An Overview of Steganography for the Computer Forensics Examiner

Introduction

Steganography is the art of covered or hidden writing. The purpose of steganography is covert communication to hide a message from a third party. This differs from cryptography, the art of secret writing, which is intended to make a message unreadable by a third party but does not hide the existence of the secret communication. Although steganography is separate and distinct from cryptography, there are many analogies between the two, and some authors categorize steganography as a form of cryptography since hidden communication is a form of secret writing (Bauer 2002). Nevertheless, this paper will treat steganography as a separate field.

Although the term steganography was only coined at the end of the 15th century, the use of steganography dates back several millennia. In ancient times, messages were hidden on the back of wax writing tables, written on the stomachs of rabbits, or tattooed on the scalp of slaves. Invisible ink has been in use for centuries—for fun by children and students and for serious espionage by spies and terrorists. Microdots and microfilm, a staple of war and spy movies, came about after the invention of photography (Arnold et al. 2003; Johnson et al. 2001; Kahn 1996; Wayner 2002).

Steganography hides the covert message but not the fact that two parties are communicating with each other. The steganography process generally involves placing a hidden message in some transport medium, called the carrier. The secret message is embedded in the carrier to form the steganography medium. The use of a steganography key may be employed for encryption of the hidden message and/or for randomization in the steganography scheme.

偽裝學是報導的或暗藏的文字藝術。偽裝學的目的是掩藏消息的隱蔽通信從第三方。這與密碼學不同，秘密文字藝術，由第三方意欲使消息不值一讀，但不掩藏秘密通信的存在。雖然偽裝學從密碼學是分開和分明的，有許多比喻在兩者之間，並且有些作者分類偽裝學作為密碼學的形式，因為暗藏的通信是秘密文字(Bauer的形式2002)。然而，本文將對待偽裝學，因為一個分開的領域。

雖然期限偽裝學只鑄造了在15世紀的結尾，對偽裝學的用途建於幾個千年。在古老時期，消息在蠟書桌後面在兔子的胃掩藏了，被寫或者刺了字在奴隸的頭皮。隱形墨水是在使用中為世紀為樂趣由孩子和學生和為嚴肅的間諜活動由間諜和恐怖分子。微粒和微縮膠片，戰爭釘書針和間諜電影，在攝影以後來了(阿諾德的發明等。 2003; 約翰遜等。 2001; Kahn 1996年; Wayner 2002)。

偽裝學掩藏隱蔽消息，但不是事實雙方與彼此聯絡。偽裝學過程一般介入安置一則暗藏的消息在某一運輸媒介，稱載體。秘密消息在載體被埋置形成偽裝學媒介。對偽裝學鑰匙的用途在偽裝學計劃也許被使用為暗藏的消息的加密並且/或者為隨機化。

As an increasing amount of data is stored on computers and transmitted over networks, it is not surprising that steganography has entered the digital age. On computers and networks, steganography applications allow for someone to hide any type of binary file in any other binary file, although image and audio files are today's most common carriers.

Steganography provides some very useful and commercially important functions in the digital world, most notably digital watermarking. In this application, an author can embed a hidden message in a file so that ownership of intellectual property can later be asserted and/or to ensure the integrity of the content. An artist, for example, could post original artwork on a Website. If someone else steals the file and claims the work as his or her own, the artist can later prove ownership because only he/she can recover the watermark (Arnold et al. 2003; Barni et al. 2001; Kwok 2003). Although conceptually similar to steganography, digital watermarking usually has different technical goals. Generally only a small amount of repetitive information is inserted into the carrier, it is not necessary to hide the watermarking information, and it is useful for the watermark to be able to be removed while maintaining the integrity of the carrier.

Steganography has a number of nefarious applications; most notably hiding records of illegal activity, financial fraud, industrial espionage, and communication among members of criminal or terrorist organizations (Hosmer and Hyde 2003).

因為增長的相當數量數據在計算機和被傳送的結束網絡被存放，它不驚奇偽裝進入了數字時代。在計算機和網絡，偽裝學應用考慮到某人在其他二進制文件掩藏二進制文件的任何類型，雖然圖像和音頻文件今天多數公用載波。

偽裝學在數字式世界，最著名地數字式水印提供一些非常有用和商業重要作用。在這種應用，作者在文件能埋置一則暗藏的消息，以便知識產權歸屬可能以後被斷言並且/或者保證內容的正直。藝術家，例如，在網站可能張貼原創藝術品。如果別人竊取文件並且要求工作作為他們自己，藝術家能以後證明歸屬，因為只有他或她可以恢復水印(阿諾德等。 2003; Barni等。 2001; Kwok 2003)。 雖然概念上相似於偽裝學，數字式水印通常有不同的技術目標。通常僅小量的反覆信息被插入載體，掩藏水印信息是不必要的，並且能被去除水印是有用的，當維護載體的正直時。

偽裝學有一定數量的惡毒應用;非法活動、財政欺騙、產業間諜活動和通信最著名地掩藏的紀錄在罪犯或恐怖分子組織之中的成員(Hosmer和海德2003)。