People often ask for « a blockchain » to prove integrity. Rarely needed. A hash-chain does the job for a single-source ledger.
The idea
Each record carries the hash of the previous record concatenated with its own:
h1 = SHA-256(record_1)
h2 = SHA-256(h1 ‖ record_2)
h3 = SHA-256(h2 ‖ record_3)
If someone tampers with record_2, then h3 (and everything after) no longer matches. A single published root proves the whole chain.
When it's enough
- Internal ledger (logs, contracts, states).
- Legal or audit proof: « here is the root at date T, here is the chain ».
When it isn't
If multiple parties don't trust each other, you need shared consensus — a real blockchain or a third-party timestamping authority. But to prove « I didn't alter my own ledger », the hash-chain is light and solid.