Implementing-cryptography-using-python

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Chapter 6 ■ Using Cryptography with Images 191print('Now we will try the wronge secret.\n')key = "AnotherKey"crypto_steganography = CryptoSteganography(key)secret = crypto_steganography.retrieve(modfile)print('The secret message is: {} \n'.format(secret))The preceding code will hide a quote from George Washington in an imagenamed ch6_secret_image.png. I converted the original file for this chapter toa PNG file so that we could examine the change in file size. The original file inthis case does not need to be in a PNG format, but it makes it easier to comparethe original with the modified version. Many times, when I have hidden datain pictures, the picture size has increased, but as you will see in Figure 6.12,the original image was 87 KB and the image with the hidden message is only75 KB. You are not able to guess which image has the secret hidden inside justby examining the file sizes.Figure 6.12: Steganography exampleAdditionally, you will notice that without the proper key, the secret messageis not revealed. So, the next question is, how can you determine if there ishidden data inside an image? A number of free tools are available online thatyou can use to embed and extract data from images. One tool that I have usedseveral times is Invisible Secrets. Now, we will explore a more complex setupwith binary data.
192 Chapter 6 ■ Using Cryptography with ImagesStoring a Binary File Inside an ImageFor our next example, we will take a media file and hide it in an image. The file Iam using for this example was retrieved from file-examples.com. The file is 747KB 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 messageand hide it in an image. The first thing that you need to do is reference theCryptoSteganography library. The larger the media file, the longer it will taketo encrypt and decrypt. In this next example, I will also be using a much largerimage file because the media file I’ve selected is too large for the secret image Iused in the previous example. As you work through this example, you may beattempting to store more data than the image will support. In those cases, youwill see an exception that states: The message you want to hide is too long. Here wewill start breaking down the code you need:>>> from cryptosteganography import CryptoSteganographyThe next step is to open the file and assign the binary data to a variable; herewe 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 keyis critical in order to extract the messages you conceal; the key you select canbe a passphrase or any selected password:>>> key = "1111222233334444!">>> crypto_steganography = CryptoSteganography(key)You can now store the encrypted file inside the image. Assign the originalfile 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 theprevious crypto_steganography object, but the code here will instantiate a newobject. This will allow you to change or modify the key if you like. Here, wewill use the same key. In addition, specify the steganography image and thename of the file you wish to store the MP3 as:>>> key = "1111222233334444!">>> crypto_steganography = CryptoSteganography(key)
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ImplementingCryptography UsingPytho
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To Stephanie, Eden, Hayden, and Ken
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viAbout the Authorbook, Shannon is
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Contents at a GlanceIntroductionxvi
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xiiContentsUsing Conditionals 16Usi
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xivContentsPseudorandomness115Break
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xviContentsInstalling and Testing W
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xviiiIntroductionprivacy advocates.
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CHAPTER1Introduction to Cryptograph
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Chapter 1 ■ Introduction to Crypt
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CHAPTER2Cryptographic Protocolsand
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Chapter 2 ■ Cryptographic Protoco
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66 Chapter 3 ■ Classical Cryptogr
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CHAPTER4Cryptographic Mathand Frequ
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Chapter 4 ■ Cryptographic Math an
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CHAPTER5Stream Ciphers and Block Ci
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242 Chapter 8 ■ Cryptographic App
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244 Chapter 8 ■ Cryptographic App
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CHAPTER9Mastering CryptographyUsing
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Chapter 9 ■ Mastering Cryptograph
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IndexSYMBOLS\ (backslash), 10- oper
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Index ■ D-D 279CIA Triad, 35-36ci
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Index ■ I-M 281hashlib module, 28
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Index ■ Q-S 283Preneel, Bart, 145
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