ブロックチェーンの基本概念

Let's get to the heart of blockchain: distributed ledgers, how data lives in blocks, and how those blocks link into an unchangeable chain.

A ledger is just a record of transactions. A bank keeps yours — centralized, owned by one entity. Blockchain sets out to change that.

A Distributed Ledger (DLT) is a database copied across many nodes, with no central admin. Everyone holds the same notebook — and blockchain is one kind of DLT.

Why does distribution matter? Transparency (everyone sees the same record), security (a hacker would have to alter every copy), and resilience if nodes drop offline.

Blockchain data is grouped into blocks — digital pages in the ledger. Each holds recent transactions, a timestamp, and a pointer to the previous block.

Every block has a hash — a unique fingerprint from its data. Change anything inside and the hash changes completely, which guarantees data integrity.

Here's the chain: each new block stores the hash of the previous one. That link creates a chronological, tamper-evident sequence of records.

That linking makes blockchain immutable: alter an old block and its hash changes, breaking the next block's reference — the network spots tampering instantly.

To add a block: gather new transactions, bundle them with the latest block's hash, validate it (e.g. mining), then append it to the chain for all to see.

Time to lock in blocks, hashes, and the chain that links them.

Recap: a blockchain is a distributed ledger where data sits in blocks, cryptographically linked by hashes into an immutable chain. Next: consensus.