Steganography

Hey guys,

I met some problems in encrypting information hidden in an image. So I have two images: one with a white font and black text, and the other could be any image (the 2 images have the same size). First, I have to replace the least significant bit of the "red" color of the image with the information contained in the "textimage". Then, extract the part in the "red" color of the resulting image which correspond to the encrypted information.

Second, I have to use an encryption key that consists of a sequence of 1, 2 and 3, corresponding to the color planes on which information will be coded, i.e. if the key is 231321, the first pixel of the image "imagedetexte.bmp" will be encoded in level 2 (ie "green"), the second pixel is encoded in the plane 3 (ie "blue"), the third in a plan, the fourth in the plane 3, the fifth in the plane 2, the sixth in plan 1.

Also, the program will incorporate a Graphic User Interface.

To sum up:

       1- The program asks if the user wants to encrypt or decrypt.
       2- Depending on the user's response, it asks the names of image files to encrypt or decrypt.
       3- Ask for the encryption key in the form of a series of 1s, 2s and 3s (in the case of encryption) or      in the form of coefficients of a polynomial (in the case of decryption).
       4- display the result (resulting image or coded key).

Thanks a lot.

[Walter Roberson]

You forgot to ask a MATLAB question ?

Answer 1

[Image Analyst]

What does "one with a white font and black text" mean? Text appears in a font, so are your letters and words black, or are they white? You can' t have it both ways unless you have some letters black and some letters white or have large letters and have a pattern, like a spotted pattern on very big letters.

For #1, you might use questdlg(). For #2 you might use uigetfile() or dir(). For #3, you might use inputdlg(). For #4 you might use imshow(), or image().

Answer 2

[Light]

i mean a picture like this one : http://i47.tinypic.com/b4jihy.jpg and the other picture could be anything

[Walter Roberson]

You still have not asked a MATLAB question ?

[Light]

I want to obtain this program: http://i45.tinypic.com/4iyg6a.jpg (incorporating GUI) which executes the tasks cited above.

[Image Analyst]

Do you know that font mainly refers to the characters themselves, not the background? So unless you have white characters on a white background (which we can't see obviously) then you don't have a white font.

I have no idea where that program came from. Since you got the screenshot of it somewhere, I think you'd have a better chance of tracking down the actual program than me.

[Walter Roberson]

"I want to obtain this program" is not a question. A question looks like, "Why do I get this Index Out Of Bounds error in the below source for a cryptography program I am working on?"

[Light]

I'm really sorry for my bad english (i'm not a native speaker) so excuse me for the misunderstanding.

Would you mind helping me to use an encryption key in my program? if it's not too much trouble.

Thank you for your help.

[Image Analyst]

Sorry, but no one knows your program or how to use it. You'd have to provide the program if you want anyone to try anything. Or better yet, track down the authors and ask them.

[Walter Roberson]

Show the source that you have so far, and show the error message that you get when you run the code.

We will not provide you with the source for the program. We will try to help you with problems you encounter when _you_ write the program.

[Light]

Here is what i have so far: http://ifile.it/fmdtslr , http://ifile.it/gt16qvo . Now the problem is that i can't implement an encryption key that consists of a sequence of 1, 2 and 3, corresponding to the color planes on which information will be coded, i.e. if the key is 231321, the first pixel of the image "imagedetexte.bmp" will be encoded in level 2 (ie "green"), the second pixel is encoded in the plane 3 (ie "blue"), the third in a plan, the fourth in the plane 3, the fifth in the plane 2, the sixth in plan 1. Thank you.

[Walter Roberson]

What part are you having difficulty with? Forming the encryption key, or using the encryption key to decide which bit-plane to code the next bit into?

[Light]

Using the encryption key to decide which bit-plane to code the next bit into.

[Walter Roberson]

Convert the key from a decimal to a vector such as [2 3 1 3 2 1]. Then to know which plane to use for the K'th bit, access TheyKey(1 + mod(K-1, length(TheKey))) . Use if/else or switch() on that value to trigger the appropriate code.

Answer 3

[Light]

I really need your help please. Thank you.

[Image Analyst]

You won't be getting help from me. Like I said, I don't know your program and don't really know encryption that well either. It's never really been a need for me or my images and programs.