To provide a scheme of embedding an electronic watermark of content authentication data for embedding an electronic watermark into a content to allow determination of whether or not the content is altered, and to provide an authentication method.
An image or audio data, as a content, is DCT transformed, and rougher quantization, which is applied in MPEG coding, is performed to a signal component of DCT coefficients that is not used for embedding the electronic watermark, and thus a hash value thereof being obtained. The hash value is embedded into the signal component of the DCT coefficients that is used for embedding the electric watermark and quantized. The content is DCT transformed after being reverse-quantized and decoded, and a hash value is extracted from the signal component of the DCT coefficients that is used for embedding the electronic watermark. In addition, the rough quantization is performed to the DCT transformed signal component and a hash value is calculated from the signal component of the DCT coefficients that is not used for embedding the electronic water mark. Then, the two hash values are compared. If a match is found therebetween, then it is authenticated that the content is not altered.
COPYRIGHT: (C)2009,JPO&INPIT
Koichi Takagi
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