Improved Wet Paper Code Using Simplified Hamming Parity-Check Matrix and Its Application in Voice-over-IP Steganography

Abstract

Wet paper code (WPC) can adaptively select the covert channel, but the computational complexities of existing solving algorithms are too large to satisfy the real-time requirement of Voice over IP (VoIP). For this reason, an improved WPC method based on simplified hamming parity-check matrix is presented. The main idea is to determine the required encoding matrix using a simplified hamming parity-check matrix and randomly expand the encoding matrix to the cover matrix according to the given cover length. Compared with the existing ones, the proposed method can effectively reduce computational complexity to only O(n), and obtain an optimal solution in any case. Moreover, it can be adapted to different cover lengths by adjusting the number of columns needed to be inserted. Employing the improved WPC, we further design a steganographic scheme without carrier negotiation for VoIP. We evaluate the proposed scheme with ITU-T G.729a as the codec of the cover speech in StegVoIP that is a prototypical covert communication system based on VoIP, and compare it with traditional approaches. The experimental results demonstrate that the proposed scheme can achieve relatively high embedding efficiency and steganographic transparency while adequately satisfying real-time requirement of VoIP services, and outperforms the traditional approaches.