Joint Transaction-Image Steganography for High Capacity Covert Communication

Conventional secret communications suffer from communication channel insecurity and lack of secrecy. Blockchain-based steganography comes up by proposing secure communication channel with the expense of low message capacity. In this paper, we propose joint steganography by utilizing blockchain-based transaction steganography and image steganography to achieve both advantages: a secure and secret communication medium that also possess a high capacity. We use image steganography to store the real hidden message while transaction steganography stores only the instruction manual to retrieve the stegano-image. We proposed group encoding and multi-field embedding to improve the capacity and robustness of transaction steganography. As a result, the joint method can achieve a high message capacity of ≈ 759 KB. The method also retaining the natural transaction pattern without generating anomalous transactions number.