A survey on security issues and solutions at different layers of Cloud computing <s> Need for security and privacy in Cloud computing <s> In past three decades, the world of computation has changed from centralized (client-server not web-based) to distributed systems and now we are getting back to the virtual centralization (Cloud Computing). Location of data and processes makes the difference in the realm of computation. On one hand, an individual has full control on data and processes in his/her computer. On the other hand, we have the cloud computing wherein, the service and data maintenance is provided by some vendor which leaves the client/customer unaware of where the processes are running or where the data is stored. So, logically speaking, the client has no control over it. The cloud computing uses the internet as the communication media. When we look at the security of data in the cloud computing, the vendor has to provide some assurance in service level agreements (SLA) to convince the customer on security issues. Organizations use cloud computing as a service infrastructure, critically like to examine the security and confidentiality issues for their business critical insensitive applications. Yet, guaranteeing the security of corporate data in the "cloud" is difficult, if not impossible, as they provide different services like Software as a service (SaaS), Platform as a service (PaaS), and Infrastructure as a service (IaaS). Each service has their own security issues. So the SLA has to describe different levels of security and their complexity based on the services to make the customer understand the security policies that are being implemented. There has to be a standardized way to prepare the SLA irrespective to the providers. This can help some of the enterprises to look forward in using the cloud services. In this paper, we put forward some security issues that have to be included in SLA. <s> BIB001 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Need for security and privacy in Cloud computing <s> The competition among cloud providers may drive prices downward, but at what cost? <s> BIB002 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Need for security and privacy in Cloud computing <s> Cloud computing carries the promise of providing powerful new models and abstractions that could transform the way IT services are delivered today. In order to establish the readiness of clouds to deliver meaningful enterprise-class IT services, we identify three key issues that ought to be addressed as first priority from the perspective of potential cloud users: how to deploy large-scale distributed services, how to deliver high availability services, and how to perform problem resolution on the cloud. We analyze multiple sources of publicly available data to establish cloud user expectations and compare against the current state of cloud offerings, with a focus on contrasting the different requirements from two classes of users -- the individual and the enterprise. Through this process, our initial findings indicate that while clouds are ready to support usage scenarios for individual users, there are still rich areas of future research to be explored to enable clouds to support large distributed applications such as those found in enterprise. <s> BIB003
Cloud computing is a merger of several known technologies including grid and distributed computing, utilizing the Internet as a service delivery network. The public Cloud environment is extremely complex when compared to a traditional data center environment  . Under the paradigm of Cloud computing, an organization surrenders direct control over major aspects of security, conferring a substantial level of trust onto the Cloud provider. A recent survey regarding the use of Cloud services made by IDC highlights that the security is the greatest challenge for the adoption of Cloud  . Virtual environments are used in Cloud to achieve multi-tenancy. Vulnerabilities in virtual machines [40] pose direct threat to the privacy and security of the Cloud services. Factors that cripple usage of Cloud services are live migration of data over the Internet, entrusting a provider for data security and privacy, vulnerabilities at browser's API, vulnerabilities in the network, and export regulations for encryption. Shared and distributed resources in the Cloud systems make it hard to develop a security model for ensuring the data security and privacy. Due to transparency issues, no Cloud provider allows its customers to implement intrusion detection or security monitoring systems extending into the management services layer behind virtualized Cloud instances. Customers may not be aware of detailed security-incidents, vulnerability, or malware reports. For example, through back channel, attackers may be able to access the content of Cloud instances and fix a kernel level rootkit BIB002 . Attacks on "physical level" such as reading out the random access memory of the virtualized hosts or subverting the virtualization layer  are known to the community. Even the host system providing the data can no longer be fully trusted since the Cloud provider owns the physical resources. Cloud service providers often establish a Service Level Agreement (SLA) to highlight security and privacy of the related services. To an extent, there is a lack of a standard methodology to design an SLA. The authors in BIB001 presented SLA related to provided services and the waivers. These waivers do not really help the customers fulfilling their losses. Cloud providers like Amazon, Google, and Salesforce alike rely on detailed SLAs to guarantee security and other parameters to their customers, for example, Amazon's EC2 provides abstraction of virtual hardware to its users, covering all types of failures including operator node failure and software node failure BIB003 . In future, SLA based Google App Engine would likely to manage all causes of failures. he rest of the paper is organized as follows: Section 2 discusses vulnerabilities, threats, and attacks relevant to Cloud. A survey on security issues at different layers in the Cloud and their existing solutions are provided in Sect. 3. Section 4 discusses the future research directions with conclusions.