Network security is becoming more and more important as people spend more and more time connected. It is a specialized field in computer networking that involves securing a computer network infrastructure. It is typically handled by a network administrator or system administrator who implements the security policy, network software and hardware needed to protect a network and the resources accessed through the network from unauthorized access. It also ensures that we have an adequate access to the network and resources to work. A network security system typically lies on the layers of protection and consists of multiple components including networking monitoring and security software in addition to hardware and the appliances. All components work together to increase the overall security of the computer network. For enhancing the security, many algorithms are widely used. Cloud Computing is a set of IT based Services that are provided to a customer over a network and these services are delivered by a third party provider who owns the infrastructure. It is often provided "as a service" over the Internet and that was typically in the form of infrastructure as a service (IaaS), platform as a service (PaaS), software as a service (SaaS), data storage as a service (DSaaS). This research paper presents what cloud computing is, security algorithms and the challenges in cloud computing.