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Cryptography
Secret writing from Caesar to your phone — 6 interactive lessons
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Unit 1: The Idea of a Cipher
1
What Are Secret Messages?
Plaintext, ciphertext, keys, and why cryptography matters today
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2
The Caesar Cipher
Shift every letter by the same amount — interactive wheel
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Unit 2: Classic Codes
3
Morse Code: Dots & Dashes
Tap your own code — and decode the most famous beeps in history
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4
Frequency Analysis
Why the letter E is a snitch — count to crack
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5
Substitution Cipher
Crack a real puzzle with your own mappings
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Unit 3: Modern Cryptography
6
Modern Cryptography
XOR, one-time pads, and the math that protects your phone
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