Steganography-Based Secret and Reliable ... Steganography-Based Secret and Reliable Communications: Improving Steganographic Capacity and Imperceptibility A thesis submitted for the

Steganography-Based Secret and

Reliable Communications: Improving

Steganographic Capacity and

Imperceptibility

A thesis submitted for the degree of Doctor of Philosophy

by

Adel Almohammad

Department of Information Systems and Computing

Brunel University

August, 2010

I

ABSTRACT

Unlike encryption, steganography hides the very existence of secret information

rather than hiding its meaning only. Image based steganography is the most

common system used since digital images are widely used over the Internet and

Web. However, the capacity is mostly limited and restricted by the size of cover

images. In addition, there is a tradeoff between both steganographic capacity and

stego image quality. Therefore, increasing steganographic capacity and enhancing

stego image quality are still challenges, and this is exactly our research main aim.

Related to this, we also investigate hiding secret information in communication

protocols, namely Simple Object Access Protocol (SOAP) message, rather than in

conventional digital files.

To get a high steganographic capacity, two novel steganography methods were

proposed. The first method was based on using 16x16 non-overlapping blocks and

quantisation table for Joint Photographic Experts Group (JPEG) compression

instead of 8x8. Then, the quality of JPEG stego images was enhanced by using

optimised quantisation tables instead of the default tables. The second method, the

hybrid method, was based on using optimised quantisation tables and two hiding

techniques: JSteg along with our first proposed method. To increase the

steganographic capacity, the impact of hiding data within image chrominance was

investigated and explained. Since peak signal-to-noise ratio (PSNR) is extensively

used as a quality measure of stego images, the reliability of PSNR for stego

images was also evaluated in the work described in this thesis. Finally, to

eliminate any detectable traces that traditional steganography may leave in stego

files, a novel and undetectable steganography method based on SOAP messages

was proposed.

All methods proposed have been empirically validated as to indicate their utility

and value. The results revealed that our methods and suggestions improved the

main aspects of image steganography. Nevertheless, PSNR was found not to be a

reliable quality evaluation measure to be used with stego image. On the other

hand, information hiding in SOAP messages represented a distinctive way for

undetectable and secret communication.

II

DEDICATION

This thesis is dedicated, with deepest love and everlasting respect, to numerous

precious persons.

To my parents for their continuous love, support and encouragement which

helped me to achieve my dream.

To my wife and daughter who I am indebted to, without their continuous

sacrifices and patience the completion of this project could not be possible.

To my brothers and all my friends, for their support and patience throughout

these stressful years.

To the principles of each and every ambitious person who knows that patience

and hard work make the dreams.

With my love…

Adel Almohammad

10 Ramadan, 1431

20 August, 2010

III

ACKNOWLEDGEMENTS

Firstly, all praise is due to Allah (Glorified and Exalted is He), without his

immeasurable blessings and favours none of this could have been possible.

During the course of this research, there have been numerous people who have

provided me with guidance, inspiration and support for completing this thesis. I am

indebted to my supervisor Dr. George Ghinea for his continuous encouragement and

support at all stages of this research. His involvement proved vital to the completion

of this thesis. I would like to thank him for his useful and valuable advice. I also owe

thanks to Professor Robert M. Hierons, my second supervisor, for his insightful and

encouraging comments and suggestions throughout this research.

On the personal front, I would like to express my gratitude to my family, for their

continuous love, support and sincere prayers during the course of this research. I must

also express my thanks to all my colleagues in the Department of Information

Systems and Computing at Brunel University. I will also like to thank my friends and

other participants who helped me a lot by participating and motivating me in the

course of my research.

Lastly but not the least, I will like to thank the Ministry of Higher Education in Syria

and the University of Aleppo for providing me a chance and funding to keep this

research going.

IV

DECLARATION

The following papers have been published (or have been submitted for

publication) as a direct result of the research discussed in this thesis:

Journals:

1. Almohammad, A., and Ghinea, G., (2010). Stego Image Quality:

Objective and Subjective Perspectives. Submitted to IEEE Transactions

on Image Processing, IEEE.

2. Almohammad, A., and Ghinea, G., (2010). Information Hiding in

Grayscale and Colour Images. Submitted to Signal Processing: Image

Communication, Elsevier.

Reviewed Conferences:

1. Alrouh, B., Almohammad, A., and Ghinea, G., (2010). Information Hiding

and SOAP Messages. The 5th International Conference for Internet

Technology and Secured Transactions (ICITST 2010), London, UK, 8-11

November, 2010, (Accepted), IEEE.

2. Almohammad, A., and Ghinea, G., (2010). Stego Image Quality and the

Reliability of PSNR. International Conference on Image Processing

Theory, Tools and Applications (IPTA 2010), Paris, France, 7-10 July,

2010, 215-220, IEEE.

3. Almohammad, A., and Ghinea, G., (2010). Image Steganography and

Chrominance Components. 10th IEEE International Conference on

Computer and Information Technology (CIT 2010), Bradford, UK, 29

June -1 July, 2010, 996-1001, IEEE.

4. Almohammad, A., Ghinea, G., and Hierons, R. M., (2009). JPEG

Steganography: a Performance Evaluation of Quantisation Tables.

International Conference on Advanced Information Networking and

Applications (AINA 2009), Bradford, UK, 26-29 May, 2009, 471-478,

IEEE.

5. Almohammad, A., Hierons, R. M., and Ghinea, G., (2008). High Capacity

Steganographic Method Based Upon JPEG. The Third International

Conference on Availability, Reliability and Security (ARES 2008),

Barcelona, Spain, 4-7 March, 2008, 544-549, IEEE.

V

TABLE OF CONTENTS

ABSTRACT ............................................................................................................. I

DEDICATION.........................................................................................................II

ACKNOWLEDGEMENTS................................................................................... III

DECLARATION................................................................................................... IV

Journals:................................................................................................................ IV

Reviewed Conferences:.......................................................................................... IV

TABLE OF CONTENTS ....................................................................................... V

LIST OF TABLES.................................................................................................. X

LIST OF FIGURES...............................................................................................XI

Chapter 1: Information Security and Steganography....................................... 1

1.1 OVERVIEW ............................................................................................... 1

1.2 RESEARCH BACKGROUND........................................................................ 2

1.2.1 Steganography and Cryptography ......................................................... 3

1.2.2 Steganography and Watermarking ........................................................ 4

1.2.3 Information Security and Steganography .............................................. 5

1.3 MOTIVATIONS AND RESEARCH PROBLEM ................................................ 8

1.4 RESEARCH AIM ........................................................................................ 9

1.5 THESIS OUTLINE ...................................................................................... 9

Chapter 2: Steganography and the Art of Covert Communication............... 12

2.1 INTRODUCTION....................................................................................... 12

2.2 STEGANOGRAPHY DEFINED.............