Steganography is the art and science of writing hidden messages. The goal is to hide information so that even if it is intercepted, it is not clear that information is hidden there. The most common method today is to hide messages in pictures. This is done using the least significant bit (LSB) method. This method depends on the fact that computers store information in bits and bytes.
When we look at bits, consider an 8-bit byte, for example, 11111111 and when converted to a decimal, it equals 255. If you change the first 1 to a 0, you get 01111111. This now equals 127 in decimal number. Changing the last bit to a zero, 11111110 when converted to decimal is 254.
This is not as big of a change as when we changed the first bit, therefore is why the last bit is referred to as the Least Significant Bit. Changing the least significant bit from a 0 to a 1 or from a 1 to a 0 makes the smallest change in the original information.
Other terms that you need to be aware of when discussing Steganography include payload, carrier, and channel. The payload is the information that is to be covertly communicated, in other words, it is the message you want to hide. Carrier is a signal, stream, or file in which the payload is hidden. The channel is the type of medium used. This may be a passive channel, such as photos, video or sound files. A channel can also be an active channel such as Voice over IP (VoIP) calls or a streaming video connection.
Information can also be hidden in video files. There are various ways to do this, including the LSB method. Whatever method is used, it is important to realize that video files are obviously larger than other file types. This provides a great deal of opportunity for hiding a lot of information.
Steganalysis is the process of analyzing a file or files for hidden content. It is a difficult task to perform, however, it can show a likelihood that a given file has additional information hidden in it. A common method for detecting LSB steganography is to examine close-color pairs. Close- color pairs consist of two colors whose binary values differ only in the LSB.
Cryptography is not so much about hiding a message, as with steganography, but rather about obfuscating the message so that it cannot be read. In other words, with steganography, the examiner may not even be aware a message is present. With cryptography, it is obvious there is a message present, but the examiner cannot easily decipher the message. Cryptography is the study of writing secret messages.
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