## 2 Related Work  
In LEO satellite networks, the service area of the satellite is constantly moving; therefore, the connection between the user and satellites needs frequent switching. How to efficiently implement switching authentication is an important research problem. Regarding identity authentication protocols in terrestrial networks, [PERSON] et al. proposed a new secure identity authentication scheme based on blockchain and identity-based cryptography. The scheme implemented a decentralized private key generator in the Ethereum blockchain, and used the identity-based encryption signature algorithm and challenge-response protocol during the authentication process. This scheme used blockchain to solve the single point of failure and identity-based encryption to avoid the complex certificate management [16], but bilinear pairs have high computational cost and system overhead. [PERSON] et al. proposed a certification public key cryptography. The key generation center gave part of the user's private key. The user selected a secret value and combined part of the private key to generate a complete private key. This method avoided the problem of private key escrow in identity based public key cryptography [18]. In the terrestrial network, the existing work uses identity-based encryption algorithm or blockchain technology to avoid complex certificate management. For the satellite networks using key authentication protocols, [PERSON] et al. proposed mutual authentication between users and satellites using a public key encryption system, which uses a key algorithm to encrypt data, and a public key encryption system can ensure the security of data transmission [19]. However, its operation is too complicated, and the reliability of authentication information is not involved. [PERSON] et al. proposed a Beidou2 navigation information authentication scheme, which uses an elliptic curve digital signature algorithm to generate digital signatures to verify the integrity and authenticity of navigation data and avoid entity disguise and data tampering [20]. However, information authentication during satellite switching is not involved. [PERSON] et al. proposed a robust key negotiation authentication scheme suitable for mobile satellite environments, providing mutual authentication, session key negotiation and correct user anonymity concepts [21], but there are problems of protocol storage, high communication cost and complex calculation. In satellite networks, most work considered optimizing the calculation method of authentication, which involved the management of certificate authority and thus suffered from the single-point-of-failure problem. In addition, the distance between the satellite and the certificate authority is varying, and the data transmission between them may need to be forwarded through multiple satellite nodes. The data volume and transmission time of trusted certificate cannot be simply ignored, which increases the communication delay in the switch authentication process. Regarding signature algorithms in the satellite networks, [PERSON] et al. designed an authentication scheme based on a proxy signature, and the authentication interaction process was only realized between mobile users and satellite nodes, thus reducing the long delay of authentication implementation [22]. Although proxy signature can avoid the problem of certificate management, each authentication needs to pass through the gateway to obtain permission, which causes a problem with too many transmission hops. In resource-constrained LEO satellite networks, the response latency of the above authentication protocols needs to be improved, and the distributed characteristics of LEO satellite networks needs attention. According to the distributed characteristics of LEO satellite networks, we adopt the blockchain technology. In the network, satellites can calculate independently, become peer nodes, and thus no longer rely on a control center.