On YASS’s Non-monotonic Security Performance

Recently, researchers have discovered unexpected bumps in the detection rate curve of yet another steganographic scheme (YASS). We refer to this abnormal phenomenon as non-monotonic security performance. This paper first analyzes this abnormality and points out that it is caused by the non-uniformity in probability of coincidence of (Formula presented.) embedding blocks and (Formula presented.) JPEG blocks. Based on this observation, we propose that further randomizing data embedding positions can overcome the non-monotonic security performance. Experimental results have demonstrated a complete removal of bumps in the detection rate curve of YASS after further randomization.