What is a blockchain?

Imagine a notebook of an apartment building’s shared expenses, with copies kept by many residents. Every new page is linked to the previous one, so that any change to older entries can be spotted. That’s roughly how a blockchain’s history is organized, minus the residents’ meeting in the lobby.

Transactions are grouped into blocks. Each block includes a cryptographic summary, the so-called hash, of the previous one. The hash works like a digital fingerprint: if the data in an old block changes, its fingerprint changes too, so the link to the following blocks no longer matches.

The network’s computers, the nodes, check data against its rules. A consensus mechanism, such as Proof of Work or Proof of Stake, determines how new blocks are added and how the network agrees on the accepted history. The cryptographic linking alone isn’t enough for security.

Why it matters

On public networks such as Bitcoin, you can verify a recorded transaction without relying solely on a company’s word. Using a block explorer, you can see, for example, whether a transfer has been included in a block.

The shared history also helps the network prevent the same coins from being spent twice. Some blockchains also support smart contracts, i.e. programs that run under the network’s rules. For us, what’s interesting is the ability to verify independently, not the “blockchain” label on its own.

What to watch out for

Not all blockchains are equally decentralized or open. There are networks where only approved participants can validate entries. Also, how resistant the history is to changes depends on each network’s design and security.

On most public blockchains, transactions are visible, so a public address doesn’t mean full anonymity. And if you send crypto to the wrong address, there’s usually no undo button. Finally, recording a piece of information on a blockchain doesn’t prove it was true in the first place, nor that the project using it is trustworthy.