本文是计算机专业的留学生作业写作范例，题目是“Steganography Using Lsb Insertion Technique Computer Science Essay（使用Lsb插入技术的隐写术计算机科学论文）”，隐写术是一种通过固定载波数据来隐藏信息的方法。数据有两种类型。它们是内部数据和外部数据。外部信息包含对数据所有者无用的可见部分或可听部分数据，内部信息包含嵌入的数据。
Abstract 摘要
Steganography is a method used for hiding a message by fixing in a carrier data. There are two types of data. They are internal data and external data .The external information contains visible part or audible part of data which is not useful for data owner and the internal information contains embedded data.
The techniques used in Steganography makes hard to detect hidden message within an image file. By this technique we are not only sending a message but also we are hiding the message. Steganography system is designed to encode and decode a secret file embedded in image file with a random Least Significant Bit (LSB) insertion technique. By using this technique the secret data are spread out among the image data in a random manner with the help of a secret key. The key generates pseudorandom numbers and identifies where and in which order hidden message is laid out. Steganography includes cryptography which is an advantage for Steganography .In cryptography, diffusion is applied to secret message.
隐写术中使用的技术很难检测出图像文件中的隐藏信息。通过这种技术，我们不仅发送了消息，而且还隐藏了消息。隐写系统是一种利用随机最小有效位(LSB)插入技术对嵌入在图像文件中的秘密文件进行编码和解码的系统。通过使用这种技术，在密钥的帮助下，秘密数据以随机的方式分布在图像数据中。密钥生成伪随机数，并确定隐藏消息的位置和顺序。隐写术包括密码学，密码学是隐写术的一个优势。密码学将扩散技术应用于秘密信息。
1.INTRODUCTION 引言
The Data transmitted comes in many forms and it is used for more than one application. Communications should be done secretly. Secret communication varies from bank transfers, corporate communications and credit card purchase.Steganography is an art of embedding a secret message into a normal message. Steganography is used in watermarking for protecting data copyrights.Unsurprisingly, methods of Steganography change because innocuous spam contents are growing frequently by embedded texts.
传输的数据有多种形式，用于多个应用程序。沟通应该秘密进行。秘密通信包括银行转账、公司通信和信用卡购买。隐写术是一种将秘密信息嵌入正常信息的艺术。隐写术是一种用于保护数据版权的水印技术。随着无害的垃圾邮件内容被嵌入文本的频繁增加，隐写术的方法也随之改变
Cryptography is technique used to make secret message scribbled for third party and are normally used in internet. The encrypted message is targeted by attackers in cryptography because it hides the message content. An another data hiding technique known as watermarking used for embedding and hiding, some symbol data or digital manifest in the digital valuable data like photo picture, digital movie, musical sound etc. Watermarking purpose is mainly used to protect ownership or copyrights of the data. In this technique, hardness of embedded evidence and hidden evidence are very small and is important. In this technique the important information is present in external information which is visible or audible.
In the Steganography technique, confidential information is made invisible to a human eye by embedding it as a dummy data such as a speech sound and a digital image. Steganography contains another research topic called as steganalysis which is used to find a stego file from the available files. Steganalysis is used in detecting suspicious image file. The suspicious image files are embedded with the crime associated information.
All traditional Steganography techniques have limited information-hiding capacity. These techniques can hide 10% or less than 10% data of a carrier data. The principle of these techniques is to replace frequency components of carrier or to replace LSB bits of multivalued image with secret information. Steganography uses image as a carrier data and it embeds secret information in bit planes .We can replace all noise like regions in the bit planes without disturbing the quality of image and is termed as B.P.C.S Steganography .BPCS Steganography is known as Bit plane complexity segmentation Steganography.
2.THEORY 理论
Steganography is used to hide confidential information from human eyes by embedding it in a carrier data such as digital image or speech sound. A carrier data is a color image having RGB color components in a multi-bit data structure. The embedded information is extracted using special extracting program and key .The techniques of Steganography are different from “file camouflage” or file deception technique.
隐写术是将机密信息嵌入数字图像或语音等载体数据中，以隐藏人眼看不到的技术。载波数据是在多位数据结构中具有RGB颜色分量的彩色图像。利用特殊的提取程序和密钥提取嵌入的信息。隐写技术不同于“文件伪装”或文件欺骗技术。
File deception is a technique used for hiding secret data in computer file and it almost looks like a Steganography. But, it is an trick to disguise a secret-data file as a normal file and is possible in files which have don’t care option. For example, Word file or JPEG image OR MPEG will allow for adding an “extra” data (extension) at the end of a regular file. Even an extra data (which can be encrypted) are added, the JPEG image, word file or MPEG looks like the original image and original sound, or document on the computer. People may think this is due to Steganography. The lengthy files are easily detected by engineers. So, file deception and Steganography are different.
The Steganography software’s that are available in the market are based on file deception. In Steganography, if output file size is increased by embedding the information then the program is called as File deception. A secret data can be made unreadable by encrypting the data. The secret data should be encrypted to make it unreadable for third party. With the help of data encryption, secret data can be safe. Data encryption is based on data scrambling and it uses a secret key. Data encryption can create a doubt to the people that owner of the data is hiding something in an image. In data encryption we can find easily that he is hiding something in a image. Therefore encryption of data is not enough. Steganography is the solution for data encryption.
There are two types of data in Steganography .they are secret data and carrier data. Secret data is very valuable when compared to the carrier data. Carrier data is a type of dummy data which is not so important but it is needed. The data which is embedded is called as stego data.If we want to recover the secret data , we can extract that data from stego data.We need a special program or a key for data extraction.
The carrier is image data which has color components of red green and blue colors in 24 bit pixel structure. The figure below shows an example of carrier image and stego image. The secret data is embedded in stego image.
Steganography is a method of hiding the secret data by fixing it in media data .For example in the figure a secret data is embedded but we can’t find in which place the secret data is embedded. The Embedded data will be very safe in the Steganography because it will hide content of the message and location of hidden image. There are many methods to embed the data .but; it is very hard to find about the method used in embedding the message.. Steganography can co-operate with cryptography to embed the encrypted data safely. In Steganography , Stego data will not have any evidence about the embedded data.
The Steganography user should discard the original carrier data after embedding such that it will not allow comparison of stego and original data. Embedded capacity should be larger. BPCS method is the method available method for image Steganography. If anyone detect the Steganography image, it is very difficult for him to retrieve the hidden image. There are three basic ways to hide a message in image. They are Injection, substitution and generation. Using Injection method we can find in which place data to be inserted and using substitution we can find least significant bits for hiding the message. Using generation method we can create a new file based on the hidden information.
留学生作业辅导
3.Method of implementation 实现方法
Least significant bit insertion is one of the important methods of implementation. In this method, the LSB bits of byte are altered so that it form bit string and represents an embedded file. By changing the LSB bits, it will cause some small differences in color which are not noticeable to human eye. After that an image is compressed and a text message is hidden in image .In LSB method, LSB bits of the covered image is altered such that they form embedded information.
最小有效位插入是一种重要的实现方法。在这个方法中，字节的LSB位被改变，从而形成位串并表示一个嵌入的文件。通过改变LSB位，它会引起一些人眼不明显的颜色差异。在LSB方法中，被覆盖图像的LSB位被改变，从而形成嵌入信息。
Embedding a message into cover image will result a stego image. For normal vision, stego image looks identical as cover image; this is because of only small changes of pixel values. Therefore there is no significant difference. The embedded message is sequentially embedded in covered image so that it is easy for a third party to recover the message by retrieving the pixels sequentially starting from the first pixel of the image. Steganography uses a key which as a better security. It is difficult to recover the embedded image without valid key.
4.LEAST SIGNIFICANT BIT INSERTION 最低有效位插入
Least significant bit insertion is the common technique used in Steganography. In LSB method, an image is used. An image is more than strings and string of bytes. Each byte in an image represents different colors. The last few bits in a color byte do not hold much significance as the first few bits. Therefore only two bits differ in last few bits that represent a color which is undistinguishable to human eyes. In LSB method, least significant bits of a cover image are altered such that we can embed information. The example shows how letter A is hidden in first 8 bytes of 3 pixels in a 24 bit image. Since the 8 bit letter A requires only 8 bytes to hide it, ninth byte of the 3 pixels used to hide the next character of the hidden message.
最低有效位插入是隐写术中常用的技术。LSB方法使用的是图像。图像不仅仅是字符串和字节串。图像中的每个字节代表不同的颜色。颜色字节的最后几位并不像前几位那么重要。因此，在代表人眼无法分辨的颜色的最后几个位元上只有两个位元不同。在LSB方法中，通过改变封面图像的最小有效位来嵌入信息。这个例子展示了字母A如何隐藏在24位图像的前8个3像素的字节中。由于8位字母A只需要8个字节来隐藏它，所以3个像素中的9个字节用于隐藏消息的下一个字符。
The five underlined bits are the 5 bits which were altered. With LSB insertion technique, on an average half of the bits of an image are changed. ‘A’ is a 8 bit letter and requires 8 bytes for hiding. The ninth byte of 3 pixels is used for hiding next character of secret message.
The slight variations of this technique allows a message to embed into two or more least significant bits per bytes, and increases the information hidden capacity of the cover object .but cover object is degraded and easily detectable.LSB insertion is easy to implement and is also easily attacked if the modifications are done wrongly. Improper modifications in color palette and simple image calculations will destroy hidden message. Image resizing and image cropping are some examples of image manipulations.
5.bmp images bmp图像
There are several formats exists for an digital image. .BMP, JPG, GIF are some formats .Each format is associated with advantage and disadvantages. Because of its simplicity, windows BMP file offers more advantages. It has an advantage of widely spreader and the information contained is minimum .Bmp file is a binary file.bmp file is pided into four sections such as file header, image header, color table and pixel data. The file header is used to know about size of the image and to learn where actual image data is located within the file.
数字图像有几种格式。bmp、JPG、GIF是几种格式。每种格式都有其优点和缺点。由于其简单性，windows BMP文件提供了更多的优势。bmp文件为二进制文件，文件分为文件头、图像头、颜色表和像素数据四个部分。文件头用来了解图像的大小，并了解实际的图像数据位于文件中的什么位置。
The Image header gives information about the image and its data format such as width and height of the image. Image header also gives information such as how many bits are used per pixel and checks whether the image data is compressed data or uncompressed data. Depending on the image data, color table will be present. When color table is not present, a set of bit masks are used to extract the color information from the image data.
When dealing with 24-bit image, color table is not present. When dealing with 8-bit image, color table consists of 256 entries. Each entry consists of four bytes of data. In these four bytes of data, first three bytes are blue, green and red colors values .The fourth byte must be equal to zero because it is not used. In 8-bit format, each pixel is represented by single byte of the data which is index in to color table. In 24-bit format, each pixel I represented by RGB component values .The pixel data holds entire hidden data and there are changes by one pixel value either positive or negative.
留学生作业辅导范文参考
6.MATLAB MATLAB矩阵实验室
The MATLAB is a language for technical computing. MATLAB integrates computation, visualization and programming in a easy way in which problems and solutions are expresses in mathematical notation. Typical uses include：Math and computation、Data acquisition、Algorithm development、Modelling, simulation and protyping、Data analysis, exploration and visualization、Application development.
MATLAB是一种用于技术计算的语言。MATLAB集成了计算，可视化和编程在一个简单的方式，其中问题和解决方案是用数学符号表示。典型应用包括:数学和计算，数据采集，算法开发，建模，仿真和原型，数据分析，探索和可视化，应用开发。
MATLAB is a system whose data element is an array without dimensions. It allows in solving computing programs such as Matrix and vectors formulations. It writes program in a scalar language such as FORTRAN within a fraction of seconds.
MATLAB can be abbreviated as a matrix laboratory. MATLAB was developed to access matrix software. The matrix software was developed by linpack and eispack projectsdeveloped .MATLAB engine incorporates LAPACK and BLAS libraries by embedding the state of art in software for matrix computation.
Matlab has evolved over a period of years with input from many users. MATLAB has become a standard tool for advanced courses such as engineering, maths, and sciences .MATLAB is like a tool for high research productivity, analysis and development.
This project explains techniques for embedding a data in an color image and also some features are added which include file types excluding bitmap images and Steganography methods. Data extracted from cover image depends on pixel values of an image.
本项目解释了在彩色图像中嵌入数据的技术，并添加了一些功能，包括不包括位图图像的文件类型和隐写方法。从覆盖图像中提取的数据依赖于图像的像素值。
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