Cryptography on the TI-83 Graphing Calculator

Lora Monfils (


The Problem
"Cryptography is the art of concealing the content of messages from an enemy who may be monitoring system activity." (DeMillo, et al., p.2) Throughout history information has been communicated with secret codes. Would the Allies have won World War II if the encryption scheme used by the Germans, the Enigma Machine, hadn't been broken?

In the following activities you will learn to encode and decode secret messages using your graphing calculator.

Grade Level

Suggested Materials
TI-83 graphing calculators, TI-83 view screen if available

Students should have an understanding of function notation and transformation, matrix operations, and the fundamentals of modular arithmetic.

Activity Description
The following five lessons will use the TI-83 graphing calculator to explore elementary cryptography.

Guided Exploration
See worksheets.

Follow-Up Suggestions
Have students develop their own encryption schemes.
Students may enjoy researching the history of cryptography.

TI-83 programs available on request.

Worksheet 1
Worksheet 2
Worksheet 3
Worksheet 4
Worksheet 5

Advanced Mathematics Activities Book. Boston: McDougall Littell/Houghton-Mifflin. Boston. 1994ff. 38-40

Chin, Frances. Al G. Braicprop & Company. DREI '97 Lesson Plan.

Clancy, Harold (Spike). Using the TI-83 to Encode a Message. DREI '97 Lesson Plan.

Clancy, Harold (Spike). Using the TI-83 to Understand RSA. DREI '97 Lesson Plan.

DeMillo, Richard A; Davida, G.I., Dobkin, D.P., Harrison, M.A., Lipton, R.J.. Applied Cryptography, Cryptographic Protocols, and the Computer Security Models. Providence: American Mathematical Society. 1983.

Malkevich, Joseph & Froelich, Gary. Loads of Codes. COMAP. 1993.

Rudich, Steven. (Carnegie Mellon University). Cryptography Lectures. DREI '97. Rutgers University.

Veles, William Yelas. (University of Arizona). The Rudiments of Cryptography. Lecture and Handout. DREI '97. Rutgers University.