This assignment consists of a three or four page explanation of an enciphering algorithm of your choosing. It is an exercise in technical writing.

• First, develop an enciphering algorithm. You may use ideas we have studied in class in combination with some of your own ideas. The algorithm should be fairly complex (i.e. it should provide some degree of security) and may consist of several steps. It must use some type of key. You should try to combine security with reasonable ease of use "by hand."

• Next, write an explanation of the algorithm. Your explanation should be written as a well-organized paper such that it could appear in a cryptology publication. Pay attention to proper written English. Your paper must include the following elements:
  • Describe how to use your algorithm to both encipher and decipher messages.
  • Include at least one example of using the algorithm to encipher a message and at least one example of using the algorithm to decipher a message.
  • Explain the role of the key in the algorithm.
  • Discuss why you think your algorithm is difficult to cryptanalyze. (What features make it hard to break?)
  • Provide some comments on what you think might be good strategies for attacking the algorithm.

  Your paper should be at least three or four pages long, 1.5- or double-spaced. You will be graded on the clarity of your explanations, the originality of your algorithm, and how well you address the strengths and weaknesses of your algorithm (the last two points above).

• Finally, choose a message and a key. Encipher the message using your algorithm together with the key. The message should be long enough to provide a reasonable chance of being broken. Alternatively, you may choose to encipher several shorter messages with the same key. Again, you should provide enough material to provide a reasonable chance of breaking the cipher.

What To Hand In

• Print two copies of your paper and label them A and B at the top of the first page. Also print two copies of the message(s) and key on separate pages.

• Staple one copy of the message(s) and key to copy A of the paper. This is for the instructor.

• Staple the other copy of the message(s) and key to copy B of the paper. This will be provided to another student who will attempt to follow the directions in the paper to decipher the message and will also write a critique of the cipher and instructions.
• Hand in both copies in class on Friday, Oct. 6.