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SECURE FILE TRANSMISSION SYSTEM USING STEGANOGRAPHIC ALGORITHM: DATA EMBBEDMENT USING JPEG

CHAPTER ONE

INTRODUCTION

1.1  Background of study

In the field of Data Communication, security-issues have got the top priority. Internet users frequently need to store, send, or receive private information. The most common way to do this is to transform the data into a different form. The resulting data can be understood only by those who know how to return it to its original form. This can be done using Steganography or Cryptography. The word steganography is of Greek origin and it means "concealed writing" from the Greek words steganos (στεγανός) meaning "covered or protected", and graphia (γραυή) meaning "writing". The first recorded use of the term was in 1499 by Johannes Trithemius in his Steganographia, a treatise on cryptography and steganography disguised as a book on magic (Choon, 2012; 2013).

Steganography is defined as the system of hiding secret or a confidential data in a cover media like image, text, video, and audio, in such a way that none other than the intended recipient knows the presence of data. In contrast to Cryptography, where the enemy is allowed to detect, intercept and modify messages without being able to violate certain security premises guaranteed by a cryptosystem, the goal of Steganography is to hide messages inside other harmless messages in a way that does not allow any enemy to even detect that there is a second message present". In this digital world, both the concepts i.e. the cryptography and steganography hide the data from the unintended recipients or an intruder. Due to this fact, the authors prefer a multilayer security by using the benefits of steganography. The steganography concept can be implemented through various formats available worldwide. Various formats preferred are .jpeg, .gif, .png, .mp3, .mp4, .doc, .docx .bmp.  Due to ease of availability of these formats on the internet, they are preferred to hide the secret message. Steganography research has been driven because of weakness in the cryptography systems that result in the security breach. Many tools and technologies created takes advantage of steganography techniques like coding in image, null ciphers, videos, audio, etc. (Cachin, 1998).

The goal of steganography is to avoid drawing suspicion to the existence of a hidden message. This approach of information hiding technique has recently become important in a number of application areas. Digital audio, video, and pictures are increasingly furnished with distinguishing but imperceptible marks, which may contain a hidden copyright notice or serial number or even help to prevent unauthorized copying directly (Chen and Wu, 2009).

Military communications system makes increasing use of traffic security technique which, rather than merely concealing the content of a message using encryption, seek to conceal its sender, its receiver or its very existence. Similar techniques are used in some mobile phone systems and schemes proposed for digital elections.

Some of the techniques used in steganography are domain tools or simple system such as least significant bit (LSB) insertion and noise manipulation and transform domain that involve manipulation algorithms and image transformation such as discrete cosine transformation and wavelet transformation. However, there are techniques that share the characteristic of both of the image and domain tools such as patchwork, pattern block encoding, spread spectrum methods and masking.

In contrast, steganography does not alter the structure of the secret message but hides it inside a cover-image so it cannot be seen. A message in cipher-text, for instance, might arouse suspicion on the part of the recipient while an “invisible” message created with steganographic methods will not. In other word, steganography prevents an unintended recipient from suspecting that the data exists. In addition, the security of classical steganography system relies on secrecy of the data encoding system. Once the encoding system is known, the steganography system is defeated. It is possible to combine the techniques by encrypting message using cryptography and then hiding the encrypted message using steganography. The resulting stego-image can be transmitted without revealing that secret information is being exchanged. Furthermore, even if an attacker were to defeat the steganographic technique and detect the message from the stego-object, he would still require the cryptographic decoding key to decipher the encrypted message.

1.2 Problem of Statement

In today’s society the most practical implementation of steganography is used in the world of computers. Data is the heart of computer communication and over the years a lot of methods have been created to accomplish the goal of using steganography to hide data. The trick is to embed the hidden object into a significantly larger object so the change is undetectable by the human ear.

As stated earlier, visible encrypted messages will draw suspicion from others. This will make them attempt to decrypt the cipher text. Indirectly it raises the chance of message being viewed by third party in the exception of sender and viewer. However, by hiding or embedding the text file into image, it is hard to raise the suspicion of others whether it contains any secret message or not as the processed image had not look different from the original image in naked eyes. This will make the message more secure. Indirectly, only the sender and receiver know the treat behind the image and hence ensure that the message can only be viewed by the sender and receiver.

1.3 Aim and Objectives

The primary aim of this project is to encode a message in an image in a way that avoids drawing suspicion to the transmission of the hidden message.

This project also comprehends the following objectives:

(i)               To store a text file (.txt) in image.

(ii)             To protect the text file (.txt) from being viewed by third party using encryption.

(iii)          To restore the stored text file in image.

1.4 Scope of the Study

          In this paper we propose a technique of combining cryptography and steganography to solve the problem of unauthorized data access. Steganography also can be implemented to cryptographic data so that it increases the security of this data. In this method we first encrypt a message using substitution cipher method and then embed the encrypted message inside a JPEG image using DCT in frequency domain. A substitution cipher is one in which each character in the plaintext is substituted for another character in the ciphertext. Thus the content of the message appears meaningless to the third party. Thus it is very difficult to detect hidden message in frequency domain and for this reason we use transformation like DCT in our proposed technique. The combination of these two methods will enhance the security of the data embedded and will satisfy the requirements such as capacity, security and robustness for secure data transmission over an open channel. Furthermore, if an attacker were to defeat the steganographic technique to detect the message from the stego-object, he would still require the cryptographic method to decipher the encrypted message. The intended receiver should be able to recover the embedded data successfully, without any errors. 

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