Encode and Decode using a picture. C programming Ubuntu 14.04 GCC compiler


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Encode and Decode using a picture. C programming Ubuntu 14.04 GCC compiler

Subject or discipline: Computer science
Title: Encode and Decode using a picture. C programming Ubuntu 14.04 GCC compiler

Project Goals
The goals of this project are to:
1. Build upon some prior projects
2. Utilize functions, multidimensional arrays, bitwise operators, and file I/O
3. Learn more about images
4. Implement a complex algorithm
5. Learn about cryptography and ethics
Important Notes:
1. Formatting: Make sure that you follow the precise recommendations for the output
content and formatting. Your assignment will be autograded
and any change in
formatting will result in a reduced grade.
2. Comments: Header comments are required on all files and recommended for the rest of
the course. Points will be deducted if no header comments are included.
Background
You are to write programs to find and hide the steganographic files
(http://en.wikipedia.org/wiki/Steganography) in the included set of images. For example, a file is
hidden this image:
=> I hope someone gets my message in a bottle.
Here’s how we did it. We have two files:
1. the mask image (left, color/grayscale)
2. the hidden file (any format)
The method for hiding data in an existing image is rather simple. A standard grayscale image is
made up of a 2-dimensional array of pixels. Each pixel is just an 8-bit unsigned char (a number
between 0 and 255). 8 bits is usually enough to encode most information for a grayscale image.
However, while your eye can probably tell the difference between a pixel value of 5 and a pixel
value of 200, you probably will not notice a small difference (say the difference between 200
and 201). We can take advantage of this to hide information that a computer can detect but a
person could not.
So, if we start with an 8-bit pixel, we can throw out the least significant bit, the one that
distinguishes the value of 200 from 201. The binary value of 200 is: 11100010 and 201 is:
11100011.
If we just toss out whatever value is in that last bit, we can hide a single bit from the file we
want to hide. (like 1 if the hidden bit should be a 1, and 0 if the hidden bit should be a 0).
More specifically, you need to:
1. Write a program to hide a file inside of another image
a. allocate memory for a properly-sized multi-dimensional array
b. for each pixel in the hidden image, encode that information along with the
mask image
c. write the new image to a file
2. Write a program to unmask the hidden file from an encoded image
a. allocate memory for a properly-sized multi-dimensional array
b. for each pixel in the encoded image, pull out the black and white information
c. save the hidden file as a new file
Your goal (for the encode portion): to write a program that will:
1. prompt the user to enter two filenames, the first is the image we wish to hide a file in,
the second is the filename of the file we wish to hide.
2. copy those images to an array
3. create new pgm file to hold changed image
4. allocate memory for the new image data
5. start at the mask image’s 0,0 pixel
6. for each bit in the hidden file
a. drop the least significant bit from the mask image current pixel value
b. add a 1 to that pixel value if the corresponding hidden file bit is a 1
c. add a 0 (or don’t) to that pixel value if the corresponding hidden file bit should
be a 0
d. move to the next pixel in the image (the next column in the image, or the next
row’s 0th column if at the max column has been reached)
7. write an EOF character in the next 8 image pixels
8. save the array to a file using the pgm image format we’ve been using for the prior
projects
Your goal (for the solve portion): to write a program that will:
1. take the first command-line argument which is the filename of an image (we will
provide two pgm images to test with)
2. read that image from the provided filename to an array
3. allocate memory for the new file
4. for each pixel in the image
a. if the last bit is zero
i. make the next corresponding bit in the hidden file a 0
b. if the last bit is one
i. make the next corresponding bit in the hidden file a 1
5. save the new file as the second command-line argument
If you recall from before, to do this you need to:
Name your files encode.c and decode.c

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One response

  1. Reblogged this on Academic Writers Estate and commented:

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