Compile all the C files using:

gcc -Wall *.c

You can create a makefile to build this project if you want

For encrypting, you have to use -e followed by an input image filename followed by a secret filename. (Note that these files must be present in the current project directory, otherwise an error message appears. Also note that the input image filename must be having ".bmp" format to avoid error while the secret file can be of any format: .c, .cpp, .txt, .vhdl etc. But the format type cannot exceed more than 4 characters because a macro MAX_FILE_SUFFIX has been set to 4. Also don't miss the dot in any filename. It will result in an error). Example -

./a.out -e beautiful.bmp secret.txt

The above input will generate an additional image file in the project directory namely "stego_img.bmp" which is default output filename. You can provide your own output filename by giving 4th argument as shown below: (Note that this filename must be having ".bmp" format, otherwise an error message will be shown)

./a.out -e beautiful.bmp secret.txt my_stegged_img.bmp

If you want to incorporate more security, you can use a passcode for encrypting operation using -p followed by the passcode. Example -

./a.out -e beautiful.bmp secret.txt my_stegged_img.bmp -p 123

(Note that the passcode can contain maximum 4 "digits". You cannot use a passcode like: 1$3q) The output image file looks exactly like the input image file. To decrypt the message inside it, use the decrypting technique.

For decrypting, you have to use -d followed by output image filename. Example -

./a.out -d stego_img.bmp

It will decrypt the secret message from the image and store it in a newly created file called "decoded.txt" which is default decoded filename. This file has the same format as that of the input secret file format. If you want to provide your own decoded filename, you can do so by using 3rd argument as shown below:

./a.out -d stego_img.bmp my_decoded_file.txt

(Note that the file format must match with that of the input secret file's format. Otherwise an error message appears)

If a passcode is used while encrypting, the above input results in an error. Now user has to provide the correct passcode as shown below:

./a.out -d stego_img.bmp my_decoded_file.txt -p 123

*In both operations, you can provide the filename by its path like: Projects/Steganography/beautiful.bmp (But the files must be in the same project directory)

Example -

./a.out -e Projects/Steganography/beautiful.bmp Projects/Steganography/secret.txt

But the file has to be present in your current project directory.