Key-Aggregate Cryptosystem For Scalable Data Sharing in Cloud

Data sharing is an important functionality in cloud storage. In this paper, we show how to securely, efficiently, and flexibly share data with others in cloud storage. We describe new public-key cryptosystems that produce constant-size ciphertexts such that efficient delegation of decryption rights for any set of ciphertexts are possible. The novelty is that one can aggregate any set of secret keys and make them as compact as a single key, but encompassing the power of all the keys being aggregated. In other words, the secret key holder can release a constant-size aggregate key for flexible choices of ciphertext set in cloud storage, but the other encrypted files outside the set remain confidential. This compact aggregate key can be conveniently sent to others or be stored in a smart card with very limited secure storage. We provide formal security analysis of our schemes in the standard model. We also describe other application of our schemes. In particular, our schemes give the first public-key patient-controlled encryption for flexible hierarchy, which was yet to be known. Key-Aggregate Cryptosystem For Scalable Data Sharing in Cloud

KEY-AGGREGATE ENCRYPTION A key aggregate encryption has five polynomial-timealgorithms as 3.1 Setup Phase The data owner executes the setup phase for an account onserver which is not trusted. The setup algorithm only takesimplicit security parameter. 3.2 KeyGen Phase This phase is executed by data owner to generate the publicor the master key pair (pk, msk). 3.3 Encrypt Phase This phase is executed by anyone who wants to send theencrypted data. Encrypt (pk, m, i), the encryption algorithmtakes input as public parameters pk, a message m, and I denoting cipher text class. The algorithm encrypts messagem and produces a cipher text C such that only a user that hasa set of attributes that satisfies the access structure is able todecrypt the message. 3.4 Cloud Storage Cloud storage is nowadays very popular storage system. Cloud storage is storing of data off-site to the physical storage which ismaintained by third party. Cloud storage is saving of digital data in logical pool and physical storage spans multiple servers which aremanage by third party. Third party is responsible for keeping data available and accessible and physical environment should beprotected and running at all time. Instead of storing data to the hard drive or any other local storage, we save data to remote storagewhich is accessible from anywhere and anytime. It reduces efforts of carrying physical storage to everywhere. By using cloud storagewe can access information from any computer through internet which omitted limitation of accessing information from same computerwhere it is stored.While considering data privacy, we cannot rely on traditional technique of authentication, because unexpected privilege escalationwill expose all data. Solution is to encrypt data before uploading to the server with user’s own key. Data sharing is again importantfunctionality of cloud storage, because user can share data from anywhere and anytime to anyone. For example, organization maygrant permission to access part of sensitive data to their employees. But challenging task is that how to share encrypted data.Traditional way is user can download the encrypted data from storage, decrypt that data and send it to share with others, but it losesthe importance of cloud storage

CONCLUSION To share data flexibly is vital thing in cloud computing. Users prefer to upload there data on cloud and among different users. Outsourcing of data to server may lead to leak the private data of user to everyone. Encryption is a on solution which provides to share selected data with desired candidate. Sharing of decryption keys in secure way plays important role. Public-key cryptosystems provides delegation of secret keys for different cipher text classes in cloud storage. The delegate gets securely an aggregate key of constant size. It is required to keep enough number of cipher texts classes as they increase fast and the cipher text classes are bounded that is the limitation.