Cloud computing is basically a combination of various computing techniques like virtualization, distributed computing, load balancing etc. In cloud computing, there are many data privacy concerns. Data,the data over cloud and during communication is important challenge. Cloud services include Infrastructure as a Service (IaaS), Platform as a Service (PaaS),and Software as a Service (SaaS). Security of data in cloud computing environment is an important challenge. This Book discuss data security technique over cloud and provides very efficient encryption based approach at storage level.It provide secure communication over the network,encryption algorithm plays a vital role. It is the fundamental tool for protecting the data..