Designing an Embedded Algorithm for Data Hiding using Steganographic Technique by File Hybridization G. Sahoo1 and R. K. Tiwari2 Presented by Pan Meng

content Introduction Hybrid File Creation Container File Supporting File Embedded Algorithm Conclusion

Current image hiding technology Substitution Least Significant Bit Masking & Filtering Analyze image first Significant Area

A good information hidden system Capability Security Robust

motivation all of the above methods used for embedding data in an image work on the principle of one image file, that means: The message embedded in must be small enough. Sacrifice capability to cater to the security. There is no level in one image, that means under coercion, the user can’t just reveal parts of the information in the image.

Hybrid file creation This hybrid file basically consists of two files, namely Container file Supporting file

Container file As the name suggests this is a file where we can store the secret data. The basic property of this container file is such that even if we change the intensity of any pixel it should look like the original image. Appropriate candidate for this purpose are cartoon images, geographical images, background images of any picture or images in any chemical reaction and like others. In order to store the secret data in such a file, the size of the container file should be proportional to the size of the secret data.

Supporting file To make the image common, we need a supporting image file so that the new hybrid file looks like the original one. The selection of supporting file will depend on the feature of the container file to ensure the above characteristics.

Container file creation

Embedding Algorithm In contrast to the LSB scheme being used for hiding the data, our main purpose here is to consider the entire byte representing any particular pixel for storing the information. Consequently, by the process of replacing the entire byte for embedding information in the container image, only one pixel can be used to store three characters, whereas by LSB technique one need a minimum of nine pixels to store these three characters as three pixels are required to store a single character.

Embedding Algorithm(2) Assume: M*N: the size of the image (byte) Z: the amount of secret data to be sent through this image P: maximum space required for storing the secret data of size is Z. Case 1: When Z < P Case 2: When Z = P Case 3: When Z > P

Case 1: When Z < P When the size of secret data is less than the image space, consider the straight line formula defined as: y = ax + b Choose a suitable choice of a and b all bytes of the secret data can be mapped entirely into the container image, such as: y = 2x + 2 Here, if the value of x=1 then y will be 4, indicating that the first byte of secret data will be stored in the first byte place of second pixel. i.e. ( 8 – bit Red position). Similarly, x=2 will give y=6 so the second secret byte data will be stored in last byte of second pixel (i.e. 8-bit Blue position).

Case 2: When Z = P Case 3: When Z > P The message is bigger or equal than the image file, the image will change to a totally different one. It’s suggested to divide the message into different containers.

a) Container file before inserting the datab) Container file after inserting the data Fig.2 Creation of Container file

Hybrid File creation Fig. 3 Merging Container file to supporting file.

After replacing all pixel values of supporting image by the container image we get the resultant hybrid or mixed image (Fig. 4). a) Supporting File b) Hybrid Image File after merge

Multiple Container File From above, it is seen that the size of the information to be under lock and key relatively depends on the size of the container image. What happens if size of the message is larger than the size of the container image file or how can a number of users (receiver) be entertained with different but similar kind of information?

Fig. 5. Hybrid Image File with Multi Container File

Conclusion Security: Multi-level security Capability: larger than LSB Robust: less than LSB

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