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Hiding information has existed for many decades in many different forms. In fact stenanography, which is the science of hiding information within content, has been arrange for thousands of years, and includes using invisible inks and to hide information. Another method of hiding information is to embed it into messages, such as in:

which, when each of the starting characters is taken, gives the message of Let the mission begin. This type of hidden information is known as a covert channel where information is added through a communications channel which is was not intended for. Other covert channels have included, in the past: Passing a briefcase in a busy place; Hiding microfilms in objects; and using templates for typewritten text. Unfortunately as we move into the Information Age, the places that covert channels can exist increases by the day and it can often be difficult to detect this type of communication in electronic transmissions.

Figure 1shows the main classifications for information hiding, including the use of:

• Covert channels. This is used a communication channel for a purpose that it was not intended for (Llamas, 2004).
• Steganography. This is the methods used to hide information in content that only the recipient knows where to look for the hidden information.
• Anonymity. This is the methods used to hide the original source of the information.
• Copyright marking. This typically involves embedded information, normally which is hidden with content.

The requirements for copyright marking is obviously a growing issue, as many content creators, such as musicians, artists, and so on, are keen to preserve their copyright on content. It is, though, a constant challenge, as many methods of copyrighting are normally flawed in some sort of way that means that copyright protection can often be overcome. The challenge is sometimes to preserve the copyright in some way which is invisible to the user, but can be revealed when required.

Figure 1: Information hiding classifications

There are literately an endless number of ways that stenography can be used. One example, is to add information into files which can not actually used, such as in images files. Figure 2 shows an example where a GIF file contains a colour table, of which, typically, not all the colours are used in any image. Thus text can be added to the file, which will never actually be seen.

Figure 2: Hiding in GIF files

Sometimes if the data is added to the table, of a colour which is in use, the affect can be seen, such as:

Before hiding	After hiding

which we cannot see the data, we can when it is blown-up:

Before hiding	After hiding

The editing can be seen from:

so that the text has affected the colour table (which appears at the start of a GIF file, and is 256, 24-bit colours.

To view the original and processed file: [Without Hidding][After Hidding]