CCBTC: A Blockchain-Based Covert Communication Scheme over Bitcoin Transactions

Blockchain can be looked at as a new channel for covert communication. Since blockchain provides a tamper-proof distributed ledger, it is possible to employ blockchain to provide persistent and anonymous covert communications. This persistence includes the persistence of one-way message distribution and the persistence of multi-party communications. In this paper, we propose a covert communication method based on Bitcoin transactions (BTC). The method converts the secret message to a decimal value via ASCII code and utilizes the decimal transaction amount as the message carrier. The decimal value of the secret message can be divided into multiple parts, to shorten the communication delay and to decrease the transaction fee, which is sent to a designated destination account. Only the recipient of the transaction who possesses the correct key can decode the transaction amount to get the secret message, and this message is persistent in the blockchain. We evaluated different ways of dividing methods, to explore the way that fewer bitcoin transactions are consumed. Besides, the sender can always update his address after each transmission to further hide the recipient of the message by unlinking. We have verified the feasibility and efficiency of the method through iterative experiments on the Bitcoin test network, which justified the applicability of the scheme.