Ethereum Accounts

In Ethereum, the state is made up of objects called “accounts”, with each account having a 20-byte address and state transitions being direct transfers of value and information between accounts. An Ethereum account contains four fields:

• The nonce, a counter used to make sure each transaction can only be processed once
• The account’s current ether balance
• The account’s contract code, if present
• The account’s storage (empty by default)

“Ether” is the main internal crypto-fuel of Ethereum, and is used to pay transaction fees. In general, there are two types of accounts: externally owned accounts, controlled by private keys, and contract accounts, controlled by their contract code. An externally owned account has no code, and one can send messages from an externally owned account by creating and signing a transaction. In a contract account, every time the contract account receives a message its code activates, allowing it to read and write to internal storage and send other messages or create contracts in turn.

Note that “contracts” in Ethereum should not be seen as something that should be “fulfilled” or “complied with”; rather, they are more like “autonomous agents” that live inside of the Ethereum execution environment, always executing a specific piece of code when “poked” by a message or transaction, and having direct control over their own ether balance and their own key/value store to keep track of persistent variables.