标题: 具回塑性及无失真资讯隐藏之研究
A study on reversible and lossless steganography
作者: 杨文超
Yang, Wen-Chao
陈玲慧
李建兴
Chen, Ling-Hwei
Lee, Chang-Hsing
资讯科学与工程研究所
关键字: 无失真;回塑性;资讯隐藏;立体影像;投影片;Lossless;Reversible;Steganography;Stereo images;PowerPoint files
公开日期: 2014
摘要: 随着电脑科技与网路技术的发展,资讯隐藏技术的发展更加多样化,利用不同载体(Cover media)(如:图片、音讯及文字档案等)的资讯隐藏技术,不断的推陈出新。由伪装媒体(Stego media)内容是否失真(即伪装媒体与载体内容是否一致),资讯隐藏技术可分成失真及无失真(Lossless)两大类。失真类的资讯隐藏技术,依据是否具备回复性(Reversibility),即原始载体是否可由伪装媒体完美的回复,又可分为可回复性(Reversible)及不可回复性(Irreversible)两类。近来,由于医学、军事及法庭科学等应用领域,载体内容不容有所失真,可回复性的资讯隐藏技术变得越来越重要。
本论文共提出两种可回复性及一种无失真的资讯隐藏技术。首先提出以数位影像为载体的可回复性资讯隐藏技术,在此技术中,我们应用边缘预测方法(Edge-oriented prediction),进行倍增误差(Prediction error expansion)的资讯隐藏。实验结果显示,透过边缘预测方法,可得到较小的估计误差,因此在相同的资讯隐藏量下,可使伪装影像达到较小的失真。
其次,我们提出以立体影像(Stereo image)为载体的可回复性资讯隐藏技术。由于立体影像的构成,来自成对不同位置之摄影机所拍摄的数位影像,成对影像中存在许多相似的影像区块,我们将资讯隐藏于这些成对的相似影像区块中。首先将两张数位影像进行数位余弦转换(Discrete Cosine Transform),依据影像区块之低频系数,找出两张影像中差异最小的相似影像区块,之后计算每对相似影像区块之中频系数的差异,再利用双向的直方图位移(Histogram shifting)资讯隐藏技术,将讯息藏于相似影像区块之差异值为0中频系数。经实验结果,藏入讯息的伪装立体影像可维持极佳的影像品质,并且有极高的资讯隐藏量。
最后,我们提出以简报档案(PowerPoint file)为载体,利用简报档案中的特效,进行无失真之资讯隐藏。在学术或商业简报中,常运用简报档案中的特效,协助主题的聚焦或时间的控制等。因此,利用简报档案中动画或时间等特效来进行资讯隐藏,不但不影响简报档案的内容正确性,更可丰富简报的呈现与吸引力,亦可抵抗档案转换攻击。经实验结果验证,我们提出的方法可以抵挡若干视觉上或统计上的攻击。
Steganography is a research topic to protect the privacy communication. The techniques can be divided to two categories: lossy steganography and lossless steganography. Lossy steganography hides message in the content of cover media and distorts the real content. On the other hand, lossless steganography hides message in the cover media and keep the real content intact. For some applications such as medical images, military images, or forensic images (provided by law), reversible property, where the cover image can be perfectly recovered from the stego image, is an important issue. Therefore, lossy steganography can be divided into two categories: reversible steganography and irreversible steganography. Reversible steganography can perfectly recover the cover media in the extraction process, whereas irreversible steganography cannot.
In this dissertation, we will propose two reversible and one lossless steganographic methods using different cover media. First, a difference expansion based reversible steganographic approach, which yields low distortion under the same embedding capacity, is proposed. An edge-oriented prediction method and a modified overflow/underflow prevention method are proposed to achieve the requirement. Experimental results have demonstrated that the proposed reversible steganographic method yields lower distortion than several well-known expansion-based reversible steganographic methods.
Second, a novel DCT-based reversible steganographic method for stereo images is proposed. Stereo images captured from a pair of CCDs simultaneously are widely used to create the illusion of 3D depth. Every pair of stereo images has many similar block pairs. In this method, we embed secret data in those similar block pairs. Experimental results have shown that the proposed method is undetectable under Chi-square analysis and outperforms other methods in terms of embedding capacity and image quality.
Finally, we propose a lossless steganographic method to embed message in a PowerPoint file. In the proposed method, we not only hide message naturally but also keep the content of the cover media intact. Furthermore, the proposed method can resist the format conversion attack. The experimental results demonstrate that the proposed method is undetectable under some visual and statistical attacks.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079323814
http://hdl.handle.net/11536/125805
显示于类别:Thesis