Steganography is the art and science of writing hidden messages in such a way that no one, apart from sender and intended recipient, suspects the existence of the message, a form of security through obscurity. The Greek word Steganography means concealed writing. In Steganography, messages do not attract attention to themselves as in cryptography. Steganography protects both messages and communicating parties. Steganography includes the concealment of information within computer files.

Steganographic Techniques for Different Media Types

  • Physical Steganography – Physical Steganography includes hidden messages within wax tablets and on messenger’s body, by using invisible ink, messages written in Morse code on knitting yarn, messages written on envelopes in the stamped areas etc.
  • Digital Steganography – Digital Steganography includes concealing messages within the lowest bits of noisy images or sound files, concealing data within encrypted data or within random data, by chaffing and winnowing, by using mimic functions, concealing messages in tampered executable files, by pictures embedded in video material, by changing the order of elements in a set etc.
    • Image Steganography for Information Cryptography in Pictures
    • Video Steganography for Information Cryptography in moving pictures
    • Audio Steganography for Information Cryptography in Sound files
  • Network Steganography – Network Steganography includes concealing messages in voice-over-IP conversations or hiding information in unused header files, by using wireless local area networks.
  • Printed Steganography – Printed Steganography involves cipher text resulting in stegotext and thus includes perturbing noise in the channel file to hide the message. Thus, only the recipient who knows the technique used to recover the message can decrypt it.
  • Text Steganography – Text Steganography involves coding of the information by Unicode Steganography, Huffman coding etc. Huffman coding assigns smaller length code words to more frequently occurring source symbols and longer length code words to less frequently occurring source symbols. Unicode coding includes usual ASCII set to look normal, while really carrying extra bits of information
  • Steganography using Sudoku Puzzle – It includes hiding of data within an image. Steganography using Sudoku puzzles has as many keys as there are possible solutions of a Sudoku puzzle which is equivalent to around 70 bits.

Applications of Steganography

  • Steganography is used by HP and Xerox brand color laser printers. Tiny yellow barely visible dots are added in each page contains printer serial numbers as well as date and time stamps.
  • Steganography can be used for digital watermarking, where a message is hidden in am image so that its source can be tracked or verified.
  • Steganography has alleged use by terrorists and by intelligence services.
  • Steganography is used in wireless application protocol.
  • Steganography is used for confidential communication and secret data storing. Increases capability to hide confidential data, strengthens secrecy of encrypted data.
  • Steganography is used to protect data against alteration.
  • Steganography is used to gain access control system for content distribution
  • Steganography is used in media database systems.

Drawbacks of Steganography

  • Steganography could accidentally degrade or render a misleading image.
  • Steganography process could be counteract and be counterproductive with the original image.
  • Someone else other than intended receiver, with a steganography detection and cracking tool could expose the message.
  • Steganography software cannot use separate hardware tools.
  • Steganography software also cannot protect watermark.