On a blockchain, ownership comes down to one thing: who controls a private key. A wallet doesn't actually hold your coins. It holds the keys that let you sign transactions, and everything else follows from how well those keys are protected. You'll learn how public and private keys, addresses and seed phrases fit together, and why losing or leaking a seed phrase can mean losing everything.
Next you'll compare custodial and non-custodial wallets, and hot, cold and hardware storage, so you can choose the right setup for different amounts of value. The module then turns to security: how a classic smart contract vulnerability such as reentrancy is exploited, and how patterns like the checks-effects-interactions order and a reentrancy guard prevent it.
With wallets and security covered, you'll be ready for the next module, Building dApps, where you'll connect a front end to your contracts and let users interact with them through their own wallets.
Andreas Antonopoulos explains why owning the private key means owning the funds, how wallets, keys and backups work, and what goes wrong when keys sit with a third party.
A beginner-friendly comparison of hot and cold wallets: how each stores keys, the trade-off between convenience and security, and which to use for which purpose.
How a reentrancy attack drains a vulnerable contract, how one contract calls another, and how a reentrancy guard and safe ordering of operations stop the exploit.