空间信息网络安全的核心是实现高效的安全服务和可靠的数据存储。本项目针对空间信息网络节点异质、链路异构、网络拓扑动态变化等特点，结合区块链去中心化、不可篡改、全网共识的特性，重点研究空间信息网络形式化安全模型及关键安全方法：1.引入可证明安全理论与形式化分析方法，提出能准确定义空间信息网络安全功能的形式化安全模型，为空间信息网络安全提供坚实的理论基础。2.利用区块链作为公共账本，研究适应长时延、高动态网络特性的分布式快速安全接入认证新方法，以解决地面用户和空间节点灵活的安全可信接入问题。3.研究时空变化的异构网络环境下跨安全域的密钥分发与更新方法，以解决跨安全域密钥管理问题。4.研究动态网络拓扑下空间节点安全可靠的数据存储方法，利用区块链保证各节点数据完整且一致。本项目研究成果将丰富密码学理论，创新空间信息网络安全方法和关键技术，推进我国空间信息网络建设进程。

The secure access authentication and the cross-security-domain key management are the major security concerns in Space Information Network (SIN). Observing the features of heterogenous nodes and communication links, and dynamic topological changes in SIN, combining the features of decentralization, untempering, and whole-system consensus in Blockchain, this project conducts researches on defining the security model, proposing new secure access authentication methods, and designing lightweight cryptographic algorithms and protocols to secure SIN. First, by introducing provable security theory and formal methodology in SIN, this project proposes a new formal security model to accurately define security-valid or security-invalid criteria, underlying a solid theoretical foundation to secure SIN. Second, based on the proposed formal security model, utilizing Blockchain as a public ledger, this project presents new approaches of seamless distributed peer-to-peer secure access authentication schemes, addressing the problem of legitimate nodes and users securely accessing SIN. Third, aiming at the challenges of cross-domain key managements and secure communications in SIN, this project puts forward new cross-domain key distribution paradigms based on advanced cryptosystems. Finally, this project focuses on secure and reliable distributed storage method, utilizing Blockchain to make data consistent and complete in all nodes, to ensure data stay dependable and robust with dynamic topological changes. By conducting this project, it is expected to broaden the cryptographic theories, innovate the network security methodologies and key technologies, and promote the deployment of SIN.