1. Steganography

2. Steganography Means “covered or secret writing” A brief history
440 BC: Tattoos on slaves heads
Wax covered tablets
WWII
Image Substitution
Null Ciphers
Microdots
Today
Technology taking advantage of these old techniques
Null ciphers
Coding in images, audio, video and microdot

3. Possible Uses of Steganography
Drawbacks
Combine explanatory information with an image
Could degrade or render an image useless
Embed corrective audio or image data in case of corrosion
Could counteract and be counterproductive with original image
Private Communications
Doesn’t hide the fact an was sent
Posting secret communications on Web to avoid transmission
Third parties with steganography detection and cracking tools can view message
Copywrite protection
Steganographic software can’t protect the watermark
Maintaining anonymity
Easier to open free Web-based

4. What It Does
Hides information needing to be kept secret in unused, redundant parts of data
Data most often hidden in:
Text/Word documents
Audio files
Digital images

5. Text Very challenging – small amounts of repetitive data
Line-shift encoding: actually shifting the line of text up or down
Value depends on whether the line was up or down from a stationary line
Word-shift encoding: uses horizontal space between words to obtain a value for the hidden message
Feature specific encoding: encoding a secret message by changing certain attributes such as the length of letters

6. Audio The MOST challenging
Sample Quantization: 16-bit linear sampling architecture used for WAV and AIFF formats
Temporal Sampling Rate: uses selectable frequencies; the higher the sample rate the more usable data will become
Perceptual Sampling: usually an MP3 file, changes statistics of audio by only encoding parts listener can perceive
Perceived sound maintained but actual signal is changed

7. Digital Images
Anything that can be encoded in a bit-stream can be hidden in digital image
Cover Images can be:
8-bit:
256 color choices
Small file size
24-bit:
16 million color choices
Large file size
Gray-scale:
Shades very only slightly from byte to byte

8. Methods of Image Encoding
Least Significant Bit Encoding
Three bits of data encoded into each pixel of 24-bit image; one bit encoded into each pixel of 8-bit image
Ex: Binary A can be hidden into 3 pixels
( )
( )
( )
Inserting Binary value of A ( ) into three pixels,
beginning from top left byte:
( )
( )
Susceptible to slight changes to image or format
8-bit images less forgiving because of color restrictions

9. Masking and Filtering
Extends image data by putting secret data over the original
Immune to manipulation
**Important: Watermarking is not Steganography
Watermarks become part of image and are noticeable

10. Algorithms & Transformations
Discrete Cosine Transformation
Used to compress JPEG images
Variances will depend on the values and methods used to calculate DCT
Luminance
Uses spread spectrum techniques or redundant pattern matching
Help protect against image processing techniques
Fourier Transformations
Wavelet Transformations
Hide information more thoroughly than masking
Support image manipulation more readily than LSB

11. Security Cryptography vs. Steganography
Cryptography: scrambles messages to obscure the messages meaning
Steganography: hides the message entirely
Stronger encryption methods result when Steganography and Cryptography are combined
Three Steganography protocols that utilizes concepts similar to Cryptography

12. Pure Steganography Least Secure
Does not require the exchange of a cipher key
Sender and receiver have to assume no third parties know of the message

13. Secret Key Steganography
Secret key must be exchanged prior to communication
Only parties who know the secret key can read the secret message
Exchanging of key makes it more vulnerable

14. Public Key Steganography
Use of both private and public key to ensure security
Sender uses public key during encoding process
Recipient uses private key during decoding process
Offers multiple levels of security

15. Steganalysis Detecting hidden messages using Steganography
Majority of stego-images do not reveal visual clues in the cover-image
Possible to detect hidden image with electronic signatures & Stego software

16. Signatures Simplest signature to recognize is increase in file size
Other signatures may become apparent in some form of manipulation to the color palette
Large increase or decrease in number of unique colors
Palette colors increasing incrementally rather than randomly
Exception: Gray-scale images do increase incrementally
Look for disproportionate number of shades of black

17. Statistical Analysis Average bytes Variation of bytes Skew Kurtosis
Average deviation
Differential values

18. Destroying or Disabling
Convert the image to different format
Any formatting:
Cropping
Blurring
Sharpening, etc.

19. References
Cole, Eric. Hiding in Plain Sight. Steganography and the Art of Covert Communication. Indianapolis, Indiana: Wiley Publishing, Inc
Jajodia, Sushil & Johnson, Neil. Exploring Steganography: Seeing
the Unseen. April 12, URL:
Radcliff, Deborah. Steganography: Hidden Data. June 10, Computer World. April 10, URL: