Anti-forging Stamps and 2D Chaotic Security Coding

In Chinese market, almost every contract needs to be sealed by a specialized contract stamp in order to make the contract official. Therefore, there are many chances that someone wants to forget this kind of stamp. Also, the automatic recognition of the authentic prints generated by the only “real” stamp must be guaranteed. By using 2D Chaotic Security Coding algorithm developed by Tao Yang, Yang's developed a special distributed 2D coding scheme for embedding IDs into seals and stamps. The software to generate patterns on anti-forging stamps is called SealSky. SealSky can robustly and efficiently recognize stamp prints by using its chaotic decoding algorithm.
The unique 2D Chaotic Security Coding technology has been developed based on the intensive study of the phenomena called spatio-temporal chaos generated by an array of identical nonlinear cells. Such array is knows as cellular neural networks, which was invented by Chua and Yang in 1987 in the Department of Electrical Engineering and Computer Sciences, University of California at Berkeley. The theory that is behind 2D Chaotic Security Coding had been developed in the Nonlinear Electronics Laboratory in the Department of Electrical Engineering and Computer Sciences, University of California at Berkeley during 1995 to 2001 by Tao Yang under the supervise of Professor L.O. Chua. The industrialization of the algorithms and implementations have been undertaken by the Department of Electrical Engineering and Computer Sciences and the Cellular Image Processing Laboratory in Yang’s Scientific Research Institute, LLC., in 2005. (September 22, 2005, Tucson, Arizona, USA.)

How it Works

The snapshot of the SealSky software is as follow.

SealSky can generate a stamp based on the stamp ID fed by the user. The stamp ID can be a name, a number or a piece of information. One example of the generated stamp is as follow.

From a scanned image of the print of a stamp, SealSky can recover the unique ID even under conditions when the prints were seriously degraded. The followings are four examples of degraded stamp prints that can still be correctly recognized. Observe that the SealSky can generate stamps with strong robustness to the quality degradation of the seal prints.
On the other hand, SealSky can also generate stamps with good anti-forging properties. Obviously, the robustness to the stamp image quality degradation and the anti-forging ability should be traded-off in different applications. This trade-off can be easily done in SealSky by setting parameters.

SealSky in Actions

We have successfully developed a set of real seals to verify the working principles backing the SealSky products. Below we show the photos of two manufactured stamps. The materials for the left and the right stamps are rubber and horn, respectively. Observe that the blank regions in the center area can be used to add other information such as graphs, logos, and characters that specified by the users. The only takes a few percentage of the stamp area to achieve robust recovery, recognition and anti-forging. Other materials can be used for making the 2D Chaotic Security Coding stamps, also, any kind of shapes can be made out of the advanced and unique 2D Chaotic Security Coding developed by Yang's.

Images of Real Prints from Two Real Stamps

The following pictures show the prints from the stamps generated by SealSky. In Chinese market, the prefer stamp pads using red for commercial and administrative purpose. Therefore, all the stamps are printed in red. The robustness of the recognition is independent of the colors of the inks. Observe that some of the prints are very faint and the ink is not uniform in many real-world stamp prints.