Abstract:

Addressing the limitations of existing blockchain-based covert communication techniques-such as permanent storage of steganographic transaction data, low extraction efficiency, insufficient embedding strength, and poor covertness, this paper proposed an innovative solution based on bitcoin's replace-by-fee (RBF) mechanism. Firstly, the sender encoded the secret message using Base64 and established a mapping between code values and transaction fee rates, leveraging the fee rate to transmit the covert data. This significantly enhances the information embedding capacity per transaction.Secondly, before the steganographic transaction was confirmed, the sender generated a replacement transaction using RBF and abandoned the original steganographic transaction, ensuring only the replacement transaction was recorded on the blockchain. This achieves “zero retention” of steganographic transactions, eliminating security risks associated with permanent data storage. At last, the receiver tracks the sender's address and monitors transaction status in real time. By querying and extracting the embedded information before the original transaction was discarded. Experimental results demonstrate that the proposed method reduces embedding and extraction time from minutes to seconds per byte of information, with an average embedding capacity of 6 bits per transaction. The system outperforms existing solutions in both covertness and anti-traceability.

Key words: covert communication, blockchain, bitcoin, RBF mechanism, derivation relationship