  With the rapid development of cloud computing, the privacy security incidents
occur frequently, especially data security issues. Cloud users would like to
upload their sensitive information to cloud service providers in encrypted form
rather than the raw data, and to prevent the misuse of data. The main challenge
is to securely process or analyze these encrypted data without disclosing any
useful information, and to achieve the rights management efficiently. In this
paper, we propose the encrypted data processing protocols for cloud computing
by utilizing additively homomorphic encryption and proxy cryptography. For the
traditional homomorphic encryption schemes with many limitations, which are not
suitable for cloud computing applications. We simulate a cloud computing
scenario with flexible access control and extend the original homomorphic
cryptosystem to suit our scenario by supporting various arithmetical
calculations. We also prove the correctness and security of our protocols, and
analyze the advantages and performance by comparing with some latest works.
