Steganography

Steganografi
What is steganography

Steganography is the art and science of writing hidden messages in such a way that no-one apart from the sender and intended recipient even realizes there is a hidden message, a form of security through obscurity. By contrast, cryptography obscures the meaning of a message, but it does not conceal the fact that there is a message.

Generally, a steganographic message will appear to be something else: a picture, an article, a shopping list, or some other message. This apparent message is the covertext. For instance, a message may be hidden by using invisible ink between the visible lines of innocuous documents.

The advantage of steganography over cryptography alone is that messages do not attract attention to themselves, to messengers, or to recipients. An unhidden coded message, no matter how unbreakable it is, will arouse suspicion and may in itself be incriminating, as in countries where encryption is illegal. Often, steganography and cryptography are used together to ensure security of the covered message.

Someone who is expert in steganography is called steganalyst.

History of steganography

The word steganography is of Greek origin and means "covered, or hidden writing". Its ancient origins can be traced back to 440 BC. Herodotus mentions two examples of steganography in The Histories of Herodotus. Demaratus sent a warning about a forthcoming attack to Greece by writing it on a wooden panel and covering it in wax. Wax tablets were in common use then as re-usable writing surfaces, sometimes used for shorthand

Another ancient example is that of Histiaeus, who shaved the head of his most trusted slave and tattooed a message on it. After his hair had grown the message was hidden. The purpose was to instigate a revolt against the Persians.

Some Techniques of Steganography

1. Writing a secret message using invisible ink.
2. Hidden messages on messenger's body: also in ancient Greece.
Herodotus tells the story of a message tattooed on a slave's shaved head, hidden by the growth of his hair, and exposed by shaving his head again.
The message allegedly carried a warning to Greece about Persian invasion plans.

This method has obvious drawbacks:
  • It is impossible to send a message as quickly as the slave can travel, because it takes months to grow hair.
  • A slave can only be used once for this purpose. (This is why slaves were used: they were considered expendable).
3. A picture of a message in microdots or microfilms.
4. In computer era, steganography can be done by inserting a secret document into other document. Any document can be used as a media, for example text file, picture file, or multimedia file such as mp3 or video file.

Practice

  • Prepare an image for cover image.
  • Prepare a secret image to be hidden.
  • Go to this site http://incoherency.co.uk/hideimage.php
  • Hit button Go!
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