International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Index Copernicus Value (2013): 6.14 | Impact Factor (2014): 5.611 Volume 4 Issue 11, November 2015 www.ijsr.net Licensed Under Creative Commons Attribution CC BY A Survey Paper on Key Aggregate Cryptosystem: A Key Assignment Scheme for Scalable Data Sharing Over Cloud Storage Rachana Gangwani 1 , H. A. Hingoliwala 2 1 M.E (Computer) Department of Computer Engineering, Jayawantrao Sawant College of Engineering, Pune, India. Savitribai Phule Pune University, Pune, Maharashtra, India-411007 2 M.E (Computer) Head of Department and Asst Prof (Computer) Department of Computer Engineering, Jayawantrao Sawant College of Engineering, Pune, India. Savitribai Phule Pune University, Pune, Maharashtra, India-411007 Abstract: Cloud storage is a model of data storage online in cloud which is accessible from multiple and connected resources, whose demand is greatly increasing. Cloud storage has a requisite functionality i.e. sharing of data securely, efficiently, flexibly over the safe network. Various schemes and methodologies are implemented to make data sharing more effective. Data security is crucial aspect in cloud storage. Providing security to a single file or a set of files is an important factor. With the introduction of encryption and decryption schemes, the storing, sharing and securing of data became rampant. The storing of these ciphertexts and the decryption keys is one of the major issues. There is a need for a mechanism which can minimize the cost of storing these ciphertexts and keys in a secured way. In this era of information, where there is presence of rich data, the true value lies in sharing, securing and storing them. Protecting user’s data privacy is one of the critical aspects of cloud storage. The survey depicts some encryption schemes introduced in this data privacy for securely and efficient sharing of confidential data over a secure channel. The present research efforts concentrates more on aggregation of these keys into a single aggregate key which will in turn reduce the burden on the network overhead. Keywords: Cloud Storage, Attribute Based Encryption, Pre Defined Hierarchy, Compact Key Encryption, Identity Based Encryption, Key Aggregate Cryptosystem. 1. Introduction Cloud storage is a cloud computing model in which data is stored on remote servers accessed from the internet, or cloud. It is maintained, operated and managed by a cloud storage service provider on a storage server that is built on the virtualization techniques. Cloud storage is also known as utility storage. Cloud storage works through a data centre virtualization, providing data owner and applications with a virtual storage architecture that is scalable according to the application requirements. Figure 1: Sharing of data in cloud storage In modern cryptography, encryption keys obtained are of two categories, symmetric and asymmetric (public) key. The public key encryption tends to be much more secured as it involves combination of two different keys, public and private key respectively. Cryptography is the way of storing and sharing the data in the form of that only those authenticated for it can access. It is the knowledge of securing the message by encoding it into an unreadable format. The basic goal of cryptography is the ability to send the data to the receiver in a way that prevents attackers from accessing it. This data is stored on cloud through the internet. The cloud storage is a cloud computing model in which the data is stored and remote servers are accessed from the internet. The cloud storage provider is maintaining, operating and managing the cloud storage on a server. Cryptographic mechanism is used to hide the data from unauthorized users. The most encryption algorithms can be broken and the data is stolen by the attacker. So a more realistic goal of cryptography is to make gaining the data too severe to be value it to the attacker. Figure 2: The encryption process converts plaintext into ciphertext Figure 3: The decryption process converts ciphertext into plaintext Paper ID: NOV151729 2375