File Encryption

20 Points, due Apr 8

This assignment is a short exercise encrypting a file. Encryption of file data keeps the contents private. Even if an encrypted file is stolen, it won't be of any use to the thief. There are a number of ways to encrypt the data used on a computer, including software that automatically encrypts the contents of an entire hard drive. This can be quite helpful for laptops or other portable devices, to protect the contents even if the device is stolen.

For this homework, we'll use some simpler software which will encrypt or decrypt a single file. This is particularly useful if you want to store the file on the cloud, or transmit it insecurely, such as as an email attachment. We'll use some free software called AES Crypt. You may install it on your computer (the best option), or you can avoid that effort and use Sandbox to encrypt your file through the browser. This is provided as a convenience, but it is not nearly as secure as performing the encryption locally, since it requires sending the unencrypted document to Sandbox for processing. But that's sufficient for this exercise.

AES Crypt uses the Advanced Encryption Standard, which considered very secure. It is a symmetric encryption algorithm, meaning the same key is used to encrypt as to decrypt.

Here's what to do:

  1. Use a word processor to create a file to encrypt. Write anything you like, so long as you include your name and write at least ten words.
  2. Encrypt the file using either AES Crypt installed on your computer, or use the AES Crypt page on Sandbox. Choose any encryption key you like, at least ten characters long. Make sure you remember it. (Writing it down is fine, at least for this exercise.)
  3. Save your encrypted file and delete the original.
  4. Attempt to open the encrypted file with the word processor you used to write the original. You should be quite unable to do so.
  5. Attempt to open and view the document with Windows Notepad or some equivalent program. You will probably need to run the program, then open the encrypted file using a file open dialog. You should see a jumbled mess that looks nothing like your original.
  6. Now, use either method (program or web page, doesn't need to be the same) to decrypt your file. Open it and verify that it is correct.
  7. Send me the encrypted file here.
  8. Since I won't be able to read it without the encryption key, you'll need to tell me that also. If we were properly conspiring to send secret missives, you would need to send this to me by some secure means. Perhaps you would slip me a note in some dark alley with dramatic music playing in the background. I would then memorize the key and burn it. But that's way too much trouble, so please just drop me an email. Say Homework 5 in the subject line, if you would, and tell me the key you used to encrypt the file you sent in the previous step.