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Steganography hides data within data to conceal the existence of a message. Text-based, IP header, image, and audio tools can be used. Steganographic activities are aided by the massive data stream, and countermeasures can be slowed.
In addition to message encryption, which protects the contents of a message, it is often desirable to conceal the very existence of a message. Steganography is the science of hiding data within data so that the message itself is not easily found. Some types of steganography tools include text-based tools, which hide messages in text letters; encode IP packets in file headers; and hide messages in images or audio files.
There are a wide variety of text-based steganography tools. These are typically low-tech methods where text is selectively arranged, formatted, or chosen to reveal hidden meaning. As a simple example, a common steganographic scheme involves selecting a fixed letter from each word in a regular message to construct a hidden message. Another option involves overlaying a mask over a strip of text to reveal the letters or words that make up a hidden message.
The Internet Protocol (IP) header bits not used in Open Systems Interconnection (OSI) packets can also be used as steganography tools. Users can exploit unused IP header bits in the OSI network layer, such as Don’t Fragment (DF) or More Fragments (MF) bits, to create a covert channel through which information can be transmitted in data packets OH YEAH. An advantage of this approach is that the packets are usually disjointed and intermingled among a huge volume of other packets unrelated to the message. If one packet in a million streaming packets, for example, contains elements of the hidden message, and the hidden message itself is split among many of these packets, uncovering the message would not be easy.
Image and audio steganography tools have become very popular thanks to the Internet. Image and audio files on the Internet are prevalent and usually large enough to hide a good deal of embedded content. There is even commercially available software that can rearrange the least significant bit (LSB) of bytes comprising digital image and audio files to embed messages. While changing these bits will reduce image or audio quality, the degradation is usually minor enough not to be noticeable to the naked eye. This steganographic technique, however, leaves a detectable statistical signature. Users can obfuscate the signature by employing haphazard cryptographic measures, but an experienced cryptographer could likely detect it.
Steganographic activities, in general, are greatly aided by the massive volumes of data streaming throughout modern society. Any part of this data stream may contain hidden and embedded data. Steganographic security countermeasures are often hampered by the fact that, while the technology exists to examine the data stream for steganographic signatures, attempting to do so can slow the data stream to the point of not being useful.
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