Asmuth-Bloom(AB) algorithm is a robust software watermark algorithm based on threshold scheme, which is originally used to secret sharing, so there is no restriction on sub-key's length.With an expanded threshold scheme, sub-key's length can be reduced.A new algorithm based on expanded threshold is proposed.Moreover, a new watermarking system is implemented on the Java platform by using dynamic graph.Experimental results show that the proposed method can reduce the data expansion, and make the recovery process easier.The conditions above mentioned are suitable for practicalized watermark system.%AB算法的门限方案原本用于密钥分存,不限制子密钥的强度,从而导致水印数据扩张,而扩展门限定义可限制子密钥的数据位宽.为此,提出基于扩展门限的水印算法,采用动态图方法在Java平台实现水印系统.实验结果证明,该水印算法能有效控制水印数据扩张,加快水印恢复速度,适于构建方便实用的软件水印系统.
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