Cloud is completely the internet dependent technology where client data is stored and maintained in the data centre of a Cloud Service Provider (CSP) like Google, Amazon, Salesforce.som and Microsoft etc. CSP is responsible for maintaining and monitoring the outsourced data. Limited control over the data may incur various security issues and threats which include data leakage, insecure interface, sharing of resources, data availability and inside attacks. The issues start from Security, Availability, Performance, Lack of Standards, Increased Usage Cost, and Struggle in integrating with on-premise IT resources. So many customers do not fully depend on the cloud environment because of their unawareness of the location where their data would be stored, its availability in their need, and data processing by others. For these reasons many of the researchers concentrates on the ¿Security¿ aspect of the cloud. Data security can be achieved by the parameters like confidentiality, integrity and availability. This research work fully concentrated on the parameter like confidentiality. In this book, various algorithms have been proposed to enhance the security of data at rest.