Abstract

The Internet of Things (IoT) technologies interconnect a broad range of network devices, differing in terms of size, weight, functionality, and resource capabilities. The main challenge is to establish the required security features in the most constrained devices, even if they are unknown to each other and do not share common pre-distributed key material. As a consequence, there is a high need for scalable and lightweight key establishment protocols. In this paper, we propose a key agreement protocol between two IoT devices without prior trust relation, using solely symmetric key based operations, by relying on a server or proxy based approach. This proxy is responsible for the verification of the authentication and the key agreement between the IoT devices, without being capable of deriving the established session key. We propose two versions. The first version does not require interactive input from the key distribution center to the proxy, but is not resistant if a compromised user and proxy are collaborating. The second version on the other hand is collision resistant, but needs an interactive key distribution center. In addition, we add the interesting features of anonymity and unlinkability of the sender and receiver in both protocol versions. The security properties of the proposed protocol are verified by using formal verification techniques.