Information Hiding Using Digital Steganography

Introduction

1.1 Background to the Study

Currently, the digital information revolution has brought significant changes in our society and daily routines. In line with the revolution, Internet and wireless network offer ubiquitous channels to deliver and exchange information. Therefore, public information exchange is secured by using an encryption method where a secret data can be encrypted to prevent the content from being intercepted. However, with the technological advancement of information security, most Internet users are not aware that sending encrypted messages will draw unnecessary attention to malicious black hats such as crackers and hackers. This is because the encrypted data appears as a string of gibberish data that might arouse suspicion. Moreover, there is a possibility of illegal exploitation attempts to the vulnerability of the encrypted messages due to curiosity and inquisitiveness of a hacker. As a result, the secret data which has been encrypted could be illegally intercepted, unauthorized tampered or even damaged during data transmission.

In order to alleviate the issue mentioned above, steganography is introduced as an alternative design to conceal a secret data into an unsuspicious cover-object so that it can be sent stealthily through a public communication channel without drawing any unnecessary attention of the black hats.

Steganography is derived from the findings of Johannes Trithemus (1462-1516) entitled Steganographia which comes from the Greek words (στεγανό-ς, γραυ-ειν), steganos literally means “covered”; and graphia means “writing”. Eventually the entire definition is defined as covered writing (Petitcolas et al., 1999).

1.2 Statements of the Problem

Over the years, numerous steganography techniques that embed secret data into cover-objects such as image, audio, video etc. have been invented and implemented. However, in the current image-based steganography technology, there are several problems arise due to

i. Distortion produced in a stego-image after embedding a secret data.

There are certain existing schemes such as Hide and Seek 4.1 and Hide in the Picture 2.1 result in a distorted stego-image after embedding a secret data. Due to this factor, the stego-image produced is able to raise suspicion and can be clearly distinguished by an attacker. Thus, researches on alleviating the distortion problem in the stego-image need to be carried out.

ii. There is a restriction on embedding certain file types during selection of secret data.

A stenographic scheme is not feasible for users if the secret data is restricted to only a few data types, for instance, text, document and image file only. Some stenographic schemes such as Gifshuffle v2.0 and EzStego only allow certain types of secret data, for instance, text and document file to be embedded (Bailey and Curran, 2006). As a result, the study on embedding other files extension is needed to be explored to ease the restriction.

iii. Limited capacity for embedding a secret data into the cover-image.

There are some existing stenographic tools which are encountering a relatively limited payload. In SecurEngine Professional v1.0 alpha, the secret data is required to be 30% of the cover-image size. In other words, a secret data needs a cover which is three times larger to fulfil the embedding ratio of 1:3. As an example, a secret data which contains of 1MB needs to be embedded in a 3MB cover. Besides, StegoMagic 1.0 has an embedding ratio of 1:8 by limiting the user to hide only 12.5% of secret data inside the cover. Apparently, there is a commercial stenographic tool named steganos Privacy Suite 2008 which consists of multiple features such as encryption, shredder, antivirus and safes for data protection (Steganos GmbH, 2009), but only allows approximately 13% (embedding ratio of 1:7.69) of secret data to be embedded in the cover. Due to the mentioned existing tools did not consider the aspect of payload as the priority, suspicion and curiosity obviously will be arisen when an unreasonably large file is sent over the network during data transmission. Hence, research on the improvement and optimization of the payload capacity is essential to be carried out.

1.3 Research Question

After understanding the problem statements which relate to the current trend of steganography development, several research questions have been formulated as follows:

Which type of cover-image would be suitable for stenographic usage?

What are the methods that can be used to embed a secret data into a cover-image?

What method can be used to retain the file size of a stego-image to prevent unnecessary suspicion?

What are the methods that can be used to embed all file formats?

1.4 Purpose of the Study

The primary objective of this dissertation is to develop a prototype which is able to embed a secret data into a bitmap cover-image as well as alleviate the above- mentioned issues which are the occurrence of a distorted stego-image, file types restriction for a secret data and improvement of the payload. In order to achieve the goal, several secondary objectives have been defined as follows:

To study and analyze the image format which is compatible for steganography usage.

To study and analyze the Least Significant Bit (LSB) substitution mechanism.

To analyze and evaluate the proposed algorithm in terms of a) accuracy, b) quality of stego-image produced, c) capacity of secret data which can be embedded and d) types of secret data which can be embedded.

1.5 Scope of the Study

The scope of study in the proposed scheme includes the implementation of a prototype which is able to

Embed various type of data file through the encoding and decoding process.

Manipulate maximum LSB(list significant bit) in an embedding mechanism

1.6 Significance of Study

Due to advances in ICT(information communication technology), most of information is kept electronically. Consequently, the security of information has become a fundamental issue. Besides cryptography, steganography can be employed to secure information. In cryptography, the message or encrypted message is embedded in a digital host before passing it through the network, thus the existence of the message is unknown. Besides hiding data for confidentiality, this approach of information hiding can be extended to copyright protection for digital media: audio, video and images. The growing possibilities of modern communications need the special means of security especially on computer network. The network security is becoming more important as the number of data being exchanged on the internet increases. Therefore, the confidentiality and data integrity are requires to protect against unauthorized access and use. This has resulted in an explosive growth of the field of information hiding.

1.7 Limitation of the Study

This project has an assumption that is both the sender and receiver must have shared some secret information before imprisonment. Pure steganography means that there is none prior information shared by two communication parties.

1.8 Operational Definition of Terms

There are some terminologies used in the field of steganography needed to be presented:

Cover-object refers to an object used as a carrier to embed messages. Many objects can be used as a cover, such as text, image, audio, HTML (Sui and Luo, 2004), XML (Takizawa et al., 2001) and even TCP/IP (Ahsan and Kundur, 2002). In the context of this research, the cover-object is a bitmap image and thus it is defined as cover-image.
Stego-object refers to the object which carries a hidden message after the process of data embedding. When given a cover-image, the secret message will be embedded into the cover-image and produces a stego-image.
Stego-image refers to a cover-image which is embedded with secret data.

Steganalysis refers to the process of detecting a secret message by distinguishing between cover-objects and stego-objects