Spike Clancy (hclancy@dimacs.rutgers.edu)

**General Information**

The TI-83 can be used to encode text messages into numbers and to create a shift cipher to encode in a different way.

**Category**

The lesson can be used as an introduction to crytography and Caesar ciphers. It also can be used in modular arithmetic or to explain translations in geometry.

**Grade Levels**

Grades 7-12

**Activity 1**

Using the TI-83 to change text into code.

**Materials**

TI-83 calculators for class

TI-83 view screen

**Procedure**

1. Use the <sto> key to store numbers to variables:

0->A : 1->B : 2->C : 3->D : ... :25 ->Z

This can be done all at once by using the following keys:

<sto>> <Alpha>

2. Use <and> {to type message}. Note commas must be used between letters.

ex) {S, P, I, K, E}

3. After typing message hit <enter> and {18 15 8 10 4} will appear on the screen.

4. Hit <sto>> (on screen ans ->) <and> <Li> and your encoded message will be encoded in list one.

5. Hit <stat> <1> to see List 1.

6. If you want to change the rules with a shift cipher, on the main screen enter <math> > <num> <2> "Round" (Math > <num> "4" FPart ((L1+4)/26*26), 2)

Note on screen reads:

Round ((FPart ((L1=4)/26*26), 2)

7. Hit <Enter> and your new list of numbers will appear

8. Match the first number to A, second to B, etc. (see step one)

**References**

__Loads of Codes__, Joseph Malkevitch and Gary Froelich, Comap, Inc.