A technology for combining digital watermarks with two-color bitmap image based on the threshold watermarking method is presented. Our technology doesn't add any thing to the digital media, but combines the watermarks in two-color bitmap image by looking for some characteristic values in the bitmap and uses the relationship between the watermarks and the characteristic values to prove the copyright protection. The choice of the characteristic values depends on the choice of a cryptographic key known by the owner of the bitmap. The benefit of using a cryptographic key is to combine the watermarks with the bitmap in a high secure way.
After extending the forgery attacks to Nyberg-Rueppel’s signatures with message recovery, Atsuko Miyaji in 1997 proposed two suitable message recovery signatures, (F1) and (F2). In this paper, another new forgery attacks to (F1), (F2) and Nyberg-Rueppel’s signatures are presented.
Li Zichen Li Zhongxian Yang Yixian , Wu Weilin (PO Box 126, Information Security Center, Beijing Univ. of Posts and Telecom., Beijing 100876)
How to distribute a secret key information to n authorized departments, denoted as: S1, S2,…, Sn, respectively. For every autherized department Si(i = 1,2,… ,n), there are qi authorized persons, and every authorized person has the same secret key information as that of any other authorized persons in the same authorized department. The secret key information can be reconstructed completely from the secret key information of any k authorized persons, if there is at least one authorized person included for every authorized department. But other cases, the secret key information cannot be reconstructed completely. In this paper, based on the algebraic semigroup theory, a secret key sharing scheme is proposed, which can satisfy the demand.
Wang Yongchuan Li Zichen Yang Yixian (Info. Security Centre of Beijing Univ. of Posts and Telecomm., P. O. Box 126, Beijing 100876)
