Design of a trustless protocol for secure message relay in inter-satellite communication

In recent years, space communications have undergone a significant transformation, driven by the rapid growth of satellite constellations and the involvement of multiple independent operators. This increasing complexity calls for secure and interoperable solutions capable of enabling collaboration between networks that do not share mutual trust. This thesis proposes a decentralized protocol for securely relaying encrypted messages between satellite constellations operated by different entities. The system addresses the challenge of cross-network message delivery, where the source and destination are covered by different satellite constellations that do not have direct communication paths. To bridge this gap, the protocol relies on intermediate nodes that act as relays and are economically incentivized to forward messages in a verifiable and secure manner. Instead of relying on a central authority, the protocol uses blockchain technology to coordinate operations in a transparent and tamper-proof way. A smart contract deployed on the Ethereum network records the message handoff, verifies that delivery conditions are met, and automatically handles payments through an escrow system. Intermediate nodes are compensated only if they provide cryptographic proof of correct forwarding and if delivery to the final recipient is confirmed. Security and authenticity are guaranteed through the combined use of public-key encryption, Zero-Knowledge Proofs (ZKPs), and digital signatures. The system has been implemented using Solidity for smart contract development, MetaMask for key and signature management, and ZoKrates for generating and verifying cryptographic proofs. Testing has been conducted on the Sepolia Ethereum testnet. This work demonstrates how a trustless protocol—where correctness and fairness are enforced by code rather than institutional trust—can support secure, auditable, and autonomous message relay in space networks. The proposed approach constitutes a concrete step toward the deployment of decentralized and resilient satellite communication infrastructures, capable of enabling cooperative scenarios among independent entities.