CSSE/MA479: Cryptography

Homework 4, due on the date listed on the schedule page

• Implement the DES algorithm given in the textbook. You need to encrypt a 64-bit string for a given number of rounds. You do not need to implement decryption.
• The program must read from a file called desinput.txt the number of iterations, the number of rounds in each iteration (which can vary from 1 to 16), the 64 bit string input message, and the key. For debugging simplicity, the message and the key will each be stored as a single 64-character string without spaces, all on one line (e.g., 10011101101010... ). Here is a sample input file (the key is last).

  You may assume that the input is always 64 bits long: no need to worry about breaking apart long messages.

  When the number of iterations is greater than one, you will use the output message from round i as the input message to round (i+1).

  You might be wondering why I am requiring you to encrypt for other than 16 rounds and other than 1 iteration. I will use the ability to change the number of rounds to test correctness. For example, if your answer is incorrect for 16 rounds, but correct for 1, it's probably a bug in how you are generating round keys.

  I will use the ability to change the number of iterations to test speed and correctness. Speed: I can run it enough times to isolate the runtime of the algorithm from the runtime of I/O. Correctness: I want to make sure that you aren't hard-coding anything specific to a given message or key.

• Output: please only display the message output from the last iteration to the console. Printing output for each of a million iterations will make your program slow and severely I/O-bound.

  If you want to display debugging output, please put a DEBUG flag of some type in your code that defaults to off. This is optional, and I won't use it unless your encryption is incorrect and you would like me to consider you for partial credit.

• In 2011, I tested for speed using a junior HP laptop with Windows 7, 32 bit.
• Submit your project including anything need to compile it (like a Makefile for anyone using C) in the dropbox on Angel.
• If you wish to use a language other than C, C++, Java, Python, or Matlab, that's fine if you don't mind working with me to install it on my machine.
• Grading:
  • (70%) Correctness of encryption. I will test it by varying the number of rounds (up to 16) for 1 iteration of DES.
  • (20%) Efficiency. I will run your program repeatedly (usually between 10^5 and 10^8 times) on my machine (for numIterations), using 16 rounds each, to determine runtimes. In addition, the fastest program will receive 20 bonus points. You may not multithread iterations to gain efficiency.
  • (10%) Elegance of code, documentation, and style. Can I open it and understand what you are doing? (Some documentation goes a long way...)
• Click here for an Excel spreadsheet containing the constants from the book and the key (also used for the example below).