Liao Yongjian, He Yichuan, Li Fagen, Jiang Shaoquan, Zhou Shijie
School of Information and Software Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China.
School of Computer Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China.
Sensors (Basel). 2018 Jan 10;18(1):176. doi: 10.3390/s18010176.
Attribute-based encryption (ABE) is a popular cryptographic technology to protect the security of users' data in cloud computing. In order to reduce its decryption cost, outsourcing the decryption of ciphertexts is an available method, which enables users to outsource a large number of decryption operations to the cloud service provider. To guarantee the correctness of transformed ciphertexts computed by the cloud server via the outsourced decryption, it is necessary to check the correctness of the outsourced decryption to ensure security for the data of users. Recently, Li et al. proposed a full verifiability of the outsourced decryption of ABE scheme (ABE-VOD) for the authorized users and unauthorized users, which can simultaneously check the correctness of the transformed ciphertext for both them. However, in this paper we show that their ABE-VOD scheme cannot obtain the results which they had shown, such as finding out all invalid ciphertexts, and checking the correctness of the transformed ciphertext for the authorized user via checking it for the unauthorized user. We first construct some invalid ciphertexts which can pass the validity checking in the decryption algorithm. That means their "verify-then-decrypt" skill is unavailable. Next, we show that the method to check the validity of the outsourced decryption for the authorized users via checking it for the unauthorized users is not always correct. That is to say, there exist some invalid ciphertexts which can pass the validity checking for the unauthorized user, but cannot pass the validity checking for the authorized user.
基于属性的加密（ABE）是一种用于保护云计算中用户数据安全的流行加密技术。为了降低其解密成本，将密文解密外包是一种可行的方法，它能让用户将大量解密操作外包给云服务提供商。为确保云服务器通过外包解密计算出的转换密文的正确性，有必要检查外包解密的正确性以保障用户数据的安全。最近，李等人针对授权用户和未授权用户提出了一种基于属性加密方案的外包解密全可验证性（ABE-VOD），它可以同时检查这两类用户转换密文的正确性。然而，在本文中我们表明他们的ABE-VOD方案无法得到他们所展示的结果，比如找出所有无效密文，以及通过检查未授权用户的转换密文来检查授权用户转换密文的正确性。我们首先构造了一些在解密算法中能通过有效性检查的无效密文。这意味着他们的“先验证后解密”技巧不可用。接下来，我们表明通过检查未授权用户来检查授权用户外包解密有效性的方法并不总是正确的。也就是说，存在一些无效密文能通过未授权用户的有效性检查，但不能通过授权用户的有效性检查。
