Cloud computing is group of services for example software system storage, network and hardware these type of services are provided to user. Cloud storage is easily access anywhere anytime of the data because cloud is work in remote location. It uses the storage service provided by the cloud provider. Data is not secure in the cloud because the unauthorized user can try to use of the private data. So providing the data security it uses the different encryption method to protect the data. The proposed system assures security for data stored in cloud by using key aggregate cryptosystem (KAC). Initially the data is divided into multiple chunks each chunks is encrypted using encryption algorithm and generate different keys. Those keys are aggregated into a single master key which is used for decrypting retrieved cloud data.

1. P. Mell and T. Grance, The NIST Definition of Cloud Computing, version 15, October 7, 2009, National Institute of Standards and Technology (NIST), Information Technology Laboratory (www. csrc. nist. gov).
2. Uma Somani,Kanika Lakhani," Implementing Digital Signature with RSA Encryption Algorithm to Enhance the Data Security of Cloud in Cloud Computing. "IEEE PDGC-2013.
3. William Stallings, Cryptography and Network Security: Principles and Practices, Fifth edition, Prentice Hall, ISBN-13: 978- 0136097044, 2010.
4. Amazon Web Services: Overview of Security Processes, may 2011.
5. F. Guo, Y. Mu, Z. Chen, and L. Xu, "Multi-Identity Single-Key Decryption without Random Oracles," in Proceedings of Information Security and Cryptology (Inscrypt '07), ser. LNCS, vol. 4990. Springer, 2007, pp. 384–398.
6. A. Sahai and B. Waters, "Fuzzy Identity-Based Encryption," in Proceedings of Advances in Cryptology - EUROCRYPT '05, ser. LNCS,vol. 3494. Springer, 2005, pp. 457–473.
7. J. Benaloh, M. Chase, E. Horvitz, and K. Lauter, "Patient Controlled Encryption: Ensuring Privacy of Electronic Medical Records, " in Proceedings of ACM Workshop on Cloud Computing Security (CCSW '09). ACM, 2009, pp. 103–114.
8. Cheng-Kang Chu, Sherman S. M. Chow, Wen-Guey Tzeng, Jianying Zhou, and Robert H. Deng, Senior Member, IEEE," Key-Aggregate Cryptosystem for Scalable Data Sharing in Cloud Storage".
9. L. M. Kaufman, "Data security in the world of cloud computing,"IEEE Security & Privacy Magazine, vol. 7, pp. 61-64, July2009.
10. K Hashizume et al. , An analysis of security issues for cloud computing, Journal of Internet Services and Applications, a Springer open journal, pp 1-13, 2013.
11. Cong Wang, Qian Wang, and Kui Ren, Wenjing Lou, Ensuring Data Storage Security in Cloud Computing.
12. K. Dubey, M. Namdev, S. Shrivastava, "Cloud-User Security Based on RSA and MD5 Algorithm for Resource Attestation and Sharing in Java Environment", IEEE sixth international conference, 2012.
13. Prakash G. L , Dr. Manish Prateek, Dr Inder Singh, ,"Efficient Data Security Method to Control Data in Cloud Storage System using Cryptographic Techniques ",IEEE International Conference on Recent Advances and Innovations in Engineering (ICRAIE-2014), May 09-11, 2014, Jaipur, India .
14. J. Benaloh, M. Chase, E. Horvitz, and K. Lauter, "Patient Controlled Encryption: Ensuring Privacy of Electronic Medical Records, " in Proceedings of ACM Workshop on Cloud Computing Security (CCSW '09). ACM, 2009, pp. 103–114.
15. R. S. Sajjan,V. Ghorpade,V. Dalimbkar," Key Aggregate Cryptosystem: A Different Approach for Cloud Data Security"(Paper accepted in AIM Conference).
16. Sandha, M. Ganaga Durga," Study on Data Security Mechanism in Cloud Computing",IEEE conference no-33344.
17. Balachandra Reddy Kandukuri, Rama Krishna Paturi and Dr. AtanuRakshit, "C loud security issues" In ServicesComputing, 2009. IEEE International Conference on, page 517520, 2009.

Cloud Computing Data Security Key Aggregate Cryptosystem