Multilevel Network Security Combining Cryptography and Steganography on ARM Platform

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Steps are

Generated key from iris image, we have taken only iris part of eye of person for more security. Key length is 128 bits.

Using Blowfish algorithm for encryption, the confidential information is encrypted.

This encrypted text then hides into every pixel of iris image.

4. Iris image is transmitted to receiver, at the receiver side, hidden data removed from image and using same encrypted key, original data recovered from encrypted text.

4. Overview of algorithm

4.1. Image Definition

To a computer, an image is a collection of numbers that constitute different light intensities in different areas of the image ^[9]. This numeric representation forms a grid and the individual points are referred to as pixels. Most images on the internet consists of a rectangular map of the image’s pixels (represented as bits) where each pixel is located and its color ^[10]. These pixels are displayed horizontally row by row. The number of bits in a color scheme, called the bit depth, refers to the number of bits used for each pixel ^[11]. The smallest bit depth in current color schemes is 8, meaning that there are 8 bits used to describe the color of each pixel ^[11].

4.2. Least Significant Bit Algorithm

Least significant bit (LSB) insertion is a common, simple approach to embedding information in a cover image ^[3]. The least significant bit in other words, the 8th bit of some or all of the bytes inside an image is changed to a bit of the secret message. When using a 24-bit image, a bit of each of the red, green and blue color components can be used, since they are each represented by a byte. In other words, one can store 3 bits in each pixel. An 800 × 600 pixel image, can thus store a total amount of 1,440,000 bits or 180,000 bytes of embedded data ^[7]. For example a grid for 3 pixels of a 24-bit image can be as follows:

When the number 200, which binary representation is 11001000, is embedded into the least significant bits of this part of the image, the resulting grid is as follows:

Although the number was embedded into the first 8 bytes of the grid, only the 3 underlined bits needed to be changed according to the embedded message. On average, only half of the bits in an image will need to be modified to hide a secret message using the maximum cover size ^[7]. Since there are 256 possible intensities of each primary color, changing the LSB of a pixel results in small changes in the intensity of the colors. These changes cannot be perceived by the human eye - thus the message is successfully hidden. With a well-chosen image, one can even hide the message in the least as well as second to least significant bit and still not see the difference ^[3].

4.3. Blowfish

Blowfish is a symmetric encryption algorithm, meaning that it uses the same secret key to both encrypt and decrypt messages.

A graphical representation of the Blowfish algorithm appears in Figure 2. In this description, a 64-bit plaintext message is first divided into 32 bits. The "left" 32 bits are XORed with the first element of a P-array to create a value I'll call P', run through a transformation function called F, then XORed with the "right" 32 bits of the message to produce a new value I'll call F'. F' then replaces the "left" half of the message and P' replaces the "right" half, and the process is repeated 15 more times with successive members of the P-array. The resulting P' and F' are then XORed with the last two entries in the P-array (entries 17 and 18), and recombined to produce the 64-bit ciphertext.

Figure 2. Blowfish algorithm

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Algorithm:

The input is a 64-bit data element== x.

Divide x into two 32-bit halves: xL, xR.

Then,

for i = 1 to 16:

xL = xL XOR Pi

xR = F(xL) XOR xR

Swap xL and xR

After the sixteenth round,

swap xL and xR again to undo the last swap.

Then,

xR = xR XOR P17 and

xL = xL XOR P18.

Finally, recombine xL and xR to get the ciphertext.

A graphical representation of F appears in Figure 2. The function divides a 32-bit input into four bytes and uses those as indices into an S-array. The lookup results are then added and XORed together to produce the output.

The P-array and S-array values used by Blowfish are precompiled based on the user's key. In effect, the user's key is transformed into the P-array and S-array; the key itself may be discarded after the transformation.

Figure 3. Graphical representation of F

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4.4. Experimental Setup

Figure 4. Experimental setup block diagram

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PC must have Visual basic 6 software to run GUI. PC com port connected to ARM kit com Port. We used two UART port of ARM kit, one is connected to PC com port and second connected to Zigbee. So transmitter can acts as a receiver or receiver can acts as transmitter if requireed. As shown in Figure 4, for practical demonstration we required two PC or Laptops, two ARM kit, two zigbee module and two serial com cables.

5. Results

At transmitter side we are created GUI in Visual Basic 6, which can be used to transmit text and iris image to ARM kit. This GUI shown in Figure 7. After sending text and Image to microcontroller, LCD shows message Device is ready to receiver data from pc. Then Send text and image button pressed, then downloading of image and text done in RAM memory of ARM controller. When PC sends text and Image to Controller then controller is ready to receive data from computer.LCD display shows the message “receiving ready”.

Figure 5. Experimental setup connection diagram transmitter side.

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Figure 6. receiving status

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After completion of successful reception of image and text to the controller. Then controller stat encoding and store encoded text in image. And stego image send to the UART1, where zigbee module is connected to controller. Whereas doing this process controller display message on LCD as below.

Figure 7. Encoding status

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Figure 8. Received image and text at receiver side

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