Image Steganography using Multi Level Hiding Technique
Image Steganography using Multi Level Hiding Technique Shaveta Chutani
Himani Goyal
Innocent Hearts Group of Institutions, Jalandhar, Punjab, India
[email protected]
Aryabhatta Group of Institutes, Barnala, Punjab, India
[email protected]
Abstract
Steganography
Steganography is the art of hiding secret information in the innocent looking cover media but the concern of the sender of the secret data remains that the secret communication embedded should not be deciphered by a hacker or examiner. Presently single level of hiding of the secret message in the cover medium is resorted to. This paper presents a novel idea of Multi Level Hiding of the secret information in the cover image. The secret information is encrypted and recursively inserted into Cover Image. LSB technique has been used to embed the data into a BMP format cover image.
Steganography is a process that involves hiding a message in an appropriate carrier for example an image or an audio file [2]. The secret message to be transmitted to the deliberate receiver is embedded in a cover media in such a manner that the existence of the embedded message is not revealed even to the vigilant auditor. Another worry of the sender of the message remains that in the eventuality of cover media being trapped on suspicion, the chances of recovering and decoding the inserted message should be minimal.
Key Words
The present image steganography techniques employ Single Level Hiding. The technique is termed as Single Level, as the secret message is directly inserted into the cover media without any additional camouflage except encryption. Usually a text message is the secret message to be transmitted to the intended recipient, but sometimes an image may also be sent as the secret message or code. The secret message may be encrypted and inserted into the Cover Medium using LSB or other transform domain techniques. The recipient deciphers the secret message or code using the shared key.
Present Technique
Steganography, LSB, Image, Multi Level Hiding (MLH), Pseudo Cover Image. Introduction Exchange of images over the internet has seen tremendous growth in recent times mainly due to increase in the online social networking and availability of internet. Digital Images make a good candidate as a potential cover medium as these may raise fewer eyebrows. Hackers and forensic examiner try to break into the steganographic content and decode it. Encryption of the message sometimes make it difficult for the hacker to retrieve the actual message but advanced algorithms and computing resources are also becoming easily available for these purposes.
Proposed Technique - Multi Level Hiding The novel idea proposed here is Multi Level Hiding. The new Multi Level Hiding technique employs multiple level insertions. In the first Level, the secret message is inserted 1
Image Steganography using Multi Level Hiding Technique
into a BMP image called Pseudo Cover Image. The Pseudo Cover Image is a BMP format digital image selected carefully so as to hold the secret message optimally. The Pseudo Cover Image containing the secret message is then inserted into the main Cover Image in the next level of hiding. The image so obtained, can be further inserted into another intermediate image, which can be inserted into the main Cover Image and so on recursively. However, in this paper dual level insertion has been discussed. Though the insertions in the first and second level have been done using the LSB technique, transform domain insertion algorithms can also be applied. The Stego Image so obtained with Multi Level Hiding is then compared visually and statistically with the original Cover Image.
In case the size of the message exceeds the holding capacity of the Pseudo Cover Image, the user is prompted to either shorten the message length or choose another appropriate sized Pseudo Cover Image.
Multi Level Hiding - Schematics
Experimental Observations
Similarly appropriate sized Cover Image is chosen so as to hold the Pseudo Cover Image and its size. After selection, the insertion takes place. The insertion of the Pseudo Cover Image in the Cover Image is done using pseudo random pixels and 1-LSB substitution. The size of the Pseudo Cover Image is also embedded in the Cover Image at pre determined pixels. The Stego Image so obtained is transmitted to the intended recipient. The message sender side schematics are shown in Figure 1.
The application MLH (Multi Level Hiding) has been developed using Matlab ver. R2011b. The secret message is first input and similarly the Pseudo Cover Image to be used is selected. The size of the secret text message is calculated and compared with the size of the Pseudo Cover Image. MLH employs 1-LSB substitution technique and thus Pseudo Cover Image is so selected that it can hold the Secret Text Message and additionally the size of the text message too. The size of the secret text message is also embedded into the Pseudo Cover Image at predetermined pixels so that accurate retrieval of the secret message can be carried out.
The MLH application was used to insert a sample secret text message “The Shipment has been sent in JY-02”. The Pseudo Cover Image, “Face.bmp” to be used was downloaded randomly from the internet. The size of the Pseudo Cover Image was 50X50X3. Similarly, the Cover Image, “Fruit.bmp”, sized 390X504X3, was downloaded from internet. The Stego Image so obtained with the MLH application was compared with the original Cover Image and results are detailed below: Visual Inspection - Visual Inspection revealed that there was no noticeable difference in the original Cover Image and the Stego Image. The Original Cover Image, Pseudo Cover Image and Stego Image are shown in Figure 2. Histogram Analysis - The histograms of the original Cover Image and the Stego Image were compared for the three different colour planes. Histogram analysis also indicates no appreciable change. The histograms of the Original Cover Image and Stego Image are also shown in Figure 3.
Figure 1: MLH – Sender side schematics 2
Image Steganography using Multi Level Hiding Technique
Figure 1: Original Cover Image, Pseudo Cover Image and Stego Image
Figure 2: Histograms of Original and Stego Image in three different colour planes
Statistical Analysis - Bit Error Rate, Mean Square Error, Mean, Standard Deviation and PSNR were calculated and are presented in Table 1.
Result and Analysis The statistics obtained using Multi Level Hiding for Original Cover Image and Stego Image, tabulated in Table 1, show that they are comparable. Visual inspection can not reveal the presence of any hidden message. Even the histograms of the Original and Stego Image in three different colour planes are comparable as no significant change has taken place.
Table1: Statistical Parameter Comparison Parameter
Original Cover Image
Stego Image
Mean
95.1754
95.1717
Std. Dev.
77.7711
77.7662
PSNR
61.0697
BER
0.0063537
MSE
0.050829
Challenges The fact that the complete Pseudo Cover Image needs to be embedded into Cover Image restricts the maximum size of the secret text 3
Image Steganography using Multi Level Hiding Technique
message that can be transmitted. Though the limitation can be avoided to certain extent, but the bigger size of the Cover Image makes it difficult to transmit the Stego Image to the intentional receiver.
more less chances to be deciphered as the embedded message will go overlooked. Thus for the same probability of being detected by a hacker or forensic examiner, the secret messages hidden with the MLH application are more secure. The MLH employs 1-LSB substitution and BMP format digital images, which were used to develop the concept. More sophisticated substitution techniques along with encryption algorithms and other formats of digital images can be developed.
Conclusion In this paper a novel idea of Multi Level Hiding has been presented. The results shown above indicate that the secret text message with the Multi Level Hiding technique has far
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