Multi User Data Sharing with Aggregated Keys in Clouds

Data sharing is an important functionality in cloud storage. Data owner maintains the shared data under cloud data centers. Semi-trusted third party servers are used to manage medical records. Personal Health Record (PHR) is used to create, manage and control their personal health data in one place through the web. Patient data can be shared with healthcare providers, family members and friends. Sensitive details are managed in medical records. Data owner decides the access privileges for the medical records. The Existing Public-key cryptosystems produce constant-size ciphertexts with efficient delegation of decryption rights for any set of ciphertexts. One can aggregate any set of secret keys and make them as compact as a single key. The secret key holder can release a constant-size aggregate key for flexible choices of ciphertext set in cloud storage. This compact aggregate key can be conveniently sent to others or be stored in a smart card with very limited secure storage. The key aggregation system is divided into five major steps. They are Setup, KeyGen, Encrypt, Extract and Decrypt. The setup process is designed to creating an account on an untrusted server by the data owner. The keygen process is executed by the data owner to randomly generate a public/master-secret key pair. Encrypt process is executed by anyone using public key and index value. Extract is carried out by the data owner for delegating the decrypting power for a certain set of ciphertext classes to a delegate. Decrypt is executed by a delegate who received an aggregate key KS generated by Extract. Patient controlled encryption scheme is designed using Key Aggregate cryptosystem (KAC).The proposed key aggregate cryptosystem is enhanced with boundary less ciphertext classes. The system is improved with device independent key distribution mechanism. The key distribution process is enhanced with security features to protect key leakage. The key parameter transmission process is integrated with the ciphertext download process.