Public & Private Keys
📋 What it is
Modern systems use a PUBLIC key (anyone can lock a message to you) and a PRIVATE key (only you can unlock it).
🗣️ Coach says
A clever modern idea: two keys. Your PUBLIC key is like an open padlock you hand out — anyone can lock a message to you with it. But only your PRIVATE key can OPEN those messages. You never have to share the secret.
🧠 Memory hook
Public key locks (share it freely); private key unlocks (keep it secret).
😂 Giggle
What do you call a pig that does cryptography?
A ham-cipher!
😲 Whoa!
Public-key cryptography (invented in the 1970s) solved a 2,000-year-old problem: how to send a secret to someone you’ve never met without first sharing a key.
✅ Quick check: You give out your PUBLIC key freely. Why is that safe?
Say your answer out loud first — then reveal.
Because the public key can only LOCK messages; only your secret PRIVATE key can unlock them, and you never share that.
Locking and unlocking use different keys, so sharing the locker is safe.
🧪 Try it! (2 minutes)
Think of a mailbox: anyone can drop mail in the slot (public), but only your key opens it (private). Same idea!