Python.ImageEncoder

Encode secret messages in .bmp images

Because I can't get my head around jpg compression and it often leads to them behaving oddly, this program seems better suited to uncompressed images. Admittedly this is far less useful in the wild but will still allow me to practice some steganography. It will be best to use bmp images here

Download

Clone

Using The Command Line

1. Press the Clone or download button in the top right
2. Copy the URL (link)
3. Open the command line and change directory to where you wish to clone to
4. Type 'git clone' followed by URL in step 2

$ git clone https://github.com/[user-name]/[repository]

More information can be found at https://help.github.com/en/articles/cloning-a-repository

Using GitHub Desktop

1. Press the Clone or download button in the top right
2. Click open in desktop
3. Choose the path for where you want and click Clone

More information can be found at https://help.github.com/en/desktop/contributing-to-projects/cloning-a-repository-from-github-to-github-desktop

Download Zip File

1. Download this GitHub repository
2. Extract the zip archive
3. Copy/ move to the desired location

Language information

Built for

This program has been written for Python 3 and has been tested with Python version 3.7.0 https://www.python.org/downloads/release/python-370/ on a Windows 10 PC.

Other versions

To install Python, go to https://www.python.org/ and download the latest version.

How to run

1. Open the .py file in IDLE
2. Run by pressing F5 or by selecting Run> Run Module

Define application constants

The default values for HEADER_SIZE, FOOTER_SIZE and MAX_SECRET_LEN are 1024. This can be changed with minimal impact on the program

• HEADER_SIZE The minimum value that I would recommend setting this to would be 256. After a quick look on Wikipedia, it looks like anywhere between 16 and 196 bytes are required for the header. Setting it at 256 or higher seems safe.

• FOOTER_SIZE It doesn't look like a bitmap has a footer. This was included for .jpg images. Play around with it if you would like but there is certainly no harm in leaving it at the default value

• MAX_SECRET_LEN This was included to stop python crashing. In a future version I will terminate the decoder when it encounters the first null character. This would likely remove the need for this. Or would certainly make it less essential. Using larger values will decrease the speed of the program but shouldn't have an adverse effect

I've done an MD5 hash of "CLEAN" and appended it to the filename to reduce the chance of overwriting an important file

Functions

Read image file in

readImg(imageName):

Write image file out

writeImg(imageName):

Get the size of the image in bytes to prevent overwriting footer

getSize(imageName):

Replace the least significant bit with a 0

writeCleanImg(inputImgName, outputImgName):

Write a secret message to the image

writeEncodedImg(inputImgName, outputImgName, secretMsg):

Calculate the LSB value to write

calculateLSB(byte, secretMsg):

Read the encoded image

readEncodedImg(inputImgName):

The CLI

cli():

Using the CLI

"Clean, Encode, Clean and Encode (.bmp only), Decode or Quit? (C, e, a, d, q)"

• Entering 'c' will clean an image (specified by its path)
• Entering 'e' will encode an image (specified by its path)
• Entering 'a' will clean and encode an image (specified by its path)
• Entering 'd' will decode an image (specified by its path)
• Entering 'q' will quit the program

"Type the name of the input image (include the file extension and path if required)"

• Enter the path to an input image

"Type the name of the output image (include the file extension and path if required)"

• If the user selected Clean, Encode, or Clean and Encode. Enter the path of an output image

"Type the secret message (max MAX_SECRET_LEN characters)"

• If the user selected Encode, or Clean and Encode. Enter a message for the program to encode in the image

Licence

MIT License Copyright (c) fredhappyface (See the LICENSE for more information.)