Fair Outsourcing Computation Based On Blockchain

Outsourcing computation has received considerable attention recently due to its grown application demands.However,the distrust between users and workers leads to the unfairness of outsourced computing,which hinders the further development of outsourced computing.Therefore,how to ensure fairness in this scenario is a significant topic.This paper studies how to outsource the commonly used algorithms in cloud/fog computing and cloud storage,especially for polynomial computing and the decryption of attribute-based encryption(ABE).According to the research,firstly,the two kinds of existing schemes cannot provide fairness,and they often need costly cryptography options.Secondly,the existing outsourced polynomial computing schemes cannot support arbitrary polynomials,and they always need the assumption of no-colluding workers.Thirdly,the existing attribute-based encryption with outsourced decryption schemes cannot outsource the existing ciphertext,and they scarcely ever support public verifiability.In order to solve the above problems,the main contributions of the paper are as following:(1)Combining the blockchain technology and Horner's method,this paper proposes an outsourced polynomial computing scheme with the support of dynamic coefficients update.This scheme applies to arbitrary polynomials without any restriction.Compared with the scheme proposed by Kumaresan et al.at CCS 2014,this scheme does not require costly cryptography technologies.Moreover,compared to the approach proposed by Dong et al.at CCS 2017,the new scheme no longer needs the assumption of two no-colluding servers.Under the assumption that the participants are rational,the proposed outsourced polynomial computing scheme is proven fair by means of game theory.(2)With the help of the transformation key technique and the sampling technique,this paper proposes a generic construction for transforming any ABE scheme(pairing-based)to a public verifiable ABE scheme with outsourced decryption.Compared to the scheme proposed by Green et al.at USENIX 2011 and its succession,this scheme enables public variability,and it supports the outsourcing of existing ABE ciphertexts.Then,this paper presents a fair outsourced ABE decryption scheme by combining the proposed publicly verifiable ABE with outsourcing decryption scheme and blockchain technology.Under the assumption of ration participants,it also gives a proof of fairness by applying game theory.The proposed schemes are implemented in an Ethereum test net,and the experimental results show that these schemes are feasible.