International Journal of Recent Technology and Engineering (IJRTE) ISSN: 2277-3878, Volume-9 Issue-2, July 2020 862 Published By: Blue Eyes Intelligence Engineering and Sciences Publication Retrieval Number: B3931079220/2020©BEIESP DOI:10.35940/ijrte.B3931.079220 Public Key Encryption for Cloud Storage Attack using Blockchain Akshay Babrekar, Rohini G. Pise Abstract: Cloud storage enables user to store data and make it available when it is requested by user. Data generated electronically is very important and it must be encrypted to make sure that the data is tramper-proof. There are two important points to be considered, keyword guessing attack and making cloud storage secure from hackers. In Keyword guessing attack the Keywords search by user are encrypted using secure mechanism and securing the cloud storage means use such techniques which assured to give Confidentiality, Integrity and Accessibility using Blockchain Technology. It is decentralized cloud storage which assist different security mechanisms to protect data. Decentralized cloud storage is itself secure than centralized cloud storage. Because the concept of decentralized is not to store data on single storage device but to store on multiple servers. While storing the data on different location it divided into small parts, and at the time of retrieving data it is available as a complete single block of original data. Whereas in centralized cloud storage data is stored on single storage device. As technology progress the risk from fraudulent users also increases. For this reason, we need some encryption, decryption and authentication mechanism to verify user and if it is authenticated allow access to use its data. There are some techniques also available where user made request on cloud server to receive data which makes cloud server to learn keywords except resulting data. In this paper we make an attempt to review encryption and decryption for cloud storage using blockchain technology to improve security of data. Keywords — Cloud storage, Keyword guessing attack, securing the cloud, Blockchain, Encryption I. INTRODUCTION Using cloud storage user can access his data via internet. These services include send and receive data from systems, where user send their data to multiple users and it is received by target receiver by searching the keywords. This also reduce the load of system which holds data and allows user to store data on the cloud server. While, using these service’s security of data remains a question. Confidentiality of data is one of the most important issue. Hence, data must be encrypted before sending. In public key encryption keywords and data kept encrypted under receiver’s public key. Resulting cyphertext data store on server, then receiver creates trapdoor to test weather cyphertext of keyword is same as trapdoor for retrieving data. Revised Manuscript Received on June 22, 2020. Akshay Babrekar, Department of Information Technology, Pimpri Chinchwad College of Engineering, Savitribai Phule Pune University, Pune, India. Email: a.babrekar.ab@gmail.com Rohini G. Pise, Department of Information Technology, Pimpri Chinchwad College of Engineering, Savitribai Phule Pune University, Pune, India. Email: rohinipise@gmail.com The main advantage of cloud server is that it is reliable. If one node fails, still user is able to retrieve the data. To gain access control on data, method use to the encryption remains a trust. In case for decentralized cloud storage slowing factor is an issue, due to independent and dynamic nature of network reduces control of owner on network on their resources. For centralized systems, Cloud Service Provider (CSP) is considered to be most trusted platform for the operation performed by authenticated users. User side encryption is first strategy to protect data but this kind of security mechanism remains unsafe in case where encrypted key is reveal or data nodes are not performing the operation which is given by owner. These operations like deleting data, reconstructing the resource entity. So, the security of encryption key is not adequate in decentralized cloud storage, additional layers security is to be needed. On the other side, reliability of DCS is increases due to independent participation of data storage resources. If attentive precaution method is used then makes it possible for data owner to completely relay on the DCS to store their data. For this purpose, there are various methods are available which can be used with blockchain technology to enhance the security level. Apart from encrypting the data, Confidentiality, Integrity and Accessibility of data is also important which can be achieved by blockchain. When user request to access data and after permission is given to user, all the transactions is captured with the help of blockchain and the data security is maintained because it makes the transactions unalterable. It is mostly promising technology which minimize the chances of attacks and threads to data. In blockchain data is divided into block and each block have its different hash as well as nonce value which is reference to the next and previous block in chain. Hash is having 256- bits and Nonce is having 32-bits so it’s approximately four billion probable combination of hash and nonce. Alteration to any one earlier block requires re-mining not only that block but also all blocks which are in chain. Hence, it is tough to exploit blockchain technology. After complete mining chain of block is accepted by rest of the nodes. II. LITREATURE SURVYE Yuan Zhang, Chunxiang Xu, Jianbing Ni, Hongwei Li, and Xuemin (Sherman) Shen; in their paper title “Blockchain-assisted Public-key Encryption with Keyword Search against Keyword Guessing Attacks for Cloud Storage” state that encryption technique use for search keyword is plays vital role in such applications where user request for some results to storage server and server respond without learning about data than search result.