Abstract: To address the issues of insufficient concealment, long extraction times for hidden information, low embedding intensity, and single application scenarios in existing blockchain covert communication schemes, a blockchain covert communication method based on Ethereum smart contracts and InterPlanetary File System (IPFS) technology was proposed. Firstly, IPFS was used to store longer ciphertexts, and the combination of on-chain and off-chain storage compensates for the low efficiency and high cost of blockchain storage. Secondly, by adopting the concepts of derived relations and codebooks, the separation of secret information and communication information was achieved. The on-chain data was the index information of the ciphertext hash rather than the ciphertext hash itself, further enhancing security. Based on the index information, a suitable smart contract was customized. Thirdly, the index information was disguised as normal contract call parameters to ensure both concealment and security. Additionally, the large storage capacity of the data field in contract call transactions further increases the information embedding volume. Finally, introducing group encryption technology into the blockchain covert communication model can effectively meet the needs of multi-user interactive scenarios. Experimental results show that proposed method can further improve time efficiency and information embedding volume, greatly enhancing concealment and security, and can be applied to interactive scenarios with multiple receiving users.

Key words: covert communication, blockchain, Ethereum, smart contract, derivation relationship, group encryption

摘要： 为了解决现有区块链隐蔽通信方案隐蔽性不足、提取隐蔽信息时间过长、隐藏容量较低、应用场景单一等问题，提出一种基于以太坊智能合约与星际文件系统技术的区块链隐蔽通信方法。首先使用星际文件系统存储较长的密文，通过链上链下联合存储弥补区块链存储效率低且成本高的缺点。其次引用派生关系和密码本的思想，实现秘密信息与通信信息的分离，上链的为密文hash的索引信息而非密文hash，进一步增强安全性。然后根据索引信息自定义适用的智能合约，将索引信息伪装成正常的合约调用参数，可以保证隐蔽性和安全性，且合约调用交易的数据字段存储容量较大，进一步提升交易的信息嵌入量。最后把群加密技术引入区块链隐蔽通信模型中,可很好地满足多用户的交互场景。实验结果表明，所提方法可进一步提高时间效率和信息嵌入量，极大地提升隐蔽性和安全性，能够适用于多接收用户的交互场景。

关键词: 隐蔽通信, 区块链, 以太坊, 智能合约, 派生关系, 群加密