Secure and Verifiable Outsourced Computation Based on Blockchain

More and more clients purchase cloud services because of its excellent storage and computing capabilities. Outsourced computation has come into our real life. Meanwhile, there are serious security issues such as privacy disclosure and dishonest behavior in outsourced computation on the cloud. Existing research attempts to solve the issues. However, when a user finds returned result is incorrect, he still cannot determine that it is caused by external attackers or dishonest cloud service providers. Based on open and tamper-proof blockchain technology, we design a verifiable outsourced computation scheme. Before uploading data, a user encrypts and signs the data. For a certain computation task, the server performs aggregation computation on the ciphertext domain and stores the results in the blockchain. Before decryption, a user checks the signature to avoid useless decryption because of invalid ciphertext. After decryption, he can further verify the correctness of plaintext computation. The whole process realizes privacy protection of data on the cloud, integrity verification of outsourced computation, and responsibility determination of malicious operations. The experiment shows that during the user query stage, ciphertext recovery and signature verification have low time overhead; the computing and communication costs of users do not increase with the increase of computing scale. Therefore, the scheme can be effectively applied to the scenario with high requirements for data privacy and computing reliability.