Abstract—Cloud computing provides the facility to access shared resources and common infrastructure, offering services on demand over the network to perform operations that meet changing business needs. The location of physical resources and devices being accessed are typically not known to the end user. It also provides facilities for users to develop, deploy and manage their applications ‘on the cloud’, which entails virtualization of resources that maintains and manages itself. Confidentiality, Integrity, Authenticity and Privacy are essential concerns for both Cloud Service Providers and consumers as well. This paper proposes a scheme for enhancing the data authenticity, privacy and integrity of cloud data with the aid of an encryption scheme and a hash function which uses message digest. Index Terms—Authenticity, cloud computing, cloud service provider, confidentiality, encryption, hash function, integrity, message digest, privacy. I. INTRODUCTION Cloud computing is defined by the National Institute of Standards and Technology (NIST) as “a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g. networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction”. It is a prototype for large-scale distributed computing that makes use of existing technologies such as virtualization, service-orientation, and grid computing. It offers a different way to acquire and manage IT resources on a large scale. There is growing interest in cloud computing from consumers and Cloud Service Providers. For example, cloud service spending worldwide rose by over 20% in 2009 when overall IT spending dropped by about 4%. In 2010, most cloud consumers are small enterprises, but large enterprises were exploring the paradigm. Business or major activity users rely in some form, on IT and IT services. These services need to be enabling and appliance-like, and there must be an economy-of-scale for the total-cost-of-ownership to be better than it would be without cyber infrastructure. Technology needs to improve end user productivity and reduce technology-driven overhead. For example, unless IT is the primary business of an organization, less than 20% of its efforts not directly connected to its primary business should have to do with IT overhead; even though 80% of its business might be conducted using electronic means [1]. Manuscript received August 16, 2012; revised September 28, 2012. The authors are with the Computer Science Department, Government Arts College, Udumalpet, Tamilnadu, India (e-mail: mgobimail@yahoo.com, srinashok@gmail.com). II. CLOUD COMPUTING Cloud computing is a computing paradigm, where a large pool of systems are connected in private or public networks, to provide dynamically scalable infrastructure for application, data and file storage. With the advent of this technology, the cost of computation, application hosting, content storage and delivery is reduced significantly. Cloud computing is a practical approach to experience direct cost benefits and it has the potential to transform a data centre from a capital-intensive setup to a variable priced environment. The idea of cloud computing is based on a very fundamental principal of reusability of IT capabilities. The difference that cloud computing brings compared to traditional concepts of “grid computing”, “distributed computing”, “utility computing”, or “autonomic computing” is to broaden horizons across organizational boundaries[2]. More and more, small businesses are moving to cloud computing, signing up with Cloud Service Providers that make sophisticated applications more affordable as well as setting up their own accounts with public social media sites like Facebook. The trend is confirmed by Microsoft in its global SMB Cloud Adoption Study 2011, which found that 49% of small businesses expect to sign up for at least one cloud service in the next three years. Although cloud computing can offer small businesses significant cost-saving benefits, the service does come with certain security risks. The top five security concerns in cloud computing are: Secure data transfer, Secure software interfaces, Secure stored data, Authorized user access and Data separation. These risks should be addressed before publishing the cloud data to its servers and applications. Cloud computing offers small businesses too many benefits to dismiss out of hand. A. Cloud Characteristics The important five characteristics of cloud computing includes [3]: 1) Service on demand: This property involves valid customers using a web site or similar control panel interface to provision computing resources such as additional computers, network bandwidth or user email accounts, without requiring human interaction between customers and the Cloud Service Provider. 2) Internetworking: The internetworking enable the customers to access computing resources over networks such as the internet from a broad range of computing devices such as laptops and smart phones. 3) Virtualization of resources: This characteristic of virtualization involves the vendors using shared computing resources to provide cloud services to multiple customers. Virtualization and multi-tenancy An Approach for Secure Data Storage in Cloud Environment M. Gobi and R. Sridevi International Journal of Computer and Communication Engineering, Vol. 2, No. 2, March 2013 206