Smart city is an important concept in urban development. The use of information and communication technology to promote quality of life and the management of natural resources is one of the main goals in smart cities. On the other hand, at any time, thousands of mobile users send a variety of information on the network, and this is the main challenge in smart cities. To overcome this challenge and collect data from roaming users, the global mobility network (GLOMONET) is a good approach for information transfer. Consequently, designing a secure protocol for GLOMONET is essential. The main intention of this paper is to provide a secure protocol for GLOMONET in smart cities. To do this, we design a protocol that is based on Li et al.’s protocol, which is not safe against our proposed attacks. Our protocol inherits all the benefits of the previous one; it is entirely secure and does not impose any more communication overhead. We formally analyze the protocol using BAN logic and compare it to similar ones in terms of performance and security, which shows the efficiency of our protocol. Our proposed protocol enables mobile users and foreign agents to share a secret key in 6.1 ms with 428 bytes communication overhead, which improves the time complexity of the previous protocol to 53%.