关键词: 云计算, Hadoop, 层次化访问控制模型, 基于密文策略的属性加密（CP-ABE）, 定长密文

Abstract: With the popularity of cloud computing, there have been increasing concerns on its security. Data owners have to encrypt outsourced data to enforce confidentiality as the cloud computing environment is untrusted. Therefore, how to achieve practicable access control of encrypted data in untrusted environment is an urgent issue to be solved. This paper proposes and implements a hierarchical attribute-based access control model with constant-size ciphertext in Hadoop cloud environment, which combines Hadoop cloud computing platform and an attribute-based encryption scheme with constant-size ciphertext. The model not only has characters of constant-size ciphertext, hierarchical authorization structure and reducing computation cost in encryption and decryption algorithms, but also through experimental verifications, the model can implement efficient access control of encrypted data in cloud environment and solve the problem of limitation of cloud storage space.

Key words: cloud computing, Hadoop, hierarchical access control model, Ciphertext-Policy Attribute-Based Encryption（CP-ABE）, constant-size ciphertext