属性加密是从基于身份加密发展而来的更具通用性的加密算法，兼具数据加密和用户访问控制的双重能力，在安全云端存储等系统中有着广阔的应用前景。由于属性加密涉及到用户属性、密钥、密文以及策略等多重因素，其密钥撤销问题尤为复杂，并成为其进一步取得实际应用的一大障碍。为了解决这个问题，本项目提出了构建“具有安全仲裁员的属性加密”的研究目标，首先对具有安全仲裁员的属性加密算法进行定义；其次，针对该算法，在理论上从攻击者能力、确定攻击目标的时机和是否要求随机预言机等三个方面建立起“选择/完全安全-抗（可重放）选择密文攻击”的随机预言机/标准安全模型；再次，借鉴双系统加密证明方法，设计由选择安全证明完全安全、以及由抗可重放选择密文攻击证明抗选择密文攻击的通用方法；最后，在不同级别的安全模型下设计可证明安全的具有安全仲裁员的属性加密方案以解决实际的密钥撤销问题，因此，本项目的研究具有重要的理论意义和实用价值。

Attributed-Based Encryption (ABE) is a generalized cryptographic primitive from Identity-Based Encryption (IBE), which offers fine-grained decryption policy according to system user’s attribute set, such that only users whose attribute set fits into the policy can decrypt data. It has got more attention in cloud storage security. However, ABE involves attribute, key, ciphertext and policy, which makes its key revocation problem more serious. Targeting on this problem, the project proposes to construct Attribute-Based Encryption with SEcurity Mediator (SEM-ABE). Firstly, it gives the formal definition of SEM-ABE. Secondly, it analyzes the different security of models according to attacker’s capability, the timing that attacker decides the victim, and whether random oracle is required, and builds Selective-RCCA ROM, Fully-RCCA ROM, Fully-CCA ROM and Fully-CCA SM. Thirdly, it designs the generic method to prove a fully secure SEM-ABE based on dual system encryption, and concludes the generic property for an SEM-ABE from RCCA secure to CCA secure. Lastly, the project proposes four provable secure SEM-ABE schemes to solve key revocation problem. The results of the project could provide a solid theoretical foundation and practical value.