Information Hiding Using CAVLC: Misconceptions and a Detection Strategy

摘要

As the most commonly used entropy coding method of H.264, CAVLC (context-based adaptive variable length coding) has been widely utilized for information hiding. Various information hiding methods directly manipulate CAVLC coefficients, which are reported to be of high payload and low computational complexity. However, things are quite different in real applications. This paper addresses two misconceptions about them: (1) The CAVLC coefficients can be modified without re-encoding process. In fact, direct modifications of the number of non-zero coefficients will change the corresponding code tables for adjacent blocks and result in decoding errors. (2) CAVLC codewords can be indiscriminately substituted. Actually, it will cause serious distortion drifts. In addition, considering steganographic security, a detection strategy is proposed based on statistical analysis of some CAVLC-based methods.