ethereum blockchain, the keyword search function on the cipher text of the decentralized storage systems is implemented, which solves the problem that the cloud server may not return all of the results searched or return wrong results in the traditional cloud storage systems. Finally, we simulated the scheme in the Linux system and the Ethereum official test network Rinkeby, and the experimental results show that our scheme is feasible.

With the improvement of living standard, people begin to pay more attention to food safety and product quality. Therefore, for consumers, it is necessary to establish a reliable system that can trace the source of products. However, most existing traceability systems tend to lack transparency, data is primarily stored within the enterprise, and the cost of tampering with data is very low. Besides, the supply chain nodes are easy to evade responsibility when product safety or quality issues arise under the traditional centralized management model, and it is difficult to trace the root of issues. The development of blockchain technology provides us with new ideas for realizing the traceability of products in supply chain scenarios. Due to its characteristics of decentralization, transparency, and immutability, blockchain can be effectively used to alleviate the above problems. In this paper, we propose a product traceability system based on blockchain technology, in which all product transferring histories are perpetually recorded in a distributed ledger by using smart contracts and a chain is formed that can trace back to the source of the products. In particular, we design an event response mechanism to verify the identities of both parties of the transaction, so that the validity of the transaction can be guaranteed. And all events are permanently stored in the form of logs as a basis for handling disputes and tracking responsible entities. Furthermore, a system prototype is constructed based on the testing framework of Truffle. The contract code is deployed on a test network TestRpc that runs in local memory, and a decentralized web page interface is implemented based on the prototype. Finally, the system security analysis and experimental results show that our solution is feasible.

Now more and more data is being outsourced to cloud services. In order to ensure the data security and privacy, data is usually stored on the cloud server in the form of ciphertext. When a user requests an access to the encrypted data, an access key distributed by a third party is needed. However if the third party is dishonest, the security of the system will be threatened. Faced with this problem, in this paper, we propose a new secure cloud storage framework with access control by using Ethereum blockchain technology. Our new scheme is a combination of Ethereum blockchain and ciphertext-policy attribute-based encryption (CP-ABE). The proposed cloud storage framework is decentralize, that is, there is no trusted third party in the system. Our scheme has three main features. Firstly, as the Ethereum blockchain technology is used, data owner can store ciphertext of data through smart contracts in a blockchain network. Secondly, data owner can set a valid access periods for data user so that the ciphertext can only be decrypted during valid access periods. Finally, as the creation and invocation of each smart contract can be stored in the blockchain, thus the function of trace is achieved. The analysis of the security and experiment show that our scheme is feasible.

The sharing of personal health records can help to improve the accuracy of the doctor's diagnosis and to promote the progress of medical research. Currently, to reduce the maintenance cost of data, personal health records are usually outsourced to a third party such as the cloud service provider. In this case, patients may lose direct control over their personal health records and the semi-trusted cloud service provider may tamper with or reveal personal health records. Therefore, ensuring the privacy and integrity of personal health records and realizing the fine-grained access control are crucial issues when personal health records are shared. As a distributed architecture with decentralized and tamper-proof features, blockchain provides a new way to protect the personal health records sharing system. In this paper, we propose a new personal health records sharing scheme with data integrity verifiable based on blockchain. Aiming at the problems of privacy disclosure, limited keyword search ability and loss of control rights in the process of personal health record sharing, the new scheme uses searchable symmetric encryption and attribute-based encryption techniques to achieve privacy protection, keyword search, and fine-grained access control. Compared with the existing similar schemes, the new scheme allows patients to distribute attribute private key for users, avoiding many security problems caused by the existing of attribute authority in the scheme. Furthermore, the new scheme uses blockchain to manage keys in the scheme, avoiding the single point failure problem of centralized key management. In particular, the new scheme stores the hash values of encrypted personal health records in blockchain, and the related index set is stored in smart contract, which can further improve the efficiency of data integrity verification. Finally, performance evaluation and security analysis indicate that our scheme is secure and feasible for practical use.

Attribute-based encryption (ABE) is suitable for mobile cloud storage to protect data confidentiality and realize fine-grained data access control. It is essential for ABE schemes to achieve attribute revocation as users' attributes may be changed frequently. Keyword search over encrypted data also needs to be solved in the mobile cloud storage. In addition, computational efficiency is a consideration for the resource-constrained mobile device. Focusing on the above-mentioned problems, an efficiently revocable and searchable ABE (RSABE) scheme for the mobile cloud storage is proposed. In our scheme, the function of attribute revocation is efficiently achieved by delegating the update of secret key and ciphertext to the powerful cloud server. Keyword search is also supported, in which data owners and users can generate the keywords index and search trapdoor, respectively, without relying on always online trusted authority. Furthermore, an outsourced decryption technology is used to reduce the computational load of decryption on user side. Our RSABE scheme is proven to be semantically secure against selective ciphertext policy and chosen plaintext attack, and to be secure against chosen keyword attack in the random oracle model. Finally, performance evaluation demonstrates that our scheme is highly efficient.

In attribute-based searchable encryption (ABSE) scheme, data owners can encrypt their data with access policy for security consideration, and encrypt keywords to obtain keyword index for privacy keyword search, and data users can search interesting keyword on keyword indexes by keyword search trapdoor. However, many existing searchable encryption schemes only support single keyword search and most of the existing attribute-based encryption (ABE) schemes have high computational costs at user client. These problems significantly limit the application of attribute-based searchable encryption schemes in practice. In this paper, we propose a verifiable and multi-keyword searchable attribute-based encryption (VMKS-ABE) scheme for cloud storage, in our new scheme, multi-keyword can be searched and the search privacy is protected. That is, the cloud server can search the multi-keyword with keyword search trapdoor but it does not know any information about the keywords searched. In the proposed scheme, many computing tasks are outsourced to the cloud proxy server, which greatly reduces the computing burden at the user client. Besides, the scheme also supports the verification of the correctness of the outsourced private key. The proposed scheme is proved secure that the keyword index is indistinguishable under the adaptive keyword attacks in the general group model, and the ciphertext is selective secure under selective plaintext attacks in the random oracle model. The security and experimental results show that our scheme is suitable for practicability.