Secret Codes

From Caesar to RSA

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Caesar shifts letters mod 26, but with only 25 keys it’s easy to break.
• Public-key cryptography (RSA) solves the key-sharing problem.
• RSA’s security rests on how hard it is to factor large numbers.

Steps

1. Caesar’s cipher
2. Easy to break
3. The key-sharing problem
4. How RSA works (in miniature)
5. Encrypt
6. Crack the Caesar cipher
7. What keeps it safe?