Location-based services are becoming more and more popular in mobile online social networks (mOSNs) for smart cities, but users’ privacy also has aroused widespread concern, such as locations, friend sets and other private information. At present, many protocols have been proposed, but these protocols are inefficient and ignore some security risks. In the paper, we present a new location-sharing protocol, which solves two issues by using symmetric/asymmetric encryption properly. We adopt the following methods to reduce the communication and computation costs: only setting up one location server; connecting social network server and location server directly instead of through cellular towers; avoiding broadcast encryption. We introduce dummy identities to protect users’ identity privacy, and prevent location server from inferring users’ activity tracks by updating dummy identities in time. The details of security and performance analysis with related protocols show that our protocol enjoys two advantages: (1) it’s more efficient than related protocols, which greatly reduces the computation and communication costs; (2) it satisfies all security goals; however, most previous protocols only meet some security goals.

在智能城市的移动在线社交网络（mOSN）中，基于位置的服务越来越受欢迎，但是用户的隐私也引起了广泛的关注，例如位置，朋友集和其他私人信息。当前，已经提出了许多协议，但是这些协议效率低并且忽略了一些安全风险。在本文中，我们提出了一种新的位置共享协议，该协议通过正确使用对称/非对称加密解决了两个问题。我们采用以下方法来减少通信和计算成本：仅设置一台位置服务器；直接连接社交网络服务器和位置服务器，而不是通过蜂窝塔连接；避免广播加密。我们引入虚拟身份来保护用户的身份隐私，并通过及时更新虚拟身份来防止位置服务器推断用户的活动轨迹。有关协议的安全性和性能分析的细节表明，我们的协议具有两个优点：（1）比相关协议更有效，大大降低了计算和通信成本；（2）满足所有安全目标；但是，大多数以前的协议仅满足某些安全性目标。