Rearranging Inv Message in the Bitcoin to Construct Covert Channels

Covert channels aim to conceal the communication behaviors and are widely applied to transmit sensitive data. Blockchains are well-suited for building state-of-the-art covert channels due to their decentralization property. Most existing blockchain-based covert channels require the sender to create transactions. Creating transactions requires a fee, and transactions with covert information are permanently stored on the blockchain. Implementing such methods needs a high cost, and the on-chain covert information faces the risk of being exposed. In this paper, we first propose a Bitcoin-based covert channel that rearranges the transaction hashes in Bitcoin inv packets. To improve undetectability and transmission efficiency, we further propose a dynamic channel link scheme and a method for establishing channels with multiple receiving nodes. The dynamic channel link scheme provides the ability to change the connection between the sender and the receiver at any moment. The multiple receiving nodes method linearly increases the transmission efficiency according to the number of nodes. Theoretical and experimental analysis shows that our scheme is undetectable and has higher transmission efficiency than existing schemes.