# Using the TI-83 to Encode a Message

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.

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 [itex] > <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.