Hash chain
Also known as: chained log · tamper-evident log
A hash chain links each log entry to the previous one by a digest, so that altering an old entry visibly breaks everything that follows.
The idea is simple: the current entry's digest is computed including the previous entry's. Each entry therefore seals the whole history before it.
The effect is to make tampering detectable rather than impossible. Someone controlling the log can rewrite it entirely — but not quietly, and not if a digest of the chain head has been published elsewhere.
It is the same family of techniques as distributed ledgers, without the distributed part: no consensus, no token, no peer network.
What it means for a small business
It is what turns "we keep logs" into something a buyer can check. Without chaining, a log demonstrates the good faith of whoever shows it, and nothing more.
So what actually applies to you?
A definition tells you what a term means, not what your organization must do. The assessment answers the second question — free, no credit card.
Updated September 1, 2026 · Educational definition; not legal advice.