A transaction without one account operator

Nadia wants to pay Leo 0.05 BTC for computer equipment. They do not use the same bank or a payment company that maintains accounts for both of them. Instead, Leo gives Nadia a Bitcoin address.

In simplified form, this is what happens:

1. Nadia enters Leo's address and the amount in her wallet.

2. Her wallet selects bitcoin recorded under spending conditions she can satisfy and constructs a transaction.

3. Nadia authorises the transaction with her signing key.

4. The signed transaction is broadcast to the Bitcoin network.

5. Participating computers check that the transaction follows the rules, including that the relevant bitcoin has not already been spent.

6. A miner includes the transaction in a block, and nodes check the block.

7. As further blocks are added, Leo becomes more confident that the payment will remain in the accepted history.

No central account operator changes a balance from Nadia to Leo. The network maintains a shared transaction history under commonly enforced rules. Bitcoin's original design combined digital signatures, public transaction ordering and proof of work to address the problem of double spending without requiring a central payment operator.¹

Several terms describe different parts of this process:

• A signature shows that the transaction satisfied the relevant cryptographic authorisation condition.

• Validation checks the transaction against the network's rules and current recorded state.

• Consensus is how participants converge on an accepted history or state.

• A confirmation records that a transaction has been included and subsequently built upon.

These are not interchangeable. A valid signature does not prove that Nadia intended to pay the address shown. Malware might have replaced Leo's address before she signed. A correctly signed transaction can also conflict with another attempted spend. Inclusion in a block does not tell Leo whether his employer, custodian or applicable law treats the payment as finally settled.

The important first principle is that crypto does not make trust, judgement or operational risk disappear. It changes the mechanism used to establish particular facts. Chapter 2 follows transactions and ownership in detail; Chapter 3 explains how networks agree on a history and resist conflicting activity.

What would Nadia and Leo actually see?

Nadia's wallet would normally show an amount, destination, estimated network fee and transaction status. After broadcast it would display a transaction identifier. Leo might see the transaction as pending before he treats the funds as available.

If Leo receives the payment through a custodian, the custodian may wait for its own confirmation threshold, screen the transaction and then credit his internal account. The blockchain transaction and the customer's credited balance are related events, not the same record.

This distinction recurs throughout the book: always identify which system produced a status and what that status establishes.