Traceable Visual Cryptography Traceable Visual Cryptography

In this paper we present a new k out of n visual cryptography scheme which does not only meet the requirements of the basic visual cryptography scheme deened by Naor and Shamir 5] but is also traceable. With a k out of n scheme it is not possible to reveal the original secret by stacking less than k transparencies. In general one can assume that it is very unlikely that there are k shareholders who would be willing to misuse their shares in order to reveal the secret in a sabotage act. But nding a coalition of 0 < t < k traitors who stack their shares and publish the result so that other coalitions of shareholders can illegaly reveal the secret is a practical scenario and therefore threatens the security of general threshold secret sharing schemes. In this paper we present the idea of traceable visual cryptography schemes which make it possible to trace the saboteurs only with the knowledge of special markings.