CORE Metadata, citation and similar papers at core.ac.uk Provided by Brunel University Research Archive 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 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. I 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 II 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. III 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 . IV 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 .................................................................... 13 2.3 COVER FILES USED FOR STEGANOGRAPHY ............................................ 13 2.4 MAIN COMPONENTS OF STEGANOGRAPHIC SYSTEMS ............................ 14 2.5 PASSIVE , ACTIVE , AND MALICIOUS WARDENS ...................................... 16 2.5.1 Passive Attack ...................................................................................... 16 2.5.2 Active Attack......................................................................................... 17 2.5.3 Malicious Attack................................................................................... 18 2.6 STEGANOGRAPHY : METHODS OF CLASSIFICATION ................................. 18 2.6.1 Cover-Type Based Classification......................................................... 18 2.6.2 Hiding Method-Based Classification................................................... 19 2.6.2.1 Insertion-Based Method.................................................................... 19 2.6.2.2 Substitution-Based Method ..............................................................