Steganography is a scientific method of concealing confidential information or data in another set of data. Steganography can be used in conjunction with cryptography for the purpose of data protection. The methods applied in steganography use images, audio or video files for protecting the different types of data. Piracy of copyrighted materials and unsanctioned observation is avoided by using steganography. (Techopedia,2017)
Steganography is extensively used for digital watermarking. A watermark is used for authentication of the source of a document. Images of graphic artists posted on web pages are digitally watermarked for proof of ownership. This is useful when there is a dispute regarding the creator of the art-work and in situations which involve copyright violation of images. A general description of process involved in steganography is provided by the following formula.
stego_medium= hidden_data +cover_medium+ stego_key. Cover_medium refers to the file which contains the hidden_data. Stego_key is used for encryption of hidden_data. Stego_medium is the final file generated and is of the same file extension as cover_medium. Typically both cover_medium and stego_medium are audio or image files.(Gordon,2015).
Electronic communications can include implementation of steganography principles in the transport layer. In an image file, the color of each hundredth pixel can be adjusted to indicate a letter. The changes performed should be ultra-fine and must not be observed by any person or machine who are not searching for them. Any method of digital steganography consist of three fundamental steps which are acquiring the message or data which is to be hidden, embedding the data into audio video or images and generating the final file stego-carrier. It is which is to be transmitted. Least significant bit(LSB) in a grey scale is replaced in a method which implements steganography. In a grey-scale(white and black) image the numerical value associated with every pixel indicates intensity information. The image comprises of different shades of grey ranging from black to white which correspond to weakest intensity and strongest intensity respectively.
The LSB substitution in a gray-scale image is performed by the following steps. The digital grey-scale is analyzed to obtain a 2-D matrix whose elements are unsigned integers in the range 0-255.The pixel values obtained are converted to binary format. RSA technique or symmetric key method is used for encrypting the confidential message. The resultant text is encoded in LSB of pixel values. The matrix pixel values are changed to one of the two values of +1 or -1. Then they are re-inserted into the grey-scale image file. The image is saved using a lossless
compression method.
Steganalysis refers to the process where the confidential message is decoded from the stegonographic image. The relevant image pixel values which contain the secret text are retrieved. They are then transformed to binary format. At every stage eight bits are converted into string format. The string is decrypted making use of the decryption key. The original confidential message is acquired after manipulation of the string(Maiti,Baksi, Zamider,Gorai, &Kisku,2011) .
References
Gordon, A. (Ed.). (2015). Official (ISC)2 Guide to the CISSP CBK (4th ed.). Auerbach Publications.
Maiti, C., Baksi, D., Zamider, I., Gorai, P., & Kisku, D. R. (2011). Data Hiding in Images Using Some Efficient Steganography Techniques. 260, 195-203. doi:10.1007/978-3-642-27183-0_21
Techopedia. (2017). Steganography. Retrieved January 23, 2017, from https://www.techopedia.com/definition/4131/steganography
