When a record must be provably unaltered, ‘put it on a blockchain’ is a common first answer. Often a simpler tool is enough. The right question is not ‘which technology?’ but ‘who needs to be able to verify what, and who do they have to trust?’
The simple version: a hash-chained log
In a hash-chained, append-only log, every entry includes a hash of the one before it. Change any past entry and every later hash stops matching. That makes tampering evident to anyone who recomputes the chain.
Its weakness: whoever runs it
If the operator controls the whole log, a determined insider could rewrite history and recompute every hash consistently. The chain protects against accidental or partial edits, not against a complete rewrite by the party holding the keys.
Anchoring changes the picture
The fix is to publish the latest hash somewhere the operator cannot quietly change: a third party, a trusted timestamping service, or a distributed ledger. After that, a rewrite no longer matches the anchor. Notice that only a small fingerprint needs to be anchored, never the records themselves.
When a blockchain earns its place
- Several parties who do not fully trust one another must agree on a shared history.
- Verification must be possible by outsiders without asking the operator.
- You need a public, independent timestamp for the anchor.
What it costs
- Operational complexity and a new class of failure modes.
- Privacy risk if anything sensitive ends up on a ledger. Anchor hashes, never content.
- Governance questions: who runs nodes, who pays, what happens if it is retired.