# A Blockchain-Based Cooperative Authentication Mechanism for Smart Grid
## 1 Introduction  
In general, a smart grid [1] is an energy management system that includes various energy production, transmission, and distribution devices. It can monitor and control energy usage in real time and can better integrate renewable and conventional energy sources. Smart devices for the smart grid, such as smart meters and smart charging posts, are being deployed in various locations to collect information or trigger events. This brings great convenience to people's lives and has become an indispensable part of our daily lives. For example, we can monitor our electricity consumption in real time through smart meters and optimize our electricity consumption plans to save energy costs [2]. We can charge our electric cars through smart charging posts to reduce carbon emissions. We can integrate renewable energy sources through smart grids for more sustainable energy development, and so on. Multi-disciplinary smart grid alliances can improve energy use efficiency and reduce costs, but they also face some security challenges. Firstly, many of the devices used in the smart grid are resource-constrained, which means that they are unable to run sophisticated algorithms to improve their security and are therefore vulnerable to attacks. Secondly, because smart grids are composed of many heterogeneous components, the communication standards and data formats of these components are not uniform, which also increases their vulnerability to attacks and threats. When a smart grid is hacked and compromised, grid information can be stolen or corrupted, which can cause damage not only to the affected area but also to other areas in terms ofeconomic and property damage. Most seriously, this could lead to a collapse of the power system and even endanger public life and health. In traditional smart grid authentication schemes, a trusted third party is usually relied upon to provide cross-domain authentication services. As with a traditional public key infrastructure (PKI) [3], there is a centralized certificate authority that can issue digital certificates for smart grid devices. During the cross-domain authentication process, devices can use this digital certificate to prove their identity. However, this method of cross-domain authentication also has shortcomings. Firstly, it is highly dependent on a third-party certificate authority. When this certificate authority is attacked, the entire system can become unavailable, leading to a single point of failure problem. Secondly, these trusted third parties may become untrustworthy at some point. For example, some organizations may compromise the privacy of their users for their own benefit, causing significant damage to the user. For these reasons, a decentralized, secure, and lightweight cross-domain authentication access mechanism is needed in a multi-domain smart grid. Blockchain is essentially a decentralized, distributed, and tamper-evident model of data sharing and transmission [4]. Its main implementation model is to store asset and transaction information on a peer-to-peer network. Blockchain has three main features: decentralization, immutability, and traceability, which enable users or devices to achieve secure transactions in an untrusted network. Due to these characteristics, its application scenarios are no longer limited to the financial field [5]. Currently, we can use the programmable nature of smart contracts to apply blockchain to various scenarios and smart grid is one of its main application scenarios [6]. Based on the above-mentioned problems faced by cross-domains, we propose a blockchain-based cross-domain authentication mechanism for multi-domain smart grid devices by combining the features of blockchain. In this mechanism, smart grids from different domains form a virtual federation in which devices from different domains can access each other's data through cross-domain authentication. The blockchain in our proposed authentication mechanism uses a federated chain.