The development in cloud computing platforms has resulted, hosting many day-to-day service applications in the cloud. To avail the services provided by different cloud service providers (CSPs), the mobile user has to register his/her identity with the CSPs. The mobile user (MU) has to remember multiple identities and credentials to access various CSPs. Many single sign-on schemes have been proposed in the literature to eliminate multiple registrations by mobile users to access CSPs. Most of these schemes rely on a trusted third party known as Registration Authority Center (RAC), which is a centralized entity to manage the identity information of all the mobile users registered with it. The centralized RAC has two operational problems, i.e., RAC has full control over the data it possesses, resulting in the possibility of the data breach and increased risk of single-point-of-failure. In this paper, we propose a blockchain based privacy preserving user authentication protocol for distributed mobile cloud environment, which solves these two traditional problems with centralized registration centers. In proposed protocol, the registration of MU and CSP are performed through public blockchain network for MU to access CSPs and the authentication was performed between MU and CSP through public blockchain. The public blockchain network stores MU and CSPs identity information. Public blockchain network provides integrity to the data stored in it and secures the system from single-point-of-failure. In addition, security analysis and performance analysis were also performed for proposed protocol and it showed that the proposed protocol is secure from all-known attacks with better performance efficiency.

最终，云计算平台得到了发展，在云中托管了许多日常服务应用程序。为了利用由不同的云服务提供商（CSP）提供的服务，移动用户必须在CSP中注册他/她的身份。移动用户（MU）必须记住多个身份和凭证才能访问各种CSP。在文献中已经提出了许多单点登录方案，以消除移动用户访问CSP的多次注册。这些方案大多数依赖于称为注册中心中心（RAC）的受信任第三方，该中心是管理向其注册的所有移动用户的身份信息的集中式实体。集中式RAC存在两个操作问题，即RAC对其拥有的数据具有完全控制权，导致出现数据泄露的可能性，并增加单点故障的风险。在本文中，我们提出了一种用于分布式移动云环境的基于区块链的隐私保护用户身份验证协议，通过集中式注册中心解决了这两个传统问题。在所提出的协议中，MU和CSP的注册是通过公共区块链网络进行的，以使MU访问CSP，而MU和CSP之间的认证是通过公共区块链进行的。公用区块链网络存储MU和CSP身份信息。公共区块链网络可为其中存储的数据提供完整性，并确保系统免受单点故障的影响。此外，