- Understanding Steganography
Steganography is the science of hiding information by embedding the hidden message within a cover media (for example, an image, audio or video carrier file) in such a way that the hidden information cannot be easily perceived to exist for the unintended recipients of the cover media. The message is not encrypted, just hidden. Steganography is kind of security through obscurity.
In digital steganography, there is a possibility of coding inside the document file ,image file etc. Media files are ideal for steganographic transmission.
The first recorded uses of steganography can be traced back to 440 BC when Herodotus mentions two examples of steganography in his Histories.
Components of Steganography:
A data stream or a file system that has hidden message inside it.
This is the medium used to hide information.
This is the message or information that needs to be hidden.
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 improves 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.
Embedding messages in steganographic system can be carried out without use of a key or with use of a key. To improve steganographic robustness key can be used as a verification option. It can make an impact on the distribution of bits of a message within a container, as well as an impact on the procedure of forming a sequence of embedded bits of a message.
Information Hiding in Noisy Data
The cover media (images or digital sound) typically has redundancies in the form of a noise component (i.e., insignificant parts) and the general principle underlying most steganographic methods is to place the secret message in the noise component of the signal.
The cover can be typically considered as a sequence of bits. In the case of a digital sound, this sequence is the sequence of samples over time. In the case of a digital image, a sequence can be obtained by vectorizing the image (i.e., by lining up the gray-scale or color values in a left-to-right and top-to-bottom order).
A simple way to hide information in a sequence of binary numbers (bytes) is to replace the least significant bit (LSB) of each byte with a bit of the secret message or replace the LSB of bytes according to a sequence of pseudo random numbers generated at both sides.
For better security, the embedding algorithm should not significantly alter the statistical profile of the cover.
Types of Steganography:
Pure Steganography does not require the prior exchange of any secret information (for example, the stego-key).In this case, the size of the cover should be at least the size of the message to be hidden. Both sender and receiver should have access to the embedding and extraction algorithms, but the algorithms should not be public. Pure Steganography is equivalent to the notion of “security-by-obscurity” since we assume the opponent does not know the embedding/ extraction algorithms in use. However, pure steganography is not very secure in practice as opponents often have a list of embedding/ extraction algorithms that could be used and could subject the captured media to rigorous steganalysis (attempts to extract the hidden information from a stego media).Here the receiver cannot easily distinguish whether the message came from the actual sender or a malicious intruder.
Secret Key Steganography
In Secret Key Steganography the sender chooses a cover and embeds the secret message into the cover using a secret key known only to the sender and receiver. The receiver can only extract the hidden message if he knows the secret key. Anyone who does not know the secret key should not be able to obtain evidence of the encoded information. The cover and the stego-objects can be perceptually similar. Secret key steganography requires the prior exchange of a secret key before the actual communication.
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A steganography software tool allows a user to embed hidden data inside a carrier file, such as an image or video, and later extract that data. The digital equivalent of invisible ink is steganography software, apps that embed files and data inside other files, hidden from everyone who doesn't know any better.