Steganography is a science of hiding information within a digital file such as image, audio, video or text called “cover”. Contemporary Steganography approach method such as LSB (Least Significant Bit) will hide the message by altering the last bit of cover media file. The alteration process will produce noise in cover media that is assumed too look innocent for human’s eyes. However, machine (computer) cannot easy to fool. This noise will raise suspicion such that the message can be detected.

In 2008, Desoky proposed a method namely Noiseless Steganography or Nostega that will not produce noise while message camouflaging process. One of the Nostega paradigm is Graphstega that avoids the arousal of suspicion in covert communications by concealing message as data points in a chart [1]. The architecture or Graphstega is shown in Figure 1.

Figure 1 Graphstega Architecture

In Graphstega, the sender will convert the message into binary string based on 8-bits ASCII code. After converting the message, the sender slices this binary string into some group such that each group contains of n bits. This group of sliced bits will be converted into decimal form such that the graph-cover can be generated into Graphstega cover.

As an example, the message that will be hidden is ’Serang malam ini!’. After the message has been converted into binary via ASCII code, the result can be obtained as follows:

0101001101100101011100100110000101101110011001110010000001101101011000010110110001100001011011010010000001101001011011100110100100100001

The binary string will be sliced into 7-bit slices as follows: 0101010 1011100 1101100 1010010 0000011 0110101 1110010 0100000 0111001 1011001 0101100 0110111 0010011 0010101 1101000 0100000 0110101 1011001 0101111 001

The result after converting the sliced bits into decimal is as follows: 41 89 46 38 11 57 78 32 54 88 45 70 11 52 64 105 55 26 36 1 Finally, generate Graphstega cover based on numbers above as shown in Figure 2.

Figure 2 Graphstega Cover

After the graph-cover was transmitted, the receiver will extract the message by convert the each value of plotted data to binary. These binary will be concatenated and converted to plain text based on ASCII code to reveal the hidden message ’Serang malam ini!’.

Reference : [1] Desoky, A. and Younis, M., Graphstega: graph steganography methodology, Journal of Digital Forensic Practice, Taylor & Francis, 2008, 2, page 27-36