Introduction
Steganography is no routine means to protect confidentiality. Normally, cryptography is used to communicate confidentially. Cryptographic algorithms—the security of which can be proven or traced back to known hard mathematical problems—are widely available. However, in contrast to steganography, cryptographic
algorithms generate messages which are recognizable as encrypted messages, although their content remains confidential.
Steganography1 embeds a confidential message into another, more extensive message which serves as a carrier. The goal is to modify the carrier in an imperceptible way only, so that it reveals nothing—neither the embedding of a message nor the embedded message itself. The functioning of a steganographic system is shown in Fig. 1: The sender creates a steganogram using the embedding function which function has two parameters:
1. a carrier medium containing randomness (e. g., noise), and
2. the message to be embedded.
1.1 Definition
The word steganography literally means covered writing as derived from Greek. It includes a vast array of methods of secret communications that conceal the very existence of the message. Among these methods are invisible inks, microdots, character arrangement (other than the cryptographic methods of permutation and substitution), digital signatures, covert channels and spread-spectrum communications.
Steganography is the art of concealing the existence of information within seemingly innocuous carriers. Steganography can be viewed as akin to cryptography. Both have been used throughout recorded history as means to protect information. At times these two technologies seem to converge while the objectives of the two differ. Cryptographic techniques "scramble" messages so if intercepted, the messages cannot be understood. Steganography, in an essence, "camouflages" a message to hide its existence and make it seem "invisible" thus concealing the fact that a message is being sent altogether. An encrypted message may draw suspicion while an invisible message will not.
