FastBOC: Towards Efficient Covert Communication Merging Blockchain and Onion Networks

Covert communication over public blockchains has emerged as a promising approach for secret data transmission. However, existing methods often suffer from high communication costs, low communication efficiency, and the risk of permanent data exposure. To overcome the above challenges, we propose FastBOC, a hybrid covert communication framework that integrates blockchain and onion networks. In FastBOC, the blockchain is employed as a covert signal channel to transmit lightweight signals, while the onion network handles high-capacity secret data transmission. This decoupling significantly reduces communication costs and avoids permanent data exposure on the blockchain. We further design an address-based encoding scheme and a dynamic port activation mechanism to enhance concealment. We implement FastBOC on the Ethereum testnet and conduct experiments to evaluate its concealment, efficiency, and cost. The results demonstrate that FastBOC (1) achieves strong concealment and (2) can transmit 1-Megabyte (MB) data within 20.11 seconds and reduce communication cost by 5–7 orders of magnitude compared to prior blockchain-based covert communication schemes.