Steganography is a process of hiding data behind an image or text. It is a form of cryptography, which is basically hiding some meaningful text in another text(which may be meaningful or not). The advantage of Steganography over cryptography is that the data which is hidden inside of an image doesn't attract user's attention as the cover is just an image or something we see in day-to-day basis. The first recorded use of the term was in 1499 by Johannes Trithemius in his Steganographia, a treatise on cryptography and steganography, disguised as a book on magic. Generally, the hidden messages appear to be (or be part of) something else: images, articles, shopping lists, or some other cover text. Steganography has been used for a long time and thus, it has developed various physical, as well as technical methods to implement it. Some physical methods include the following:
- Hidden messages within a wax tablet: in ancient Greece, people wrote messages on wood and covered it with wax that bore an innocent covering message.
- Hidden messages on paper written in secret inks, under other messages or on the blank parts of other messages.
- Messages written in Morse code on yarn and then knitted into a piece of clothing worn by a courier. Some digital methods include:
- Concealing messages within the lowest bits of noisy images or sound files.
- Concealing data within encrypted data or within random data. The message to conceal is encrypted, then used to overwrite part of a much larger block of encrypted data or a block of random data (an unbreakable cipher like the one-time pad generates ciphertexts that look perfectly random without the private key). Steganography is what really an interesting practise. Imagine the number of steganographic images you have seen till now but you didn't have the slightest idea that it's a cover or what's hiding behind it and you simply ignored it!