Modern information technology/4. Information Security

Loza T.Y.

State higher education institution

"National Mining University"

The use of steganography method for the hidden transmission of messages in images

In the age of high technology information is the most important part of our lives. In view with this problem of information security concerned experts in the field of computer security as well as many ordinary computer users. This article discusses a method of protecting information as digital steganography.

The first records about the use of steganography appeared in ancient Greece. In this age of information technology science have given fresh impetus to the development and improvement. Advances in computer technology and multimedia gave impetus to the development of new methods to ensure the security of digital data transmission over communication channels. Based on the sampling inaccuracies and redundancy of the analog signal, these methods allow you to hide secret messages in a file container. A distinctive feature of the method is to hide the fact of communication.

The greatest popularity in recent times received a part of the digital steganography, which is used to conceal confidential messages in images transmitted over computer networks.

Particular interest was caused to steganography methods after several countries have imposed restrictions on the use of cryptosystems. But the problems of protection of property rights in the digital information caused many works in the field of watermarking - special labels, insensibly implemented in image or other digital media in order to control its use.

To encrypt the information that will be integrated into a container file (graphic image) is formed by a hidden information transmission channel, called a stenographic system or simply stegosystem. The scheme of stegosystem work is presented in the figure (Fig. 1).

Figure 1. The general model of stegosystem work.

To improve the reliability of steganographic system necessary to consider the following points in its construction:

· The enemy has a full understanding of the steganographic system and details of its implementation. The only information that remains unknown potential enemy is the key by which only the holder can establish the fact of the presence and content of the hidden message;

· If the enemy somehow finds out about the fact of the existence of hidden message, it should not allow him to remove such messages to other data as long as the key is kept secret;

· A potential enemy should be devoid of any technical or other advantages in the recognition or disclosure of secret messages.

One of the most popular algorithms for embedding secret information into a digital signal is a method of replacing the least significant bit (LSB).

We know that people do not perceive all the information included in the image, and if you replace less significant bits in the color components of the pixel with concealed messages, man will not be able to identify this on eye. Consistently producing such replacement, starting with the pre-specified pixel, can be implemented message. The idea of the method is simple, but in such a trivial form it is not highly effective.

Advantages of the method:

· The size of the container file is not changed;

· When replacing each of the least significant bit in one pixel changes are not visually noticeable;

· The ability to change the number of replaceable bits in accordance with the size of hidden information.

Disadvantages:

· Processing of container file leads to an almost complete loss of hidden data.

The following is an operation principle of algorithm LSB on the example of 24-bit RGB-image. Each pixel of the image in BMP format is encoded by three bytes, according to the intensity of one of the three component colors (red - R, Green - G, and blue – B, Fig. 2).

Figure 2. Representation of the color pixel in the BMP-image.

As a result of mixing of the three channels of pixel becomes necessary shade. To illustrate the operating principle of the method LSB is necessary to paint each of three bytes in the form of bits. Least significant bits (in the figure they are located on the right, Fig. 3) are less noticeable effect on the final image than the most ones. From this it can be concluded that the replacement of one or two younger, the least significant bits for other arbitrary bits so insignificantly distort the shade of pixel that the audience will not even notice the change.

It is assumed that you want to hide in a pixel of the image six bits: 101100. To achieve the result you need to break them into groups by twos and then replace the least significant bits of the original image by data (Fig. 3.).

Figure 3. The initial and modified color components

The result will be obtained by a new shade of the pixel that is virtually indistinguishable from the original (Fig. 4.). These colors will be difficult to discern even on monotonous fill. As practice shows, the replacement of two least significant bits rarely perceived by the human eye and does not affect the quality of the final image.

Figure 4. Pixel color with implemented data

Then you need to calculate the useful volume of the RGB-container.

Each channel of the eight bits two of them are engaged the hidden information, which corresponds to 25%. Thus, you can hide useful information of a quarter of the total size of the image with the confidence that the naked eye these changes will not be noticeable.

All BMP containers should be divided into two classes: the "clean" and noisy. In the "clean" image trace a link between least significant bit, which is changing, and the other 7-bits of elements of the color, and traced significant dependence of bits to each other. Implementation of the message in a "clean" image destroys the existing dependencies, which is very easy to diagnose by passive observer. If the image is noisy (e.g., obtained from a scanner or a digital camera), then determine the attachment becomes much more difficult. Thus, for LSB method is recommended to use the files that were not created on the computer initially as a container file.

Digital steganography is the dynamic and rapidly developing science that uses the methods and achievements of cryptography, digital signal processing, communication theory and information. Along with the ordinary user major companies operating in the field of multimedia are also interested in it, seeking to protect their content from illegal use. It does not attract attention, as opposed to clean cryptography. Analysis of trends in digital steganography shows that in the next few years, interest in the development of its methods will grow more and more.

References:

1. Computer steganography. Theory and Practice. G.F. Konakhovich

2. The foundations of modern cryptography. S.G. Barichev, V.V. Gon-charov, R. E. Serov

3. Gribunin V.G., Binding J.H., Turintsev I.V. Digital steganography. - Moscow: Solon Press, 2002. - 272 pp., ill.

4. Journal "Information Security " #4, 2007