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数字水印与加密联合编码的研究

On joint coding for watermarking and encryption

Neri Merhav

摘要:

在继续早期的作品中,联合信息嵌入和无损压缩(复合信号)的问题进行了研究,在没有\cite{MM03}和存在\cite{MM04}的攻击,在这里,我们认为额外的成分保护水印的秘密对未经授权的一方,它没有访问合法的各方共享的秘密密钥。换句话说,我们研究了三个目标的联合编码问题:信息嵌入,压缩和加密。我们的主要结果是一个编码定理,它提供了以下参数之间最佳可实现的权衡的单字母表征:复合信号和覆盖文本之间的失真,合法接收机重构水印时的失真,复合信号的可压缩性(具有和不具有密钥),以及水印的模糊性,以及给定复合信号的其重构版本。在攻击-免费的情况下,如果密钥是独立的covertext,这个编码定理产生了一个{ \it三倍}分离原则,告诉渐近地,对于长块码,没有最优性丢失,首先应用率失真代码的水印源,然后加密压缩码字,最后,嵌入到covertext使用的嵌入方案\cite{MM03}。然而,在更一般的情况下,这种分离原理不再有效,因为密钥扮演嵌入单元使用的辅助信息的附加角色。

英文摘要:

In continuation to earlier works where the problem of joint information embedding and lossless compression (of the composite signal) was studied in the absence \cite{MM03} and in the presence \cite{MM04} of attacks, here we consider the additional ingredient of protecting the secrecy of the watermark against an unauthorized party, which has no access to a secret key shared by the legitimate parties. In other words, we study the problem of joint coding for three objectives: information embedding, compression, and encryption.Our main result is a coding theorem that provides a single--letter characterization of the best achievable tradeoffs among the following parameters: the distortion between the composite signal and the covertext, the distortion in reconstructing the watermark by the legitimate receiver, the compressibility of the composite signal (with and without the key), and the equivocation of the watermark, as well as its reconstructed version, given the composite signal. In the attack--free case, if the key is independent of the covertext, this coding theorem gives rise to a {\it threefold} separation principle that tells that asymptotically, for long block codes, no optimality is lost by first applying a rate--distortion code to the watermark source, then encrypting the compressed codeword, and finally, embedding it into the covertext using the embedding scheme of \cite{MM03}. In the more general case, however, this separation principle is no longer valid, as the key plays an additional role of side information used by the embedding unit.

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