MCS 150 Lab 8

1. Make sure your computer is booted up in Fedora (Linux).
2. Open a terminal shell.
3. Enter the following commands (note the space dot at the end):
   
   cp ~holte/public/crypts/hillcipher.m .
   xmaple &
    
4. In your Maple worksheet make sure you have an execution prompt, >
   If you don't, Insert > Execution group > After cursor
5. Enter the following Maple commands:
   
   read "hillcipher.m";
   plain := "hello world";
   cipher := hill(plain, 2, 3, 5, 6);
   hill(cipher, 24, 1, 19, 8);
6. Relate this to what we learned in class.
7. Apply your learning. Let's do the example in Sinkov, pp. 115-120.
   • Use the matrix at the bottom of p. 115 (with entries 7, 9, 3, 12) to encipher the message on p. 116, "prepare to evacuate at once". Note how much easier this is than doing page 117.
   • Read pp. 118-119 to learn why the deciphering matrix has entries 18, 19, 15, 17.
   • Decipher your enciphered message using the hill command and this deciphering matrix.
8. Check by hand that if you multiply the 2-by-2 matrix with entries 3, 4, 11, 23 by itself and reduce modulo 26 that you get the identity matrix, the 2-by-2 matrix with entries 1, 0, 0, 1. As Sinkov notes in Section 4.3, such a matrix may serve both to encipher and to decipher. Show me your calculation.
9. The crypt in Sinkov problem 71, page 139, was enciphered by Hill's digraphic cipher using this matrix. Decipher the message. Show me the deciphered message.