Cloud computing has developed from various technologies such as autonomic computing, virtualization, grid computing, and other technologies, and the secure storage is essential and important for it due to it provides virtualized resources on Internet. Therefore, Data owner must encrypt his documents locally before uploading it in the public cloud storage to prevent unauthorized access to his data. Sometimes, the data owner wants to share some of his encrypted documents that stored in the cloud with other authorized users, so, he must send the secret key for each document for all authorized users, but this way has many limitations due to the difficulty of key management and key distribution. To overcome drawback of this approach we proposed system to generate a single key used for multiple number of documents and users depending on two techniques asymmetric cryptography and symmetric cryptography. Asymmetric cryptography used the IBC of the data owner to generate his private key and split the private key into two parts give one part to all authorized users and the other part send to Semi-Trusted Third Party (STTP). While symmetric cryptography used by combined secret key with the encrypted file properties and decrypted the result by the public key of the data owner by using asymmetric cryptography (RSA algorithm). Finally, many results were obtain from implementing the proposed system, among these results; the data owner could add or revoke any user without change the master secret key, also the data owner not need to share multi keys with authorized users. As well as, the system overcame the problem on difficulty of searching over encrypted data through encryption key in a public cloud.
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