Web3 Fundamentals: Chains, Keys & Wallets

The junior tier of the Web3 track. Strip the hype and learn what a blockchain actually is: an append-only log that anyone can verify, keys that prove ownership without a login, and a JSON-RPC API you can call from any language you already know. You build a mini chain and break it, sign and verify messages with real public-key cryptography, then talk to Ethereum mainnet live from the sandbox: current block, balances, gas prices, and a stablecoin's total supply read straight out of the contract with hand-encoded calldata. By the end you can read anything on-chain and explain what a wallet is really doing when you click Confirm.

5 lessons · ~2 hours

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What a blockchain actually is. The rest of the course unlocks with a free account.

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1. Reading the Chain

What a blockchain actually is
A blockchain is an append-only log where every block commits to the hash of the one before it, so changing history means redoing all of it in public.
Keys, addresses & signatures
There is no login. A private key signs, a public key verifies, and your address is just a hash of the public key, which is why losing the key means losing the account.
Talk to Ethereum with JSON-RPC
Every wallet, explorer and dApp talks to a node over one plain HTTP API. Call it yourself with fetch and read the live chain.
Transactions, gas & what a wallet does
A transaction is a signed instruction with a nonce and a gas budget. Gas is the price of using a shared computer, and a wallet is the program that prices, signs and broadcasts for you.
Tokens, NFTs & reading a contract
A token is a contract that keeps a balance mapping. Call its functions by hand with eth_call, decode the 32-byte answers, and the ABI stops being a mystery.