DAKEs: Decentralized Authenticated Key Exchange Protocols via Blockchain for Smart City

Authenticated key exchange (AKE) is a classic problem in cryptography, where two participants want to exchange their secret keys without being guessed feasibly. Recently, there has been renewed interest in this problem in the smart city since millions of devices and servers in this environment may involve the problem. New challenges are raised at the same time. One of the greatest challenges is how to facilitate communication between participants. Traditionally, a trusted third party (TTP) is needed to provide a trusted way to exchange keys. However, devices in the smart city environment are usually distributed and trustless. A central trusted mechanism is not suitable for many applications in it. The second challenge is that the requirements in the applications of the smart city are diverse. Finally, a practical AKE protocol should be efficient and easy to integrate. To address these challenges, we provide a fully decentralized AKE protocol framework called DAKEs. To the best of our knowledge, DAKEs enjoy the most comprehensive security properties to fulfil diverse requirements. The decentralization of DAKEs is captured by using the blockchain while avoiding the availability problem of other similar blockchain-based schemes. Our test is conducted in a real-world test network of Ethereum. The result shows that DAKEs are efficient and at a low cost.