Top Banner

Click here to load reader

Steganography and Digital Watermarking Jonathan Cummins, Patrick Diskin, Samuel Lau, Robert Parlett

Dec 18, 2015



  • Slide 1
  • Steganography and Digital Watermarking Jonathan Cummins, Patrick Diskin, Samuel Lau, Robert Parlett.
  • Slide 2
  • Introduction Steganography (covered writing, covert channels) Protection against detection (data hiding) Protection against removal (document marking) Watermarking (all objects are marked in the same way) Fingerprinting (identify all objects, every object is marked specific) Source: Richard Popa.
  • Slide 3
  • Why not Encryption? Steganography (hide existence of the secret message, but do not use encryption) Encryption (encrypt the message, but do not hide the message) Confidentiality Anybody can see both parties are communicating in secret. Suspicious. Ideally nobody can see both parties are secretly communicating. Innocent. Source: Richard Popa.
  • Slide 4
  • History 440 B.C. Histiaeus shaved the head of his most trusted slave and tattooed it with a message which disappeared after the hair had regrown. To instigate a revolt against Persians. 1 st and 2 nd World Wars German spies used invisible ink to print very small dots on letters. Microdots Blocks of text or images scaled down to the size of a regular dot. Current Special inks are used to write a hidden messages on bank notes. Industry demands for digital watermarking and fingerprinting of audio and video.
  • Slide 5
  • Copyright Watermarking Why is it so important? Internet has lead to sharing of information e.g. digital libraries. However problem of ownership is introduced. People can simply copy shared information and claim it is theirs. Cannot detect when people have violated copyright of material. Could cause massive losses in revenue for the copyright holders. Global piracy costs music recording industry over 2.8bn a year. Need a way of prosecuting individuals for use of non-copyright materials.
  • Slide 6
  • Hiding Information Digitally Requirements Secret data integrity must remain after being embedded in stego object. The stego object must remain unchanged or almost unchanged to naked eye. In watermarking, changes in stego object have no effect on watermark. We assume the attacker knows secret data is hidden inside the stego object.
  • Slide 7
  • Basic Principle in Steganography Encoder Decoder Cover Image Secret Image Key Stego Object Original Cover Secret Image Communications Channel
  • Slide 8
  • Types of Steganography Fragile Hidden information destroyed as soon as object is modified. Protocols tend to be easy to implement. Useful in proving objects have not been manipulated and changed e.g. evidence in a court of law. Robust It should be infeasible to remove the hidden data without degrading the perceived quality of the data. Protocols are more complex. One single protocol may not withstand all object manipulations. Useful in copyright watermarking.
  • Slide 9
  • Steganography Techniques Binary Files Text Document XML Images LSB, DCT, Wavelet Audio Midi, MP3 Other Types
  • Slide 10
  • Information Hiding in Binary Files If we change or remove something in a binary file, execution could be different. We can use a serial key or authors logo to achieve copyright protection. Cracks and key generators are widely available for common programs. Method for watermarking the binary source: b, c, d must be done in same order, but a can be executed at any time. a = 2;b = 3; c = b + 3;a = 2;c = b + 3; a = 2;c = b + 3;d = b + c; a = 2;
  • Slide 11
  • Information Hiding in Binary Files W = {w 1, w 2, w 3, w 4,....., w n }(Watermark)w i {0, 1} Divide program into n blocks. 0 = code left unchanged, 1 = two instructions are switched. To decode we need the original binary file. Comparing the original and marked binary files, we can recover W. Not resistant to attacks. If the attacker has enough copies, he can recover W.
  • Slide 12
  • Information Hiding in Documents Originals and photocopied materials look different on paper. Electronic originals and copied materials are identical. Data hiding in documents uses embedded marks. Marks can be same or different on all copies. Can be achieved by: Altering text formatting, Altering characteristics of characters. Alterations not visible but decodable.
  • Slide 13
  • Information Hiding in Documents General protocol in document hiding. A page of doc is represented by a function, f. Codeword assigned to document decides which line is to be altered. Differential Encoding Technique generally used. Require a encoder and decoder. Encoder Codebook Original Document Marked Documents
  • Slide 14
  • Information Hiding in Documents One of three techniques are applied to hiding data: Line Shift Coding - Vertical shifting of lines Word Shift Coding - Horizontal spacing between each word Shift of words slightly left or right, decided by codebook An Example of this Feature Coding - Analyse document, then pick features to change e.g. text height Shifts lines up slightly up or down Lines to be shifted decided by Codebook Shifted up slightly h+i h-i AnExampleofthis Example is shifted to the left. this is shifted to the right
  • Slide 15
  • Text Techniques White Space manipulation Text viewers cant see white space at the end of lines. Using a documents grammar to hide information The auto drives fast on a slippery road over the hill changed to Over the slope the car travels quickly on an ice-covered street. Encoding text with a different meaning By using a cipher key.
  • Slide 16
  • Text Techniques Text being hidden: I'm having a great time learning about computer security. Dear Friend, Especially for you - this red-hot intelligence. We will comply with all removal requests. This mail is being sent in compliance with Senate bill 2116, Title 9 ; Section 303 ! THIS IS NOT A GET RICH SCHEME.Why work for somebody else when you can become rich inside 57 weeks. Have you ever noticed most everyone has a cellphone & people love convenience. Well, now is your chance to capitalize on this. WE will help YOU SELL MORE and sell more ! You are guaranteed to succeed because we take all the risk ! But don't believe us. Ms Simpson of Washington tried us and says "My only problem now is where to park all my cars". This offer is 100% legal. You will blame yourself forever if you don't order now ! Sign up a friend and you'll get a discount of 50%. Thank-you for your serious consideration of our offer. Dear Decision maker ; Thank-you for your interest in our briefing. If you are not interested in our publications and wish to...
  • Slide 17
  • Text Techniques XML Universal format for structured data and documents. Basic technology for information exchange. Due to this security is a growing factor which Steganography can help solve Different components in which data can be hidden css, dtd, xsl.
  • Slide 18
  • Text Techniques Using tag structure to hide information Stego key: 0 1 Stego data: Bit String: 01110
  • Slide 19
  • Text Techniques Using white space in tags Stego key:,, or 0,, or 1 Bit String: 101100 Alice 01
  • Slide 20
  • Text Techniques Containment of elements stego key: SOMETHING 0 SOMETHING 1 Using the order of elements stego key: NAME ID 0 ID NAME 1
  • Slide 21
  • Image Techniques Simple Watermarking A simple way of watermarking images is to embed another image into them. This embedded image can be a company logo or name etc. +=
  • Slide 22
  • Image Techniques LSB Least Significant Bit A simple yet effective way of hiding data in an image for any purpose. The least significant bits of the host image are used to hide the most significant bits of the hidden image (for image-in-image hiding). The least significant bits can always be used to hide other data types. The next example will show how image-in-image hiding works via this method.
  • Slide 23
  • Image Techniques Store host image and hidden image in memory. Pick the number of bits you wish to hide the hidden image in. Scan through the host image and alter its LSBs with the hidden images MSBs. So when 4 bits are used to hide information Host Pixel: 10110001 Secret Pixel: 00111111 New Image Pixel: 10110011 To extract the hidden image, you basically take out the LSBs from the host image and create a new image from them.
  • Slide 24
  • Image Techniques Original ImagesBit Level 1Bit Level 4Bit Level 7
  • Slide 25
  • Image Techniques This method works best when both the hidden image and host image have equal priority in terms of the number of bits used. Not a very good way of watermarking as it is easy to remove the hidden data. The hidden data can easily be corrupted by noise. The LSBs can be used to store other information like text the only limitation is the size of the data you wish to store.
  • Slide 26
  • Image Techniques DCT (Direct Cosine Transformation) DCTs convert images from the spatial domain to the frequency domain. High frequencies correspond to rapidly changing pixel values. Low frequencies correspond to slowly changing pixel values. Used to compress JPEG images and can be used as part of a information hiding technique.
  • Slide 27
  • Image Techniques A Quantizer is used as part of the JPEG compression technique. It lowers the accuracy of the DCT coefficients which are obtained by executing a DCT on 8x8 blocks of the host image. These values can be tweaked to be all ev