使用阈下信道的可逆R-S数字水印

Reversible R-S Digital Watermarking Using the Subliminal Channel

由于难以获得足够的冗余水印容量,一些面向内容认证的可逆水印方案仅嵌入了用对称算法加密的杂凑值,它的数据尺寸显著地小于数字签名,但这使不诚实的验证者能伪造合法的内容.然而研究发现,虽然当前公钥签名的长度是杂凑值的数倍,但通过使用阈下信道,在方案中引入公钥签名仅需增加数个字节的容量.据此,一个改进的R-S(regular-singular)可逆数字水印方案被提出,它采用RSA-PSS公钥签名,并利用签名中阈下信道存储部分或全部压缩的R-S向量.该方案仅需增加4个字节的额外水印容量,也具有篡改定位功能和可靠的安全性.

Because of the difficulty of making adequate redundant capacity for watermarking, some reversible watermarking schemes for content authentication just embed a symmetrically encrypted hash value, the size of which is significantly smaller than that of a digital signature. It makes a dishonest verifier be capable of fabricating legal contents. However, the research finds that introducing a public-key signature, which is usually several times longer than a hash code, can only need several bytes more capacity if the subliminal channel in the signature scheme can be used. And it is shown that RSA-PSS （RSA-probabilistic signature scheme） has such an channel. Then an improved reversible R-S （regular-singular） watermarking exploitable subliminal scheme, which adopts RSA-PSS, is proposed. It still produces the redundant watermarking capacity by compressing the R-S vector but stores partial or entire compressed R-S vector in the subliminal channel. As a result, the new scheme only needs 4 bytes more additional capacity. By the reduced size of overall embedded data, the new scheme can even partition an original image into several tens of blocks and embed data block-wise so that it has the capability of localizing tampering. And by not revealing any information directly about the private key, it has reliable security also.