This paper presents three encoding strategies based on digital logic for steganography on Voice over IP (VoIP), which aim to enhance the embedding transparency. Differing from previous approaches, our strategies reduce the embedding distortion by improving the similarity between the cover and the covert message using digital logical transformations, instead of reducing the amount of the substitution bits. Therefore, by contrast, our strategies will improve the embedding transparency without sacrificing the embedding capacity. Of these three strategies, the first one adopts logical operations, the second one employs circular shifting operations, and the third one combines the operations of the first two. All of them are evaluated through comparing their prototype implementations with some existing methods in a prototypical covert communication system based on VoIP (called StegVoIP). The experimental results show that the proposed strategies can effectively enhance the embedding transparency while maintaining the maximum embedding capacity.

Differing from applying steganography on storage cover media, steganography on Voice over IP (VoIP) must often delicately balance between providing adequate security and maintaining low latency for real-time services. This paper presents a novel real-time steganography model for VoIP that aims at providing good security for secret messages without sacrificing real-time performance. We achieve this goal by employing the well-known least-significant-bits (LSB) substitution approach to provide a reasonable tradeoff between the adequate information hiding requirement (good security and sufficient capacity) and the low latency requirement for VoIP. Further, we incorporate the m-sequence technique to eliminate the correlation among secret messages to resist the statistical detection based on the fact that the distribution of the LSBs in the stego-speech is not uniform and to provide a short-term security protection of secret messages. To accurately recover secret messages at the receiver side, we design a synchronization mechanism based on the RSA key agreement and the synchronized sequence transmission using techniques of the protocol steganography, which can effectively enhance the flexibility of the covert communication system and be extended to other steganography schemes based on real-time systems. We evaluate the effectiveness of our model with ITU-T G.729a as the codec of the cover speech in StegTalk, a covert communication system based on VoIP. The experimental results demonstrate that our techniques provide good security and transparency for transmitting secret messages while adequately meeting the real-time requirement of VoIP.1

存储系统采用流水处理技术有两个前提条件：（1）在前一个I/O命令没有完全结束之前，系统能获取下一个I/O命令的有关信息；（2）不同部件应能同时操作，资源不发生冲突网络磁盘阵列满足这两个条件，可以在I/O调度过程中采用流水处理技术根据I/O调度进程的重叠度，流水调度方式可以分为固定流水方式和柔性流水方式在固定流水方式中，多进程按照固定的重叠方式执行；而在柔性流水方式中，则通过判断进程的完成顺序，在一定程度上自由组合多个进程进行重叠实验结果证明，在多用户进程的条件下，两种流水调度方式都能提高网络磁盘阵列的带宽利用率。