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·5 min read·The DecisionChain Team
Hash Chains 101: How Immutable Logs Actually Work
You don't need a blockchain. You need a hash chain. Here is the mechanic that makes an audit log verifiable — in one page.
A hash chain is the simplest cryptographic structure that turns a log into evidence. Each record carries the hash of the previous record; change any record and every downstream hash breaks.
The mechanic
For each record r_i:
h_i = sha256(canonical(r_i) || h_{i-1})Store h_i next to the record. That is the entire construction.
What it gives you
- Detection. Any change to any past record invalidates every subsequent hash.
- Portability. A verifier only needs the records and the starting hash — not your database, not your app.
- Anchoring. Publishing
h_nto an external witness locks in every record up to that point.
What it doesn't give you
Hash chains prove records were not altered. They don't prove records were written honestly in the first place. Pair the chain with strong input capture and an operator-independent anchor to close that gap.