Attribute‐based signature (ABS) is a widely used cryptographic primitive, that provides both data integrity and fine‐grained privacy protection. However, the signing overhead of ABS is usually too large, making it unsuitable for resource‐constrained devices. Using cloud computing technology, the notion of outsourced attribute‐based signatures (OABS) was introduced to overcome this drawback. In OABS, the user can outsource him/her signing tasks to the signing‐cloud service provider (S‐CSP). The previous notion of privacy of OABS does not take the S‐CSP's attack into account, so it is not strong enough. To conform to the reality of cloud computing, we present a more accurate notion of privacy, called perfect privacy, which ensures that any adversary, even the S‐CSP, cannot identify which policy is used to generate the signature. Then, we propose a key‐policy OABS scheme for circuits based on multilinear mapping with perfect privacy. By using the outsourcing technique, in our scheme, the computation cost of the signer is only three or four pairing operations, which is independent of the complexity of the policy and the size of the attribute set. Our scheme achieves three advantages: perfect privacy, expressive policy, and constant signing cost, simultaneously.

中文翻译：

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基于属性的外包签名，为云计算中的电路提供了完美的隐私

基于属性的签名（ABS）是一种广泛使用的加密原语，可提供数据完整性和细粒度的隐私保护。但是，ABS的签名开销通常太大，使其不适用于资源受限的设备。使用云计算技术，引入了基于属性的外包外包签名（OABS）的概念来克服此缺点。在OABS中，用户可以将他/她的签名任​​务外包给签名云服务提供商（S-CSP）。以前的OABS隐私概念没有考虑到S-CSP的攻击，因此不够强大。为了符合云计算的现实，我们提出了一个更准确的隐私概念，称为完美隐私，这可以确保任何对手，甚至是S-CSP，都无法识别用于生成签名的策略。然后，我们提出了一种基于多线性映射且具有完美隐私性的电路关键策略OABS方案。通过使用外包技术，在我们的方案中，签名者的计算成本仅为三到四个配对操作，这与策略的复杂性和属性集的大小无关。我们的方案具有三个优势：完美的隐私，富有表现力的政策以及不变的签约成本。