Cloud computing (CC) is one of the most prominent storage and computing platforms being researched nowadays. CC platforms are providing the opportunity for sharing resources, information, and services among the users of the entire world. For data storage and processing, cloud security considerations are critical. Because data in a cloud based environment must be protected from hackers, network security has been a key concern in recent years. Data should be encrypted and outsourced to the cloud to safeguard it from malicious intruders. Cryptography is essential for protecting data from various assaults and cloud storage platforms. To overcome the security threat new types of cryptography techniques can be introduced. Though a variety of firewall systems exist, there are still threats or attacks on the data or information which is transmitted over the cloud. The invention focuses on addressing the flaws that are inherent in network security by using advanced encryption techniques to encrypt data over the cloud. In this research work, a blockchain (BC) based user authentication system and improvised public-key cryptosystem are proposed which is based on Rivest-Shamir-Adleman (RSA) to support a private key cryptosystem. The proposed work comes under the following phases: user registration, login, authentication, BC, sensitive data identification, data splitting, and data security. Finally, the performance of the proposed framework in comparison with existing techniques determines strong results and proves to be more secure.