International OPEN ACCESS Journal Of Modern Engineering Research (IJMER) | IJMER | ISSN: 2249–6645 | www.ijmer.com | Vol. 4 | Iss. 5| May. 2014 | 38| Secure File Sharing In Cloud Using Encryption with Digital Signature Miss. N. Kanchana 1 , Mr. S. Balamurugan 2 1, 2 (PG Student, Assistant Professor, Sri Manakula Vinayagar Engineering College, Pondicherry-605106) I. Introduction Cloud computing is a type of computing that relies on sharing computing resources rather than having local servers or personal devices to handle applications. It comes into focus only when you think about what IT always needs: a way to increase capacity or add capabilities on the fly without investing in new infrastructure, training new personnel, or licensing new software. "the cloud" is essentially a metaphor for the Internet. Marketers have further popularized the phrase "in the cloud" to refer to software, platforms and infrastructure that are sold "as a service", i.e. remotely through the Internet. Typically, the seller has actual energy-consuming servers which host products and services from a remote location, so end-users don't have to; they can simply log on to the network without installing anything. Cloud computing providers offer their services according to several fundamental models: infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS). (A) Software as a Service Delivery of software applications over the internet. The software is frequently delivered using a one-to- may approach and is not customized. Hence on the supply-side, the provider is managing one application from one or more dedicated locations, whilst on the demand-side; customers are not required to make any hardware (such as servers) or software investments. For example: Gmail, hotmail, yahoo. (B) Platform as a service Delivery of a computing platform for the development of services and applications from a cloud. This category of service tends to be not as mainstream as the other "-aaS" options. Since it is used almost exclusively by programmers. For example: Google App Engine, Amazon EC2,Microsoft Azure Platform. (C) Infrastructure as a Service Delivery and remote management of computer and networking hardware, as well as processing power, as a service over the internet. Customers can purchase storage, processing power, networking capability etc, as and when needed, and commensurate with their actual needs. For Example: Storage-Dropbox, icloud, Adrive, mozy, amazon web service. Web hosting- Go daddy, bluehost, fatcow. Virtual Servers-IBM, Rimu Hosting. II. Advanced Encryption Standard (AES) AES is a symmetric-key algorithm, meaning the same key is used for both encrypting and decrypting the data. Block length: 128 bits (P = C = {0,1}1 2 8 ) Key lengths: 128, 192, 256 bits (K = {0,1}1 2 8 , ...) The key size used for an AES cipher specifies the number of repetitions of transformation rounds that convert the input, called the plaintext, into the final output, called the ciphertext. The number of cycles of repetition are as follows: • 10 cycles of repetition for 128-bit keys. • 12 cycles of repetition for 192-bit keys. • 14 cycles of repetition for 256-bit keys. Abstract: This paper we discuss about the data sharing in a cloud with multiple owner by generating keys and digital signature. The proposed methodology suggests the encryption of the files to be uploaded on the cloud. To ensure the security of data, we proposed a method by implementing AES algorithm. The integrity and confidentiality of the data is achieved by not only encrypting it but also providing Digital Signature for successful authentication. It provides two way security for data sharing. Keywords: Cloud, Encryption, Integrity, Confidentiality, Digital Signature.