# Cryptography: Math and Codes

 Placement Test Available Enroll in this Course

Prerequisites: Qualifying math score and completion of grade 4 math

Course Format: Individually Paced

Course Length: Typically 3 months

Course Code: CMC

## Course Description

Description

Cryptography: Math and Codes introduces students to the exciting practice of making and breaking secret codes. This popular course is designed for for mathematical enrichment for students in grades 6-9.

Students begin with simple Caesar Ciphers, learning to encrypt and decrypt messages as well as the history behind the cipher. They will move through history and more advanced mathematical concepts to learn substitution ciphers, Vigenère ciphers, and multiplicative and affine ciphers. Students will need to put all their newly acquired knowledge to the test by finishing with public key cryptography and the modern day RSA cryptosystem. This course intersects the disciplines of mathematics, computer science, and electrical engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce.

Throughout the course, students will have the opportunity to encrypt and decrypt messages, invent their own ciphers, discuss relevant historical events and literature, and learn some mathematical concepts that are often not seen until college!

Mathematical Topics covered Include:

• positive and negative numbers
• decimals and percents
• data analysis and probability
• prime numbers and factorization
• modular arithmetic
• inverses
• exponentiation

Assignments are based on a text that is purchased separately by the student.

## Materials Needed

There is a textbook purchase required for this course:

The Cryptoclub: Using Mathematics to Make and Break Secret Codes. Janet Beissinger and Vera Pless (AK Peters, 2006)

## List of Topics

### Introduction to Cryptography

• Caesar Ciphers
• ROT13
• Steganography
• Sending Messages with Numbers
• Breaking Caesar Ciphers
• Navajo Code Talkers

### Substitution Ciphers

• Keyword Ciphers
• Cryptography in Fiction
• Letter Frequencies
• Breaking Substitution Ciphers
• Nomenclators

### Vigenère Ciphers

• Combining Caesar Ciphers
• Transposition Ciphers
• Cracking Vigenère Ciphers Using Key Length
• Factorization
• Solving Problems Using Number Theory
• Cracking Vigenère Ciphers Using Common Factors
• Long Keywords

### Modular Arithmetic

• Introduction to Modular Arithmetic
• The Zimmerman Telegram
• Applications of Modular Arithmetic
• Check Digits

### Multiplicative and Affine Ciphers

• Multiplicative Ciphers
• Using Inverses to Decrypt
• The Enigma Machine
• Affine Ciphers
• Atbash and Pigpen Ciphers

### Math for Modern Cryptography

• Finding Prime Numbers
• Properties of Exponents
• Raising to Powers in Modular Arithmetic
• Numeration Systems

### Public Key Cryptography

• The RSA Cryptosystem
• Cryptographic Hash Functions
• Revisiting Inverses in Modular Arithmetic
• Sending RSA Messages

## Demo

Demo

In addition to the textbook, there are interactive websites and videos in the course.

In a Caesar Cipher, the alphabet is shifted a certain number of places and each letter of a message is replaced by the corresponding shifted letter. With this tool, you can shift the alphabet using the cipher wheel then encrypt your own message!

Sample Quiz

## System Requirements

CTYOnline courses require a properly-maintained computer with Internet access and a recent-version web browser (such as Firefox, Safari, or Internet Explorer) with the Adobe Flash plugin. Students are expected to be familiar with standard computer operations (e.g. login, cut & paste, email attachments, etc).

This course uses an online classroom for individual or group discussions with the instructor. The classroom works on standard computers with the Adobe Flash plugin, and also tablets or handhelds that support the Adobe Connect Mobile app.