Cake: Compatible authentication and key exchange protocol for a smart city in 5g networks

In a smart city, there are different types of entities, such as nature persons, IoT devices, and service providers, which have different computational limitations and storage limitations. Un-fortunately, all of the existing authentication and key exchange (AKE) protocols are designed for either client–server or client–client authentication, including the ones designed for smart cities. In this paper, we present the idea of a compatible authentication and key exchange (CAKE) protocol which provides cross-species authentication. We propose the first CAKE protocol for a smart city that any two valid entities can authenticate with each other and create a secure session key without the help of any third party, while there is also no password table and no public key issuing problem. The entity can be a natural person having biometrics, an IoT device embedded with a physical unclonable function (PUF), or a service provider. Moreover, we extend the CAKE protocol to an anonymous CAKE (ACAKE) protocol, which provides natural persons an anonymous option to protect their privacy. In addition, both the proposed CAKE and ACAKE protocols can deal with the entity revocation problem. We define the framework and the security model of CAKE and ACAKE protocols. Under the security model, we formally prove that the proposed protocols are secure under the elliptic curve computational Diffie–Hellman (ECCDH) problem, the decisional bilinear Diffie–Hellman (DBDH) problem, and hash function assumptions. Comparisons with the related protocols are conducted to demonstrate the benefits of our protocols. Performance analysis is conducted and the experience results show that the proposed protocols are practical in a smart city.