Making data in cloud secure and usable: fully homomorphic encryption with symmetric keys

Today, cloud offers unlimited computing capabilities at affordable price. However, securing data in cloud ensuring usability and availability of data presents a challenge. Benefits promised by cloud computing cannot be availed fully until security issues are properly addressed. Homomorphic encryption ensures data security during computation as well. Most of the currently available homomorphic encryption schemes are based on public key cryptosystems causing large overhead. We propose a symmetric key encryption scheme with fully homomorphic evaluation capabilities, applicable even in multiuser environment. We also present a protocol for using the proposed scheme to private data processing in clouds. The proposed scheme requires a key size linearly proportional to security parameter causing computational overhead proportional to security parameter.