A relay-chain-powered Ciphertext-Policy Attribute-Based Encryption in Intelligent Transportation Systems

The rapid growth of Intelligent Transportation Systems (ITS) requires secure, efficient, and context-aware data sharing across heterogeneous and geographically distributed participants. We propose a relay-chain-driven architecture that couples a context-aware smart contract with a modified Ciphertext-Policy Attribute-Based Encryption (CP-ABE) scheme to support dynamic access control under low-latency constraints. The relay-chain contract evaluates event metadata (type, time, region) and selects an appropriate policy strictness, On-Board Units (OBUs) then encrypt and store ciphertext on regional blockchains, while the relay chain maintains global attribute definitions, revocation state, and cross-region discovery. The model proposes a context-aware smart contract on a worldwide relay chain that checks data properties, including event type, time, and geographical region, to determine the appropriate encryption policy. From such relay-directed judgement, On-Board Units (OBUs) encrypt data using CP-ABE and store ciphertext on localised regional blockchains, thereby avoiding reliance on symmetric encryption or off-chain storage. Robust, multi-attribute access rules protect high-sensitivity events, whereas common updates use lighter policies to reduce processing burdens. The crypto system also adds traceability and low-latency revocation, with global enforcement managed through the relay chain. This distributed, scalable model strikes a proper balance between real-time responsiveness and security, making it highly suitable for next-generation vehicular networks that operate across multi-jurisdictional domains. • Relay-chain smart contract selects high/low-security CP-ABE by event context. • OBUs do end-to-end CP-ABE; ciphertext stored on regional blockchains, no offload. • Dual-mode ciphertext: strict attribute policies for sensitive, light for routine. • Two-layer federation: regional chains store data; global relay coordinates policies. • CP-ABE embeds pseudonymous IDs in keys; q-SDH revocation ensures accountability.