Dr. Navin Rajpal
Reader , SIT
Guru Gobind Singh Indraprastha University
Phone: 23862856 (O); 27056154 (R),9811489759(mob)
Bharati Vidyapeeth College of Engg,
Email: [email protected]
Bharati Vidyapeeth College of Engg
Email: [email protected]
Pravesh Raja Jindal
Bharati Vidyapeeth College of Engg,
Email: [email protected]
1. Brief Introduction
The steganography consists of techniques to allow the communication between two persons, hiding not only the contents but also the very existence of the communication in the eyes of any observer. These techniques use a second perceptible message, with meaning disjoined by the secret message. This second message works as a “Trojan horse”, and is a container of the first one.
2. Brief of a non linear forward feedback shift register?
A Non-Linear feedback shift Register (NLFFSR) is a mechanism for generating binary sequences . Figure 1 shows a general model of an n-bit NLFFSR. It is a Non linear forward feedback shift register with a feedback function f.
3. Brief of pseudo random binary pattern generation using nlffers
NLFFSRs make extremely good pseudorandom binary pattern generators [8,9,10]. When this register is loaded with any given initial value (except 0 which will generate a pseudorandom binary pattern of all 0s). The only signal necessary for the generation of the binary pattern is a clock pulse. With each clock pulse a bit of the binary sequence is produced. A model of 4-bit LFSR is considered to demonstrate the functioning of NLFFSR with the feedback function f =1+x+x4 nonlinear feedback shift register generator. Its initial bit values are used (1111). The output sequence Zn: 111101011001000……….. Generated by NLFFSR is periodic of period 15.
4. Brief of how to error protect the data
To error code the data we use first the concept of duplicating the bits and then applying concept of the redundancy bits. To enhance the performance of the error coding we duplicate each of the crypted bit eight times and then apply the Block technique to this stretched data stream, this work we do ensures that the data hidden in the image is secure even against the heavy distorting.
5. Brief of how the steganography works
Hiding data in an image requires two files. The first file, called the “cover-image”, will be the innocent looking image that holds the hidden information. The second file will contain the information to be hidden. When combined, the two files will generate a “stego-image”. There exists a number of ways to create a stego-image from the given cover-image and the data to be hidden. These include least significant bit(LSB) insertion, masking and filtering, redundant pattern encoding, and other spread spectrum methods.
6. Brief of icorporating hte crypted and error coded binary pattern in hte Image
The amount of data that can be hidden in the Image directly depends on the size of the image. To a computer, an image is an array of numbers that represent light intensities at various points (pixels). Digital Images are generally stored as storing each pixels color information with a particular header telling how the image should be read and interpreted. We leave the header as it as and modify the pixel’s color information bits. The amount of the color information stored for each pixel depends upon the color depth of the image.
4.1 Calculating R values
In first step, we place each bit of the original data in its appropriate place in the 7bit unit. Then we calculate the even parity for the various bit combinations. The parity value for each combination is the value of the corresponding R bit. The value of the cryptic ‘A’ is 00000000.Now we will apply the error code in it first taking the first 4 bits and then applying the steps we just mentioned we get a seven bit error coded data as 0000000.Now again to the next 4 bit we do the same and get another seven bit coded data as 0000000. So the cryptic ‘A’ has become 0000000 0000000 after error coding.
4.2 Error Detection & Correction
Now imagine that by the time the above transmission is received a error in the bit has occurred. The receiver recalculates four new VRC using the same sets of bits used by the sender plus the relevant parity(R) bit for each set. Then it assembles the new parity values into a binary number in order of r position (R4R2R1). Now the decimal value we get is the precise location of the bit in error. Once the bit is identified, the receiver can reverse its value and correct the error. Now after the bit sequence has been recovered we compress the bit sequence which we have duplicated 8 times, during error coding. We may find that many bits in the block of 8 bits have changed, so we compress this block to a value which is in majority in the block. This makes our error coding technique very robust and useful.
How hte steganography works
The design principle of steganographic systems is based on the premise that most communication channels – such as telephone lines and radio broadcasts – transmit signals accompanied by some kind of noise [4, 5]. This noise can be replaced by a transformed secret signal indistinguishable from the noise without the secret key. In this way, the secret signal can be transmitted undetected. In the same way hiding data in an image requires two files. The first file, called the “cover-image”, will be the innocent looking image that holds the hidden information. The second file will contain the information to be hidden. When combined, the two files will generate a “stego-image”. There exists a number of ways to create a stego-image from the given cover-image and the data to be hidden. These include least significant bit (LSB) insertion, masking and filtering, redundant pattern encoding, and other spread spectrum methods [4, 5, 6].
Incorporating the crypted and error coded binary sequence in the Images
The amount of data that can be hidden in the Image directly depends on the size of the image. To a computer, an image is an array of numbers that represent light intensities at various points (pixels). Digital Images are generally stored as pixels color information with a particular header telling how the image should be read and interpreted. We leave the header as it as and modify the pixel’s color information bits. The amount of the color information stored for each pixel depends upon the color depth of the image. The bit stream is hidden in the Image using the LSB insertion technique.
Summary and Conclusion
In this paper, we have presented a review of the field of Steganography and concentrated on improving the security of the data hidden by first crypting data by strong crypting mechanism using NLFFSR and then further error coding it for much improved security. After it we hide this data in the image using the LSB insertion technique. This technique of hiding secret information is highly safe and reliable to hide the Copyright in the Images. By choosing the best techniques of different fields we achieve the best security in the method of Steganography to hide Copyright. Illustration of this Technique using a Image of a sample map.
Figure 2 : A sample cover Image.
Figure 3: The stego-image after hiding the text
Figure 4: The stego-image after distorting the image
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