01-06-2012, 10:41 AM
Steganography: Digital Data Embedding Techniques
stegnography imple.docx (Size: 3.2 MB / Downloads: 34)
Abstract
In this article there is a basis overview of the Steganography is presented. The steganographic data flow is described and formalized. Last Significant Bits modification technique is described in both – theoretical terms and practical implementations. Security schemas that could be used in data embedding procedure are classified based on key influence to data shuffling procedure. There are main steganalysis approaches for hidden data allocation and detection is presented with necessary narrations for deep understanding.
Q&A Section
Discussion topic for this eBook is available at the scientific community forum
Term “Steganography”
Wikipedia says: “Steganography is the art and science of writing hidden messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message, a form of security through obscurity.” The word steganography is of Greek origin and means "concealed writing" from the Greek words steganos (στεγανός) meaning "covered or protected", and graphing (γράφειν) meaning "to write".
Different definition of term “steganography” can be found in different sources. From our perspective steganography is the science about information hiding, when the fact of information hiding is hidden.In comparison with cryptography that hides a secret message via coding, the purpose of steganography is hiding the fact of secret message transmission. Steganography has been widely used, from the ancient times up to present day. Wax tablets, secret inks, microdots are the examples of physical steganography.
Computer steganography
is a part of classical steganography that based on computer platform features. For example, steganographic file system StegFS for Linux, data hiding in not-used areas of file format, exchange of symbols in file captions, text steganography etc.
Digital steganography
is a part of classical steganography that based on hiding or embedding additional information in digital files. After secret messages embedding, these digital files can be changed, but the size of file and its visual perception should be the same.
LSB Technique: Host and Modified Audio Files
The main parameters of audio signals are their amplitude, frequency and phase. Steganographic modifications suitable for all these options, but before the insertion procedure is necessary to evaluate the limits of modifying the parameters of a container, and also introduced at the same distortion. Bandwidth, reliability, stability steganography system will largely be determined by the degree of modification of audio-container.
LSB: Several Bits Replacement
Bandwidth of the steganographic system that uses LSB coding algorithm is high, compared with systems using a modification of the spectral characteristics. Thus, when data is embedded into images with 24-bit color by replacing only the least significant bits, the maximum amount of embedded data is 12,5% of the container.
Due to the fact that most of the images and audio files in a digital representation have considerable redundancy, there is a possibility to increase steganography capacity by using not only LSB, but also high-order bits, up to the third significant bit. From the picture it’s possible to see that even when 3 significant bits are replaced (shown at picture 'c'), the modified container visual perception is the same. In this case the capacity of container increases to 37,5%.
Steganographic Data Embedding SECURITY Schemes Classification
The choice of embedding algorithm in the most cases is driven by the results of the steganographic channel robustness analysis . One of the areas that improve steganographic robustness is usage of a key scheme for embedding messages. Various key steganographic schemes have various levels of protection. Key scheme term means a procedure of how to use key steganographic system based on the extent of its use. However, when the steganographic robustness is increased a bandwidth of the whole embedding system is decreased. Therefore the task of a scheme selection for achieving the optimal values of the steganographic system is not trivial.