CPSC 430 Spring 2003
Homework 2
Due Friday 1/24

  1. Using a 2x2 Hill cipher with key k, plaintext DECEPTIVE becomes ciphertext UVKASSITOG. Determine k. (Use the technique in YOUR book, which is the one we originally discussed in class.) Show all of your work.

    Notice that the ciphertext is one character longer than the plaintext -- this is because a dummy letter was added to the end of the plaintext to form the final pair when enciphering. You don't need to know what this letter is, you just can't use the last letter in the plaintext (or pair of letters in the ciphertext) in your analysis.

  2. Is the k you found in (a) a good key? Explain. (Hint: How does the receiver decrypt the ciphertext?)
You may discuss this among yourselves.