本文是计算机专业的留学生作业格式范例，题目是“Review on Video Steganography Technique（视频隐写技术综述）”，在信息安全时代，隐写术是一种最安全的方法，用于隐藏图像、音频、视频、文本文件等任何数字封面对象中存在的秘密数据。图像隐写技术由于易于数据嵌入和提取，在过去的几十年里得到了广泛的研究。在任何数字对象中隐藏嵌入数据的存在是隐写的主要目的。
Abstract 摘要
In the era of information security, Steganography is a most secure method, used for concealing existence of secret data in any digital cover object such as image, audio, video and text files. In the last several decades broad research has been done on image steganography technique due to their easiness of data embedding and data extraction. Hide the existence of the embedded data in any digital object is the main objective of steganography.
The main key factors of steganography are Undetectability, robustness and capacity of the concealed data that separate it from related techniques like cryptography and watermarking. Nowadays, video files are much more accepted because of large size and memory requirements. This paper intends to provide a survey on various video steganographic technique and covering its fundamental concepts.
隐写术的主要关键因素是不可检测性、鲁棒性和隐藏数据的容量，这些数据将其与相关技术如密码学和水印分开。如今，视频文件越来越被接受，因为大的尺寸和内存要求。本文拟对各种视频隐写技术进行综述，并涵盖其基本概念。
1.Introduction引言
Today’s digital world it is very important for secret communication of any private information in safe and secure manner, it has created new challenge of information security. Here a most important question arise that which method we choose for containing its integrity and degree of security. Several methods have been proposed for addressing the issue of information security like cryptography, steganography and watermarking. In Cryptography information encrypted in such form that it becomes meaningless to eavesdroppers using any encryption algorithms such as DES but how strong is the encryption algorithm, it could be broken. Data can be easily replicated and distributed without owner’s consent due to lack of security. Watermarking modified the original data by embedding a watermark containing key information such as logo or copyright codes to protect the intellectual properties of digital content. Moreover, in some situation it was necessary to distribution of information without anyone detecting that the communication happened. So steganography comes arise in digital world to handle this case. Steganography technique is the art and science of invisible data communication.
在当今的数字世界中，任何私人信息的安全保密通信都是非常重要的，这给信息安全带来了新的挑战。这里出现了一个最重要的问题，即我们选择哪种方法来包含它的完整性和安全性。人们提出了几种解决信息安全问题的方法，如密码学、隐写术和水印。在密码学中，以这种形式加密的信息对窃听者来说变得毫无意义，使用任何加密算法，如DES，但加密算法有多强，它就可能被破坏。由于缺乏安全性，无需所有者的同意，数据可以很容易地复制和分发。为了保护数字内容的知识产权，水印通过嵌入包含标志或版权代码等关键信息的水印来修改原始数据。此外，在某些情况下，有必要在没有任何人察觉到通信发生的情况下分发信息。所以数字世界出现了隐写术来处理这个问题。隐写技术是一门无形数据通信的艺术和科学。
The word steganography originated from the Greek language and derived from two Greek words “stegos” which stands for “cover” and “grafia” which stands for “writing” [1].Steganography developed driven by the necessity to conceal the existence of a secret data communication. Although steganography and cryptography both technique are try to protect data, but neither steganography nor cryptography alone is perfect. Consequently it is better to combine both technique together to increase the degree of security of the system [2]. Though steganography is technique for the communication being between two parties. So main concern of steganography is to conceal the existence of the data communication and protecting the hidden data against any alterations that may happen during communication such as format change or compression but integrity should be maintain. The major difference between Steganography and Cryptography is that the cryptography keeps the contents of information secret while steganography keeps the existence of information secret [3].
As video steganography is the focus of this review paper which can be viewed as an extension of image steganography. Really, video is a stream of a sequence of successive and equally time-spaced still images. So several image steganographic techniques are relevant to videos as well. Hu et al. [28],], Langelaar et al. [38], Shang [74], and Sherlyetal [76] extended various image data hiding techniques to video.
2.Video steganographic techniques视频隐写术
There are various applications such as intelligence agencies and military communications where video steganography can be employed [4]. Lie et al. [5], Yilmaz et al. [6] and Robie et al. [7] proposed another types of applications like video error correction during communication and for transmitting additional information without requiring more band-width [8]. Video steganography was used for hiding data in a video captured by a surveillance system was demonstrated by Zhang et al. [9].
在情报机构和军事通信等领域，视频隐写术可以被应用于[4]。Lie et al. [5]， Yilmaz et al.[6]和robbie et al.[7]提出了另一种类型的应用，如通信过程中的视频纠错，以及在不需要更多带宽的情况下传输额外信息[8]。视频隐写术用于隐藏由监视系统捕获的视频中的数据，由Zhang et al.[9]演示。
There are various signal processing transform like DWT, FFT and DCT, any one of them can be used as video stenographic technique to hide data in the frequency domain of the cover object. Secret data can be hide either on per pixel basis or group of pixels called blocks [10]. Video steganographic techniques can classify in a number of ways. Sherly et al. [11] categorize them according to compression, compressed techniques [12, 13] and uncompressed video techniques [15]. Video steganographic techniques can also be classified on the basis of domain of embedding, these are transform domain techniques [14, 16] and spatial domain techniques [17]. Shirali-Shahreza [18] stated that video steganographic techniques can be also categorized on the basis of considering the video as a sequence of still images [17, 19]. Or utilizing the video saving format for data hiding [20]. Or finding new dimensions in the video which helps in the steganographic process [12, 15]. The fallowing figure depicts these possible classifications.
This paper will discuss classification based on embedded domain and cover-up all the literature related to video steganography.
3.Least Significant Bit (LSB)最低有效位(LSB)
Bit Substitution-based steganography techniques replace the cover bit with the binary equivalent of secret data bit. The main advantages of bit substitution methods are the simple implementation and the high data hiding capacity in comparison to other techniques. Bit Substitution-based technique have many methods such as Least Significant Bit (LSB) method, Bit Plane Complexity Segmentation (BPCS) and Tri-way Pixel Value Differencing (TPVD) etc. Least significant bit (LSB) insertion is an oldest and most famous bit substitution-based approach for embedding data in a carrier file like video or image and it is capable of embedding huge secret data. Least significant bit technique operates by altering LSB bits of the cover file to conceal the secret data bit.
基于比特替换的隐写技术将隐藏位替换为与秘密数据位等价的二进制位。与其他技术相比，比特替换方法的主要优点是实现简单，数据隐藏容量大。基于位替换的方法有:最小有效位(LSB)法、位平面复杂度分割(BPCS)法和三向像素值差分(TPVD)法等。最低有效位(Least significant bit, LSB)插入是一种最古老、最著名的基于比特替换的将数据嵌入视频或图像等载体文件的方法，它能够嵌入大量的机密数据。最低有效位技术通过改变封面文件的LSB位来隐藏秘密数据位。
Most of the bit substitution-based methods that exist are really inspired by the LSB technique. Data hiding technique developed to hide the secret data in definite frames of the video file and in definite position of the frame by LSB substitution using different polynomial equation. In this technique data will be hidden on the basis of stego key which is in the form of polynomial equations with different coefficients [22]. A. T. Thahab [23] proposed Digital Color Video Steganography Using YCbCr Color Space and Dynamic Least Significant Bit technique is apply to hide video data file inside the other video cover object .This techniques also found on the basis of least significant bit algorithm.
4.Bit Plane Complexity Segmentation (BPCS)位平面复杂度分割(BPCS)
Normally the idea behind the LSB technique is to modify the least significant bits of the pixel with the binary equivalent of secret data. If more significant bits are used to hide the data then it deteriorating the quality of image. Due to this disadvantage of this technique leads to evolution of other technique which trying to overcome this disadvantage. Kawaguchi and Eason proposed Bit Plane Complexity Segmentation (BPCS) technique [24] and Chang et al. proposed Tri-Way Pixel-Value Differencing [25] .BPCS technique can be applied in the both spatial domain and transform domain [26,13] to address this problem.
通常，LSB技术背后的思想是用加密数据的二进制等价来修改像素中最不重要的位。如果更多的有效位被用来隐藏数据，那么它会恶化图像的质量。由于这一技术的缺点，导致了其他技术的发展，试图克服这一缺点。Kawaguchi和Eason提出了比特平面复杂度分割(Bit Plane Complexity Segmentation, BPCS)技术[24]，Chang等提出了三向像素值差分[25].BPCS技术可以应用在空间域和变换域[26,13]来解决这个问题。
The basic idea of BPCS technique is to break down an image/frame into the bit planes and every bit plane treated as a slice of the image which is made up from all the bits of a definite significant location from each binary digit. Regions in the bit plane are categorized into informative and noise-like after that noise-like regions are substituted with the secret information and maintain the perceived quality. Jalab et al. [19] implemented the BPC technique for hiding data in MPEG video format frames.
This technique works in the YCbCr colour space instead of red, green and blue (RGB) components of a pixel for removing the correlation between the RGB and also decreasing the distortion produced by data embedding process. It is well-known that Human Visual System (HVS) are sensitive modifications in smooth parts than noise-like. Therefore, the BPCS method was applied for computing the complexity of every region in the cover frame. The complexity of every region of the bit plane is computed as the number of on edge transitions from 0 to 1 and 1 to 0, both vertically and horizontally.
5.Tri-way Pixel-Value Differencing (TPVD) 三向像素值差分(TPVD)
It is another bit substitution-based method is the Tri-way Pixel-Value Differencing (TPVD) [13] which is a modified form of the Pixel-Value Differencing method. To maintain the visual quality of cover object it is intuitive to think that data should be concealed in complex parts of the object. It hides the data in the difference of two neighbour pixels value which are classified into ranges, larger range index shows a sharp area where more secret data can be concealed and smaller range index shows a smooth area where less secret data can be concealed.
另一种基于位替换的方法是三路像素值差分(tvd)[13]，它是像素值差分方法的一种改进形式。为了保持覆盖对象的视觉质量，直观地认为数据应该隐藏在对象的复杂部分。将相邻两个像素值的差值划分为范围来隐藏数据，范围指数越大，可以隐藏的秘密数据越多;范围指数越小，可以隐藏的秘密数据越少，可以隐藏的秘密数据越少。
In the data hiding process first partitioning the cover object image/frame into non-overlapping chunks of two neighbour pixels and its range are determined. After that number of secret data bits to be concealed is computed based on the range index. Lastly, the essential number of secret data bits is extracted from the secret data and corresponding their decimal value is used to generate a new difference and the pixel values are adjusted accordingly. This method provides high capacity and imperceptibility for human vision of the concealed secret data. Sherly et al. [11] implemented this technique to hide data in MPEG compressed videos and stated that secret data are hidden in the macro-blocks of the “I” frame with maximum scene modification and in macro-blocks of the P and B frames with maximum magnitude of motion vectors.
6.Transform domain techniques变换域技术
Although Bit substitution-based methods are the simplest way for data hiding, but vulnerability is main disadvantage to any cover alteration like compression, format change, etc. This data embedding techniques can be easily cracked by an attacker. Transform domain methods are more complex than Bit substitution-based methods and try to improve the perceptual transparency and the robustness of the generated stego-objects.
虽然基于位替换的方法是最简单的数据隐藏方法，但漏洞是任何覆盖更改(如压缩、格式更改等)的主要缺点。这种数据嵌入技术很容易被攻击者破解。与基于位替换的方法相比，变换域方法更为复杂，并试图提高生成的隐写对象的感知透明性和鲁棒性。
Any transform-domain technique contains of at least these phases, first transformed the cover object into the frequency domain, in second phase secret data is concealed in some or all of the transformed coefficients. In final phase modified coefficients are transformed back to the original form of the cover. Discrete Cosine Transform (DCT), Discrete Fourier Transform (DFT) and Discrete Wavelet Transform (DWT) are types of transform domain. Raja et al. [27] Stated that DFT methods introduce round-off errors which do not make it ideal for data hiding applications.
So due to this reason Discrete Fourier Transform methods are not popular in steganography. But, few techniques in steganography used DFT based steganography like McKeon [28] used the 2D DFT for steganography in videos.
This paper presents a short review on video steganographic techniques and the key algorithms of video steganography. Steganography, cryptography, and watermarking technique and their differences is also discussed. An overview of steganography is presented and mainly focus on video steganography and its applications. Various video steganography techniques and classification of the existing video techniques are explained which are based on spatial domain, transform domain and other techniques. Advantages and disadvantages of these techniques are focused. Steganography techniques are mainly struggling for achieving a high data embedding rate. It is a good substitute channel for hide data in video files because it have many outstanding features such as large capacity and good imperceptibility. This paper delivers effective review on the design of a video steganographic system.
本文对视频隐写技术及其关键算法进行了综述。本文还讨论了隐写术、密码学和水印技术及其区别。综述了隐写术的研究现状，重点介绍了视频隐写术及其应用。阐述了各种视频隐写技术以及现有视频隐写技术的分类，包括空间域、变换域等技术。重点介绍了这些技术的优缺点。隐写技术的主要目标是实现高数据嵌入率。它具有大容量、良好的隐蔽性等特点，是视频文件中隐藏数据的一种很好的替代通道。本文对视频隐写系统的设计进行了有效的回顾。
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