Stegnography Basics

What is Steganography?
Hiding a secret message within an ordinary message and extracting it at the destination to maintain confidentiality of the data.
Example: Popular method is hiding a file inside an image or using image file as a cover.
http://www.wikihow.com/Hide-a-File-in-an-Image-File
Techniques:

• Substitution Techniques
• Transform Domain Techniques
• Cover Generation Techniques
• Spread Spectrum Techniques
• Distortion Techniques
• Statistical Techniques

Classification:
Technical Steganography:
Uses physical and chemical means to hide the existence of a message.Example – Invisible ink, Microdots, In Computers (Uses redundant information in pictures, text, sound etc)
Linguistic Steganography:
Uses written natural language to hide the message in the carrier in some non-obvious ways.

1. Semagrams – Uses visual symbols or signs. Further classified into visual(Eg Doodles) or Text semagrams (small changes in font size, color etc)
2. Open codes – Hide in a specifically designed patter – unclear to the normal user.
   1. Jargon Code- Only a group of people  can understand
   2. Covered Ciphers (Null Ciphers and Grille Cipher): Hidden openly in the carrier medium.