In this pervasive world, we can access anything from anywhere. To have a secret communication, we need a technology such that no one is able to read or modify the secret message. The message should be sent without any intrusion by eavesdroppers. The secret message could be encrypted using cryptography and communicated. But a third party might suspect the presence of the secret message in this case. So, in order to hide the presence of the secret message, steganography is employed. Human eyes are imperceptible to the LSB changes in images and thus messages could be hidden in them. Image steganography will be powerful if there is not a proper sequence in the changes done to the pixels. In this proposed methodology, the secret logo is embedded in an image resulting in the stego-image 1. This is embedded in one more image resulting in stego image 2 which is again embedded in one more image to achieve 3rd level security. To get the secret logo we need to do the same process in the reverse manner. MSE and PSNR are calculated for the proposed method all levels.
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Information hiding is an important technique to secure the precious data during communication (Amirtharajan and Balaguru, 2009; Amirtharajan et al., 2011; Amirtharajan and Rayappan, 2012a, b). Information has to be secured in a sky-scraping manner and communicated in such a way that no one can predict and corrupt the message. As a defense to protect their data against their enemies, information hiding plays a vital role (Stefan and Fabin, 2000). A person who wants to share a secret with others needs the art of steganography to have a secure communication.
In olden days, people used invisible inks, puts tattoos on shaved heads, used wax for covering words on wooden tablets and newspaper clippings. Steganography is used these days to secure data against malicious users (Padmaa et al., 2011) obliterating the secret content along with its being (Rajagopalan et al., 2012). In this field, different carriers are used to carry the secret message such as text, images, movies and protocols (Zhu et al., 2011; Zaidan et al., 2010; Hmood et al., 2010a, b). Thus the saying a picture speaks more than thousands of words would be apt here. In nature, the fruit hides a seed. Here image is used as a fruit and seed is the text message. The chief requirements of Information hiding are capacity and imperceptibility. Imperceptibility is an inherent quality of image (Zanganeh and Ibrahim, 2011) steganography wherein the message is embedded in the cover in such a manner that both the cover and the stego-image are hard to distinguish by the human eyes. But cryptography tries to scramble it (Rajagopalan et al., 2012; Schneier, 2007; Zaidan et al., 2010). Hiding capacity is another important requirement by which a significant number of bits have to be embedded without affecting the imperceptibility (Thanikaiselvan et al., 2011a, b; Thenmozhi et al., 2012). Images are the widely used medium in World Wide Web with the advantage of limited perception of colors.
In this study, security is largely taken good care of in conjunction with the other steganographic imputes. The primary intent of this work is to accomplish an outflanked steganographic model intended for unavowed sharing. All this model employs is K-bit embedding proficiency in all the three steps yielding difficult-to-differentiate image results ascertaining imperceptibility, confidentiality and lustiness.
Digital images are made up of pixels. The popular method of hiding in images is to insert the binary encoded data in the Least Significant Bits of the image pixels (Cheddad et al., 2010). Image distortion is minimal in the LSB insertion technique in which the LSB of the image pixel is replaced by the messages bit. For example if we choose the last LSB to embed then 3 bits of the message are stored in the LSBs of the Red, Green and Blue planes respectively. The resulting stego-image will be identical to the original image for the human vision (Amirtharajan and Rayappan, 2012c, d; Cheddad et al., 2010). In the randomized method, instead of embedding the message bits in a sequential manner, the bits are stored in random. Pseudo random number generator is used to generate the index of the pixel where the message bits are going to be embedded (Janakiraman et al., 2012a, b). In the block-matching procedure, the cover image with the highest similarity is searched for each block of the secret image and embedded in the LSBs of similar blocks (Amirtharajan and Rayappan, 2012a, b). A different method of steganography is proposed by mapping the pixels of the image to English letters and special characters. More surveys on steganography are available by Rajagopalan et al. (2012), Thenmozhi et al. (2012) and Cheddad et al. (2010) for detailed technical descriptions.
In this proposed methodology, three level image hiding has been used. In the first level the secret logo embedded in the cover-image1 produces the stego-image 1. In the second level, the stego-image 1 is then embedded in another image to produce stego-image 2. In the third level the stego-image 2 is embedded in another image to give the final stego-image. The block diagrams for embedding and extracting the secret logo are given in Fig. 1 and 2, respectively.Algorithm for level 1:
Algorithm for level 2:
|Fig. 1:||Block diagram for embedding the secret logo|
|Fig. 2:||Block diagram for extracting the secret logo|
RESULTS AND DISCUSSION
In this study, hiding has been done by using three level hierarchy image hiding. The Secret logo has been embedded at last level to achieve high security. In each level a different algorithm has been used. The results are shown in Fig. 3-5. Figure 3 represents the result of First Level embedding. Figure 4 represents the results of Second Level Embedding and Fig. 5 represents the result of Third Level Embedding. The implementation has been simulated by using Java (jdk1.6). The calculated Mean Square Error (MSE), Peak Signal to Noise Ratio (PSNR) readings for two sample input is tabulated in Table 1 and 2.
Three level hierarchy image hiding: If one level embedding is used to hide secret logo then it gives less complexity and if the level is increased then the complexity is also increased proportionally.
|Fig. 3(a-c):||First level embedding, (a) Cover image 1 (175x175), (b) Secret logol 1 (60x61) and (c) Stego image 1 (175x175)|
|Fig. 4(a-c):||Second level embedding, (a) Cover image 2 (175x175), (b) Secret logol 2 (63x59) and (c) Stego image 2 (175x175)|
|Fig. 5(a-c):||Third level embedding, (a) Cover image 2 (350x350), (b) Secret image 1 (175x175) and (c) Stego image 2 (350x350)|
|Table 1:||Sample input 1-Secretlogol|
|Table 2:||Sample input II-Secretlogo 2|
In the digital era, we live in, information transmission happens in milli seconds while infiltrating happens in nano seconds. Because of this, the integrity of the information is not maintained. Certain information like the high secrets of the army if infiltrated like this would cause destruction and loss on a large scale. Cryptography and steganography are ways of encrypting and hiding data. This proposed method has triple layer protection. If the secret image adapt some existing cryptographic techniques along with this steganographic technique then its hard for hackers to decrypt it.
- Amirtharajan, R., R.R. Subrahmanyam, P.J.S. Prabhakar, R. Kavitha and J.B.B. Rayappan, 2011. MSB over hides LSB: A dark communication with integrity. Proceedings of the IEEE 5th International Conference on Internet Multimedia Systems Architecture and Application, December 12-14, 2011, Bangalore, Karnataka, India, pp: 1-6.
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