Unit 2 · Level 1 · Wallets & keys
Keys, not coins
Surprise: there are no coins inside your crypto wallet. Every coin lives on the blockchain, a shared ledger copied across thousands of computers. Your wallet holds keys: a private key that signs and spends, and a public address others use to send you funds. Think of a mailbox on a public street: anyone can drop letters in the slot (your address), but only the person with the key can open it (your private key).
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What you get asked
You buy 0.1 BTC. Where does it actually live?
Coins never leave the blockchain; they're entries in a shared ledger. Your wallet just holds the keys that control those entries.
The ___ key is the secret you use to sign transactions and spend your funds.
Private key signs and spends; the public address only receives. One is a secret, the other is a mailbox slot.
Match each piece to its job
Mailbox on a public street: the slot is your address, the key opens it, and the street itself is the chain.
A friend wants to send you some ETH. What do you give them?
Addresses are made to be shared, like telling someone where your mailbox is. Keys and seed phrases never leave your hands.
Someone learns your private key. What can they do?
To the blockchain, the key IS the owner. There's no second check and no fraud department. Guard it like the deed to your house. 🐜
The rest of this unit
Keys, seed phrases, and custody: how to truly own your coins.