Frequency Analysis

Letters leave fingerprints

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Each language has a characteristic letter frequency pattern.
• Substitution ciphers preserve this pattern, so counting letters breaks them.
• Frequency analysis needs enough text to work.

Steps

1. Letters aren’t equal
2. Crack the shift
3. Hard cases
4. Brute force
5. Expected E’s
6. The first codebreaker