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What does a blockchain let participants agree on?

Two requests can be signed correctly and still conflict. Their order matters.

  1. TransactionValidate and include
  2. Valid blockConfirm under protocol
  3. Shared history
Relationship sketch · arrows show responsibilities and connections, not a complete protocol sequence.

Copying a record to many people does not make them agree on its contents. A blockchain lets participants check transactions against shared rules and maintain an ordered history. A transaction is a request to change the recorded state.

Two valid signatures, one acceptable transfer

Imagine a digital entitlement that can be transferred only once. Its holder signs two requests, giving it to two different recipients. Each recipient could see a correctly signed request and believe they now hold the entitlement.

The system needs to accept one request first, then reject the other against the updated state. In Bitcoin, a transaction spends previously unspent transaction outputs. An output cannot be spent again in the accepted history. Copying data, checking signatures and resolving this conflict are separate jobs.

Agreement is not observation

If the entitlement represents a box of goods, agreement on its transfer does not prove the goods are in a warehouse. Someone still has to check the warehouse and its evidence. A chain helps participants verify what was accepted under its rules; it does not observe the physical world.

Before assessing a blockchain proposal, write down what its participants need to agree on. If there is no identifiable shared state or conflict to resolve, the reason for adding a chain remains unclear.

Book and verification sources

This lesson develops a question from 《区块链实战》, Chapters 1 and 6, with the references below. It is a new explanation, not a book excerpt.

Check your understanding

Can two requests both be accepted just because both signatures are valid?

Not necessarily. If both use the same one-use entitlement, the shared history determines which remains valid. Signatures answer only part of the question.

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Terms

  • Blockchain

    A distributed ledger that links records cryptographically and uses shared validation and consensus rules to establish an accepted transaction history.