Implementing-cryptography-using-python

192 Chapter 6 ■ Using Cryptography with Images
Storing a Binary File Inside an Image
For our next example, we will take a media file and hide it in an image. The file I
am using for this example was retrieved from file-examples.com. The file is 747
KB in size. If you would like to use the same file, you can find it here: https://
file-examples.com/index.php/sample-audio-files/sample-mp3-download/.
Our goal here is to use the CryptoSteganography module to take a secret message
and hide it in an image. The first thing that you need to do is reference the
CryptoSteganography library. The larger the media file, the longer it will take
to encrypt and decrypt. In this next example, I will also be using a much larger
image file because the media file I’ve selected is too large for the secret image I
used in the previous example. As you work through this example, you may be
attempting to store more data than the image will support. In those cases, you
will see an exception that states: The message you want to hide is too long. Here we
will start breaking down the code you need:
>>> from cryptosteganography import CryptoSteganography
The next step is to open the file and assign the binary data to a variable; here
we use 'message':
>>> mediafile = “file_example_MP3_700KB.mp3”
>>> message = None
>>> with open(mediafile, "rb") as f:
>>> message = f.read()
Next, create a key and pass it into the CryptoSteganography object. The key
is critical in order to extract the messages you conceal; the key you select can
be a passphrase or any selected password:
>>> key = "1111222233334444!"
>>> crypto_steganography = CryptoSteganography(key)
You can now store the encrypted file inside the image. Assign the original
file and modified file variables:
>>> origfile = "dogs.png"
>>> modfile = "steg_audio_dogs.png "
>>> crypto_steganography.hide(origfile, modfile, message)
Now that we have our media hidden, it is time to extract it. You can use the
previous crypto_steganography object, but the code here will instantiate a new
object. This will allow you to change or modify the key if you like. Here, we
will use the same key. In addition, specify the steganography image and the
name of the file you wish to store the MP3 as:
>>> key = "1111222233334444!"
>>> crypto_steganography = CryptoSteganography(key)