10-06-2017, 06:45 AM
Abstract:
Steganography is the art of hiding the fact that communication is taking place, by hiding information in
other information. Many different carrier file formats can be used, but digital images are the most
popular because of their frequency on the Internet. For hiding secret information in images, there exists a
large variety of steganographic techniques some are more complex than others and all of them have
respective strong and weak points. Different applications have different requirements of the
steganography technique used. For example, some applications may require absolute invisibility of the
secret information, while others require a larger secret message to be hidden. This paper intends to give
an overview of image steganography, its uses and techniques. It also attempts to identify the requirements
of a good steganographic algorithm and briefly reflects on which steganographic techniques are more
suitable for which applications.
1. Introduction
Since the rise of the Internet one of the most important factors of information technology and communication
has been the security of information. Cryptography was created as a technique for securing the secrecy of
communication and many different methods have been developed to encrypt and decrypt data in order to keep
the message secret. Unfortunately it is sometimes not enough to keep the contents of a message secret, it may
also be necessary to keep the existence of the message secret. The technique used to implement this, is called
steganography.
Steganography is the art and science of invisible communication. This is accomplished through hiding
information in other information, thus hiding the existence of the communicated information. The word
steganography is derived from the Greek words stegos meaning cover and grafia meaning writing [1]
defining it as covered writing . In image steganography the information is hidden exclusively in images.
The idea and practice of hiding information has a long history. In Histories the Greek historian Herodotus writes
of a nobleman, Histaeus, who needed to communicate with his son-in-law in Greece. He shaved the head of one
of his most trusted slaves and tattooed the message onto the slave s scalp. When the slave s hair grew back the
slave was dispatched with the hidden message . In the Second World War the Microdot technique was
developed by the Germans. Information, especially photographs, was reduced in size until it was the size of a
typed period. Extremely difficult to detect, a normal cover message was sent over an insecure channel with one
of the periods on the paper containing hidden information [3]. Today steganography is mostly used on
computers with digital data being the carriers and networks being the high speed delivery channels.
Steganography differs from cryptography in the sense that where cryptography focuses on keeping the contents
of a message secret, steganography focuses on keeping the existence of a message secret . Steganography and
cryptography are both ways to protect information from unwanted parties but neither technology alone is perfect
and can be compromised. Once the presence of hidden information is revealed or even suspected, the purpose of
steganography is partly defeated . The strength of steganography can thus be amplified by combining it with
cryptography.
Two other technologies that are closely related to steganography are watermarking and fingerprinting . These
technologies are mainly concerned with the protection of intellectual property, thus the algorithms have different
requirements than steganography. These requirements of a good steganographic algorithm will be discussed
below. In watermarking all of the instances of an object are marked in the same way. The kind of information
hidden in objects when using watermarking is usually a signature to signify origin or ownership for the purpose
of copyright protection . With fingerprinting on the other hand, different, unique marks are embedded in
distinct copies of the carrier object that are supplied to different customers. This enables the intellectual property
owner to identify customers who break their licensing agreement by supplying the property to third parties [5].
In watermarking and fingerprinting the fact that information is hidden inside the files may be public knowledge
sometimes it may even be visible while in steganography the imperceptibility of the information is crucial
. A successful attack on a steganographic system consists of an adversary observing that there is information
hidden inside a file, while a successful attack on a watermarking or fingerprinting system would not be to detect
the mark, but to remove it.