Course / Foundations / Lesson 7

Wallets and keys, without the fear

Your public key is your account number. Your private key is your password - except there's no "forgot password." Lose it and it's gone.

16:43 to 20:00 - Week 3 with Bob Sakdev About the series

What's going on

A wallet doesn't "hold" your coins the way a leather wallet holds cash - the coins live on the blockchain. The wallet holds your keys, and the keys are everything. Bob keeps it simple: your public key is like your account number. You can share it freely so people can send you funds. Your private key is like your password - a series of words you must never share.

The catch that trips up every beginner: there is no "forgot password" button. Banks can reset your login because a bank controls your account. With self-custody, you control it, which means if you lose your private key, your access is gone forever. Bob's advice is blunt - print it, or write it by hand, and store it somewhere safe.

Wallets come in three flavors. Hot wallets (like MetaMask) live online and are convenient but more exposed - good for small, everyday amounts. Cold wallets are offline hardware devices, like a USB stick; once unplugged they touch nothing, so they're best for serious savings. Custodial wallets are held for you by an exchange like Binance - easiest for beginners, but you're trusting the platform, just like a bank.

Real-world impact

Bob runs all three himself: a custodial wallet on a regulated local exchange for convenience, a hot MetaMask plugin for active use, and a cold wallet for tokens he bought and never intends to trade. Matching the wallet to the job is the whole skill.

Key terms

Public key
Your account number - safe to share so people can send to you.
Private key / seed phrase
Your password, usually 12 to 24 words. Never share it. No recovery if lost.
Hot / Cold / Custodial
Online (convenient) / offline hardware (secure) / held by an exchange (easy, trust-based).