Accounts, Transactions, and What EIP-7702 Broke

Where this sits

• The previous lesson covered how a block gets proposed and finalized, and stopped at the block's edge. This one opens it.
• A block is an ordered list of transactions. A transaction is an instruction to change accounts. So accounts come first.

Two kinds of account, one shape

Every address on Ethereum holds the same four fields, whether a person or a contract sits behind it.

The difference between the two account types is what those last two fields contain:

• Externally owned account (EOA) — controlled by a private key. codeHash is the hash of the empty string, storage is empty. Can start a transaction.
• Contract account — controlled by its code. Has a real codeHash and usually real storage. Cannot start a transaction; it only ever runs because something called it.

Where addresses come from

• EOA: the last 20 bytes of the Keccak-256 hash of the public key. No registration step — every private key already has an address, funded or not.
• CREATE: derived from the creator's address and its nonce. Deploy from the same account twice and the second contract lands somewhere else.
• CREATE2: derived from the creator's address, a chosen salt, and a hash of the creation code. Same three inputs, same address, on any chain, forever. That is what makes an address computable before anything is deployed to it.

What a transaction is

A signed instruction from an EOA. The signature is the authorisation; there is no separate login.

• to — the recipient. An EOA to move ETH, a contract to run code, or empty to deploy a contract.
• value — wei to transfer.
• data — the calldata: the bytes handed to the recipient's code. For a contract call, a 4-byte function selector followed by encoded arguments.
• nonce — must equal the sender account's current nonce.
• gasLimit and fees — the ceiling on work, and the price paid for it.

The nonce does more than it looks

• Replay protection. A signed transaction is valid at exactly one nonce. Once used, resubmitting it does nothing.
• Ordering. Transactions from one account execute in nonce order, always. Nonce 6 cannot execute before nonce 5, even if it pays far more.
• Head-of-line blocking. A stuck transaction at nonce 5 stalls every later one from that account. The fix is to replace nonce 5 with a higher fee, not to send nonce 6 again.
• The chain ID is signed too, so a transaction for mainnet is invalid on other chains.

What the fee pays for

• Every unit of work costs gas. Gas is not a currency — it is a unit of work, priced in ETH at execution time.
• Since EIP-1559, a transaction pays a base fee set by the protocol from how full recent blocks were, plus a priority fee to the proposer.
• The base fee is burned. It goes to nobody, which removes the incentive for a proposer to fake congestion.
• Unused gas is refunded. An out-of-gas failure is not: the work was done, so it is paid for, and the state changes are thrown away.

EOAs can now hold code

EIP-7702 (Final) is the most recent change to this model, and it breaks the clean split above.

• A type 0x04 transaction carries an authorization list of [chain_id, address, nonce, y_parity, r, s] tuples, each signed by the EOA it applies to.
• For each valid authorization, the EOA's code is set to a 23-byte delegation indicator: 0xef0100 || address. The 0xef prefix is a banned opcode, so the value can never be mistaken for real code.
• Calls to that EOA now execute the delegate's code, in the EOA's own storage. Authorizing the zero address clears it again.

Why it matters

• "Is this address a contract?" has no stable answer. Checking for empty code was always a weak test — it is false during a constructor — and EIP-7702 makes it false for ordinary wallets too.
• Anything precomputing addresses depends on which derivation it used. CREATE2 addresses are stable across chains; CREATE addresses depend on a nonce that any other deployment moves.
• Nonce ordering shapes everything that sends transactions. Relayers, bots and batch jobs sending from one key are serialised by protocol rule; scaling that out means more keys, not more gas.
• Fee behaviour follows from the burn. The base fee is not negotiable and not payable to anyone, so bidding higher only competes for position within a block, never for inclusion in a cheaper one.

Where to go deeper

• ethereum.org on accounts — the four fields, address derivation, and the EOA/contract split in more detail.
• EIP-7702, specifically its backwards-compatibility section, which enumerates what delegation breaks.
• Any transaction on a block explorer: read its nonce, its input data, its gas used against its gas limit, and the split between burned base fee and proposer tip.