The CT watermark algorithm
is a relatively new software watermarking algorithm. To evaluate the robustness
of the CT watermark algorithm, we tried to simulate the unauthorized detection
of watermark attacks on the CT watermark. The main concern of this thesis is to
explore the effect of the watermark size ratio of watermarked programs on the accuracy
of attackers’ detection function.
We simulate attackers by
using the statistical pattern classification method to detect the existence of
a CT watermark. The adversaries’ behaviour is confined by a set of rules proposed
by the CT watermark algorithm designers, which I extend. We judge the success of
attackers by the false positive and false negative rates of attackers’
detection function.
Results showed that when
the watermarked programs that the attackers used to train their detection
function and the watermarked programs to be detected both have a high watermark
size ratio, the attackers’ detection function will be accurate. So restricting
the watermark size ratio of CT watermarked programs should increase their
robustness.
We suggest two ways to
amend this problem. One way is to use the numeric watermark option in the
watermark embedding procedure to reduce the watermark size ratio. Another way
is to denote those programs which will cause a high watermark size ratio as being
unsuitable to be CT watermarked.