Biblio

Leading steganography systems make use of the Syndrome-Trellis Code (STC) algorithm to minimize a distortion function while encoding the desired payload, but this constrains the distortion function to be additive. The Gibbs Embedding algorithm works for a certain class of non-additive distortion functions, but has its own limitations and is highly complex. In this short paper we show that it is possible to modify the STC algorithm in a simple way, to minimize a non-additive distortion function suboptimally. We use it for two examples. First, applying it to the S-UNIWARD distortion function, we show that it does indeed reduce distortion, compared with minimizing the additive approximation currently used in image steganography, but that it makes the payload more – not less – detectable. This parallels research attempting to use Gibbs Embedding for the same task. Second, we apply it to distortion defined by the output of a specific detector, as a counter-move in the steganography game. However, unless the Warden is forced to move first (by fixing the detector) this is highly detectable.

In this paper, we present a new kind of near-optimal double-layered syndrome-trellis codes (STCs) for spatial domain steganography. The STCs can hide longer message or improve the security with the same-length message comparing to the previous double-layered STCs. In our scheme, according to the theoretical deduction we can more precisely divide the secret payload into two parts which will be embedded in the first layer and the second layer of the cover respectively with binary STCs. When embed the message, we encourage to realize the double-layered embedding by ±1 modifications. But in order to further decrease the modifications and improve the time efficient, we allow few pixels to be modified by ±2. Experiment results demonstrate that while applying this double-layered STCs to the adaptive steganographic algorithms, the embedding modifications become more concentrative and the number decreases, consequently the security of steganography is improved.